Re: Could we use jprobe to skip kprboed function

[Daniel Baluta]

On Tue, Feb 26, 2019 at 11:59 AM wuzhouhui  wrote:
>
> Hi,
>
> The documentation of jprobe says that we must call jprobe_return()
> before return. I'm wondering what if we don't call jprobe_return, and
> could we use it to skip probed function?

Hi,

Please keep in mind the jprobe is likely to be removed unless it was already.

https://lwn.net/Articles/735667/

thanks,
daniel.

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Re: Kernel API's for ADC

[Daniel Baluta]

On Wed, Jul 25, 2018 at 1:25 PM, chandrasekhar  wrote:
> Hi,
>
>
>
> Are there any kernel API's for ADC. I am using NXP IMX6UL processor. I have
> to read ADC values in kernel space instead of sysfs/userspace.

It depends on the type of driver used. Either input or IIO.

The sysfs interface for IIO is described here:

https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-bus-iio


thanks,
Daniel.

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Re: New to the Kernel Newbie

[Daniel Baluta]

Hi,

You can have a look at our Linux kernel labs:

https://linux-kernel-labs.github.io/master/

For example, start with a short introduction to Linux kernel:

https://linux-kernel-labs.github.io/master/labs/introduction.html

then create a simple kernel module:

https://linux-kernel-labs.github.io/master/labs/kernel_modules.html

Hope this helps.

thanks,
Daniel.


On Mon, May 21, 2018 at 12:24 PM, Janakiramireddy Tamma
 wrote:
> Hello,
>
> I am completely new to the kernel newbie, can some one help me where can I
> get started.
>
> Thanks
> Janaki Rami Reddy
>
>
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Re: Add IIO example to the kernelnewbies wiki

[Daniel Baluta]

Sure, you can do that. Nice to see that you are using Diolan DLN-2 adapter.

thanks,
Daniel.

On Mon, Apr 2, 2018 at 8:06 PM, Gaston Gonzalez  wrote:
> Hi,
>
> I'm testing an AD7746 eval board using a Diolan DLN-2 adapter. I wrote
> some basic notes about the installation an instanciation process for my
> own use. But then I thought it could be useful for someone else. So
> maybe I could put this in the kernel newbies page under the IIO section?
>
> If you think is worth it, I would be glad to add it to the wiki page.
>
> Best regards,
>
> Gaston
>
> Notes:
>
> The setup
> =
>
> AD7746-EVAL BOARD --> Diolan DLN-2 Adapter --> Thinkpad T430
>
> The connection between the AD7746 eval board and adapter is as detailed
> in [2] I2C Interface Configuration Options, External connection (pag 4).
>
> The connection between Diolan DLN-2 and the T430 is USB straighforward.
>
> Drivers
> ===
>
> Both in mainline kernel:
>
>  - Diolan DLN-2 driver: I2C_DLN2 (prompt Diolan DLN-2 USB I2C adapter)
> Loc: drivers/i2c/busses/
>  - AD7746: AD7746
> Loc: drivers/staging/iio/cdc/
>
> Bus of interest
> ===
>
>  $  sudo i2cdetect -l
>
> We get something like:
>
>  ...
>  i2c-10  i2c dln2-i2c-1-1.2:1.0-0I2C adapter
>  ...
>
> So our bus is the number 10.
>
> Getting the address
> ===
>
>  $ sudo i2cdetect -y -r 10
>
> We get something like:
>
>   0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
> 00:  -- -- -- -- -- -- -- -- -- -- -- -- --
> 10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
> 20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
> 30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
> 40: -- -- -- -- -- -- -- -- 48 -- -- -- -- -- -- --
> 50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
> 60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
> 70: -- -- -- -- -- -- -- --
>
> 3. Device instantiation:
>
>  # echo add7746 0x48 > /sys/bus/i2c/devices/i2c-10/new_device
>
> We must see something like:
>
> $ cd /sys/bus/i2c/devices/i2c-10/10-0048/
> $ ls
> driver  iio:device0  modalias  name  power  subsystem  uevent
>
> $ cd iio:device0
> $ ls
> dev  in_capacitance-capacitance_calibbias
> in_capacitance0_calibbias_calibration
> in_capacitance-capacitance_sampling_frequency
> in_capacitance0_calibscale   in_capacitance-capacitance_scale
> in_capacitance0_calibscale_calibration   in_capacitance_sampling_frequency
> in_capacitance0-capacitance2_calibscale  
> in_capacitance_sampling_frequency_available
> in_capacitance0-capacitance2_offset  in_capacitance_scale
> in_capacitance0-capacitance2_raw in_temp0_input
> in_capacitance0_offset   in_temp1_input
> in_capacitance0_raw  in_voltage0_calibscale_calibration
> in_capacitance1_calibbias_calibrationin_voltage0_raw
> in_capacitance1_calibscale   in_voltage1_supply_raw
> in_capacitance1_calibscale_calibration   in_voltage_sampling_frequency
> in_capacitance1-capacitance3_calibscale  
> in_voltage_sampling_frequency_available
> in_capacitance1-capacitance3_offset  in_voltage_scale
> in_capacitance1-capacitance3_raw name
> in_capacitance1_offset   power
> in_capacitance1_raw  subsystem
> in_capacitance_calibbias uevent
>
> Checking the permits:
>
> $ ll
> -r--r--r-- 1 root root 4096 mar 31 09:57 dev
> --w--- 1 root root 4096 mar 31 09:57 in_capacitance0_calibbias_calibration
> -rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance0_calibscale
> --w--- 1 root root 4096 mar 31 09:57 
> in_capacitance0_calibscale_calibration
> -rw-r--r-- 1 root root 4096 mar 31 09:57 
> in_capacitance0-capacitance2_calibscale
> -rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance0-capacitance2_offset
> -rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance0-capacitance2_raw
> -rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance0_offset
> -rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance0_raw
> --w--- 1 root root 4096 mar 31 09:57 in_capacitance1_calibbias_calibration
> -rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance1_calibscale
> --w--- 1 root root 4096 mar 31 09:57 
> in_capacitance1_calibscale_calibration
> -rw-r--r-- 1 root root 4096 mar 31 09:57 
> in_capacitance1-capacitance3_calibscale
> -rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance1-capacitance3_offset
> -rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance1-capacitance3_raw
> -rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance1_offset
> -rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance1_raw
> -rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance_calibbias
> -rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance-capacitance_calibbias
> -rw-r--r-- 1 root root 4096 mar 31 09:57 
> in_capacitance-capacitance_sampling_frequency
> -rw-r--r-- 1 root root 4096 mar 31 09:57 

Announce Linux kernel labs project

[Daniel Baluta]

Hi all,

The Linux kernel labs documentation is a collection of "labs" for
various device driver topics. For each topic there are two parts: a
walk-through which explain the basic concepts and a hands-on part which
contains a few exercises.

The kernel labs are integrated with Linux kernel Documentation
system:

https://github.com/linux-kernel-labs/linux

To view the generated Linux kernel labs documentation have a look at:

https://linux-kernel-labs.github.io/

We kindly appreciate your feedback, directly here or via
Issues/Pull Requests on github.

thanks,
Daniel.

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Re: Problem in loading module of Software trigger

[Daniel Baluta]

Hi,

On Sun, Mar 26, 2017 at 9:51 PM, SIMRAN SINGHAL
 wrote:
> On Sun, Mar 26, 2017 at 1:47 PM, Jonathan Cameron
>  wrote:
>> Insmod will not pick up dependencies in the same way modprobe will.
>>
>> Make sure to also insmod industrialio.ko and iio-sw-trigger.ko before the sw 
>> trigger module. I
>>  think those are the only ones you will need.
>
> Thanks
>
> modprobe works for me as it's depended on industrialio-sw-trigger.ko
>
> But now I am facing one more probem with iio_generic_buffer in tools/iio
>
> I am trying to execute iio_generic_buffer:
> as given I can use -N   -t 
>
> I create trigger with name trig-sample present in
> /config/iio/triggers/trig-sample.

How did you create the trigger here?

The trigger must be created according to its type. So far
we have only hrtimer trigger type, so creating a trigger
implies creating a directory in:

/config/iio/triggers/hrtimer

See:

http://lxr.free-electrons.com/source/Documentation/iio/iio_configfs.txt#L83
>
> $./iio_generic_buffer -N iio_dummy_part_no
> iio device number being used is 0
> Failed to find the trigger my_dummy_device-trigger
>
> Its giving me ^ this error:
>
> What wrong I am doing?
>
> I have loaded all the modules including iio_dummy_evgen, iio_dummy.
>
> How I will be pass trig-sample as an argument to it?
> and one more question how can I find Trigger-number of a trigger.
>
> I am facing same problem with iio_event_monitor:-
>
> $ ./iio_event_monitor /sys/bus/iio/devices/iio_evgen/poke_ev0
>
Here you should use the device node. It is usually /dev/iio:device0.

If there is not already created by a daemon there, create it using

mknod /dev/iio:device0 c major minor.

The major and minor can be found in /sys/bus/iio/devices/iio:device0/dev file/

> getting following error:-
> Failed to retrieve event fd
>
> Same with all other events.
>
> This is working fine for me:
> echo 1 > /sys/bus/iio/devices/iio_evgen/poke_ev0

thanks,
Daniel.

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Re: Linux Kernel Based Research Projects

[Daniel Baluta]

On Tue, Oct 4, 2016 at 4:08 AM, Robert P. J. Day <rpj...@crashcourse.ca> wrote:
> On Sun, 2 Oct 2016, Daniel Baluta wrote:
>
>> On Sun, Oct 2, 2016 at 2:54 PM, Shyam Saini <mayhs11sa...@gmail.com> wrote:
>> > Hi everyone,
>> >
>> > I'm final year computer science undergraduate student. I want to do my
>> > major project based on linux kernel.
>> >
>> > Would you please suggest me some areas in the kernel which have some
>> > projects. To be more specific, I want know on going research areas in
>> > kernel. Or some ideas which are not yet implemented.
>>
>> Would you be interested in taking a look at lguest? [1]
>>
>> I will be having a presentation about lguest and how one learn
>> linux kernel internals by studying lguest code
>> this week at LinuxCon Europe [2]
>>
>> Porting it on x86_64 or any other architecture will be a very cool project
>> but I warn you it won't be trivial :).
>>
>> thanks,
>> Daniel.
>>
>> [1] http://lguest.ozlabs.org/
>> [2] http://sched.co/7o92
>
>   Reference [1] claims, "Those crazy guys at Red Hat have an
> experimental port of lguest to x86-64: you can grab their git tree."
> so why do you say porting to x86_64 wouldn't be trivial?

First of all because the linux kernel changed a lot since then.
Second, because I think their code wasn't upstream ready.

Daniel.

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Re: Linux Kernel Based Research Projects

[Daniel Baluta]

On Mon, Oct 3, 2016 at 12:48 PM, shyam  wrote:
> Thanks a lot for your reply,
> I'ld like attend your session but right now I'm in India. So, couldn't
> manage everything so early to attend linuxCon Europe.
>
> Apart from this thing,
> I'ld like to work on lguest to port it on x86_64 architecture.
> May you please tell me why it is not been ported yet for x86_64 architecture
> and can we discuss it further and start work on its porting.

It is not yet ported because lack of time and experience with
x86_64 arch specifics in my case :).

Also, note that this is not a trivial task :), but I think it
worths the effort.

See here the discussion with people who worked on
porting it to x86_64.

https://marc.info/?l=lguest=131810934128197=2

thanks,
Daniel.

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Re: Linux Kernel Based Research Projects

[Daniel Baluta]

On Sun, Oct 2, 2016 at 2:54 PM, Shyam Saini  wrote:
> Hi everyone,
>
> I'm final year computer science undergraduate student. I want to do my
> major project based on linux kernel.
>
> Would you please suggest me some areas in the kernel which have some
> projects. To be more specific, I want know on going research areas in
> kernel. Or some ideas which are not yet implemented.

Would you be interested in taking a look at lguest? [1]

I will be having a presentation about lguest and how one learn
linux kernel internals by studying lguest code
this week at LinuxCon Europe [2]

Porting it on x86_64 or any other architecture will be a very cool project
but I warn you it won't be trivial :).

thanks,
Daniel.

[1] http://lguest.ozlabs.org/
[2] http://sched.co/7o92

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Re: How to debug ethernet driver ?

[Daniel Baluta]

On Mon, Aug 1, 2016 at 10:26 PM, Ran Shalit  wrote:
> Hello,
>
> I am writing ethernet network driver.
> I would like to ask if there are any steps which can help when
> debugging ethernet driver, or is it that the first test should already
> involve transmit/recieve packets to/from ip stack ?
>
> Any tips for debugging and testing a new ethernet driver will be appreciated,

You can start by testing the loopback mode (perhaps). Also, use wireshark
or tcpdump for capturing the packets.

Daniel.

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Re: pushing other commits upstream

[Daniel Baluta]

On Mon, Jul 18, 2016 at 1:49 AM, Alexander Couzens  wrote:
> Hi,
>
> I would like to push patches from somebody else upstream.
> I'm talking of commits of the TI's beagleboard repo [1].
>
> What do I need to take care of?

