Re: mount --bind /A /A multiplies mount entries

[Karel Zak <kzak@redhat.com>]

On Mon, Nov 04, 2013 at 12:09:12PM +0100, Bernhard Voelker wrote:
>   $ ./mount | grep sdb
>   /dev/sdb on /home type ext4 (rw,relatime,data=ordered)
>   /dev/sdb on /home type ext4 (rw,relatime,data=ordered)

 Yes, it seems correct, use findmnt(8) to see what happen.  It's more
 tricky :-) (or see /proc/self/mountinfo where is Id<->Parent
 relationship described by two first columns).

 ... and don't forget that mounts are propagated in shared trees, so
 try to compare:

  mkdir /mnt/test

  mount --bind /mnt/test /mnt/test
  mount --make-private /mnt/test
  mount --bind /mnt/test /mnt/test
  mount --bind /mnt/test /mnt/test

 and:

  mount --bind /mnt/test /mnt/test
  mount --make-shared /mnt/test
  mount --bind /mnt/test /mnt/test
  mount --bind /mnt/test /mnt/test

you can also try to mount something else to /mnt/test/A to see what
happen.

> This is probably a kernel bug

 I don't think it's bug :-)

>, but as bind mounts to self
> are not that much of use, wouldn't it be worthwhile to
> prohibit it at all in mount(8)?

  mount --bind  /A /A

 is pretty common operation if you want to create a mountpoint
 from non-mountpoint directory.

    Karel

-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com