GNU bug report logs - #19570
bug: df and bind mounts

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

From: Vladimir A. Pavlov <pv4 <at> bk.ru>
To: bug-coreutils <at> gnu.org
Subject: bug: df and bind mounts
Date: Mon, 12 Jan 2015 02:36:37 +0300

[Message part 1 (text/plain, inline)]

Hello,

I have an issue with df (both in version 8.23 and in master branch).

I have tmpfs mounted as /run . There is /run/cgs/httpd subdirectory in
/run (just a subdirectory, not a tmpfs or another mount). This
/run/cgs/httpd is bind-mounted to /usr/cgs/httpd/run.

The current algorithm in df.c:filter_mount_list() chooses the bind
mountpoint since it has the leading slash in the "device" name
("/run/cgs/httpd" vs "run") which is wrong in my setup.

The similar (but not the same) issue is fixed by commit:
http://git.savannah.gnu.org/cgit/coreutils.git/commit/src/df.c?id=ed1a495b3ccb2665a13229ca866f2115bd768d17

I guess the "let real devices with / in the name win" replacement branch
should only be applied if mountpoints are the same as well.

Below is the data to reproduce the bug.

=== /etc/mtab (partial) ===
run /run tmpfs rw,noatime,nodiratime,nodev,noexec,mode=0755,size=1m 0 0
/run/cgs/httpd /usr/cgs/httpd/run none rw,bind 0 0
======

=== Real output (git) ===
Filesystem      Size  Used Avail Use% Mounted on
/run/cgs/httpd  1.0M  8.0K 1016K   1% /usr/cgs/httpd/run
======

=== Expected output (with the attached patch applied) ===
Filesystem      Size  Used Avail Use% Mounted on
run             1.0M  8.0K 1016K   1% /run
======

-- 
Vladimir A. Pavlov

[coreutils-8.23-df_bindmount_fix.patch (application/x-patch, attachment)]

Message #8 received at 19570 <at> debbugs.gnu.org (full text, mbox):

From: Pádraig Brady <P <at> draigBrady.com>
To: "Vladimir A. Pavlov" <pv4 <at> bk.ru>, 19570 <at> debbugs.gnu.org
Subject: Re: bug#19570: bug: df and bind mounts
Date: Mon, 12 Jan 2015 01:31:19 +0000

On 11/01/15 23:36, Vladimir A. Pavlov wrote:
> Hello,
> 
> I have an issue with df (both in version 8.23 and in master branch).
> 
> I have tmpfs mounted as /run . There is /run/cgs/httpd subdirectory in
> /run (just a subdirectory, not a tmpfs or another mount). This
> /run/cgs/httpd is bind-mounted to /usr/cgs/httpd/run.
> 
> The current algorithm in df.c:filter_mount_list() chooses the bind
> mountpoint since it has the leading slash in the "device" name
> ("/run/cgs/httpd" vs "run") which is wrong in my setup.
> 
> The similar (but not the same) issue is fixed by commit:
> http://git.savannah.gnu.org/cgit/coreutils.git/commit/src/df.c?id=ed1a495b3ccb2665a13229ca866f2115bd768d17
> 
> I guess the "let real devices with / in the name win" replacement branch
> should only be applied if mountpoints are the same as well.
> 
> Below is the data to reproduce the bug.
> 
> === /etc/mtab (partial) ===
> run /run tmpfs rw,noatime,nodiratime,nodev,noexec,mode=0755,size=1m 0 0
> /run/cgs/httpd /usr/cgs/httpd/run none rw,bind 0 0
> ======
> 
> === Real output (git) ===
> Filesystem      Size  Used Avail Use% Mounted on
> /run/cgs/httpd  1.0M  8.0K 1016K   1% /usr/cgs/httpd/run
> ======
> 
> === Expected output (with the attached patch applied) ===
> Filesystem      Size  Used Avail Use% Mounted on
> run             1.0M  8.0K 1016K   1% /run
> ======
> 

Thanks for the analysis and patch,
Current tests pass at least with it.
I'll analyse a little more, add tests and probably push.

thanks!
Pádraig.

Message #11 received at 19570 <at> debbugs.gnu.org (full text, mbox):

From: Bernhard Voelker <mail <at> bernhard-voelker.de>
To: Pádraig Brady <P <at> draigBrady.com>, 
 "Vladimir A. Pavlov" <pv4 <at> bk.ru>, 19570 <at> debbugs.gnu.org
Subject: Re: bug#19570: bug: df and bind mounts
Date: Mon, 12 Jan 2015 22:27:13 +0100

On 01/12/2015 02:31 AM, Pádraig Brady wrote:
> On 11/01/15 23:36, Vladimir A. Pavlov wrote:
>> run /run tmpfs rw,noatime,nodiratime,nodev,noexec,mode=0755,size=1m 0 0
>> /run/cgs/httpd /usr/cgs/httpd/run none rw,bind 0 0

> Thanks for the analysis and patch,
> Current tests pass at least with it.
> I'll analyse a little more, add tests and probably push.

hmm, tmpfs is problematic anyway, as one can specify anything
as the dummy backing source device:

  $ mount -t tmpfs hello:/world /mnt
  $ mount -t tmpfs something /mnt
  $ mount -t tmpfs / /mnt
  $ findmnt /mnt
  TARGET SOURCE       FSTYPE OPTIONS
  /mnt   hello:/world tmpfs  rw,relatime
  /mnt   something    tmpfs  rw,relatime
  /mnt   /            tmpfs  rw,relatime

  $ df -a --out=source,target | grep /mnt
  hello:/world   /mnt
  something      /mnt
  /              /mnt

I'd almost tend to recommend to classify tmpfs as dummy
file system like procfs etc.

