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To: linux-btrfs@vger.kernel.org
From: Kai Krakow <hurikhan77@gmail.com>
Subject: Re: A user cannot remove his readonly snapshots?!
Date: Sat, 16 Sep 2017 13:47:48 +0200
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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

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