A user cannot remove his readonly snapshots?!

A user cannot remove his readonly snapshots?!

[Ulli Horlacher]

I have my btrfs filesystem mounted with option user_subvol_rm_allowed

tux@xerus: btrfs --version
btrfs-progs v4.4

tux@xerus: uname -a
Linux xerus 4.4.0-93-generic #116-Ubuntu SMP Fri Aug 11 21:17:51 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux

tux@xerus: id
uid=1000(tux) gid=100(users) groups=100(users)

tux@xerus: btrfs subvolume snapshot -r /test/tux/zz /test/tux/zz/.snapshot/2017-09-15_1824.test
tux@xerus: btrfs subvolume delete /test/tux/zz/.snapshot/2017-09-15_1824.test
Delete subvolume (no-commit): '/test/tux/zz/.snapshot/2017-09-15_1824.test'
ERROR: cannot delete '/test/tux/zz/.snapshot/2017-09-15_1824.test': Read-only file system

root can delete this snapshot, but not the user. Why?

-- 
Ullrich Horlacher              Server und Virtualisierung
Rechenzentrum TIK         
Universitaet Stuttgart         E-Mail: horlacher@tik.uni-stuttgart.de
Allmandring 30a                Tel:    ++49-711-68565868
70569 Stuttgart (Germany)      WWW:    http://www.tik.uni-stuttgart.de/
REF:<20170915163736.GD32347@rus.uni-stuttgart.de>

Re: A user cannot remove his readonly snapshots?!

[Austin S. Hemmelgarn]

On 2017-09-15 12:37, Ulli Horlacher wrote:
> I have my btrfs filesystem mounted with option user_subvol_rm_allowed
> 
> tux@xerus: btrfs --version
> btrfs-progs v4.4
> 
> tux@xerus: uname -a
> Linux xerus 4.4.0-93-generic #116-Ubuntu SMP Fri Aug 11 21:17:51 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux
> 
> tux@xerus: id
> uid=1000(tux) gid=100(users) groups=100(users)
> 
> tux@xerus: btrfs subvolume snapshot -r /test/tux/zz /test/tux/zz/.snapshot/2017-09-15_1824.test
> tux@xerus: btrfs subvolume delete /test/tux/zz/.snapshot/2017-09-15_1824.test
> Delete subvolume (no-commit): '/test/tux/zz/.snapshot/2017-09-15_1824.test'
> ERROR: cannot delete '/test/tux/zz/.snapshot/2017-09-15_1824.test': Read-only file system
> 
> root can delete this snapshot, but not the user. Why?
> 
Add 'user_subvol_rm' to the mount options and try again.

It's because of a poor decision made regarding permissions surrounding 
subvolume operations.  The original argument was to prevent accidental 
data loss (stupid argument, rm -rf is just as bad and nearly as fast on 
most modern systems), and that behavior has never been changed.  In 
fact, I'd advocate using that option on everything, because otherwise 
you have trivial resource exhaustion issues (users can create a resource 
they then can't remove).  Ideally, normal users wouldn't be able to 
create or delete subvolumes unless explicitly allowed (possibly through 
delegation by ownership or something).

Re: A user cannot remove his readonly snapshots?!

[Ulli Horlacher]

On Fri 2017-09-15 (13:08), Austin S. Hemmelgarn wrote:
> On 2017-09-15 12:37, Ulli Horlacher wrote:
> 
> > I have my btrfs filesystem mounted with option user_subvol_rm_allowed
> > tux@xerus: btrfs subvolume delete /test/tux/zz/.snapshot/2017-09-15_1824.test
> > Delete subvolume (no-commit): '/test/tux/zz/.snapshot/2017-09-15_1824.test'
> > ERROR: cannot delete '/test/tux/zz/.snapshot/2017-09-15_1824.test': Read-only file system
> > 
> > root can delete this snapshot, but not the user. Why?
> > 
> 
> Add 'user_subvol_rm' to the mount options and try again.

root@xerus:~# mount -vo user_subvol_rm /dev/sdd4 /test
mount: wrong fs type, bad option, bad superblock on /dev/sdd4,
       missing codepage or helper program, or other error

       In some cases useful info is found in syslog - try
       dmesg | tail or so.

root@xerus:~# dmesg | tail -2
[1514588.018991] BTRFS info (device sdd4): unrecognized mount option 'user_subvol_rm'
[1514588.028430] BTRFS: open_ctree failed

user_subvol_rm is not listed on
https://btrfs.wiki.kernel.org/index.php/Mount_options

Did you mean user_subvol_rm_allowed?
I have already used this option, without success. See above.


