GNU bug report logs - #16539
df command, possible bug?

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Message #19 received at 16539 <at> debbugs.gnu.org (full text, mbox):

From: Bernhard Voelker <mail <at> bernhard-voelker.de>
To: Pádraig Brady <P <at> draigBrady.com>, 
 16539 <at> debbugs.gnu.org, crubel <at> compro.net
Subject: Re: bug#16539: More details on df command output for you
Date: Sun, 26 Jan 2014 00:55:16 +0100

On 01/25/2014 04:19 AM, Pádraig Brady wrote:
> On 01/24/2014 10:27 PM, Bernhard Voelker wrote:
>> The above is the result of df suppressing duplicate entries like
>> bind mounts.  This filtering is done based on the device number.
>> As this example shows, a few exports of directories of the same file
>> system from "host" are mounted - yet it's the same file system.
> 
> Right. Essentially df is showing storage for available file systems.
> Noting that df also has a --total option, it makes sense by default
> to not repeat file systems. This can be overridden easily with the
> -a option as noted above.
> 
> Actually we should in fact be merging more entries!
> Notice the following:
> 
>>> tmpfs                 4095336     4688   4090648   1% /run
>>> tmpfs                 4095336     4688   4090648   1% /var/run
>>> tmpfs                 4095336     4688   4090648   1% /var/lock
> 
> Hopefully the attached patch addresses this
> (and a couple of other test issues).

Good idea.

I think we're on the right way - and the patch looks good to me.
Thanks.

However, I remember some other corner cases with eclipsed file
systems in the Fedora bug tracker. I think we're quite close
to solve them all this time (hopefully).
The idea was to trust the order of mount entries returned by
the kernel, i.e. in the loop over the mount entries, if the
mount point is the same one as a previous one, then we should
process the one mounted later.

E.g. the situation where 2 file systems are mounted on the
same mount point:

  $ findmnt | grep loop
  └─/mnt                           /dev/loop0     ext4                rw,relatime,data=ordered
    └─/mnt/dir                     /dev/loop1     ext4                rw,relatime,data=ordered
      └─/mnt/dir                   /dev/loop2     ext4                rw,relatime,data=ordered

df - the new one with your patch - still shows the wrong device:

  $ src/df | grep loop
  /dev/loop0        122835      1551    112110   2% /mnt
  /dev/loop1        122835      1550    112111   2% /mnt/dir

It should say /dev/loop2 here. BTW the numbers are correct.

Have a nice day,
Berny

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