Thanks for the recent repost (18-Aug-2009) of your patches at:
http://people.redhat.com/mpatocka/patches/kernel/new-snapshot/devel
The interface seems to be in-line with what we want. I noticed that
you can't have dm-snapshot and dm-multisnapshot loaded in the kernel
at the same time (kmem_cache_create: duplicate cache
dm_snap_tracked_chunk -- in the module init function). You will also
want to run your patches through 'linux/scripts/checkpatch.pl'. It
mostly gets angry about the 80 characters / line breakage, but there
is some other things it catches.
brassow
On Jul 27, 2009, at 6:24 AM, Mikulas Patocka wrote:
Hi
The new release of shared snapshots can be found here:
http://people.redhat.com/mpatocka/patches/kernel/new-snapshots/devel/
It has the interface we talked about on Linux Tag.
So look at it as a last chance to review the interface. And also
test it.
To create a snapshot, you have to:
- send a message
- ask for status, get the snapshot id
- suspend (this creates the snapshot, when the filesystem is
quiescent)
- resume
Then, you can attach the snapshots by loading "multisnap-snap" target.
If the table line contains argument "sync-snapshots", it
synchronizes the
snapshot list against what is given on the table --- i.e. creates
snapshots that are on the table but are not in the store and deletes
those
that are not in the store but are on the table.
Other changes:
- make more structures private (move them to dm-multisnap-
private.h), so
that ABI doesn't change if these are chaged.
- snapshot IDs are treated as strings, not numbers.
- metadata cache size can be specified as an argument to the "mikulas"
exception store.
- an argument "preserve-on-error" that says that on error or overflow,
writes to the origin should be disabled.
- if you don't specify this, the origin continues operation, but
snapshots are irreversibly damaged by this (use for non-important
snapshots such as backups)
- if you specify this, the data are always preserved, the whole
thing just halts on error (user when snapshots contain some
important data.
- fixed two bad bugs in dm-bufio.
Known bugs:
- that read-vs-realloc race (that I already fixed in the old
snapshots a
year ago) is present there. I'll fix it, but it isn't so trivial as in
unshared snapshots.
Mikulas
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