GNU bug report logs - #15955
df hides original mount point instead of bind mount

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Phillip Susi <psusi <at> ubuntu.com>
To: bug-coreutils <at> gnu.org
Subject: df hides original mount point instead of bind mount
Date: Fri, 22 Nov 2013 16:59:12 -0500

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Without /etc/mtab, df tries to hide mount points by detecting
duplicates and only showing the *last* instance in /proc/mounts, but
this causes the bind mount to be shown rather than the original.  It
should show the *first* instance instead.
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Message #8 received at 15955 <at> debbugs.gnu.org (full text, mbox):

From: Bernhard Voelker <mail <at> bernhard-voelker.de>
To: Phillip Susi <psusi <at> ubuntu.com>
Cc: 15955 <at> debbugs.gnu.org
Subject: Re: bug#15955: df hides original mount point instead of bind mount
Date: Sat, 23 Nov 2013 02:11:08 +0100

tag 15955 notabug
thanks

On 11/22/2013 10:59 PM, Phillip Susi wrote:
> Without /etc/mtab, df tries to hide mount points by detecting
> duplicates and only showing the *last* instance in /proc/mounts, but
> this causes the bind mount to be shown rather than the original.  It
> should show the *first* instance instead.

Thanks for the bug report.
However, IIRC that behavior was fixed in v8.21.  Since then, df(1)
shows the *shortest* mount point for the same bind mount.
Looking into the Fedora bug tracker, this method of reducing duplicates
among (possibly mass) bind mounts seems also not to have too many fans,
but until now we didn't find a better method.

Have a nice day,
Berny

Message #11 received at 15955 <at> debbugs.gnu.org (full text, mbox):

From: Phillip Susi <psusi <at> ubuntu.com>
To: Bernhard Voelker <mail <at> bernhard-voelker.de>
Cc: 15955 <at> debbugs.gnu.org
Subject: Re: bug#15955: df hides original mount point instead of bind mount
Date: Sat, 23 Nov 2013 20:08:05 -0500

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On 11/22/2013 08:11 PM, Bernhard Voelker wrote:
> Thanks for the bug report.
> However, IIRC that behavior was fixed in v8.21.  Since then, df(1)
> shows the *shortest* mount point for the same bind mount.
> Looking into the Fedora bug tracker, this method of reducing duplicates
> among (possibly mass) bind mounts seems also not to have too many fans,
> but until now we didn't find a better method.

Yes, that explains it; I had bound a longer path to /mnt to test.  Why not show the oldest mount point instead?

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Message #14 received at 15955 <at> debbugs.gnu.org (full text, mbox):

From: Bernhard Voelker <mail <at> bernhard-voelker.de>
To: Phillip Susi <psusi <at> ubuntu.com>
Cc: 15955 <at> debbugs.gnu.org
Subject: Re: bug#15955: df hides original mount point instead of bind mount
Date: Sun, 24 Nov 2013 11:24:42 +0100

On 11/24/2013 02:08 AM, Phillip Susi wrote:
> On 11/22/2013 08:11 PM, Bernhard Voelker wrote:
>> Thanks for the bug report.
>> However, IIRC that behavior was fixed in v8.21.  Since then, df(1)
>> shows the *shortest* mount point for the same bind mount.
>> Looking into the Fedora bug tracker, this method of reducing duplicates
>> among (possibly mass) bind mounts seems also not to have too many fans,
>> but until now we didn't find a better method.
> 
> Yes, that explains it; I had bound a longer path to /mnt to test.
> Why not show the oldest mount point instead?

Thanks for the suggestion, but that is not possible.  For the kernel,
all bind mounts are actually equal among each other, and there's no
information about "bind" flags in /proc/self/mounts (which 'df' uses).

Have a nice day,
Berny

Message #17 received at 15955 <at> debbugs.gnu.org (full text, mbox):

From: Phillip Susi <psusi <at> ubuntu.com>
To: Bernhard Voelker <mail <at> bernhard-voelker.de>
Cc: 15955 <at> debbugs.gnu.org
Subject: Re: bug#15955: df hides original mount point instead of bind mount
Date: Sun, 24 Nov 2013 18:29:53 -0500

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On 11/24/2013 05:24 AM, Bernhard Voelker wrote:
> Thanks for the suggestion, but that is not possible.  For the kernel,
> all bind mounts are actually equal among each other, and there's no
> information about "bind" flags in /proc/self/mounts (which 'df' uses).