-- 
Ullrich Horlacher              Server und Virtualisierung
Rechenzentrum TIK         
Universitaet Stuttgart         E-Mail: horlacher@tik.uni-stuttgart.de
Allmandring 30a                Tel:    ++49-711-68565868
70569 Stuttgart (Germany)      WWW:    http://www.tik.uni-stuttgart.de/
REF:<38b35e41-313a-1eed-667a-ee3138c8170d@gmail.com>

Re: A user cannot remove his readonly snapshots?!

[Peter Grandi]

>  [ ... ] mounted with option user_subvol_rm_allowed [ ... ]
> root can delete this snapshot, but not the user. Why? [ ... ]

Ordinary permissions still apply both to 'create' and 'delete':

  tree$  sudo mkdir /fs/sda7/dir
  tree$  btrfs sub create /fs/sda7/dir/sub
  ERROR: cannot access /fs/sda7/dir/sub: Permission denied

  tree$  sudo chmod a+rwx /fs/sda7/dir
  tree$  btrfs sub create /fs/sda7/dir/sub
  Create subvolume '/fs/sda7/dir/sub'

  tree$  btrfs sub delete /fs/sda7/dir/sub
  Delete subvolume (no-commit): '/fs/sda7/dir/sub'
  ERROR: cannot delete '/fs/sda7/dir/sub': Operation not permitted
  tree$  sudo mount -o remount,user_subvol_rm_allowed /fs/sda7
  tree$  btrfs sub delete /fs/sda7/dir/sub
  Delete subvolume (no-commit): '/fs/sda7/dir/sub'

  tree$  btrfs sub create /fs/sda7/dir/sub
  Create subvolume '/fs/sda7/dir/sub'

  tree$  sudo chmod a-w /fs/sda7/dir
  tree$  btrfs sub delete /fs/sda7/dir/sub
  Delete subvolume (no-commit): '/fs/sda7/dir/sub'
  ERROR: cannot delete '/fs/sda7/dir/sub': Permission denied

  tree$  sudo chmod a+w /fs/sda7/dir
  tree$  btrfs sub delete /fs/sda7/dir/sub
  Delete subvolume (no-commit): '/fs/sda7/dir/sub'
  tree$  sudo rmdir /fs/sda7/dir

Re: A user cannot remove his readonly snapshots?!

[Ulli Horlacher]

On Fri 2017-09-15 (22:07), Peter Grandi wrote:
> >  [ ... ] mounted with option user_subvol_rm_allowed [ ... ]
> > root can delete this snapshot, but not the user. Why? [ ... ]
> 
> Ordinary permissions still apply both to 'create' and 'delete':

My user tux is the owner of the snapshot directory, because he has created it!

tux@xerus:/test/tux/zz: id
uid=1000(tux) gid=100(users) groups=100(users)

tux@xerus:/test/tux/zz: ll .snapshot/
drwxr-xr-x  tux      users    - 2017-09-15 18:22:26 .snapshot/2017-09-15_1822.test
drwxr-xr-x  tux      users    - 2017-09-15 18:22:26 .snapshot/2017-09-15_1824.test
drwxr-xr-x  tux      users    - 2017-09-15 18:57:39 .snapshot/2017-09-15_1859.test

tux@xerus:/test/tux/zz: btrfs subvolume delete .snapshot/2017-09-15_1859.test
Delete subvolume (no-commit): '/test/tux/zz/.snapshot/2017-09-15_1859.test'
ERROR: cannot delete '/test/tux/zz/.snapshot/2017-09-15_1859.test': Read-only file system

-- 
Ullrich Horlacher              Server und Virtualisierung
Rechenzentrum TIK         
Universitaet Stuttgart         E-Mail: horlacher@tik.uni-stuttgart.de
Allmandring 30a                Tel:    ++49-711-68565868
70569 Stuttgart (Germany)      WWW:    http://www.tik.uni-stuttgart.de/
REF:<22972.16657.822204.646994@tree.ty.sabi.co.uk>

Re: A user cannot remove his readonly snapshots?!