Well, basically apply the patch from beagleboard repo into your repo. This
will keep the patch author and Signed-off-by line.

Then, add your Signed-off-by line and don't forget to Cc the original author.

Good luck.

:)

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Re: looking for tutorials

[Daniel Baluta]

On Mon, Jun 13, 2016 at 5:43 PM, ty armour  wrote:
> I need tutorials on kernel development. And on complete operating system
> development. I would prefer them to be in assembly because it is faster, but
> it seriously needs to get done.
>
> If you are interested, simply post all of the tutorials and other relevant
> information to coding kernels that you can
>
> and show the references, like actually say okay so in order to do this we
> need to look for this in the assembler manual.
>
> Thanks and have fun

You can start by reading the code for lguest:

http://lxr.free-electrons.com/source/drivers/lguest

It has very good documentation and it covers a lot of
OS fundamental blocks.

Daniel.

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Re: [PATCH] HC-SR04 ultrasonic ranger IIO driver

[Daniel Baluta]

On Wed, Jun 1, 2016 at 12:05 AM,   wrote:
> From: Johannes Thoma 
>
> The HC-SR04 is an ultrasonic distance sensor attached to two GPIO
> pins. The driver based on Industrial I/O (iio) subsystem and is
> controlled via configfs and sysfs. It supports an (in theory) unlimited
> number of HC-SR04 devices.
>
> Datasheet to the device can be found at:
>
> http://www.micropik.com/PDF/HCSR04.pdf
> Signed-off-by: Johannes Thoma 

Please send this to the linux-iio mailing list (linux-...@vger.kernel.org )

thanks,
Daniel.

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Re: How to enable IIO driver in 3.18 kernel

[Daniel Baluta]

On Wed, Jun 1, 2016 at 5:26 PM, Munagala Naresh
 wrote:
> Thanks for the response.
>
> From the "cat /proc/devices", I could see "iio" listed like this.
>
> / # cat /proc/devices
> cat /proc/devices
> Character devices:
>   1 mem
>   4 /dev/vc/0
>   4 tty
>   5 /dev/tty
>   5 /dev/console
>   5 /dev/ptmx
>  --
> 250 iio
> 251 pps
>  -
>
> I could see few other deices @ /dev/. CONFIG_DEVTMPFS is not set in the
> def config. I will try it by adding "CONFIG_DEVTMPFS=y" and
> "CONFIG_DEVTMPFS_MOUNT=y".

Please don't use top posting.

You can look into /sys/bus/iio/devices/iio:device0/dev and get the
MAJOR and MINOR,
then create the device node manually, using:

mknod /dev/iio:device0 c MAJOR MINOR

Not sure why are you mentioning /proc/devices here.

thanks,
Daniel.

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Re: make oldconfig forces HWMON to be inbuilt

[Daniel Baluta]

On Fri, May 20, 2016 at 7:35 AM, Ani Sinha  wrote:
> Hi guys :
>
> I am seeing this weird issue where even though my original kernel
> configuration tries to build HWMON as a module, when I do 'make
> oldconfig', it forces HWMON to be built into the kernel. Is there
> anyway I can find what configuration is forcing this change?
> CONFIG_HWMEM is a tristate symbol.

Did you mean CONFIG_HWMON?

Run make menuconfig and use / CONFIG_HWMON to find its
place in config hierarchy. It should be under "Device Drivers" ->
Hardware Monitoring Support.

Then press "?" to find more info about CONFIG_HWMON symbol.
Look for "Selected by".

thanks,
Daniel.

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Re: git send-email

[Daniel Baluta]

On Sun, May 22, 2016 at 2:29 PM, Tobin Harding  wrote:
> Workflow -
>
> $ git format-patch -s -1
>
> add patch comment then
>
> $ git send-email
>
> Question please -
>
> Who should the email be sent to without having a 'To' address repeated in the 
> CC
> field generated by `git send-email`.
>
> To rephrase the question: git send-email CC's everyone who may be interested
> according to get_maintainers.pl. Will I annoy people if I address them in the 
> To
> field as well as the CC field.

I usually add only the maintainer and the mailing list as To: and the
rest in Cc.

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Re: if block style when condition spams to multiple lines.

[Daniel Baluta]

On Thu, May 19, 2016 at 9:07 PM, Daniel.  wrote:
> What is the preferred way to ident if statement when the condition
> spams to multiple lines, ex:
>
> if (cond1 &&
> cond2 &&
> cond3) {
> ...
> ...
> }

^ this one is preferred.

>
> or
>
> if (cond1 &&
> cond2 &&
> cond3)
> {
>...
>...
> }
>
> or if only one statement inside body
>
> if (cond1 &&
> cond2 &&
> cond3
> ...
>
> Also, usualy, I align the remaining lines from codition to one
> column after the parenthesis that starts the condition and usually
> I need spaces to do that. Is that okay? With no spaces would be:
> if (cond1 &&
> cond2)
> {
> ...
>
> Regards,
> --
> "Do or do not. There is no try"
>   Yoda Master
>
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>

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Re: Is there anyone on MAC kernel

[Daniel Baluta]

On Tue, May 10, 2016 at 12:26 PM, Robert Clove  wrote:
> Hi,
>
> I am looking for some with whom i can discuss my mac kernel problems.
> If you know someone please mail me .

Hi,

It doesn't work this way. Please describe your problem here.

What is the issue and how did you try to fix it?

Daniel.

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Re: i2c driver develpment with diolan DLN-2 / ACPI?

[Daniel Baluta]

On Sat, Apr 30, 2016 at 6:10 PM, Martin Kepplinger <mart...@posteo.de> wrote:
> Am 2016-04-27 um 13:51 schrieb Daniel Baluta:
>> On Wed, Apr 27, 2016 at 2:36 PM, Martin Kepplinger <mart...@posteo.de> wrote:
>>> Hi roberta or anyone who uses a diolan i2c/spi bridge device,
>>>
>>> I try to do get the kernel driver for the connected chip loaded, but I'm
>>> having some trouble getting it right.
>>>
>>> Cables are connected to the device (i2c), and the (mainline) kernel
>>> driver for the diolan DLN-2 device is compiled and loaded on plugin.
>>>
>>> I don't use any of their (userspace) software.
>>>
>>> Now I get a new i2c bus and can manually instanciate my driver
>>>
>>> root@laptop:/sys/bus/i2c/devices/i2c-7# echo mma8452 0x1c > new_device
>>>
>>> and the driver loads. (Now for development, later maybe for merging) I
>>> added acpi support, I guess I'd need it, but ACPI_HANDLE(>dev)
>>> isn't true (during probe) hence we don't continue. I append my
>>> adding-acpi-patch below.
>>>
>>> How do you do it?
>>>
>>> Do *you* manually instantiate your i2c-driver during development with
>>> your diolan device or should it somehow even get loaded automatically?
>>>
>>
>> Hi Martin,
>>
>> Please also use the following two patches:
>>
>> https://lkml.org/lkml/2014/12/16/290
>> https://lkml.org/lkml/2014/12/16/289
>>
>> How does your setup looks like?
>>
>
> Those patches don't apply anymore, also because of API changes. I save
> them but I'll ignore the ACPI problem for now. Oh well, for development
> only, I skip it and go ahead and try to write and read registers.
>
> Different problem:
>
> i2c_smbus_read_byte_data always returns with "Protocol Error".
>
> DLN-2 jumpers are correct. Is there anything special to consider, using
> the DLN-2, regardless of which chip you are talking to?
>

Please check the wiring. Also make sure you run at the correct
voltage for your specific chip.

One other thing, is the firmware version.

http://dlnware.com/Downloads

AFAIK Diolan by default comes in U2C compatiblity mode
which will not work with DLN2 drivers.

Daniel.

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Re: i2c driver develpment with diolan DLN-2 / ACPI?

[Daniel Baluta]

On Wed, Apr 27, 2016 at 2:36 PM, Martin Kepplinger  wrote:
> Hi roberta or anyone who uses a diolan i2c/spi bridge device,
>
> I try to do get the kernel driver for the connected chip loaded, but I'm
> having some trouble getting it right.
>
> Cables are connected to the device (i2c), and the (mainline) kernel
> driver for the diolan DLN-2 device is compiled and loaded on plugin.
>
> I don't use any of their (userspace) software.
>
> Now I get a new i2c bus and can manually instanciate my driver
>
> root@laptop:/sys/bus/i2c/devices/i2c-7# echo mma8452 0x1c > new_device
>
> and the driver loads. (Now for development, later maybe for merging) I
> added acpi support, I guess I'd need it, but ACPI_HANDLE(>dev)
> isn't true (during probe) hence we don't continue. I append my
> adding-acpi-patch below.
>
> How do you do it?
>
> Do *you* manually instantiate your i2c-driver during development with
> your diolan device or should it somehow even get loaded automatically?
>

Hi Martin,

Please also use the following two patches:

https://lkml.org/lkml/2014/12/16/290
https://lkml.org/lkml/2014/12/16/289

How does your setup looks like?

> thanks so much for any help,
>
>  martin
>
>
> --- a/drivers/iio/accel/mma8452.c
> +++ b/drivers/iio/accel/mma8452.c
> @@ -33,6 +33,7 @@
>  #include 
>  #include 
>  #include 
> +#include 
>
>  #define MMA8452_STATUS 0x00
>  #define  MMA8452_STATUS_DRDY   (BIT(2) | BIT(1) | BIT(0))
> @@ -1434,6 +1435,19 @@ static const struct of_device_id mma8452_dt_ids[] = {
>  };
>  MODULE_DEVICE_TABLE(of, mma8452_dt_ids);
>
> +static const char *mma8452_match_acpi_device(struct device *dev, int *data)
> +{
> +const struct acpi_device_id *id;
> +
> +id = acpi_match_device(dev->driver->acpi_match_table, dev);
> +if (!id)
> +return NULL;
> +
> +*data = (int)id->driver_data;
> +
> +return dev_name(dev);
> +}
> +
>  static int mma8452_probe(struct i2c_client *client,
>  const struct i2c_device_id *id)
>  {
> @@ -1441,21 +1455,35 @@ static int mma8452_probe(struct i2c_client *client,
> struct iio_dev *indio_dev;
> int ret;
> const struct of_device_id *match;
> +   const char *name = NULL;
> +   int dev_id = 0;
>
> -   match = of_match_device(mma8452_dt_ids, >dev);
> -   if (!match) {
> -   dev_err(>dev, "unknown device model\n");
> -   return -ENODEV;
> -   }
> +pr_info("mma probe running!!\n");
>
> indio_dev = devm_iio_device_alloc(>dev, sizeof(*data));
> if (!indio_dev)
> return -ENOMEM;
>
> data = iio_priv(indio_dev);
> +   i2c_set_clientdata(client, indio_dev);
> data->client = client;
> +
> +   match = of_match_device(mma8452_dt_ids, >dev);
> +   if (match) {
> +   if (id)
> +   name = id->name;
> +   data->chip_info = match->data;
> +   } else if (ACPI_HANDLE(>dev)) {
> +   name = mma8452_match_acpi_device(>dev, _id);
> +   pr_info("mma acpi ok. found id %d\n", dev_id);
> +   /* TODO chip_info setting*/
> +   data->chip_info = _chip_info_table[dev_id];
> +   } else {
> +   dev_err(>dev, "unknown device model\n");
> +   return -ENODEV;
> +   }
> +
> mutex_init(>lock);
> -   data->chip_info = match->data;
>
> ret = i2c_smbus_read_byte_data(client, MMA8452_WHO_AM_I);
> if (ret < 0)
> @@ -1475,11 +1503,10 @@ static int mma8452_probe(struct i2c_client *client,
> }
>
> dev_info(>dev, "registering %s accelerometer; ID 0x%x\n",
> -match->compatible, data->chip_info->chip_id);
> +name, data->chip_info->chip_id);
>
> -   i2c_set_clientdata(client, indio_dev);
> indio_dev->info = _info;
> -   indio_dev->name = id->name;
> +   indio_dev->name = name;
> indio_dev->dev.parent = >dev;
> indio_dev->modes = INDIO_DIRECT_MODE;
> indio_dev->channels = data->chip_info->channels;
> @@ -1669,6 +1696,17 @@ static const struct dev_pm_ops mma8452_pm_ops = {
>mma8452_runtime_resume, NULL)
>  };
>
> +static const struct acpi_device_id mma8452_acpi_match[] = {
> +   { "MMA8451", mma8451 },
> +   { "MMA8452", mma8452 },
> +   { "MMA8453", mma8453 },
> +   { "MMA8652", mma8652 },
> +   { "MMA8653", mma8653 },
> +   { "FXLS8471", fxls8471 },
> +   { },
> +};
> +MODULE_DEVICE_TABLE(acpi, mma8452_acpi_match);
> +
>  static const struct i2c_device_id mma8452_id[] = {
> { "mma8451", mma8451 },
> { "mma8452", mma8452 },
> @@ -1684,6 +1722,7 @@ static struct i2c_driver mma8452_driver = {
> .driver = {
> .name   = "mma8452",
> .of_match_table = of_match_ptr(mma8452_dt_ids),
> +   

Re: How to correctly decode fun+X/Y

[Daniel Baluta]

On Thu, Dec 3, 2015 at 8:14 PM, Matwey V. Kornilov
 wrote:
> Hello,
>
> I have the following stack trace:
>
> [ 1351.381696] a.out   S c0afb050 0  1676   1658 0x
> [ 1351.387048] [] (__schedule) from []
> (schedule+0x58/0xcc)
> [ 1351.392436] [] (schedule) from []
> (tty_port_block_til_ready+0x1a8/0x35c)
> [ 1351.396937] [] (tty_port_block_til_ready) from []
> (uart_open+0x118/0x158)
> [ 1351.402560] [] (uart_open) from []
> (tty_open+0x11c/0x600)
> [ 1351.407043] [] (tty_open) from []
> (chrdev_open+0xb4/0x188)
> [ 1351.412556] [] (chrdev_open) from []
> (do_dentry_open+0x230/0x330)
> [ 1351.417038] [] (do_dentry_open) from []
> (vfs_open+0x64/0x6c)
> [ 1351.422470] [] (vfs_open) from []
> (do_last+0x510/0xd94)
> [ 1351.426909] [] (do_last) from []
> (path_openat+0x8c/0x270)
> [ 1351.432398] [] (path_openat) from []
> (do_filp_open+0x70/0xd4)
> [ 1351.436815] [] (do_filp_open) from []
> (do_sys_open+0x120/0x1e4)
> [ 1351.442117] [] (do_sys_open) from []
> (SyS_open+0x28/0x30)
> [ 1351.447046] [] (SyS_open) from []
> (ret_fast_syscall+0x0/0x34)
>
>
> Could please explain, how to correctly decode
> tty_port_block_til_ready+0x1a8/0x35c to the instruction or line of code
> using gdb?

