Btrfs users - Aug 2007 - Subdirectory snapshots

Hi Chris and everyone else,

 First let me congratulate you for the nice job on btrfs. I've been stress 
testing it with parallel kernel compiles intermixed with snapshot taking, up 
to about ~100 load avg on a dual core box and it's doing quite well :-)

 I noticed that when creating snapshots it seems to always snapshot an entire 
subvolume, that is if one does:

test1:/mnt# btrfsctl -s snap1 /mnt/default/dir1/dir2

Now /mnt/snap1 will be a subvolume containing everything /mnt/default 
contains, instead of only the "dir2" contents. Is there any plans or
interest
on making snapshotting of subdirectories possible?
 The above feature would come in even more handy if the location of snapshots 
would not be limited to the root of the filesystem, i.e. a snapshot could 
reside alongside normal directories (I'm thinking here unprivileged users 
taking snapshots of parts of their own home dirs and such).

 I understand that btrfs uses a tree of tree roots to keep track of 
snapshots/subvolumes, and by reading the design document I'm not sure if
that
would be a showstopper to the above features; despite that, since every 
extent is reference counted it would seem possible to implement it.

 Anyway, you can count on me to test this or any other upcoming features!

Thank you and best regards

Claudio Martins

On Wed, 8 Aug 2007 03:43:57 +0100
Claudio Martins <ctpm@ist.utl.pt> wrote:
> 
>  Hi Chris and everyone else,
> 
>  First let me congratulate you for the nice job on btrfs. I've been
> stress testing it with parallel kernel compiles intermixed with
> snapshot taking, up to about ~100 load avg on a dual core box and
> it's doing quite well :-)
Good to hear ;)
> 
>  I noticed that when creating snapshots it seems to always snapshot
> an entire subvolume, that is if one does:
> 
> test1:/mnt# btrfsctl -s snap1 /mnt/default/dir1/dir2
> 
> Now /mnt/snap1 will be a subvolume containing everything /mnt/default 
> contains, instead of only the "dir2" contents. Is there any plans
or
> interest on making snapshotting of subdirectories possible?
That's correct.  I do plan making snapshots per subdirectory, there are
just a few things on the todo list that have to come first.
>  The above feature would come in even more handy if the location of
> snapshots would not be limited to the root of the filesystem, i.e. a
> snapshot could reside alongside normal directories (I'm thinking here
> unprivileged users taking snapshots of parts of their own home dirs
> and such).
Yes
> 
>  I understand that btrfs uses a tree of tree roots to keep track of 
> snapshots/subvolumes, and by reading the design document I'm not sure
> if that would be a showstopper to the above features; despite that,
> since every extent is reference counted it would seem possible to
> implement it.
Basically I'll have to make it possible to have a directory entry
anywhere in the tree point to a tree root.  Before that can happen I
need to unify the inode numbers across the whole FS.  Not a huge task,
but I want to get tree locking and enospc out of the way first.

Thanks,
Chris