[Ulli Horlacher]

On Fri 2017-09-15 (23:44), Ulli Horlacher wrote:
> On Fri 2017-09-15 (22:07), Peter Grandi wrote:
> 
> > >  [ ... ] mounted with option user_subvol_rm_allowed [ ... ]
> > > root can delete this snapshot, but not the user. Why? [ ... ]
> > 
> > Ordinary permissions still apply both to 'create' and 'delete':
> 
> My user tux is the owner of the snapshot directory, because he has created it!

I can delete normal subvolumes but not the readonly snapshots:

tux@xerus:/test/tux/zz/.snapshot: btrfs subvolume create test
Create subvolume './test'

tux@xerus:/test/tux/zz/.snapshot: ll
drwxr-xr-x  tux      users    - 2017-09-15 18:22:26 2017-09-15_1822.test
drwxr-xr-x  tux      users    - 2017-09-15 18:22:26 2017-09-15_1824.test
drwxr-xr-x  tux      users    - 2017-09-15 18:57:39 2017-09-15_1859.test
drwxr-xr-x  tux      users    - 2017-09-15 23:58:51 test

tux@xerus:/test/tux/zz/.snapshot: btrfs subvolume delete test
Delete subvolume (no-commit): '/test/tux/zz/.snapshot/test'

tux@xerus:/test/tux/zz/.snapshot: btrfs subvolume delete 2017-09-15_1859.test
Delete subvolume (no-commit): '/test/tux/zz/.snapshot/2017-09-15_1859.test'
ERROR: cannot delete '/test/tux/zz/.snapshot/2017-09-15_1859.test': Read-only file system

-- 
Ullrich Horlacher              Server und Virtualisierung
Rechenzentrum TIK         
Universitaet Stuttgart         E-Mail: horlacher@tik.uni-stuttgart.de
Allmandring 30a                Tel:    ++49-711-68565868
70569 Stuttgart (Germany)      WWW:    http://www.tik.uni-stuttgart.de/
REF:<20170915214434.GG32347@rus.uni-stuttgart.de>

Re: A user cannot remove his readonly snapshots?!

[Kai Krakow]

Am Sat, 16 Sep 2017 00:02:01 +0200
schrieb Ulli Horlacher <framstag@rus.uni-stuttgart.de>:

> On Fri 2017-09-15 (23:44), Ulli Horlacher wrote:
> > On Fri 2017-09-15 (22:07), Peter Grandi wrote:
> >   
>  [...]  
> > > 
> > > Ordinary permissions still apply both to 'create' and 'delete':  
> > 
> > My user tux is the owner of the snapshot directory, because he has
> > created it!  
> 
> I can delete normal subvolumes but not the readonly snapshots:
> 
> tux@xerus:/test/tux/zz/.snapshot: btrfs subvolume create test
> Create subvolume './test'
> 
> tux@xerus:/test/tux/zz/.snapshot: ll
> drwxr-xr-x  tux      users    - 2017-09-15 18:22:26
> 2017-09-15_1822.test drwxr-xr-x  tux      users    - 2017-09-15
> 18:22:26 2017-09-15_1824.test drwxr-xr-x  tux      users    -
> 2017-09-15 18:57:39 2017-09-15_1859.test drwxr-xr-x  tux
> users    - 2017-09-15 23:58:51 test
> 
> tux@xerus:/test/tux/zz/.snapshot: btrfs subvolume delete test
> Delete subvolume (no-commit): '/test/tux/zz/.snapshot/test'
> 
> tux@xerus:/test/tux/zz/.snapshot: btrfs subvolume delete
> 2017-09-15_1859.test Delete subvolume (no-commit):
> '/test/tux/zz/.snapshot/2017-09-15_1859.test' ERROR: cannot delete
> '/test/tux/zz/.snapshot/2017-09-15_1859.test': Read-only file system

See "man mount" in section btrfs mount options: There is a mount option
to allow normal user to delete snapshots. But this is said to has
security implication I cannot currently tell. Maybe someone else knows.


-- 
Regards,
Kai

Replies to list-only preferred.

Re: A user cannot remove his readonly snapshots?!