$ gdb ./vmlinux

list *(tty_port_block_til_ready+0x1a8)

HTH,
Daniel.

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Re: i want to use the script in kernel script folder.

[Daniel Baluta]

On Tue, Nov 17, 2015 at 7:10 AM, 윤영석  wrote:
>
> hi,
> i want to use a script in kernel, but i can't use this.
> in my terminal.
> yoon@pc:~/project/aosp/kernel/linux/scripts$ ./checkpatch.pl sortextable.c
> Must be run from the top-level dir. of a kernel tree

Hi,

You can try ./checkpatch.pl -f --no-tree 

thanks,
Daniel.

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Re: Regirect /var/log/log/syslog messages to our own txt file

[Daniel Baluta]

On Sat, Sep 19, 2015 at 9:29 PM, Gunjan Mehta  wrote:
> Hi,
>
> I am working on a project, where i print my log messages in
> /var/log/log/syslog like
>
> project_my:info::project started
> project_my:debug::value of a is 1
>
> i want to redirect project_my:info messages in info.txt file and
> project_my:debug  in debug.txt file.

Hi Gunjan,

If I'm not wrong this depends on your syslog daemon.

For example using rsyslog, you have an /etc/rsyslog.conf file
useful for configuring rsyslog.

If you are talking about kernel messages than adding:

kern.debug -/your/debug/file.txt
kern.info   -/your/info/file.txt

HTH,
Daniel.

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Re: kernel.c//Starting for The Journey of The Kernel;

[Daniel Baluta]

On Thu, Sep 17, 2015 at 7:56 AM, GanesH AvacharE
 wrote:
> if I have to start with the basics of the OS then what sequence should I
> follow?

You can start with Operating Systems Concepts book.

http://www.amazon.com/Operating-System-Concepts-Abraham-Silberschatz/dp/0470128720

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Re: samples driver is not compiling and building at present dir .ko file

[Daniel Baluta]

On Fri, Aug 21, 2015 at 10:25 AM, ravi ranjan Mishra
raviranjanmishr...@gmail.com wrote:
 Hi,

 Just for learning purpose , i need to compile the sample directory in
 mainline kernel .
 can anybody tell to how build samples directory through make.

Use:

$ make menuconfig,

to select CONFIG_SAMPLES=y, then
in the root of your kernel sources run:

$ make samples/

thanks,
Daniel.

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Re: Is there any tool can format source code according to kernel coding rule?

[Daniel Baluta]

On Mon, Aug 3, 2015 at 6:35 AM, Nan Xiao xiaonan830...@gmail.com wrote:
 Hi all,

 I am just wondering whether there is a script/tool which format source code
 according to kernel coding rule automatically? Such as tab, space, brace,
 etc.


Try scripts/Lindent from the kernel source tree.

Daniel.

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Re: How can I locate a struct's defination?

[Daniel Baluta]

On Sun, Aug 2, 2015 at 8:01 AM, Navy Cheng nav...@126.com wrote:
 Hi,
 I use emacs and tags to read kernel source. The tags is create by

 make tags

 in the kernel source tree. When I want to find a struct's defination,
 something goes wrong. For example: when I find *dentry* , the first
 result is:

 struct rchan_buf
 {
...
 struct dentry *dentry;  /* channel file dentry */
...
 }

 There are so many items like this before I find

 struct dentry
 {
 
 }

Usually the definition has the curly brace on the same line, like this:

struct dentry {.

Just search for {, it work in vim.

Daniel.

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Re: Unit in which generic_buffer.c application gives data for sensors.

[Daniel Baluta]

On Thu, Jul 2, 2015 at 10:46 AM, s.rawat imsaurabhra...@gmail.com wrote:
 Hi,
 What are the unit in which the generic_buffer.c application gives the
 accelerometer , Gyro and Magnetometer values.
 Thanks in advance !

Hi,

Look for process_scan function in generic_buffer.c. It says:
process_scan() - print out the values in SI units.

Then, look inside IIO ABI file [1] for units associated with _raw attributes.
There you'll find:

* accel - m/s^2
* gyro - rad/s
* magneto - Gauss

thanks,
Daniel.

[1] http://lxr.free-electrons.com/source/Documentation/ABI/testing/sysfs-bus-iio

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Re: Unit in which generic_buffer.c application gives data for sensors.

[Daniel Baluta]

On Thu, Jul 2, 2015 at 2:53 PM, s.rawat imsaurabhra...@gmail.com wrote:
 On Thu, Jul 2, 2015 at 4:13 PM, Daniel Baluta daniel.bal...@gmail.com wrote:

 * accel - m/s^2
 * gyro - rad/s
 * magneto - Gaus

 I get the data as below :

 in_accel_x 71000 71000.0 in_accel_y -45000 -45000.0 in_accel_z
 -1003000 -1003000.0

 This seems correct except I think the data from the device is
 definitely not in m/s2 , seems like it is in  μg.What would be
 correct - telling the  device firmware writer to change the fw to
 send data in m/s2 or I convert this data to m/s^2 at host end?


What driver is this? generic_buffer application reads the data
from device buffer than applies the offset and the scale.

Perhaps, your driver doesn't correctly expose the scale?

thanks,
Daniel.

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Re: About guiding hello world module submission

[Daniel Baluta]

On Wed, Jun 24, 2015 at 7:49 AM, Mayur Patil linuxcra...@gmail.com wrote:
 Hi All,

I am conducting one workshop at FUDCon in which I am trying to teach how
 to write

 and send your first linux kernel device driver. Could please suggest me the
 place where I

 can guide the students to send the device driver?

Not sure what do you want to achieve with this. To show students
how to contribute to the Linux kernel you can find small coding style
issues in the drivers/staging/ directory and send them to Greg KH.

We are doing this every year and its a lot of fun.

You can start with this video:
https://www.youtube.com/watch?v=LLBrBBImJt4

thanks,
Daniel.

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Re: Suggested environments for kernel development

[Daniel Baluta]

On Sun, May 3, 2015 at 8:11 PM, Lewis Clark le...@lewmpk.uk wrote:
 I would really like to know how you guys do your kernel development.
 What distro do you use and whats the process?

 I’m very comfortable with debian, but i’ve heard it’s not the easiest distro 
 to build kernels for as you need to build to a .deb and apply it that way.

You can use whatever distro you like. Anyhow, for rapidly booting
kernels I use qemu :).

Daniel.

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Re: Writing driver for a net device which does not support interrupt

[Daniel Baluta]

On Tue, Mar 24, 2015 at 3:34 AM, Freeman Zhang
freeman.zhang1...@gmail.com wrote:
 Hi phil,

 Thanks for your reply! I googled timer, it might be a solution except
 that interval granularity is a little bit large. This device is for high
 performance network. I'm not sure whether the missmatch will cause problem.

Google for high resolution timers.

Daniel.

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Re: Sysfs requirement for running generic_buffer.c application - IIO sensors

[Daniel Baluta]

On Mon, Mar 23, 2015 at 7:27 AM, s.rawat imsaurabhra...@gmail.com wrote:
 I have two system having different kernel version and drivers(IIO) on which
 i can run the generic_buffer.c application .On one system it works fine but
 on the other it does not give the input reports data.

What kernel versions are you using? Why are you using different drivers? :D

thanks,
Daniel.

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Re: Delaying an interrupt handler

[Daniel Baluta]

On Mon, Mar 23, 2015 at 2:18 PM, Milton Krutt mil...@krutt.org wrote:
 Hi.
 It is known that no semaphore synchronization should be
 used inside an interrupt handler.

 Anyway, I am looking at a freeBSD device driver (written by
 a profesionist) and there are semaphores inside an interrupt
 handler's subroutine.

 Since I should port to linux that driver, I ask you how can I
 reach such synchronization under linux; I tried to use semaphores
 inside my handler but I got complains, and I don't want to break
 the law, so no semaphores for me.

Perhaps spinlocks could be the solution :).

2.6.10 please no - :), Linux kernel is now at 4.0.

Daniel.

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Re: CHECK: Alignment should match open parenthesis

[Daniel Baluta]

On Fri, Mar 13, 2015 at 3:47 PM, Nicholas Mc Guire der.h...@hofr.at wrote:
 On Fri, 13 Mar 2015, Nicholas Mc Guire wrote:

 On Fri, 13 Mar 2015, palik imre wrote:

  On Friday, 13 March 2015, 13:43, Nicholas Mc Guire der.h...@hofr.at 
  wrote:
   On Fri, 13 Mar 2015, palik imre wrote:
  
  
Sorry for the silly question, but I have some issues with this 
checkpatch.pl warning.
   
I mean Documentation/CodingStyle says:
   
Outside of comments, documentation and except in Kconfig, spaces are 
never
used for indentation, and the above example is deliberately broken.
   
But checkpatch.pl claims I should align to open parentheses.  These 
two things seem to be contradictory to me.  Could somebody clarify 
this?
  
   
   leading tabs *followed* by spaces to align parameters to a function are 
   fine
 
  The emacs settings in Documentation/CodingStyle seem to contradict to you,
  as it is set up to use c-lineup-arglist-tabs-only
 
 The problem is that CodingStyle does not explicitly address
 parameter alignment for functions that do not fit on a single line
 but checkpatch.pl does

 you can try it out - if you align to the opening braces with spaces
 with preceding TABs it will not fuss and this is also common practice.

 here is a quick shot at summarizing this


 If the parameter list to a functions would exceed the 80 char limit then break
 it at the separators, and align to opening braces, e.g.:

 ret = fw_load_from_user_helper(fw, name, device,
opt_flags, timeout);

 or:

 int =
 wait_for_completion_interruptible_timeout(data-completion,
   PMI_TIMEOUT);

 Note that this is indented by tabs and then aligned with spaced to fit the
 opening braces. If you can not fit it even if you break the parameter list
 at the commas then indent by tabs only but *significantly* to the left of
 the opening braces, e.g.:

 int ret = wait_for_completion_interruptible_timeout(
 info-done, usecs_to_jiffies(TIMEOUT_US));


 would be suprised if there is no writeup somewhere alredy
 but I did not find this covered in Documentations anywhere.

I think it would be a coding idea to have this in CodingStyle doc :).

Daniel.

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Re: CHECK: Alignment should match open parenthesis

[Daniel Baluta]

On Fri, Mar 13, 2015 at 5:33 PM, Nicholas Mc Guire der.h...@hofr.at wrote:
 On Fri, 13 Mar 2015, Daniel Baluta wrote:

 On Fri, Mar 13, 2015 at 3:47 PM, Nicholas Mc Guire der.h...@hofr.at wrote:
  On Fri, 13 Mar 2015, Nicholas Mc Guire wrote:
 
  On Fri, 13 Mar 2015, palik imre wrote:
 
   On Friday, 13 March 2015, 13:43, Nicholas Mc Guire der.h...@hofr.at 
   wrote:
On Fri, 13 Mar 2015, palik imre wrote:
   
   
 Sorry for the silly question, but I have some issues with this 
 checkpatch.pl warning.

 I mean Documentation/CodingStyle says:

 Outside of comments, documentation and except in Kconfig, spaces 
 are never
 used for indentation, and the above example is deliberately broken.

