Re: Does unmount() sync dirty buffers
[Apparently I forgot to cc list] On Tue, Feb 14, 2012 at 10:04 PM, Manish Katiyar mkati...@gmail.com wrote: On Tue, Feb 14, 2012 at 7:43 PM, Ravishankar cybera...@gmail.com wrote: Hello, When we unmount a file system with the umount command or the umount() system call, does the kernel sync the dirty buffers before the file system is unmounted?I am assuming that the file system is not 'busy' (i.e no open files etc) and no force options are specified. When I did a walk-through of do_umount() call in fs/namespace.c, I could not find calls to sync any dirty pages that might exist. yes, most of the filesystem have their own function to sync fs. Look for the function pointer sync_fs For eg..for ext4 generic_shutdown_super - sync_filesystem - __sync_filesystem - sync_fs - ext4_sync_fs -- Thanks - Manish -- Thanks - Manish ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Using Sysfs uevents.
Hi, I was playing with sysfs and I'm able to create kset and kobjects within them as well. I need to know how do I use the uevents of these kobjects that I create. For example while reading the code I found that certain events like ADD, DEL a couple more were there are apparently fired. Now currently I'm not handling these events, the ops field is null, so they don't bother me hence they are not mandatory? If I were to actually do something with these events what it should be? Since my module runs fine and the uevents are supposed to be for userland applications (Hotplug) but the point is again how will a userspace application get to know about it? Does the application needs to create netlink sockets for it? If it does then why bother with the uevents of kobject? ::DISCLAIMER:: --- The contents of this e-mail and any attachment(s) are confidential and intended for the named recipient(s) only. It shall not attach any liability on the originator or HCL or its affiliates. Any views or opinions presented in this email are solely those of the author and may not necessarily reflect the opinions of HCL or its affiliates. Any form of reproduction, dissemination, copying, disclosure, modification, distribution and / or publication of this message without the prior written consent of the author of this e-mail is strictly prohibited. If you have received this email in error please delete it and notify the sender immediately. Before opening any mail and attachments please check them for viruses and defect. --- ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: [QUESTION] staging/easycap fix
Ezequiel,
The post: Intro to V4L2:
http://www.linuxfordevices.com/c/a/Linux-For-Devices-Articles/Intro-to-V4L2/
And the post: The VIVI driver; a great starting point for V4L2 driver writers:
http://lwn.net/Articles/203971/
May be useful.
[]'s
Peter
2012/2/14 Greg KH g...@kroah.com:
On Tue, Feb 14, 2012 at 07:01:25PM -0300, Ezequiel García wrote:
Hi Greg,
It's only recommended if you have a compiler that doesn't check for
such foolish things.
Understood. Thanks both.
Another question (hope you don't mind me asking so much):
I noticed easycap does lots of (redundant?) checks as:
pvideo_device = video_devdata(file);
if (!pvideo_device) {
return -EFAULT;
}
Is this bad, good or doesn't matter?
(There are more examples where the check is clearly not needed but
this one makes me doubt a bit)
Depends on what video_devdata() does, and how it could ever be NULL.
Maybe I'm focusing on small issues (as you already pointed out),
do you think this kind of patches would be accepted?
Of course, I would submit separate patches, one for each change:
1. split probe function
2. remove redundant checks
3. clean comment style
... and so on.
That sounds great.
Also, I'm reading driver cx231xx as it's also an usb video capture.
Do you think it's a good code reference? Can you give me further reference?
