On Wed, Oct 1, 2014 at 3:41 AM, Anand Jain <anand.j...@oracle.com>
wrote:
Hi Chris,
Thanks for commenting. Some clarifying comments as below.
On 30/09/2014 22:23, Chris Mason wrote:
On Mon, Sep 29, 2014 at 1:09 AM, Anand Jain <anand.j...@oracle.com>
wrote:
From: Anand Jain <anand.j...@oracle.com>
(added RFC prefix to the patch header)
(as of now just an experimental interface)
This patch introduces profs interface /proc/fs/btrfs/devlist,
which as of now exports all the members of kernel fs_devices.
The current /sys/fs/btrfs interface works when the fs is
mounted, and is on the file directory hierarchy and also has
the sysfs limitation max output of U64 per file.
Here btrfs procfs uses seq_file to export all the members of
fs_devices. Also shows the contents when device is not mounted,
but have registered with btrfs kernel (useful as an alternative
to buggy ready ioctl)
An attempt is made to follow the some standard file format
output such as ini. So that a simple warper python script will
provide end user useful interfaces.
Further planning to add few more members to the interface such as
group profile info. The long term idea is to make procfs
interface a onestop btrfs application interface for the device and
fs info from the kernel, where a simple python script can make
use of it.
Hi Anand,
We're going to have a really hard time getting a new proc interface
merged in, and after we've recently fixed up all (most?) of our sysfs
races, I'd rather not have to do it all over again with /proc.
This does not use fsid/devid based file-directory. So races as were
in sysfs implementation does not apply here. (But there are
opportunity
to optimize the code at the place mentioned in the code as todo).
Right, proc has different races ;) Again the bar for new interfaces in
proc is really very high. It's not the direction the rest of the
kernel is using.
I know
the lack of a seq interface is a difficult compromise to make in
sysfs,
but at this point I think we're stuck with it. Which specific part
do
you hope to improve by dumping more information out in a single file?
Since its a single file and dumping most of the members of fs_devices
we would ensure the interface will remain unchanged for a long time
and helps debugging. This is hard to do when we layout files per
parameter value.
Less clutter. But needs python script abstraction to provide what
user want. Better than using ioctls.
file-parameter-layout might introduce races. So here there is no file
parameter layout, its just one file /proc/fs/btrfs/devlist, provides
an interface which is compatible with parser such as python
configparser, with which application can organize it using a simple
script.
Further,
This also exports all registered devices which may not be mounted.
(sysfs implementation does not).
For these features, we need to work within the sysfs and udev
frameworks. It will integrate better with the direction the distros
are using for management in general. I really understand that in some
ways the proc interface would be easier to write and easier to use, but
this is one of those times that consistency with the rest of the kernel
comes first.
Thanks again for the time you've spent improving the device management
side of things. For now, sysfs and udev are the best choices overall.
-chris
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