[Ulli Horlacher]

On Sat 2017-09-16 (01:22), Kai Krakow wrote:

> > tux@xerus:/test/tux/zz/.snapshot: btrfs subvolume delete
> > 2017-09-15_1859.test Delete subvolume (no-commit):
> > '/test/tux/zz/.snapshot/2017-09-15_1859.test' ERROR: cannot delete
> > '/test/tux/zz/.snapshot/2017-09-15_1859.test': Read-only file system
> 
> See "man mount" in section btrfs mount options: There is a mount option
> to allow normal user to delete snapshots.

As I wrote first: "I have mounted with option user_subvol_rm_allowed"

tux@xerus:/test/tux/zz/.snapshot: mount | grep /test
/dev/sdd4 on /test type btrfs (rw,relatime,space_cache,user_subvol_rm_allowed,subvolid=5,subvol=/)

This does not help. A user cannot remove a readonly snapshot he just has
created.


-- 
Ullrich Horlacher              Server und Virtualisierung
Rechenzentrum TIK         
Universitaet Stuttgart         E-Mail: horlacher@tik.uni-stuttgart.de
Allmandring 30a                Tel:    ++49-711-68565868
70569 Stuttgart (Germany)      WWW:    http://www.tik.uni-stuttgart.de/
REF:<20170916012248.0870f72d@jupiter.sol.kaishome.de>

Re: A user cannot remove his readonly snapshots?!

[Goffredo Baroncelli]

On 09/15/2017 06:37 PM, Ulli Horlacher wrote:
> I have my btrfs filesystem mounted with option user_subvol_rm_allowed
> 
> tux@xerus: btrfs --version
> btrfs-progs v4.4
> 
> tux@xerus: uname -a
> Linux xerus 4.4.0-93-generic #116-Ubuntu SMP Fri Aug 11 21:17:51 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux
> 
> tux@xerus: id
> uid=1000(tux) gid=100(users) groups=100(users)
> 
> tux@xerus: btrfs subvolume snapshot -r /test/tux/zz /test/tux/zz/.snapshot/2017-09-15_1824.test
> tux@xerus: btrfs subvolume delete /test/tux/zz/.snapshot/2017-09-15_1824.test
> Delete subvolume (no-commit): '/test/tux/zz/.snapshot/2017-09-15_1824.test'
> ERROR: cannot delete '/test/tux/zz/.snapshot/2017-09-15_1824.test': Read-only file system
> 
> root can delete this snapshot, but not the user. Why?

You should change the "ro" property to false before deleting it

	btrfs property set /test/tux/zz/.snapshot/2017-09-15_1824.test ro false


BR
G.Baroncelli

-- 
gpg @keyserver.linux.it: Goffredo Baroncelli <kreijackATinwind.it>
Key fingerprint BBF5 1610 0B64 DAC6 5F7D  17B2 0EDA 9B37 8B82 E0B5

Re: A user cannot remove his readonly snapshots?!

[Ulli Horlacher]

On Sat 2017-09-16 (10:10), Goffredo Baroncelli wrote:

> > tux@xerus: btrfs subvolume snapshot -r /test/tux/zz /test/tux/zz/.snapshot/2017-09-15_1824.test
> > tux@xerus: btrfs subvolume delete /test/tux/zz/.snapshot/2017-09-15_1824.test
> > Delete subvolume (no-commit): '/test/tux/zz/.snapshot/2017-09-15_1824.test'
> > ERROR: cannot delete '/test/tux/zz/.snapshot/2017-09-15_1824.test': Read-only file system
> > 
> > root can delete this snapshot, but not the user. Why?
> 
> You should change the "ro" property to false before deleting it
> 
> 	btrfs property set /test/tux/zz/.snapshot/2017-09-15_1824.test ro false

tux@xerus: btrfs property set /test/tux/zz/.snapshot/2017-09-15_1824.test ro false
tux@xerus: btrfs subvolume delete /test/tux/zz/.snapshot/2017-09-15_1824.test
Delete subvolume (no-commit): '/test/tux/zz/.snapshot/2017-09-15_1824.test'

That's it! It works (now)! Great! Thanks!