Have a nice day,
Berny

Message #14 received at 19570 <at> debbugs.gnu.org (full text, mbox):

From: Pádraig Brady <P <at> draigBrady.com>
To: Bernhard Voelker <mail <at> bernhard-voelker.de>, 
 "Vladimir A. Pavlov" <pv4 <at> bk.ru>, 19570 <at> debbugs.gnu.org
Subject: Re: bug#19570: bug: df and bind mounts
Date: Mon, 12 Jan 2015 23:04:04 +0000

On 12/01/15 21:27, Bernhard Voelker wrote:
> On 01/12/2015 02:31 AM, Pádraig Brady wrote:
>> On 11/01/15 23:36, Vladimir A. Pavlov wrote:
>>> run /run tmpfs rw,noatime,nodiratime,nodev,noexec,mode=0755,size=1m 0 0
>>> /run/cgs/httpd /usr/cgs/httpd/run none rw,bind 0 0
> 
>> Thanks for the analysis and patch,
>> Current tests pass at least with it.
>> I'll analyse a little more, add tests and probably push.
> 
> hmm, tmpfs is problematic anyway, as one can specify anything
> as the dummy backing source device:
> 
>   $ mount -t tmpfs hello:/world /mnt
>   $ mount -t tmpfs something /mnt
>   $ mount -t tmpfs / /mnt
>   $ findmnt /mnt
>   TARGET SOURCE       FSTYPE OPTIONS
>   /mnt   hello:/world tmpfs  rw,relatime
>   /mnt   something    tmpfs  rw,relatime
>   /mnt   /            tmpfs  rw,relatime
> 
>   $ df -a --out=source,target | grep /mnt
>   hello:/world   /mnt
>   something      /mnt
>   /              /mnt
> 
> I'd almost tend to recommend to classify tmpfs as dummy
> file system like procfs etc.

I see what you mean.
However we take dummy to mean,
no associated storage in the memory hierarchy,
which tmpfs clearly has.

Pádraig

Message #19 received at 19570-done <at> debbugs.gnu.org (full text, mbox):

From: Pádraig Brady <P <at> draigBrady.com>
To: "Vladimir A. Pavlov" <pv4 <at> bk.ru>, 19570-done <at> debbugs.gnu.org
Subject: Re: bug#19570: bug: df and bind mounts
Date: Fri, 26 Jun 2015 18:29:33 +0100

On 12/01/15 01:31, Pádraig Brady wrote:
> On 11/01/15 23:36, Vladimir A. Pavlov wrote:
>> Hello,
>>
>> I have an issue with df (both in version 8.23 and in master branch).
>>
>> I have tmpfs mounted as /run . There is /run/cgs/httpd subdirectory in
>> /run (just a subdirectory, not a tmpfs or another mount). This
>> /run/cgs/httpd is bind-mounted to /usr/cgs/httpd/run.
>>
>> The current algorithm in df.c:filter_mount_list() chooses the bind
>> mountpoint since it has the leading slash in the "device" name
>> ("/run/cgs/httpd" vs "run") which is wrong in my setup.
>>
>> The similar (but not the same) issue is fixed by commit:
>> http://git.savannah.gnu.org/cgit/coreutils.git/commit/src/df.c?id=ed1a495b3ccb2665a13229ca866f2115bd768d17
>>
>> I guess the "let real devices with / in the name win" replacement branch
>> should only be applied if mountpoints are the same as well.
>>
>> Below is the data to reproduce the bug.
>>
>> === /etc/mtab (partial) ===
>> run /run tmpfs rw,noatime,nodiratime,nodev,noexec,mode=0755,size=1m 0 0
>> /run/cgs/httpd /usr/cgs/httpd/run none rw,bind 0 0
>> ======
>>
>> === Real output (git) ===
>> Filesystem      Size  Used Avail Use% Mounted on
>> /run/cgs/httpd  1.0M  8.0K 1016K   1% /usr/cgs/httpd/run
>> ======
>>
>> === Expected output (with the attached patch applied) ===
>> Filesystem      Size  Used Avail Use% Mounted on
>> run             1.0M  8.0K 1016K   1% /run
>> ======
>>
> 
> Thanks for the analysis and patch,
> Current tests pass at least with it.
> I'll analyse a little more, add tests and probably push.

df v8.24 will read /proc/self/mountinfo if available
and so won't hit this issue in practise as the
bind mount location won't be passed to, or presented by df.
I.E. the "Filesystem" for a particular device id will
not switch representations.

thanks,
Pádraig.

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