I'm aware of that, but the order they are reported in /proc/mounts at least seems to be the order they were mounted in, which seems like it would be a better thing to decide which to show and hide than the length of the path.



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Message #20 received at 15955 <at> debbugs.gnu.org (full text, mbox):

From: Bernhard Voelker <mail <at> bernhard-voelker.de>
To: Phillip Susi <psusi <at> ubuntu.com>
Cc: 15955 <at> debbugs.gnu.org
Subject: Re: bug#15955: df hides original mount point instead of bind mount
Date: Wed, 27 Nov 2013 00:37:54 +0100

On 11/25/2013 12:29 AM, Phillip Susi wrote:
> On 11/24/2013 05:24 AM, Bernhard Voelker wrote:
>> Thanks for the suggestion, but that is not possible.  For the kernel,
>> all bind mounts are actually equal among each other, and there's no
>> information about "bind" flags in /proc/self/mounts (which 'df' uses).
> 
> I'm aware of that, but the order they are reported in /proc/mounts at
> least seems to be the order they were mounted in, which seems like it
> would be a better thing to decide which to show and hide than the
> length of the path.

As already mentioned, the current implementation is not ideal.
It is a compromise between the requirements which hit 'df' at that time:

* showing the real root file system instead of early-boot rootfs:

  $ src/df -a | grep ' /$'
  rootfs            12095032   7988888   3491744  70% /
  /dev/sda1         12095032   7988888   3491744  70% /

* suppressing massive bind-mounts with hundreds or thousands of bind
  mounts of the same file system:

    $ for f in $(seq 1000) ; do
        mkdir dir$f \
          && mount -o bind /etc dir$f ; \
      done
  and then look at 'df' vs. 'df -a'.

* IIRC there was a another issue re. shortening mount information like:
  /dev/disk/by-id/scsi-SATA_Hitachi_HDS7210_JP2911N03AR0WV-part1

This has to be discussed in the context of Fedora's currently open
bug reports.

Thanks & have a nice day,
Berny

Message #23 received at 15955 <at> debbugs.gnu.org (full text, mbox):

From: Phillip Susi <psusi <at> ubuntu.com>
To: Bernhard Voelker <mail <at> bernhard-voelker.de>
Cc: 15955 <at> debbugs.gnu.org
Subject: Re: bug#15955: df hides original mount point instead of bind mount
Date: Tue, 26 Nov 2013 20:48:57 -0500

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On 11/26/2013 06:37 PM, Bernhard Voelker wrote:
> As already mentioned, the current implementation is not ideal. It
> is a compromise between the requirements which hit 'df' at that
> time:
> 
> * showing the real root file system instead of early-boot rootfs:
> 
> $ src/df -a | grep ' /$' rootfs            12095032   7988888
> 3491744  70% / /dev/sda1         12095032   7988888   3491744  70%
> /

That doesn't seem to be at all related since the path on both is
exactly the same, not one longer than the other, and is filtered by
the fstype being "rootfs".  For that matter, this has always seemed
like a bug in the kernel to me: rootfs isn't mounted in /, it is
mounted above / and therefore is not visible to this process, so it
shouldn't be shown in /proc/mounts.

> * suppressing massive bind-mounts with hundreds or thousands of
> bind mounts of the same file system:
> 
> $ for f in $(seq 1000) ; do mkdir dir$f \ && mount -o bind /etc
> dir$f ; \ done and then look at 'df' vs. 'df -a'.

Yes, the whole topic is hiding bind mounts; the question is how to
choose which one to hide.  Why use the path length instead of which
was mounted first?

> * IIRC there was a another issue re. shortening mount information
> like: 
> /dev/disk/by-id/scsi-SATA_Hitachi_HDS7210_JP2911N03AR0WV-part1

Again, that seems totally unrelated.  The by-id is a symlink so it is
followed to the underlying devnode and that's what is reported in
/proc/mounts, and it doesn't have anything to do with the length of
the mount point.


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