 But checkpatch.pl claims I should align to open parentheses.  These 
 two things seem to be contradictory to me.  Could somebody clarify 
 this?
   

leading tabs *followed* by spaces to align parameters to a function 
are fine
  
   The emacs settings in Documentation/CodingStyle seem to contradict to 
   you,
   as it is set up to use c-lineup-arglist-tabs-only
  
  The problem is that CodingStyle does not explicitly address
  parameter alignment for functions that do not fit on a single line
  but checkpatch.pl does
 
  you can try it out - if you align to the opening braces with spaces
  with preceding TABs it will not fuss and this is also common practice.
 
  here is a quick shot at summarizing this
 
 
  If the parameter list to a functions would exceed the 80 char limit then 
  break
  it at the separators, and align to opening braces, e.g.:
 
  ret = fw_load_from_user_helper(fw, name, device,
 opt_flags, timeout);
 
  or:
 
  int =
  wait_for_completion_interruptible_timeout(data-completion,
PMI_TIMEOUT);
 
  Note that this is indented by tabs and then aligned with spaced to fit the
  opening braces. If you can not fit it even if you break the parameter list
  at the commas then indent by tabs only but *significantly* to the left of
  the opening braces, e.g.:
 
  int ret = wait_for_completion_interruptible_timeout(
  info-done, usecs_to_jiffies(TIMEOUT_US));
 
 
  would be suprised if there is no writeup somewhere alredy
  but I did not find this covered in Documentations anywhere.

 I think it would be a coding idea to have this in CodingStyle doc :).

 At this level of detail it would be almost unmaintainable
 and also you would end up with far too many rules to actually
 keep them in mind. That is the job of tools like checkpatch.pl
 they can have all the myriads of corner cases encoded without
 creating a burden to the developers/maintainers.

I see. Thanks!

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Re: Getting error failed to setup attributes on Adding Custom Fields in accelerometer HID driver

[Daniel Baluta]

+ linux-iio list.

On Thu, Feb 26, 2015 at 8:04 AM, s.rawat imsaurabhra...@gmail.com wrote:
 I have modified the hid-sensor-accel_3d.c driver to add the custom fields -
 CHANNEL_SCAN_DATA_MOTION and HID_USAGE_SENSOR_DATA_CUSTOM_VALUEX ( X =
 2,3,4).
 Below are my modifications :

 enum accel_3d_channel {
 CHANNEL_SCAN_INDEX_X,
 CHANNEL_SCAN_INDEX_Y,
 CHANNEL_SCAN_INDEX_Z,
 CHANNEL_SCAN_DATA_MOTION,
 CHANNEL_CUSTOM_VALUE_2,
 CHANNEL_CUSTOM_VALUE_3,
 CHANNEL_CUSTOM_VALUE_4,
 ACCEL_3D_CHANNEL_MAX,

 static const u32 accel_3d_addresses[ACCEL_3D_CHANNEL_MAX] = {
 HID_USAGE_SENSOR_ACCEL_X_AXIS,
 HID_USAGE_SENSOR_ACCEL_Y_AXIS,
 HID_USAGE_SENSOR_ACCEL_Z_AXIS,
 HID_USAGE_SENSOR_DATA_MOTION_STATE,
 HID_USAGE_SENSOR_DATA_CUSTOM_VALUE2,
 HID_USAGE_SENSOR_DATA_CUSTOM_VALUE3,
 HID_USAGE_SENSOR_DATA_CUSTOM_VALUE4
 };



 /* Channel definitions */
 static const struct iio_chan_spec accel_3d_channels[] = {
 {
 ..
 ..
 ..
 {
 .type = IIO_ACCEL,
 .modified = 1,
 .channel2 = IIO_MOD_X,
 .info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
 .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_OFFSET) |
 BIT(IIO_CHAN_INFO_SCALE) |
 BIT(IIO_CHAN_INFO_SAMP_FREQ) |
 BIT(IIO_CHAN_INFO_HYSTERESIS),
 .scan_index = CHANNEL_SCAN_DATA_MOTION,
 },
 {
 .type = IIO_ACCEL,
 .modified = 1,
 .channel2 = IIO_MOD_X,
 .info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
 .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_OFFSET) |
 BIT(IIO_CHAN_INFO_SCALE) |
 BIT(IIO_CHAN_INFO_SAMP_FREQ) |
 BIT(IIO_CHAN_INFO_HYSTERESIS),
 .scan_index = CHANNEL_CUSTOM_VALUE_2,
 },
 {
 .type = IIO_ACCEL,
 .modified = 1,
 .channel2 = IIO_MOD_X,
 .info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
 .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_OFFSET) |
 BIT(IIO_CHAN_INFO_SCALE) |
 BIT(IIO_CHAN_INFO_SAMP_FREQ) |
 BIT(IIO_CHAN_INFO_HYSTERESIS),
 .scan_index = CHANNEL_CUSTOM_VALUE_3,
 },
 {
 .type = IIO_ACCEL,
 .modified = 1,
 .channel2 = IIO_MOD_X,
 .info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
 .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_OFFSET) |
 BIT(IIO_CHAN_INFO_SCALE) |
 BIT(IIO_CHAN_INFO_SAMP_FREQ) |
 BIT(IIO_CHAN_INFO_HYSTERESIS),
 .scan_index = CHANNEL_CUSTOM_VALUE_4,
 }



 /* Capture samples in local storage */
 static int accel_3d_capture_sample(struct hid_sensor_hub_device *hsdev,
 unsigned usage_id,
 size_t raw_len, char *raw_data,
 void *priv)
 {
 struct iio_dev *indio_dev = platform_get_drvdata(priv);
 struct accel_3d_state *accel_state = iio_priv(indio_dev);
 int offset;
 int ret = -EINVAL;

 switch (usage_id) {
 case HID_USAGE_SENSOR_ACCEL_X_AXIS:
 case HID_USAGE_SENSOR_ACCEL_Y_AXIS:
 case HID_USAGE_SENSOR_ACCEL_Z_AXIS:
 case HID_USAGE_SENSOR_DATA_MOTION_STATE:
 case HID_USAGE_SENSOR_DATA_CUSTOM_VALUE2:
   case HID_USAGE_SENSOR_DATA_CUSTOM_VALUE3:
   case HID_USAGE_SENSOR_DATA_CUSTOM_VALUE4:
 offset = usage_id - HID_USAGE_SENSOR_ACCEL_X_AXIS;



 /* Parse report which is specific to an usage id*/
 static int accel_3d_parse_report(struct platform_device *pdev,
 struct hid_sensor_hub_device *hsdev,
 struct iio_chan_spec *channels,
 unsigned usage_id,
 struct accel_3d_state *st)
 {
 int ret;
 int i;

 for (i = 0; i = CHANNEL_CUSTOM_VALUE_4; ++i) {  //previously 
 CHANNEL_SCAN_INDEX_Z
 ret = sensor_hub_input_get_attribute_info(hsdev,



 After build /insmod i get the following dmesg :

 hid_sensor_accel_3d:HID-SENSOR-200073.3 auto : failed to setup attributes
 hid_sensor_accel_3d:HID-SENSOR-200073.3 auto.failed with error -1


 I am not getting what else I have to modify to avoid this error .If i remove
 the portion in bold(and use this original code
 :http://lxr.free-electrons.com/source/drivers/iio/accel/hid-sensor-accel-3d.c)
 I can happily insert the module without any error and can interact with the
 driver using my application.


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Re: from WHERE platform driver's probe is called?

[Daniel Baluta]

On Fri, Nov 21, 2014 at 3:16 PM, Sunil Shahu sunil.roc...@yahoo.in wrote:
 Hello,

 I am looking into platform driver and devices and understood HOW platform
 driver's probe is called from kernel doc and following forum.
 http://comments.gmane.org/gmane.linux.kernel.kernelnewbies/37050

 For further information I went through code in platform_driver_register()
 and got lost. I looked web but could not find substantiation information.

 I am still not able to locate from WHERE this probe function is called and
 WHO calls it?
 Can someone please point to source code or some other document related to
 this?

Does dump_stack() help?

Daniel.

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Re: fd type from number

[Daniel Baluta]

On Tue, Aug 19, 2014 at 6:38 PM, Loris Degioanni lo...@draios.com wrote:
 (resending making sure this is not part of another thread)

 I'm looking for an efficient way to determine the type of an fd (file,
 socket...) given its number, from a kernel module.
 The closest thing I found by looking at the kernel sources is
 sockfd_lookup(), which works but is limited to telling me if the fd is a
 socket or not.

 Is there something else I can look at?

https://www.kernel.org/doc/Documentation/filesystems/files.txt

See point 4.

Daniel.

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Re: A new way to dive into the kernel!

[Daniel Baluta]

 It's there any solution to this issue?

 I'm using mutt, It's ok.
Hi,

Evolution works for me.

thanks,
Daniel.

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Re: How can I 'getchar()' in module code?

[Daniel Baluta]

On Tue, Dec 3, 2013 at 4:20 PM, Bernd Petrovitsch
be...@petrovitsch.priv.at wrote:
 On Die, 2013-12-03 at 08:38 -0500, valdis.kletni...@vt.edu wrote:
 On Tue, 03 Dec 2013 20:35:41 +0800,  said:
  For debugging purpose, I want something like 'getchar()' that can pause
  execution in the module code. Do any candidates I can choose?

I think there is a way to stop execution :). Run your image under
qemu, and use gdb to
set breakpoints.

thanks,
Daniel.

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Re: How can I 'getchar()' in module code?

[Daniel Baluta]

On Tue, Dec 3, 2013 at 2:35 PM, 乃宏周 naive...@gmail.com wrote:
 For debugging purpose, I want something like 'getchar()' that can pause
 execution in the module code. Do any candidates I can choose?

No.

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Re: Can mm_struct of a process be null?

[Daniel Baluta]

On Fri, Nov 15, 2013 at 6:24 PM, Paul Davies C pauldavi...@gmail.com wrote:
 Hi,
 I happen to find this code snippet in the kernel source :

 struct mm_struct *mm=current-mm;

 /* some other code */

 if(mm){ /*==Why is this here? */
 /*read the contents by locking*/
 }

 The if  checks whether the mm_struct of the current process is NULL or not.
 That means the mm_struct of a process can become NULL. How can that happen?

mm_struct points to a process address space. It is NULL for kernel threads.

Daniel.

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Re: Initial git repository - kernel tree

[Daniel Baluta]

On Mon, May 13, 2013 at 10:51 AM, Kevin Wilson wkev...@gmail.com wrote:
 Hello,
 I have a question about git patches.
 When I run
 git log include/linux/skbuff.h
 and page down till the end, I reach
 1da177e Linux-2.6.12-rc2

 (I do it on the net-next tree.)

 git show 1da177e gives:
 Author: Linus Torvalds torva...@ppc970.osdl.org
 Date:   Sat Apr 16 15:20:36 2005 -0700

 Linux-2.6.12-rc2

 Initial git repository build. I'm not bothering with the full history,
 even though we have it. We can create a separate historical git
 archive of that later if we want to, and in the meantime it's about
 3.2GB when imported into git - space that would just make the early
 git days unnecessarily complicated, when we don't have a lot of good
 infrastructure for it.

 Let it rip!

 So this is the initial patch from 2005.

 Now, does it mean that prior to this patch all patches
 were not handled by git ? or was there some merging
 from an old tree to a new tree where history of git
 patches was removed in the new tree ?

Hi Kevin,

Please check this https://git.kernel.org/cgit/linux/kernel/git/tglx/history.git/

thanks,
Daniel.

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Re: misc device question

[Daniel Baluta]

On Wed, Dec 19, 2012 at 10:36 AM, Kevin Wilson wkev...@gmail.com wrote:

 Hello,kernelnewbies

 I am trying to develop a misc driver in 3.7.0 kernel.

 As a basis I copy and paste this code, *without any change*,

 http://virtlog.com/2008/03/25/linux-miscdevice-sample/

 And build it.
 after insmod I have :
 [root@n miscDevice]\ls -al /dev/mymisc
 crw--- 1 root root 10, 59 Dec 19 10:24 /dev/mymisc


 However, when trying to open this file I get:
 open: No such file or directory

 Any ideas why ?


You should implement open. Check this out [1]


 The program with which I try to open the device is simple, a few lines
 following here:
 int main()
 {
   int fd;

   fd = open(/dev/mymodule, O_RDONLY);

Isn't this supposed to be called /dev/mymisc ?

 if (fd == -1) {
 perror(open);
 exit(1);
 }
   printf(open succeeded\n);

 }


thanks,
Daniel.

[1] http://lxr.linux.no/#linux+v3.7.1/drivers/char/efirtc.c#L282
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Re: Linux Kernel Development

[Daniel Baluta]

On Sun, Sep 9, 2012 at 12:16 PM, Kaushal Shriyan
kaushalshri...@gmail.com wrote:
 On Sun, Sep 9, 2012 at 9:02 AM, Alexandru Juncu alex.ju...@rosedu.org wrote:
 On 9 September 2012 06:15, Kaushal Shriyan kaushalshri...@gmail.com wrote:
 Hi,

 I am interested to contribute to linux kernel development process. I
 have been working on Linux for the last ten years and have been a
 great fan of Linux OS since beginning. Any good references to start
 learning C and understand the linux kernel source code.