I don't know, ask the linux-media developers on their list for a good
reference driver to follow, they would know best.
thanks,
greg k-h
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peter.se...@gmail.com
gpg id: 48274C36
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System call trace
Can we see trace of how the system call works? What are the functions are called in kernel space? For example we want to trace cp command. Then what are the functions is get called by that in kernel space? like how the inode allocation take place for new destination file etc. Is any tool for that? -- Regards, Swapnil Gaikwad. ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: System call trace
On Wed, Feb 15, 2012 at 4:38 PM, Swapnil Gaikwad swapnilgai...@gmail.com wrote: Can we see trace of how the system call works? What are the functions are called in kernel space? For example we want to trace cp command. Then what are the functions is get called by that in kernel space? like how the inode allocation take place for new destination file etc. Is any tool for that? I think strace [0][1] is what you are looking for. strace executable will list all the system calls made by the executable during runtime (you can filter what calls you want traced). A syscall is by definition a function that is ran in kernel space, called by the userspace. If you want to see what function is called when there's a certain syscall, you should take a look at the syscall descriptor table. It's an array for function pointers. You can talke a look at the kernel' source code to see the implementation of the syscall. Now, to track what the kernel is doing, while in a syscall, I can't remember a tool that would do that... maybe somebody else can help. [0] http://linux.die.net/man/1/strace [1] http://en.wikipedia.org/wiki/Strace -- Alexandru Juncu ROSEdu ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: System call trace
Hi :) On Wed, Feb 15, 2012 at 21:38, Swapnil Gaikwad swapnilgai...@gmail.com wrote: Can we see trace of how the system call works? What are the functions are called in kernel space? For example we want to trace cp command. Then what are the functions is get called by that in kernel space? like how the inode allocation take place for new destination file etc. Is any tool for that? Besides using strace, you might find User Mode Linux useful in this case. Just attach gdb to the UML kernel, put breakpoint into system call entry, and then do step to follow how it goes. Note that UML might not precisely mimic real kernel, but at least it will give you idea. Other than that, cscope and/or websites like lxr.linux.no are your best friend for such code exploration :) -- regards, Mulyadi Santosa Freelance Linux trainer and consultant blog: the-hydra.blogspot.com training: mulyaditraining.blogspot.com ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: Using Sysfs uevents.
On Wed, Feb 15, 2012 at 06:17:28PM +0530, Pranay Kumar Srivastava wrote: Hi, I was playing with sysfs and I'm able to create kset and kobjects within them as well. Nice, but why? Almost no one ever should be touching raw sysfs kobjects and ksets. I need to know how do I use the uevents of these kobjects that I create. For example while reading the code I found that certain events like ADD, DEL a couple more were there are apparently fired. Now currently I'm not handling these events, the ops field is null, so they don't bother me hence they are not mandatory? They are created by the kobject core automatically for you. If I were to actually do something with these events what it should be? Since my module runs fine and the uevents are supposed to be for userland applications (Hotplug) but the point is again how will a userspace application get to know about it? Does the application needs to create netlink sockets for it? If it does then why bother with the uevents of kobject? No, udev grabs all of these events and allows other programs to subscribe to it and get that information. You don't have to write your own program to do this, the infrastructure is all there already. But I wouldn't really worry about it to much, you shouldn't be messing with kobjects directly anyway, why not use 'struct device' instead? thanks, greg k-h ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
arm assembly doubt
Hi ,
I am trying to understand how system call is implmented in linux for
arm.And I am not that familiar with arm assembly.
Could any body please help me to understand what exactly this ^ does
in this instruction stmdb r8,{sp,lr}^
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Subin Gangadharan
I am not afraid and I am also not afraid of being afraid.
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Re: arm assembly doubt
Hi,
On Feb 15, 2012, at 11:30 PM, subin gangadharan wrote:
Hi ,
I am trying to understand how system call is implmented in linux for
arm.And I am not that familiar with arm assembly.
Could any body please help me to understand what exactly this ^ does
in this instruction stmdb r8,{sp,lr}^
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Subin Gangadharan
I am not afraid and I am also not afraid of being afraid.
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Example:
LDFMD sp!, {r0-r12, pc}^
- The ^ qualifier specifies that the CPSR is restored from the SPSR.
It must be used only from a privileged mode.
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Dual booting of Smartphone
Hi All, I know its pre-mature to ask this question but is there any support of dual booting in smartphones which can allow me have two different OS's ( for ex. Android 2.1 + Android 2.3 ) on a single phone? There may be other combinations as well. Is this something which we are looking at near future or is it just a dream at this moment? Regards, Abhijit Pawar ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
