[Pkg-sysvinit-devel] Bug#494001: `mount -o loop' runs out of loop devices

Roger Leigh rleigh at codelibre.net
Sun Jun 21 12:49:14 UTC 2009

On Mon, Jun 01, 2009 at 02:19:51PM +1200, Dmitry Maksyoma wrote:
> `mount -o loop' runs out of loop devices when /etc/mtab is a symlink to
> /proc/mounts.

Just rechecking this issue, and it no longer occurs for me:

% uname -a
Linux ravenclaw 2.6.30-1-amd64 #1 SMP Sun Jun 14 15:00:29 UTC 2009 x86_64 GNU/Linux
% ls -l /etc/mtab
lrwxrwxrwx 1 root root 12 2009-06-21 13:29 /etc/mtab -> /proc/mounts
% dd if=/dev/zero of=/tmp/l1 bs=1024 count=4096
% /sbin/mkfs -t ext2 /tmp/l1
% sudo mount -o loop /tmp/l1 /mnt
% sudo losetup -a
/dev/loop0: [0011]:175224 (/tmp/l1)
% grep /mnt /etc/mtab /proc/mounts
/etc/mtab:/dev/loop0 /mnt ext2 rw,relatime,errors=continue 0 0
/proc/mounts:/dev/loop0 /mnt ext2 rw,relatime,errors=continue 0 0
% sudo umount /mnt
% sudo losetup -a
% grep /mnt /etc/mtab /proc/mounts

I get the same loopback release with /etc/mtab as a regular file.

This may be due to the new kernel or new util-linux in unstable,
but it is now freeing the loop devices correctly.  It must be in
the new util-linux, because it's putting the loop device, rather
than the loopback filename, as the source in /etc/mtab such that
it always matches /proc/mounts.  Previously they differed, and
this resulted in the loop device not being freed when the loop
device was used.  This is no longer the case.  (I'm not familiar
with the util-linux source, but I can't actually see this change
and it /looks/ like it uses the old behaviour, but this may be
just a special case for certain use cases.  The observed
behaviour is what we want though!)

Dmitry, can you confirm this on your system?  Your bug report
shows you are using stable; do you have a system running
unstable you can check on (or if anyone else can check this as
I have above?)

Since this was IIRC the only blocker for #494001 (replacing
/etc/mtab with a symlink), it looks like this can now go
ahead if anyone else can confirm the loop issue is fixed.


  .''`.  Roger Leigh
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