 Regards,

 Kaushal

 Hello!

 You could start by looking through the site of this community [0].
 They have some pointers.

 You should take a look at this video [1] first. It's a brief intro on
 how the Linux Kernel community works.

 But first, you should be familiar with C programming (it's good if you
 did some system programming in C). If you have the basic C experience
 and if you want to go onto kernel programming (not that hard) you
 should try reading some books (I would recommend these [2] [3]).

 After that, use the source! And if you get stuck, ask around (here,
 for example).

 Good luck and happy hacking!

 [0] http://kernelnewbies.org/KernelHacking
 [1] http://www.youtube.com/watch?v=LLBrBBImJt4
 [2] http://www.amazon.com/Linux-Kernel-Development-3rd-Edition/dp/0672329468
 [3] 
 http://www.amazon.com/Understanding-Linux-Kernel-Third-Edition/dp/0596005652/ref=pd_bxgy_b_text_z

 --
 Alexandru Juncu

 ROSEdu
 http://rosedu.org

 Hi,

 I am totally new to C Programming Language. How do i start learning C
 and which books or tutorials i need to refer.


I would recommend 'The C programming language' by K R :)[1].

thanks,
Daniel

[1] http://www.amazon.com/C-Programming-Language-2nd-Edition/dp/0131103628

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Re: Profiling my Modules

[Daniel Baluta]

On Thu, Apr 26, 2012 at 10:33 AM, Rishi Agrawal
rishi.b.agra...@gmail.com wrote:
 Hi All,

 I have a kernel module which has functions which take a lot of time in
 execution. I am curious to know how can I profile it, and find out the
 functions taking most of the time.

 I saw Oprofile, but it seems that I will have to build the whole kernel, and
 also that it will be difficult to profile my module through it.

 Any trick or tool will do.

Hello,

Have a look at perf [1].

thanks,
Daniel.

[1] https://perf.wiki.kernel.org/

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Re: slacks usage,..

[Daniel Baluta]

On Mon, Mar 5, 2012 at 11:00 AM, trisha yad trisha1ma...@gmail.com wrote:
 Hi All,

 I am going through below topic http://patches.linaro.org/6833/. I
 could not got the meaning of slacks. Why I need this ..
 Is there some real example of need of slacks.

Have you tried searching for it? :D [1].

thanks,
Daniel.

[1] https://lwn.net/Articles/369549/

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Re: Check if specific functionally is built into the kernel

[Daniel Baluta]

On Sun, Feb 26, 2012 at 7:08 PM, Arokux B. aro...@gmail.com wrote:
 Dear all,

 I have the following problem. Some functionality can be either built
 into the kernel or it can be build as a module. In the latter case the
 application should load the module.

 Is there a general approach to test if specific functionality is built
 statically or as a module?

If available, you can check .config file.
(e.g check if CONFIG_X_OPTION=Y or CONFIG_X_OPTION=m).

thanks,
Daniel.

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Re: cross compile linux

[Daniel Baluta]

On Sat, Feb 11, 2012 at 9:05 AM, chromaticwt zac zac.3.14...@gmail.com wrote:
 what is the proper way to cross compile the linux kernel from one arch to
 another? specifically,
 i386 - ppc.

You should use a cross-compiler. I recommend you crosstool-ng.
Use google for references. [1]

thanks,
Daniel.

[1] 
http://forum.samdroid.net/wiki/showwiki/How+to+build+cross+toolchains+for+ARM+crosstool-NG

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Re: How to create patch for checkpatch.pl cleanups

[Daniel Baluta]

On Sun, Feb 5, 2012 at 11:00 PM, kashyap gada kashyapg...@yahoo.com wrote:
 Hello Linux Newbies, I'm one too. I was looking out for some clean up work
 and I ran the checkpatch.pl script. I came across a file with some 400
 errors and 200 warnings. Now there were bunch of 80 char per line warning ,
 braces and related things. I don't want to be sending patches for each and
 every error or warning I fix as it becomes tedious and If i send lots of
 correction patches in one go the kernel maintainers wont accept it. I want
 to know Can we correct all similar errors or warnings in one patch? or
 series of patches?

Regarding 80 chars per line issues, people are discussing right now
on increasing the limit to 100. See [1].

For the other issues, just send a patch with all the changes. It should
be fine since you are modifying one single file.

thanks,
Daniel.

[1] https://lkml.org/lkml/2012/2/5/141

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Re: How to use /proc

[Daniel Baluta]

On Sun, Feb 5, 2012 at 11:07 PM, Surenkumar Nihalani su...@gatech.edu wrote:
 Hello Guys,

 I am CS student trying to write a kernel module as a part of my class
 assignment. I wanted to know, from within kernel, how do I read and write
 data to my proc file?
 I need to store state from last call of my function.

Hello,

Have you tried searching on the internet? :D [1].

Another approach is to see how an existing proc
entry is handled. Look for example at /proc/sched_debug [2].

thanks,
Daniel.

[1] http://www.ibm.com/developerworks/linux/library/l-proc/index.html
[2] http://lxr.linux.no/linux+v3.2.4/kernel/sched_debug.c#L393

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Re: using sizeof operator

[Daniel Baluta]

On Sun, Jan 22, 2012 at 10:17 PM, Sukrit Sangwan
sukritsang...@gmail.com wrote:
 I found an instance where sizeof(struct xyz) is used instead of
 sizeof(variablename).
 I want to ask if it would be appropriate to contact the author about the
 same.

Well, this doesn't really matter, but the recommended practice is to use
sizeof(*pointer);

Please keep intact Cc's list.

thanks,
Daniel.

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Re: [OOT] About the symbols in binary file.

[Daniel Baluta]

On Fri, Jan 20, 2012 at 11:56 AM, nilesh nilesh.tay...@netscout.com wrote:
 Hi,

 The question is not completely related to kernel. But I came across
 similar question when debugging in kernel.

 I tried dissecting the SSL library using 'nm' command. It is showing the
 list of symbols along with some generic addresses (to be used when
 relocating).
 Also there are some characters 't', 'T', 'U'. I guess these correspond
 to properties of symbols - like static, extern etc.

 Could someone please point out what exactly each character corresponds to?
 I mean looking at the character, we should be able to denote if it's a
 static symbol or inline etc. Do we have any such mapping?

man nm :)

thanks,
Daniel.

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Re: multiple definition error from dl-addr.c with addition of printf, in glibc compilation

[Daniel Baluta]

On Thu, Dec 8, 2011 at 10:59 AM, solmac john johnsol...@gmail.com wrote:
 Hi All,

 in glibc-2.13/nptl/sigaction.c, i just put a simple printf(test\n); and my
 glibc compilation fails. Just adding a printf gives me multiple definitions
 of _itoa from dl-addr.c and i have no idea why. Can any body please tell me
 why is this happening and possible solution. For better clarity here is the

Are there any variable declarations after printf?

thanks,
Daniel.

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Re: How to hook the system call?

[Daniel Baluta]

On Wed, Nov 23, 2011 at 11:22 AM, Alexandru Juncu alex.ju...@rosedu.org wrote:
 On Wed, Nov 23, 2011 at 10:40 AM, Geraint Yang geraint0...@gmail.com wrote:
 Hello everyone,

 I am going to hook a system call like 'read' or 'send' by modifying the
 sys_call_table, but it seems that the sys_call_table is in read only page,
 how can I set modify the sys_call_table ? Or if there any method that I can
 use to hook a system call in module without modify the kernel source?

 Thanks!

 On a 2.6.35 kernel, it worked for me just by changing an entry in the
 sys_call_table, within a kernel module.  Something like this:

Alex,
I am pretty sure that you are using a hacked version of 2.6.35.

Geraint,
In order to be able to hook a syscall you must do the following:

1. export syscall_table in arch/x86/kernel/i386_ksyms_32.c

extern void* sys_call_table[];
EXPORT_SYMBOL(sys_call_table);

2. make sys_call_table writebale. In arch/x86/kernel/entry_32.S
you must have:

.section .data,a
#include syscall_table_32.S

thanks,
Daniel.

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Re: x86 kernel build chain - how bzImage gets created

[Daniel Baluta]

On Tue, Nov 22, 2011 at 12:46 PM, Graeme Russ graeme.r...@gmail.com wrote:
 Hi All,

 Hopefully this will help demystify the build process

 Notation:
 primary input file (file size in bytes)
  |
  + additional input file
  |
  * command
  |
  \- output file (file size in bytes)

 The file sizes are arbitrary and are based on the current configuration
 options I have set for a small kernel. They are simply there to illustrate
 the relative differences in file sizes.

Great! Thanks for sharing this.

 Note that vmlinux.o is not used to generate bzImage but I've included it
 for completeness

[...]
 + net/built-in.o
 |
 * ld -m elf_i386 -r -o vmlinux.o
 |
 \-vmlinux.o (2,889,050)

What is the purpose of vmlinux.o then?

thanks,
Daniel.

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Re: Trouble removing character device

[Daniel Baluta]

On Wed, Oct 19, 2011 at 7:04 PM, Kai Meyer k...@gnukai.com wrote:
 I can't seem to get my character device to remove itself from the
 /proc/devices list. I'm calling all of the following functions like so:

 alloc_chrdev_region(dev, 0, 5, my_char);
 cdev_init(my_cdev, my_ops);
 cdev_add(my_cdev, MKDEV(my_major, my_minor), 1);
 cdev_del(my_cdev);
 unregister_chrdev_region(my_major, 5);

 It seems like I'm missing something, but I can't find it. I'm
 referencing the Linux Device Drivers v3, chapter 3. In the example code,
 the scull_cleanup_module function calls cdev_dell and
 unregister_chrdev_region, just like I do.

 To be clear, after I unload my module (after calling cdev_del and
 unregister_chrdev_region), my my_char string still shows up in
 /proc/devices.

Did you check  return codes for all functions?
Also, can you post a link to the code?

thanks,
Daniel.

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Re: Getting 'bad file number' error writing to device driver

[Daniel Baluta]

On Mon, Oct 17, 2011 at 6:49 PM, Philip Anil-QBW348
anil.phi...@motorolasolutions.com wrote:
 -Original Message-
 From: Daniel Baluta [mailto:daniel.bal...@gmail.com]
 Sent: Saturday, October 15, 2011 3:34 AM
 To: Philip Anil-QBW348
 Cc: kernelnewbies@kernelnewbies.org
 Subject: Re: Getting 'bad file number' error writing to device driver

 On Sat, Oct 15, 2011 at 2:42 AM, Philip Anil-QBW348
 anil.phi...@motorolasolutions.com wrote:
 I am calling the driver from an Android program (OMAP4/Blaze). It calls a
 c++ program via JNI which then calls the device driver.
 Someone suggested it might be a permissions problem - the program is running
 in user mode.

 on Blaze board, /system/bin
 # ls -l
 -rwxrwxrwx system   system   7636 2011-09-30 03:53 mydriver

 Will strace still be useful?
 In general, in Linux, how does one enable a user program to call a custom
 device driver?

 Please don't top post! :)

 strace will be useful to check the parameters for open, write system calls.

 EBADF  fd is not a valid file descriptor or is not open for writing.
 Ok, so either open fails, or you don't have the permission to write
 into /dev/mydriver file.

 --
 I apologize for 'top-posting' (I did not know that was undesirable - most 
 email clients and also Google newsgroups put one's reply at the top.).
 Yes, the /dev/mydriver had permissions 600. I did a chmod to 666 and it 
 worked.
 I am performing security testing and want to see if a program running in user 
 mode can elevate its privileges to call the device driver which has 
 permissions 600.
 Any ideas how it can?
 Anil

Maybe setuid bit can help you ([1]). When this bit is set, a certain program
can run with the privileges of its owner.

thanks,
Daniel.

[1] http://en.wikipedia.org/wiki/Setuid

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Re: Getting 'bad file number' error writing to device driver

[Daniel Baluta]

On Sat, Oct 15, 2011 at 2:42 AM, Philip Anil-QBW348
anil.phi...@motorolasolutions.com wrote:
 I am calling the driver from an Android program (OMAP4/Blaze). It calls a
 c++ program via JNI which then calls the device driver.
 Someone suggested it might be a permissions problem - the program is running
 in user mode.

 on Blaze board, /system/bin
 # ls -l
 -rwxrwxrwx system   system   7636 2011-09-30 03:53 mydriver

 Will strace still be useful?
 In general, in Linux, how does one enable a user program to call a custom
 device driver?

Please don't top post! :)

strace will be useful to check the parameters for open, write system calls.

EBADF  fd is not a valid file descriptor or is not open for writing.
Ok, so either open fails, or you don't have the permission to write
into /dev/mydriver file.

Another thing that I can think of, is that your driver's write
function is wrong, and returns
-EBADF in some case ?

Can you give us a pointer to your driver?

thanks,
Daniel.

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Re: Why can the kernel be stuck by a busy kernel thread ?