Up to now I was thinking about a sudo solution, but this is not necessary
any more. Less complex solutions are always better :-)

I *love* this mailing list :-)

-- 
Ullrich Horlacher              Server und Virtualisierung
Rechenzentrum TIK         
Universitaet Stuttgart         E-Mail: horlacher@tik.uni-stuttgart.de
Allmandring 30a                Tel:    ++49-711-68565868
70569 Stuttgart (Germany)      WWW:    http://www.tik.uni-stuttgart.de/
REF:<ce51b681-b86a-242a-1ac1-106454c32ddb@libero.it>

Re: A user cannot remove his readonly snapshots?!

[Goffredo Baroncelli]

On 09/16/2017 01:22 AM, Kai Krakow wrote:
> Am Sat, 16 Sep 2017 00:02:01 +0200
> schrieb Ulli Horlacher <framstag@rus.uni-stuttgart.de>:
> 
>> On Fri 2017-09-15 (23:44), Ulli Horlacher wrote:
[...]
> 
> See "man mount" in section btrfs mount options: There is a mount option
> to allow normal user to delete snapshots. But this is said to has
> security implication I cannot currently tell. Maybe someone else knows.

"btrfs sub del" removes a subvolume independently by its contents: it doesn't check the subvolume files/directories and their permission/ownership. 

This is different from a "rm -rf", which (e.g.) can't delete a directory owned by a different user with files

ghigo@venice:/tmp$ mkdir d
ghigo@venice:/tmp$ mkdir d/d
ghigo@venice:/tmp$ touch d/d/f
ghigo@venice:/tmp$ sudo chown nobody d/d
ghigo@venice:/tmp$ rm -rf d
rm: cannot remove 'd/d/f': Permission denied

In the past I proposed to allow an ordinary user to remove an *empty* subvolume with a simple rmdir (if he has the permissions). This would solve this kind of problem.

https://www.spinics.net/lists/linux-btrfs/msg06499.html

or to relax the check around "btrfs sub del", so an user can remove an _empty_ subvolume

https://www.spinics.net/lists/linux-btrfs/msg06522.html

> 
> 
BR
G.Baroncelli

-- 
gpg @keyserver.linux.it: Goffredo Baroncelli <kreijackATinwind.it>
Key fingerprint BBF5 1610 0B64 DAC6 5F7D  17B2 0EDA 9B37 8B82 E0B5

Re: A user cannot remove his readonly snapshots?!

[Peter Grandi]

[ ... ]

> I can delete normal subvolumes but not the readonly snapshots:

It is because of ordinary permissions for both subvolumes and
snapshots:

  tree$  btrfs sub create /fs/sda7/sub
  Create subvolume '/fs/sda7/sub'

  tree$  chmod a-w /fs/sda7/sub
  tree$  btrfs sub del /fs/sda7/sub
  Delete subvolume (no-commit): '/fs/sda7/sub'
  ERROR: cannot delete '/fs/sda7/sub': Permission denied

  tree$  chmod u+w /fs/sda7/sub
  tree$  btrfs sub del /fs/sda7/sub
  Delete subvolume (no-commit): '/fs/sda7/sub'

It is however possible to remove an ordinary read-only
directory, *as long as its parent directory is not read-only
too*:

  tree$  mkdir /fs/sda7/sub
  tree$  chmod a-w /fs/sda7/sub
  tree$  rmdir /fs/sda7/sub; echo $?
  0

IIRC this came up before, and the reason for the difference is
that a subvolume root directory is "special" because its '..'
entry points to itself (inode 256), that is if it is read-only
its parent directory (itself) then is read-only too.

Re: A user cannot remove his readonly snapshots?!

[Ulli Horlacher]

On Sat 2017-09-16 (11:04), Goffredo Baroncelli wrote:

> In the past I proposed to allow an ordinary user to remove an *empty* subvolume with a simple rmdir (if he has the permissions). This would solve this kind of problem.
> or to relax the check around "btrfs sub del", so an user can remove an _empty_ subvolume

This would help a lot!
Where can I sign this petition? :-)

-- 
Ullrich Horlacher              Server und Virtualisierung
Rechenzentrum TIK         
Universitaet Stuttgart         E-Mail: horlacher@tik.uni-stuttgart.de
Allmandring 30a                Tel:    ++49-711-68565868
70569 Stuttgart (Germany)      WWW:    http://www.tik.uni-stuttgart.de/
REF:<2d343791-7b32-bd53-a03d-a5b26465d358@libero.it>

Re: A user cannot remove his readonly snapshots?!

