Re: what is /.udev for ?

["J. Bruce Fields" <bfields@fieldses.org>]

On Thu, Feb 10, 2005 at 06:19:56AM -0600, Ron Johnson wrote:
> I'll file bugs against gtkdiskfree & pydf.  Now that I understand
> this more (thanks, MdI), I see that df has a way to exclude bind 
> mounts.
> 
> $ df -T
> Filesystem    Type   1K-blocks      Used Available Use% Mounted on
> /dev/hda3     ext3     9843308   5430908   3912380  59% /
> tmpfs        tmpfs      501936         0    501936   0% /dev/shm
> /dev/hda2     ext3       46668     20415     23844  47% /boot
> /dev/hda5 reiserfs     2995936   1988176   1007760  67% /home
> /dev/hda6     ext3   105280504  79520128  20412340  80% /data
> /dev       unknown     9843308   5430908   3912380  59% /.dev
> none         tmpfs        5120      2564      2556  51% /dev
> 
> $ df -x unknown
> Filesystem           1K-blocks      Used Available Use% Mounted on
> /dev/hda3              9843308   5430908   3912380  59% /
> tmpfs                   501936         0    501936   0% /dev/shm
> /dev/hda2                46668     20415     23844  47% /boot
> /dev/hda5              2995936   1987864   1008072  67% /home
> /dev/hda6            105280504  79523152  20409316  80% /data
> none                      5120      2564      2556  51% /dev

Hm.  On my system, at least, df -T has "none", not "unknown", in the
Type column for bind mounts.

But in any case, excluding all bind mounts doesn't work in general.
Consider an example:

mount /dev/hda7 /mnt/
mount --bind /mnt/foo /A
mount --bind /mnt/bar /B
umount /mnt/

Now you're left with two different pieces of the filesystem on /dev/hda7
mounted.  But both mounts are bind mounts.  Surely you don't want to
exclude both.  You could include only one but not the other if you
wanted, though this is somewhat inelegant since the choice is completely
arbitrary--there's no way to decide whether /A or /B is the more
important mountpoint to list.

So --bind mounts are just like hard links; multiple names for the same
object (or parts of the same object).

In something like df I think the sensible thing to do is just to
continue to list all bind mounts, even when it's redundant.

For a graphical tool I think you'd only want one visual object for each
filesystem, but you'd want all the paths that filesystem is mounted on
listed, so you might end up with filesystems that are labeled by a list
of names instead of a single name.

--Bruce Fields