[Daniel Baluta]

On Fri, Oct 14, 2011 at 5:04 PM, Parmenides mobile.parmeni...@gmail.com wrote:
 Hi,

   I code a kernel module which do some nop. When inserted into the
 kernel, the kernel will be stuck and can not reponse my keypress
 anymore. So, I have to reboot to get out. Why?

Is kernel preemption activated? Could you check for # grep
CONFIG_PREEMPT .config?

thanks,
Daniel.

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Re: Getting 'bad file number' error writing to device driver

[Daniel Baluta]

Hello,

 I am trying to write to mydriver but get a 'Bad file number' error.

 int fd = open(/dev/mydriver,O_RDWR);

 this opens successfully as fd is not -1.

 ssize_t bytesToWrite = strlen(buf);

 value is: bytesToWrite 28

 ssize_t bytesWritten = write(fd,buf,bytesToWrite);

 value is: bytesWritten -1

 __android_log_print(ANDROID_LOG_INFO,__FILE__,ANIL
 strerror(errno) %s,  strerror(errno));

 value is: strerror(errno) Bad file number

Please use strace and let us know the full trace of system calls.
Also, if possible
could you paste the 'write' function of your driver?

thanks,
Daniel.

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TCP_DELACK_MIN vs TCP_ATO_MIN

[Daniel Baluta]

Hello,

RFC2582, Section 4.2 says:

... an ACK SHOULD be generated for at least every second
full-sized segment, and MUST be generated within 500 ms
of the arrival of the first unacknowledged packet. .


I guess that the delayed ACK timeout is computed in tcp_send_delayed_ack:

===
void tcp_send_delayed_ack(struct sock *sk)
{
struct inet_connection_sock *icsk = inet_csk(sk);
int ato = icsk-icsk_ack.ato;
unsigned long timeout;

   /*  */
/* Stay within the limit we were given */
timeout = jiffies + ato;



Can one explain what is the difference between TCP_DELACK_MIN and
TCP_ATO_MIN, specifically if the timeout (ato) is always in the interval
[TCP_DELACK_MIN, TCP_DELACK_MAX] ?

I want to make the delayed ack timeout configurable as some guys tried
here [1],
so for this reason I plan to make TCP_DELACK_MIN and TCP_DELACK_MAX
tunable via proc entries.

thanks,
Daniel.

[1] http://kerneltrap.org/mailarchive/linux-netdev/2008/9/9/3245554

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Re: TCP_DELACK_MIN vs TCP_ATO_MIN

[Daniel Baluta]

 Now the default value is of both the macros is same.

 But if you want to make delayed ack timeout configurable, then I think you
 should give proc interface for TCP_DELACK_MIN.

Thanks Rohan. Then also I have to export TCP_DELACK_MAX since I think
ato cannot grow over this value.

thanks,
Daniel.

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Re: how to use hashmap in kernel module?

[Daniel Baluta]

On Mon, Sep 19, 2011 at 9:23 AM, Jon Zhou jon.z...@jdsu.com wrote:
 Hi

 I want to hashmap to store datat in kernel module, how can I do this? Any 
 existed code?
Hello,

There are a lot of places where hashes are used. Just grep for 'hash'
 through the kernel sources.

For example have a look at futex_queues [1].

thanks,
Daniel.

[1] http://lxr.linux.no/linux+v3.0.4/kernel/futex.c#L150

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TCP - RST flag

[Daniel Baluta]

Hello,

Please help me understanding the behavior of the following
TCP conversation.

You can find bellow a snippet of the (FTP) conversation captured both
on client (C) and server (S).

[client]$ tcpdump  -n  -r client-6-conv.cap
[P1] 49.045690 IP 10.10.0.1.21  10.10.0.20.58277: Flags [P.], seq
197:220, ack 81, win 757, length 23
[P2] 49.046600 IP 10.10.0.20.58277  10.10.0.1.21: Flags [.], ack 220,
win 738, length 0
[P3] 49.047462 IP 10.10.0.20.58277  10.10.0.1.21: Flags [P.], seq
81:87, ack 220, win 738, length 6
[P5] 49.048757 IP 10.10.0.1.21  10.10.0.20.58277: Flags [F.], seq
242, ack 87, win 757, length 0
[P6] 49.048794 IP 10.10.0.20.58277  10.10.0.1.21: Flags [.], ack 220,
win 738, options [nop,nop,sack 1 {242:243}], length 0
[P4] 49.048801 IP 10.10.0.1.21  10.10.0.20.58277: Flags [P.], seq
220:242, ack 87, win 757, length 22
[P7] 49.048833 IP 10.10.0.20.58277  10.10.0.1.21: Flags [.], ack 243,
win 715, length 0
[P8] 49.049566 IP 10.10.0.20.58277  10.10.0.1.21: Flags [F.], seq 87,
ack 243, win 715, length 0
[P9] 49.050889 IP 10.10.0.1.21  10.10.0.20.58277: Flags [R], seq
1672731590, win 0, length 0

[server]$ tcpdump  -n  -r server-6-conv.cap
[P1] 49.059740 IP 10.10.0.1.21  10.10.0.20.58277: Flags [P.], seq
197:220, ack 81, win 757, length 23
[P2] 49.061394 IP 10.10.0.20.58277  10.10.0.1.21: Flags [.], ack 220,
win 738, length 0
[P3] 49.061760 IP 10.10.0.20.58277  10.10.0.1.21: Flags [P.], seq
81:87, ack 220, win 738, length 6
[P4] 49.062794 IP 10.10.0.1.21  10.10.0.20.58277: Flags [P.], seq
220:242, ack 87, win 757, length 22
[P5] 49.062843 IP 10.10.0.1.21  10.10.0.20.58277: Flags [F.], seq
242, ack 87, win 757, length 0
[P6] 49.063808 IP 10.10.0.20.58277  10.10.0.1.21: Flags [.], ack 220,
win 738, options [nop,nop,sack 1 {242:243}], length 0
[P7] 49.063823 IP 10.10.0.20.58277  10.10.0.1.21: Flags [.], ack 243,
win 715, length 0
[P8] 49.064271 IP 10.10.0.20.58277  10.10.0.1.21: Flags [F.], seq 87,
ack 243, win 715, length 0
[P9] 49.064481 IP 10.10.0.1.21  10.10.0.20.58277: Flags [R], seq
1672731590, win 0, length 0

What happens is that servers sends packets P4 and P5, but client
receives P5 before P4.
Since SACK is enabled, client will send a SACK (P6) ack-ing P5.

Then client sees P4, and will send an ack (P7) for P4, then sends P8
with FIN flag set.
What I don't understand, is why server responds with RST (P9) instead of ACK?

This is was obtained on 2.6.32.43. I have also attached full capture files.

I am reading TCP's RFC and kernel code, but so far I haven't reached
a conclusion.

thanks,
Daniel.


server-6-conv.cap
Description: Binary data


client-6-conv.cap
Description: Binary data
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Re: TCP - RST flag

[Daniel Baluta]

On Tue, Aug 23, 2011 at 11:55 PM, Eric Dumazet eric.duma...@gmail.com wrote:
 Le mardi 23 août 2011 à 23:31 +0300, Daniel Baluta a écrit :
 Hello,

 Please help me understanding the behavior of the following
 TCP conversation.

 You can find bellow a snippet of the (FTP) conversation captured both
 on client (C) and server (S).

 [client]$ tcpdump  -n  -r client-6-conv.cap
 [P1] 49.045690 IP 10.10.0.1.21  10.10.0.20.58277: Flags [P.], seq
 197:220, ack 81, win 757, length 23
 [P2] 49.046600 IP 10.10.0.20.58277  10.10.0.1.21: Flags [.], ack 220,
 win 738, length 0
 [P3] 49.047462 IP 10.10.0.20.58277  10.10.0.1.21: Flags [P.], seq
 81:87, ack 220, win 738, length 6
 [P5] 49.048757 IP 10.10.0.1.21  10.10.0.20.58277: Flags [F.], seq
 242, ack 87, win 757, length 0
 [P6] 49.048794 IP 10.10.0.20.58277  10.10.0.1.21: Flags [.], ack 220,
 win 738, options [nop,nop,sack 1 {242:243}], length 0
 [P4] 49.048801 IP 10.10.0.1.21  10.10.0.20.58277: Flags [P.], seq
 220:242, ack 87, win 757, length 22
 [P7] 49.048833 IP 10.10.0.20.58277  10.10.0.1.21: Flags [.], ack 243,
 win 715, length 0
 [P8] 49.049566 IP 10.10.0.20.58277  10.10.0.1.21: Flags [F.], seq 87,
 ack 243, win 715, length 0
 [P9] 49.050889 IP 10.10.0.1.21  10.10.0.20.58277: Flags [R], seq
 1672731590, win 0, length 0

 [server]$ tcpdump  -n  -r server-6-conv.cap
 [P1] 49.059740 IP 10.10.0.1.21  10.10.0.20.58277: Flags [P.], seq
 197:220, ack 81, win 757, length 23
 [P2] 49.061394 IP 10.10.0.20.58277  10.10.0.1.21: Flags [.], ack 220,
 win 738, length 0
 [P3] 49.061760 IP 10.10.0.20.58277  10.10.0.1.21: Flags [P.], seq
 81:87, ack 220, win 738, length 6
 [P4] 49.062794 IP 10.10.0.1.21  10.10.0.20.58277: Flags [P.], seq
 220:242, ack 87, win 757, length 22
 [P5] 49.062843 IP 10.10.0.1.21  10.10.0.20.58277: Flags [F.], seq
 242, ack 87, win 757, length 0
 [P6] 49.063808 IP 10.10.0.20.58277  10.10.0.1.21: Flags [.], ack 220,
 win 738, options [nop,nop,sack 1 {242:243}], length 0
 [P7] 49.063823 IP 10.10.0.20.58277  10.10.0.1.21: Flags [.], ack 243,
 win 715, length 0
 [P8] 49.064271 IP 10.10.0.20.58277  10.10.0.1.21: Flags [F.], seq 87,
 ack 243, win 715, length 0
 [P9] 49.064481 IP 10.10.0.1.21  10.10.0.20.58277: Flags [R], seq
 1672731590, win 0, length 0

 What happens is that servers sends packets P4 and P5, but client
 receives P5 before P4.
 Since SACK is enabled, client will send a SACK (P6) ack-ing P5.

 Then client sees P4, and will send an ack (P7) for P4, then sends P8
 with FIN flag set.
 What I don't understand, is why server responds with RST (P9) instead of ACK?

 This is was obtained on 2.6.32.43. I have also attached full capture files.

 I am reading TCP's RFC and kernel code, but so far I haven't reached
 a conclusion.

 TCP in RFC 1122 section 4.2.2.13:

  A host MAY implement a half-duplex TCP close sequence, so that an
  application that has called CLOSE cannot continue to read data from the
  connection. If such a host issues a CLOSE call while received data is
  still pending in TCP, or if new data is received after CLOSE is called,
  its TCP SHOULD send a RST to show that data was lost.

So, this means that server's CLOSE operation is issued while received
data is still pending? I will analyze ftp's server code, but this is strange
since P4 [221 Have a nice day!\r\n] it is generated as a response for
P3 [QUIT\r\n]. So P4 must have been fully received.

Also, looking at the capture no data is received from the client after
server calls CLOSE (P5) (there are only ACKs and FIN - P6, P7, P8).

 This is why some apps first call shutdown(), then drain receive queue,
 then close()

This makes sense :).

thanks Eric.

Daniel.

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Re: TCP - RST flag

[Daniel Baluta]

On Wed, Aug 24, 2011 at 12:50 AM, Eric Dumazet eric.duma...@gmail.com wrote:
 Le mercredi 24 août 2011 à 00:32 +0300, Daniel Baluta a écrit :
 On Tue, Aug 23, 2011 at 11:55 PM, Eric Dumazet eric.duma...@gmail.com 
 wrote:

  TCP in RFC 1122 section 4.2.2.13:
 
   A host MAY implement a half-duplex TCP close sequence, so that an
   application that has called CLOSE cannot continue to read data from the
   connection. If such a host issues a CLOSE call while received data is
   still pending in TCP, or if new data is received after CLOSE is called,
   its TCP SHOULD send a RST to show that data was lost.

 So, this means that server's CLOSE operation is issued while received
 data is still pending? I will analyze ftp's server code, but this is strange
 since P4 [221 Have a nice day!\r\n] it is generated as a response for
 P3 [QUIT\r\n]. So P4 must have been fully received.


 tcpdump only shows TCP stack did receive the frame, not that it was
 _read_ by application.

 Only strace could eventually say if the input queue was really drained
 before the close().
 Maybe server decided to close the connexion before reading the QUIT
 command from client.

 Also, looking at the capture no data is received from the client after
 server calls CLOSE (P5) (there are only ACKs and FIN - P6, P7, P8).

 That doesnt matter.

 If data was received (and ACKnowledged by TCP stack) _before_ close(fd),
 but not yet read by application, TCP must send an RST to be RFC
 compliant.

I see. Thanks a lot for your explanations. I will further use strace
to see what's going on.

Daniel.