[Ulli Horlacher]

On Sat 2017-09-16 (10:10), Goffredo Baroncelli wrote:
> On 09/15/2017 06:37 PM, Ulli Horlacher wrote:

> > I have my btrfs filesystem mounted with option user_subvol_rm_allowed
> 
> You should change the "ro" property to false before deleting it
> 
> 	btrfs property set /test/tux/zz/.snapshot/2017-09-15_1824.test ro false

Still one problem is left: 
How can I test a subvolume for the mount option user_subvol_rm_allowed?
df only works for the root subvolume:

root@xerus:/test/tux# df -T .
Filesystem     Type  1K-blocks   Used Available Use% Mounted on
/dev/sdd4      btrfs  54524928 103372  52326324   1% /test

root@xerus:/test/tux# df -T zz
Filesystem     Type 1K-blocks   Used Available Use% Mounted on
-              -     54524928 103372  52326324   1% /test/tux/zz

root@xerus:/test/tux# mount | grep /test
/dev/sdd4 on /test type btrfs (rw,relatime,space_cache,user_subvol_rm_allowed,subvolid=5,subvol=/)

How do I know the btrfs filesystem for a given subvolume?
Do I really have to manually test the diretory path upwards?


-- 
Ullrich Horlacher              Server und Virtualisierung
Rechenzentrum TIK         
Universitaet Stuttgart         E-Mail: horlacher@tik.uni-stuttgart.de
Allmandring 30a                Tel:    ++49-711-68565868
70569 Stuttgart (Germany)      WWW:    http://www.tik.uni-stuttgart.de/
REF:<ce51b681-b86a-242a-1ac1-106454c32ddb@libero.it>

Re: A user cannot remove his readonly snapshots?!

[Marat Khalili]

On 16/09/17 13:19, Ulli Horlacher wrote:
> How do I know the btrfs filesystem for a given subvolume?
> Do I really have to manually test the diretory path upwards?

It was discussed recently: the answer is, unfortunately, yes, until 
someone patches df to do it for us. You can do it more or less 
efficiently by analyzing /proc/mounts .

--

With Best Regards,
Marat Khalili

Re: A user cannot remove his readonly snapshots?!

[Kai Krakow]

Am Sat, 16 Sep 2017 09:36:33 +0200
schrieb Ulli Horlacher <framstag@rus.uni-stuttgart.de>:

> On Sat 2017-09-16 (01:22), Kai Krakow wrote:
> 
> > > tux@xerus:/test/tux/zz/.snapshot: btrfs subvolume delete
> > > 2017-09-15_1859.test Delete subvolume (no-commit):
> > > '/test/tux/zz/.snapshot/2017-09-15_1859.test' ERROR: cannot delete
> > > '/test/tux/zz/.snapshot/2017-09-15_1859.test': Read-only file
> > > system  
> > 
> > See "man mount" in section btrfs mount options: There is a mount
> > option to allow normal user to delete snapshots.  
> 
> As I wrote first: "I have mounted with option user_subvol_rm_allowed"
> 
> tux@xerus:/test/tux/zz/.snapshot: mount | grep /test
> /dev/sdd4 on /test type btrfs
> (rw,relatime,space_cache,user_subvol_rm_allowed,subvolid=5,subvol=/)
> 
> This does not help. A user cannot remove a readonly snapshot he just
> has created.

Yes, sorry, I only later discovered the other posts.


-- 
Regards,
Kai

Replies to list-only preferred.

Re: A user cannot remove his readonly snapshots?!

[Kai Krakow]

Am Sat, 16 Sep 2017 13:43:23 +0300
schrieb Marat Khalili <mkh@rqc.ru>:

> On 16/09/17 13:19, Ulli Horlacher wrote:
> > How do I know the btrfs filesystem for a given subvolume?
> > Do I really have to manually test the diretory path upwards?  
> 
> It was discussed recently: the answer is, unfortunately, yes, until 
> someone patches df to do it for us. You can do it more or less 
> efficiently by analyzing /proc/mounts .

Or you do "btrfs device stats .", it shows the associated device(s). You
can put any path instead of "." in the command.

Next, look at "lsblk <devicepath>".

