On Thu, 19 Nov 2009, Mike Snitzer wrote:
> Permit in-use snapshot exception data to be 'handed over' from one
> snapshot instance to another. This is a pre-requisite for patches
> that allow the changes made in a snapshot device to be merged back into
> its origin device and also allows device resizing.
>
> The basic call sequence is:
>
> dmsetup load new_snapshot (referencing the existing in-use cow device)
> - the ctr code detects that the cow is already in use and allows the
> two snapshot target instances to be linked together
> dmsetup suspend original_snapshot
> dmsetup resume new_snapshot
> - the new_snapshot becomes live, and if anything now tries to access
> the original one it will receive -EIO
> dmsetup remove original_snapshot
>
> (There can only be two snapshot targets referencing the same cow device
> simultaneously.)
>
> Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Acked-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
> + down_read(&_origins_lock);
> + (void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest);
> + if (snap_src && snap_dest) {
> + down_write_nested(&snap_src->lock, SINGLE_DEPTH_NESTING);
> + down_write(&snap_dest->lock);
I'd suggest to use the "_nested" version for the nested lock, it is a
convention.
down_write(&snap_src->lock);
down_write_nested(&snap_dest->lock, SINGLE_DEPTH_NESTING);
Mikulas
> + __handover_exceptions(snap_src, snap_dest);
> + up_write(&snap_dest->lock);
> + up_write(&snap_src->lock);
> + }
> + up_read(&_origins_lock);
--
dm-devel mailing list
dm-devel@xxxxxxxxxx
https://www.redhat.com/mailman/listinfo/dm-devel