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Re: One more question on alignment

[Daniel Baluta]

On Sat, Aug 6, 2011 at 10:17 PM, subin gangadharan
subingangadha...@gmail.com wrote:
 Hi,
 This is a text excerpt from the article [1].
 Below paragraph I didn't understand quite well.Mainly in bold letters.Could
 anybody please explain how this will lead to an infinite loop.

It seems self-explanatory. Most atomic ops are written to retry upon a failed
store, and  on PowerPC an atomic store to an unaligned address always fails,
thus the processor will infinitely try to store the value, without having
the chance to fix the unaligned access (as would have happened if an exception
was thrown).


 Unfortunately, the PowerPC does not throw an exception when atomically
 storing to an unaligned address. Instead, the store simply always fails.
 This is bad because most atomic functions are written to retry upon a failed
 store, under the assumption they were preempted. These two circumstances
 combine to where your program will go into an infinite loop if you attempt
 to atomically store to an unaligned address. Oops.

thanks,
Daniel.

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Re: question about staging tree branches

[Daniel Baluta]

On Tue, Jul 12, 2011 at 7:01 PM, Greg KH g...@kroah.com wrote:
 On Tue, Jul 12, 2011 at 12:15:17PM +0530, Prashant Shah wrote:
 Hi,

 There are 4 branches in the staging tree

   remotes/staging/master
   remotes/staging/ralink
   remotes/staging/staging-linus
   remotes/staging/staging-next

 Is the staging-linus is what Linus merges and staging-next is merged
 by linux-next tree ?

 No, staging-linus is what goes to Linus for this kernel release, after
 the -rc1 kernel is out.  It is picked up in the linux-next daily
 releases.

 staging-next is what goes to Linus for the next kernel release after
 this one.  It too is picked up in the linux-next daily releases.

 ralink is an old branch of mine that I need to delete that has an
 obsolete ralink driver in it that I was working on cleaning up.  Anyone
 remember what the command to delete a remote branch is?  I always need
 to look it up...

According to Google ([1]) this should be:
# git push remote :remote_branch

thanks,
Daniel.

[1] http://yuji.wordpress.com/2010/06/11/git-delete-remote-branch/

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Re: timer problem

[Daniel Baluta]

Hello Prashant,

 struct timer_list tim;

 void timfunc(unsigned long data)
 {
[..]
        schedule_timeout(10 * HZ);
[..]
 }

 static int __init init_testmod(void)
 {
        init_timer(tim);
        tim.expires = jiffies + HZ*5;
        tim.data = 1000;
        tim.function = timfunc;
        add_timer(tim);
        return 0;
 }

You can find here ([1]) a good source for documenting
on kernel timers API.

Basically, the kernel has a list with registered timers and
runs the associated handlers when timeout expires.

Looking at your code, you've initialized the timer but you didn't
added it to kernel timers list.

You can find here a simple example of how to setup a timer ([2]).

Please read this [3], and figure out why even after you'll correctly
setup the timer, your timer handler will cause you trouble.

thanks,
Daniel.


[1] http://www.ibm.com/developerworks/linux/library/l-timers-list/index.html
[2] http://lxr.linux.no/linux+v2.6.39/arch/blackfin/kernel/nmi.c#L176
[3] http://www.kernel.org/pub/linux/kernel/people/rusty/kernel-locking/c557.html

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Re: Problem in compiling kernel

[Daniel Baluta]

On Wed, Jun 29, 2011 at 9:28 AM, Mulyadi Santosa
mulyadi.sant...@gmail.com wrote:
 On Wed, Jun 29, 2011 at 01:08, Daniel Baluta daniel.bal...@gmail.com wrote:
 On Tue, Jun 28, 2011 at 8:39 PM, Ponkumaran Annadurai
 aspkuma...@gmail.com wrote:


 I got struck in making initrd file, I got the following error


 root@rocker:/boot# mkinitramfs -o  initrd.img-2.6.39.1 2.6.39.1Y

 2.6.39.1Y? - shouldn't it be 2.6.39.1.

 Daniel, I guess Ponkumaran did something (wrong) with extra
 version...what do you think?

Mulyadi, I don't see how he could have changed EXTRA_VERSION from Makefile.

Ponkumaran, could you try running:
# mkinitramfs -o  initrd.img-2.6.39.1 2.6.39.1

thanks,
Daniel.

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Re: Problem in compiling kernel

[Daniel Baluta]

On Wed, Jun 29, 2011 at 4:37 PM, Ponkumaran Annadurai
aspkuma...@gmail.com wrote:


 On Wed, Jun 29, 2011 at 12:42 PM, Daniel Baluta daniel.bal...@gmail.com
 wrote:

  I got struck in making initrd file, I got the following error
 
 
  root@rocker:/boot# mkinitramfs -o  initrd.img-2.6.39.1 2.6.39.1Y
 
  2.6.39.1Y? - shouldn't it be 2.6.39.1.
 
  Daniel, I guess Ponkumaran did something (wrong) with extra
  version...what do you think?


 Mulyadi, I don't see how he could have changed EXTRA_VERSION from
 Makefile.

 No, I didn do anything in the Makefile

 Ponkumaran, could you try running:
 # mkinitramfs -o  initrd.img-2.6.39.1 2.6.39.1

 I tried this one first but I was prompted that the folder 2.6.39.1 is not
 found in /lib/modules. Then I found a folder named 2.6.39.1Y thats why I
 used this name. But now I guess that this Y is given by me during
 configuration in the place for local version option. Is that any problem
 with that?

I don't know :). I would recommend you to start a fresh install. It's
obvious that you've did something wrong in the first time.

Compiling the kernel should be fairly easy.
thanks,
Daniel.

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Re: Problem in compiling kernel

[Daniel Baluta]

 Have you tried to setup some sort of cross-compilation environment?
 Could you check CROSS_COMPILE env variable?

  Yes, I have given yes for that option during configuration

OK, then that's your problem. CROSS_COMPILE is a string
pointing to your cross compiler prefix.

thanks,
Daniel.

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Re: Problem in compiling kernel

[Daniel Baluta]

On Tue, Jun 28, 2011 at 2:07 PM, Ponkumaran Annadurai
aspkuma...@gmail.com wrote:


 On Tue, Jun 28, 2011 at 1:13 PM, Daniel Baluta daniel.bal...@gmail.com
 wrote:

  Have you tried to setup some sort of cross-compilation environment?
  Could you check CROSS_COMPILE env variable?

   Yes, I have given yes for that option during configuration

 OK, then that's your problem. CROSS_COMPILE is a string
 pointing to your cross compiler prefix.

 thanks,
 Daniel.


 Yes, It worked. Thank you sir. But I couldn't understand the reason. Can you
 explain this to me?

Please keep kernelnewbies to CC:, so that other can read about this problem
if they hit it.

The reason for which it didn't work is that you haven't set a valid
cross-compiler
prefix in CROSS_COMPILE

When you set a cross-compiler prefix, the value stored in CROSS_COMPILE is
concatenated with the name of each tool used to compile your kernel.

For example, objdump will be used as ${CROSS_COMPILE}objdump. You set
CROSS_COMPILE=Y, and the tool to be used is now named Yobjdump, which
obviously doesn't exist.

Valid values for CROSS_COMPILE look like this: CROSS_COMPILE=
mips64-octeon-linux-gnu-.

Hope that things are now more clear.

thanks,
Daniel

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Re: Problem in compiling kernel

[Daniel Baluta]

On Mon, Jun 27, 2011 at 7:21 PM, Ponkumaran Annadurai
aspkuma...@gmail.com wrote:
 Hello,

 I encountered the following error while compiling the kernel version
 linux-2.6.39.1. So I am giving here what I got on my screen.

 root@rocker:/usr/src/linux-2.6.39.1# make
   CHK include/linux/version.h
   CHK include/generated/utsrelease.h
   CC  kernel/bounds.s
   GEN include/generated/bounds.h
   CC  arch/x86/kernel/asm-offsets.s
   GEN include/generated/asm-offsets.h
   CALL    scripts/checksyscalls.sh
   HOSTCC  scripts/genksyms/genksyms.o
   SHIPPED scripts/genksyms/lex.c
   SHIPPED scripts/genksyms/parse.h
   SHIPPED scripts/genksyms/keywords.c
   HOSTCC  scripts/genksyms/lex.o
   SHIPPED scripts/genksyms/parse.c
   HOSTCC  scripts/genksyms/parse.o
   HOSTLD  scripts/genksyms/genksyms
   CC  scripts/mod/empty.o
 /bin/sh: Yobjdump: not found
   HOSTCC  scripts/mod/mk_elfconfig
   MKELF   scripts/mod/elfconfig.h
   HOSTCC  scripts/mod/file2alias.o
   HOSTCC  scripts/mod/modpost.o
   HOSTCC  scripts/mod/sumversion.o
   HOSTLD  scripts/mod/modpost
   HOSTCC  scripts/selinux/genheaders/genheaders
   HOSTCC  scripts/selinux/mdp/mdp
   HOSTCC  scripts/kallsyms
   HOSTCC  scripts/conmakehash
   HOSTCC  scripts/recordmcount
   CC  init/main.o
 /bin/sh: Yobjdump: not found
   CHK include/generated/compile.h
   UPD include/generated/compile.h
   CC  init/version.o
 /bin/sh: Yobjdump: not found
   CC  init/do_mounts.o
 /bin/sh: Yobjdump: not found
   CC  init/do_mounts_rd.o
 /bin/sh: Yobjdump: not found
   CC  init/do_mounts_initrd.o
 /bin/sh: Yobjdump: not found
   CC  init/do_mounts_md.o
 /bin/sh: Yobjdump: not found
   LD  init/mounts.o
 /bin/sh: Yld: not found
 make[1]: *** [init/mounts.o] Error 127
 make: *** [init] Error 2

Have you tried to setup some sort of cross-compilation environment?
Could you check CROSS_COMPILE env variable?

thanks,
Daniel.

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Re: threading problem

[Daniel Baluta]

Hello Murali,

 I have a device driver which provides the IOCTL function for the
 application to interact.

 when the application sends the IOCTL CMD_GO, my driver has to toggle a
 GPIO every 500 m Sec. until a 3 minute timeout occurs or a CMD_STOP
 IOCTL is received.

 I tried the DECLARE_WORK, DECLARE_DELAYED_WORK and also
 kernel_thread() to meet this requirement with no success.


Could you please show us the code?

thanks,
Daniel.

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Getting started with kernel sources [Was: No subject]

[Daniel Baluta]

On Thu, Jun 16, 2011 at 2:41 PM, Venkateswarlu P
p.venkatesh...@gmail.com wrote:
 how to understand the kernerl source  files in a simple way


 what header  files i have to understand first


 for example  to understand  do_fork() function  for process
 creation  which is defined in  kernel/fork.c

There's no shortcuts. :)

Use dump_stack() in various places and check
what functions are called.
Also use lxr ([1]) for code browsing.

Please add a relevant Subject description to your emails.

thanks,
Daniel.

[1] http://lxr.linux.no/

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Re: Linux module for causing a system hard lock-up

[Daniel Baluta]

Hello,

 Could anyone please let me know how can I achieve this?

Is hard lockup detector enabled in your system? Could you
post your .config.

thanks,
Daniel.

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show_regs vs dump_stack in watchdog_timer_fn

[Daniel Baluta]

Hello,

Why the stack isn't always dumped in watchdog_timer_fn ([1])?

Registers content is useful, but without a stack trace it's very
hard to find the task which caused system softlockup.


thanks,
Daniel.

[1] http://lxr.linux.no/linux+v2.6.39/kernel/watchdog.c#L292

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Re: OS Books suggestion

[Daniel Baluta]

Hello,

 * The design of unix operating system (Bach)

 * Modern operative systems (Tanenbaum)

 * Operating Systems design and implementation(Tanenbaum)

 I haven't done formal Computer Science studies, and I don't the time to read 
 the three of them, but as I am working very close to the linux kernel, I am 
 trying to sharp my skills a little.

I would further suggest:
  * kernel area: Linux Kernel Development [1]
  * OS area: Operating Systems Concepts [2]
  * systems area: The Linux Programming Interface [3]

Anyhow, while reading books it's ok in the beginning
to really have a progress in your learning progress
you should start looking at the code.


thanks,
Daniel.

[1] http://www.amazon.com/Linux-Kernel-Development-Robert-Love/dp/0672325128
[2] 
http://www.amazon.com/Operating-Concepts-Seventh-Abraham-Silberschatz/dp/0471694665
[3] http://nostarch.com/tlpi

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Re: Can we map a device address to two different memory locations?

[Daniel Baluta]

On Fri, May 27, 2011 at 1:49 PM, sandeep kumar
coolsandyfor...@gmail.com wrote:
 Hi all,
 Memory mapping is done so that CPU can access the devices, which it cant
 unless.

 Now the question is can we memory map a one device resource(say some
 iomemory) to two different memory locations?
 the other way of seeing at this question is,
 Will ioremap() gives different 'virtual addresses' when called multiple
 times?

I can't see any reasons for which you can't do that.
The best way to find out, is to try it.

thanks,
Daniel.