The problem is that the root subvolume id may not be mounted anywhere,
so /proc/mounts may not help.

On my system:

$ sudo btrfs device stats .
[/dev/bcache16].write_io_errs    0
[/dev/bcache16].read_io_errs     0
[/dev/bcache16].flush_io_errs    0
[/dev/bcache16].corruption_errs  0
[/dev/bcache16].generation_errs  0
[/dev/bcache48].write_io_errs    0
[/dev/bcache48].read_io_errs     0
[/dev/bcache48].flush_io_errs    0
[/dev/bcache48].corruption_errs  0
[/dev/bcache48].generation_errs  0
[/dev/bcache32].write_io_errs    0
[/dev/bcache32].read_io_errs     0
[/dev/bcache32].flush_io_errs    0
[/dev/bcache32].corruption_errs  0
[/dev/bcache32].generation_errs  0

$ lsblk /dev/bcache16
NAME     MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
bcache16 254:16   0 925,5G  0 disk /mnt/btrfs-pool


-- 
Regards,
Kai

Replies to list-only preferred.

Re: A user cannot remove his readonly snapshots?!

[Ulli Horlacher]

On Sat 2017-09-16 (13:47), Kai Krakow wrote:

> Or you do "btrfs device stats .", it shows the associated device(s).

tux@xerus:/test/tux/zz: btrfs device stats .
ERROR: getting dev info for devstats failed: Operation not permitted

Not possible for a normal user.


-- 
Ullrich Horlacher              Server und Virtualisierung
Rechenzentrum TIK         
Universitaet Stuttgart         E-Mail: horlacher@tik.uni-stuttgart.de
Allmandring 30a                Tel:    ++49-711-68565868
70569 Stuttgart (Germany)      WWW:    http://www.tik.uni-stuttgart.de/
REF:<20170916134748.00a7e1d8@jupiter.sol.kaishome.de>

Re: A user cannot remove his readonly snapshots?!

[Austin S. Hemmelgarn]

On 2017-09-15 15:32, Ulli Horlacher wrote:
> On Fri 2017-09-15 (13:08), Austin S. Hemmelgarn wrote:
>> On 2017-09-15 12:37, Ulli Horlacher wrote:
>>
>>> I have my btrfs filesystem mounted with option user_subvol_rm_allowed
>>> tux@xerus: btrfs subvolume delete /test/tux/zz/.snapshot/2017-09-15_1824.test
>>> Delete subvolume (no-commit): '/test/tux/zz/.snapshot/2017-09-15_1824.test'
>>> ERROR: cannot delete '/test/tux/zz/.snapshot/2017-09-15_1824.test': Read-only file system
>>>
>>> root can delete this snapshot, but not the user. Why?
>>>
>>
>> Add 'user_subvol_rm' to the mount options and try again.
> 
> root@xerus:~# mount -vo user_subvol_rm /dev/sdd4 /test
> mount: wrong fs type, bad option, bad superblock on /dev/sdd4,
>         missing codepage or helper program, or other error
> 
>         In some cases useful info is found in syslog - try
>         dmesg | tail or so.
> 
> root@xerus:~# dmesg | tail -2
> [1514588.018991] BTRFS info (device sdd4): unrecognized mount option 'user_subvol_rm'
> [1514588.028430] BTRFS: open_ctree failed
> 
> user_subvol_rm is not listed on
> https://btrfs.wiki.kernel.org/index.php/Mount_options
> 
> Did you mean user_subvol_rm_allowed?
Yes, that's what I meant, sorry about the confusion.
> I have already used this option, without success. See above.
I missed that, sorry.

Re: A user cannot remove his readonly snapshots?!

[Austin S. Hemmelgarn]

On 2017-09-16 10:28, Ulli Horlacher wrote:
> On Sat 2017-09-16 (13:47), Kai Krakow wrote:
> 
>> Or you do "btrfs device stats .", it shows the associated device(s).
> 
> tux@xerus:/test/tux/zz: btrfs device stats .
> ERROR: getting dev info for devstats failed: Operation not permitted
> 
> Not possible for a normal user.
> 
`btrfs fi show` should be possible for a normal user, and that also 
lists devices.  Alternatively, you can check /sys/fs/btrfs and correlate 
UUID's (possibly easier programmatically than analyzing regular output).