Re: [PATCH -V14 0/11] Generic name to handle and open by handlesyscalls

From: J. Bruce Fields
Date: Wed Jul 07 2010 - 09:17:48 EST


On Wed, Jul 07, 2010 at 03:10:21PM +0200, Miklos Szeredi wrote:
> On Wed, 7 Jul 2010, J. Bruce Fields wrote:
> > On Wed, Jul 07, 2010 at 12:57:26PM +1000, Neil Brown wrote:
> > > The trouble with /proc/mounts is that it is somewhat clumsy to parse
> > > (remember to handle \0ctal escapes) and doesn't include major/minor number
> > > which is the primary key for identifying filesystems in Linux
> > > (see /sys/class/bdi/MAJOR:MINOR which is e.g. the best place to configure
> > > read-ahead for a filesystem).
> > >
> > > So /proc/mounts could work (and would probably be better than a new syscall)
> > > but I would really rather see something sane in /sys for
> > > inspecting/configuring filesystems (rather than each filesystem doing their
> > > own independent thing in /sys/fs).
> >
> > If you use sys or proc, is it possible to get the uuid from a file
> > descriptor or pathname without races?
>
> You can do stat/fstat to find out the device number (which is unique,
> but not persistent)

Is it really unique over time? (Can't a given st_dev value map to one
filesystem now, and another later?) And it must also have the same
problems as libblkid (e.g. btrfs subvolumes share the same st_dev).

--b.

> then look for the major:minor calculated from
> st_dev in /proc/self/mountinfo.
>
> Thanks,
> Miklos
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