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Re: how to download a specific kernel version from kernel.org

[Daniel Baluta]

Try this:

http://www.kernel.org/pub/linux/kernel/v2.6/linux-2.6.35.tar.gz

thanks,
Daniel.

On Mon, May 23, 2011 at 2:08 PM, sandeep kumar
coolsandyfor...@gmail.com wrote:
 Hi all,
 I want to download kernel version 2.6.35 for a specific reason.
 I have a patch which is to be applied to that specific kernel revision.

 But in kernel.org i m finding only 2.6.35.13 only.(May be i cudnot find it)

 Pls tell me How to download that?

 Thanks in advance..

 --
 With regards,
 Sandeep Kumar Anantapalli,

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Re: Linux kernel test suites

[Daniel Baluta]

On Sat, May 21, 2011 at 2:33 AM, Abu Rasheda rcpilot2...@gmail.com wrote:
 Can someone pass me pointer to Linux kernel test suite ? I am
 specially interested in iptables (netfilter) and socket APIs.

Hello Abu,

Linux Test Project can be a good starting point ([1]).

thanks,
Daniel.

[1] http://ltp.sourceforge.net/

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Re: unlocked_ioctl explanation

[Daniel Baluta]

2011/5/19 Ezequiel García elezegar...@yahoo.com.ar

 Thanks Dave for your answer. I guess the same question has been answered 
 several times before. For the interest reader, I've found these:

 http://unix.stackexchange.com/questions/4711/what-is-the-difference-between-ioctl-unlocked-ioctl-and-compat-ioctl

 http://lwn.net/Articles/119652/

 http://www.mail-archive.com/kernelnewbies@nl.linux.org/msg00269.html

 I have a remaining question, though. In the lwn article I read this:

 The ioctl() system call has long been out of favor among the kernel 
 developers, who see it as a completely uncontrolled entry point into the 
 kernel.

 Is this pointing that ioctl() is planning to get removed from the kernel ? In 
 that case what's the currently preferred mechanism for giving 'control 
 commands' to device drivers ?

I would bet for 'sysfs'.

thanks,
Daniel.

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Re: tools to identify bugs in driver

[Daniel Baluta]

On Thu, May 12, 2011 at 7:34 AM, Amit Nagal helloin.a...@gmail.com wrote:
 Hi ,

 What are the mandatory tools that must be run to identify potential
 bugs ( say memory , locking etc )
 in a linux device driver ?

Turning on DEBUG_SLAB might be a good option.
Have a look for all available options under make menuconfig's
Kernel Hacking section.

thanks,
Daniel.

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Re: char driver error

[Daniel Baluta]

 i create a character special file using mknod in /dev directory.

 i try to write data to my file by echo -n abcd  /dev/memory 

 and when i try to read from that file i get  the last char was written
 to that file that is d

Hello Aravind,

Can you post the output for:
$ strace -n abcd  /dev/memory
$ strace cat /dev/memory a

thanks,
Daniel.

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Re: char driver error

[Daniel Baluta]

OK. See how write and read works.

 $strace echo -n abcd  /dev/memory(/home/aravind/me
 write(1, abcd, 4)                     = 1
 write(1, bcd, 3)                      = 1
 write(1, cd, 2)                       = 1
 write(1, d, 1)                        = 1

$ strace cat /dev/memory(/home/aravind/memory)

 read(3, d, 32768)                     = 1
 write(1, d, 1d)                        = 1

Please allocate space for more than 1 char, and also
correct memory_write

  tmp=buf+count-1; - tmp=buf+*f_ps-1;

thanks,
Daniel.

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Re: perhaps confused about operation of alloc_chrdev_region()

[Daniel Baluta]

Hi Robert,

 static int __init bsr_init(void)
 {
        struct device_node *np;
        dev_t bsr_dev = MKDEV(bsr_major, 0);   --- 

You are right, this seems to be completely useless.

Go on make a patch, compile and send it.

thanks,
Daniel.

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Interpreting call trace

[Daniel Baluta]

Hello,

I have the following stack trace:

[3992.172/0] BUG: soft lockup - CPU#0 stuck for 61s! [events/0:39]
[ 3992.215/0] Pid: 39, comm: events/0 Tainted: PW  2.6.32 #1 X8DTT-H
[ 3992.222/0] RIP: 0010:[8115f989]  [8115f989]
__write_lock_failed+0x9/0x20
[ 3992.231/0] RSP: 0018:880028203908  EFLAGS: 0287
[ 3992.236/0] RAX: 88063ce0bfd8 RBX: 880028203920 RCX: 814e1b00
[ 3992.243/0] RDX: 8800282144e0 RSI: 880028203abc RDI: 814e1b04
[ 3992.250/0] RBP: 8100c6f3 R08: 0004 R09: 880028203ab0
[ 3992.257/0] R10: 88061851fa08 R11:  R12: 880028203880
[ 3992.264/0] R13: 88060404f800 R14: 814e1b04 R15: 8101fd88
[ 3992.272/0] FS:  () GS:88002820()
knlGS:
[ 3992.280/0] CS:  0010 DS: 0018 ES: 0018 CR0: 8005003b
[ 3992.286/0] CR2: 7f9cc9fb9000 CR3: 01001000 CR4: 06f0
[ 3992.293/0] DR0:  DR1:  DR2: 
[ 3992.300/0] DR3:  DR6: 0ff0 DR7: 0400
[ 3992.307/0] Call Trace:
[ 3992.309/0]  IRQ  [81374e12] ? _write_lock_bh+0x22/0x30
[ 3992.316/0]  [81297751] ? neigh_create+0x2f1/0x6b0
[ 3992.321/0]  [81374f00] ? _read_unlock_bh+0x10/0x20
[ 3992.327/0]  [81296401] ? neigh_lookup+0xd1/0xf0
[ 3992.333/0]  [81297b96] ? neigh_event_ns+0x86/0xc0
[ 3992.338/0]  [812f2cdb] ? arp_process+0x9fb/0xbf0
[ 3992.344/0]  [812f2ffc] ? arp_rcv+0x11c/0x130

How could one interpret this?

For example having:
[ 3992.316/0]  [81297751] ? neigh_create+0x2f1/0x6b0
[ 3992.321/0]  [81374f00] ? _read_unlock_bh+0x10/0x20

means that _read_unlock_bh has been called  finished ? Or it has been
interrupted by
next function in trace (neigh_create).

Any other info about interpreting call traces are welcomed.


thanks,
Daniel.

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Re: query regarding kernel daemon

[Daniel Baluta]

 A daemon sleeps in the background. User can enter a string through the proc
 interface. Whenever a string is entered, the daemon is woke. The daemon
 keeps a copy of the last entered string in a variable. Initially the
 variable is initialized to NULL. When the daemon wakes, it checks if the
 string entered is same as the previous one or a new string is entered. When
 the string is entered, in case the new or the old strings are NULL, or in
 case the entered string is same as the old string the daemon goes back to
 sleep (with the help of the function interruptible_sleep_on().

Don't use interruptible_sleep_on use wait_event* instead.

thanks,
Daniel.

[1] http://lxr.linux.no/linux+v2.6.38/include/linux/wait.h#L570

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Re: Scheduling policy

[Daniel Baluta]

On Mon, Apr 4, 2011 at 4:13 PM, Laurențiu Dascălu
dascalu.laurent...@gmail.com wrote:
 Hello,

 I'm trying to implement a simple scheduling policy in the Linux kernel,
 but I'm not sure if I correctly understand the sched_class interface.
 Specifically, I would like to know more about the following functions:

There's some useful information about sched_class interface
inside [1], check 'Scheduler Classes', page 89.


 * put_prev_task(struct rq *rq, struct task_struct *prev)
 Q: It means the prev was preempted and I have to reschedule another
 task? Or I have just to add prev to the running queue?

put_prev_task first announces to the scheduler class that the currently running
task is going to be replaced by another one.

So I guess, that prev was preempted but it is still in the running queue. Now
the scheduler has to dequeue it, and to schedule another task.


 The code should look something like:

 if (prev-se.on_rq)
 {
   enqueue_task(rq, prev);
 }

 or I'm wrong?

Why do you want to enqueue prev? Isn't rq supposed to hold
the current running tasks?

 * task_tick(struct rq *rq, struct task_struct *p, int queued)
 Q: Should I preempt the task p, by calling resched_task? What does
 queued means?


thanks,
Daniel.

[1] Professional Linux Kernel Architecture, W. Mauerer

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Re: why only C?

[Daniel Baluta]

On Sun, Apr 3, 2011 at 10:17 PM, mohit verma mohit89m...@gmail.com wrote:
 Hi list,
 I have a very basic question.

How much time have you tried documenting on this topic [1]?

thanks,
Daniel.

[1] http://answers.google.com/answers/threadview/id/718661.html

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Re: how to get kernel functions calling stack/invokation ordert

[Daniel Baluta]

 Is there a way to find, in the kernel src tree, which routine/function is
 calling another function OR kernel function invocation stack order?
 This would be helpful for me to know the various steps/functionalities
 involved during executing something in kernel space.

At runtime you can use dumpstack() [1].
Otherwise, just for reading the code I suggest cscope [2].

thanks,
Daniel.

[1] http://lxr.linux.no/linux+v2.6.38/arch/x86/kernel/dumpstack.c#L198
[2] http://cscope.sourceforge.net/

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Re: how to get kernel functions calling stack/invokation ordert

[Daniel Baluta]

 Is there a way to find, in the kernel src tree, which routine/function is
 calling another function OR kernel function invocation stack order?
 This would be helpful for me to know the various steps/functionalities
 involved during executing something in kernel space.

At runtime you can use dumpstack() [1].
Otherwise, just for reading the code I suggest cscope [2].

thanks,
Daniel.

[1] http://lxr.linux.no/linux+v2.6.38/arch/x86/kernel/dumpstack.c#L198
[2] http://cscope.sourceforge.net/

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Re: Snooping on sockets/file descriptors

[Daniel Baluta]

On Thu, Mar 31, 2011 at 10:29 PM, Vimal j.vi...@gmail.com wrote:
 Hi,

 Is it possible for an application (say snoop, with sufficient
 privileges) to monitor data on any socket/file descriptor in the
 system?

 Here's an example:  suppose we have a browser and it creates a tcp
 socket to connect to a URL.  Whenever the browser issues a read() and
 data is pushed to user space, I want snoop to get notified and made
 available a copy of the same data that the browser read.

 ptrace can be used to do it, but then there are several ways the app
 can read data.  It could use read(), or recv() or recvmsg().  Is there
 a better way to deal with this complexity?

 It's like the action of tee on any socket/file descriptor in the system.

How about tcpdump?

thanks,
Daniel.

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Re: what is the kernel symbol for user space grant access driver

[Daniel Baluta]

Hello,

 I want to know with respect to an image here
 http://bderzhavets.files.wordpress.com/2010/04/pv-2-6-32-12.png
 I have already compiled a kernel
 it mentions to enable  user space grant access driver
 While compiling I did not notice it how can I now verify post compile
 some symbol CONFIG_*
 which can tell me if I included it?
 How can I find out can such a thing be looked some where in .config file?

Compile the kernel with and without that option enabled
than diff the .configs.

thanks,
Daniel.

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Re: messages printed lots of times

[Daniel Baluta]

 i am putting a printk() on link_path_walk() kernel function ( the pathname
 resolution function). i access that printk() only at some special condition
 (like if pathname passed to link_path_walk() matches with some name) . but
 when it gets hit  like when i pass pathname via unlink(2) , lots of messages
 are written to dmesg ( or /var/log/messages) . i could not understand why
 these lots of messages are being written  ? (i was hoping for only one
 message)

Try to printout the name of the process on behalf of which the kernel
runs link_path_walk
using current-comm.

Then filter out the printks done by your application.

thanks,
Daniel.

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Re: syscalls performance

[Daniel Baluta]

Hi Mauro,

On Fri, Feb 25, 2011 at 7:03 PM, Mauro Romano Trajber traj...@gmail.com wrote:
 I was doing some performance tests of system calls and I find an interesting
 behavior.
 Using RDTSC to count the CPU cycles, a single call to the getpid() consumes
 about 7k of CPU clock cycles and ten calls consume approximately 9,800
 cycles.
 The fact is that from the second call, the CPU cycles grows at a rate of
 about 350 CPU cycles per call.
 Why does this happen? There is some hardware optimization when the syscall
 ID is already in EAX register ?

Use strace and check to number of getpid() syscalls.
You'll notice that only 1 system call is made, glibc caching the pid value.

thanks,
Daniel.

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Re: syscalls performance

[Daniel Baluta]

On Fri, Feb 25, 2011 at 8:22 PM, Mauro Romano Trajber traj...@gmail.com wrote:
 Thanks Enrico and Daniel, you're right. glibc was caching getpid(); but this
 is not the root cause of this behavior.
 Going further, I decide to use call getpid without glibc, using
  syscall(SYS_getpid) to test this behavior and it happened again.
 Calling it once, the test consumes about 7k CPU cycles and 10 calls consumes
 about 10k CPU cycles.
 Any ideas ?

Can you post a pointer to your code and information about how you got
this numbers?

thanks,
Daniel.

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