determining filesystem mount points

determining filesystem mount points

[Russell Coker]

What's a good way of determining the mount point for a BTRFS filesystem in a 
shell script?

/home/user might be a filesystem, a directory under a filesystem /home, a 
directory under a subvol /home of /, a subvol of /, or a subvol of the /home 
filesystem.  How do I determine which it is?

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My Main Blog         http://etbe.coker.com.au/
My Documents Blog    http://doc.coker.com.au/

Re: determining filesystem mount points

[Bart Noordervliet]

Hi Russell,

all of the information you need should be available from the 'mount'
and 'btrfs subvol list' commands. Though I realise it can be awkward
to parse it out of there, this will be the only way to get accurate
information in the face of bind-mounts and other fancy tricks. One
other datapoint that you might be able to use is that btrfs, I
believe, always shows inode number 256 for subvolumes in 'stat'. Keep
in mind there that the root subvolume is, as the name implies, also
technically a subvolume.

Regards, Bart

On Sat, Dec 29, 2012 at 6:04 AM, Russell Coker
<russell+btrfs@coker.com.au> wrote:
> What's a good way of determining the mount point for a BTRFS filesystem in a
> shell script?
>
> /home/user might be a filesystem, a directory under a filesystem /home, a
> directory under a subvol /home of /, a subvol of /, or a subvol of the /home
> filesystem.  How do I determine which it is?
>
> --
> My Main Blog         http://etbe.coker.com.au/
> My Documents Blog    http://doc.coker.com.au/
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Re: determining filesystem mount points

[Russell Coker]

On Sat, 29 Dec 2012, Bart Noordervliet <bart@noordervliet.net> wrote:
> all of the information you need should be available from the 'mount'
> and 'btrfs subvol list' commands. Though I realise it can be awkward
> to parse it out of there, this will be the only way to get accurate
> information in the face of bind-mounts and other fancy tricks. One
> other datapoint that you might be able to use is that btrfs, I
> believe, always shows inode number 256 for subvolumes in 'stat'. Keep
> in mind there that the root subvolume is, as the name implies, also
> technically a subvolume.

What I want to do is to have shell scripts create snapshots and then 
automatically remove them.  As the output of "btrfs subvol list" is relative 
to the root of the filesystem even if we don't consider bind mounts and other 
complications it becomes difficult to generate a "btrfs subvol delete" command 
that is correct from a shell script.

Perhaps the best solution would be to have an option to "btrfs subvol list" to 
give output with fully qualified paths.

-- 
My Main Blog         http://etbe.coker.com.au/
My Documents Blog    http://doc.coker.com.au/

Re: determining filesystem mount points

[Anand Jain]

> Perhaps the best solution would be to have an option to "btrfs subvol list" to
> give output with fully qualified paths.

  This patch does that.

    http://comments.gmane.org/gmane.comp.file-systems.btrfs/20040


-Anand