On Mon, Oct 05 2009 at 3:00pm -0400,
Mike Snitzer <snitzer@xxxxxxxxxx> wrote:
> From: Mikulas Patocka <mpatocka@xxxxxxxxxx>
>
> Handover of the exception store. This is needed for merging (to allow reload of
> the table) and it also enables origin or snapshot resize.
>
> The supported call sequences are:
>
> new_snapshot->ctr
> old_snapshot->suspend
> old_snapshot->dtr
> new_snapshot->resume
>
> and
>
> new_snapshot->ctr
> old_snapshot->suspend
> new_snapshot->resume
> old_snapshot->dtr
>
> There may not be more than two instances of a given snapshot. LVM always creates
> at most two; if there are more, the user misuses dmsetup.
>
> Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
> Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
...
> +/* _origins_lock must be held */
> +static struct dm_snapshot *find_duplicate(struct dm_snapshot *snap)
> +{
...
I just noticed that find_duplicate should be renamed to __find_duplicate
to use the convention of a '__' prefix on all dm-snap.c functions that
require the _origins_lock.
Here is an updated patch (doesn't change any snapshot-merge patches that
follow):
Handover of the exception store. This is needed for merging (to allow reload of
the table) and it also enables origin or snapshot resize.
The supported call sequences are:
new_snapshot->ctr
old_snapshot->suspend
old_snapshot->dtr
new_snapshot->resume
and
new_snapshot->ctr
old_snapshot->suspend
new_snapshot->resume
old_snapshot->dtr
There may not be more than two instances of a given snapshot. LVM always creates
at most two; if there are more, the user misuses dmsetup.
Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
---
drivers/md/dm-snap.c | 85 +++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 85 insertions(+)
Index: linux-2.6/drivers/md/dm-snap.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-snap.c
+++ linux-2.6/drivers/md/dm-snap.c
@@ -72,6 +72,9 @@ struct dm_snapshot {
/* Origin writes don't trigger exceptions until this is set */
int active;
+ /* Exception store will be handed over from another snapshot */
+ int handover;
+
mempool_t *pending_pool;
atomic_t pending_exceptions_count;
@@ -505,6 +508,33 @@ static int dm_add_exception(void *contex
return 0;
}
+/* _origins_lock must be held */
+static struct dm_snapshot *__find_duplicate(struct dm_snapshot *snap)
+{
+ struct dm_snapshot *dup;
+ struct dm_snapshot *l;
+ struct origin *o;
+
+ o = __lookup_origin(snap->origin->bdev);
+ if (!o)
+ return NULL;
+
+ dup = NULL;
+ list_for_each_entry(l, &o->snapshots, list)
+ if (l != snap && bdev_equal(l->cow->bdev,
+ snap->cow->bdev)) {
+ if (!dup) {
+ dup = l;
+ } else {
+ DMERR("Multiple active duplicates, "
+ "user misuses dmsetup.");
+ return NULL;
+ }
+ }
+
+ return dup;
+}
+
#define min_not_zero(l, r) (((l) == 0) ? (r) : (((r) == 0) ? (l) : min(l, r)))
/*
@@ -635,6 +665,7 @@ static int snapshot_ctr(struct dm_target
s->valid = 1;
s->active = 0;
atomic_set(&s->pending_exceptions_count, 0);
+ s->handover = 0;
init_rwsem(&s->lock);
spin_lock_init(&s->pe_lock);
@@ -670,6 +701,11 @@ static int snapshot_ctr(struct dm_target
spin_lock_init(&s->tracked_chunk_lock);
+ down_read(&_origins_lock);
+ if (__find_duplicate(s))
+ s->handover = 1;
+ up_read(&_origins_lock);
+
/* Metadata must only be loaded into one table at once */
r = s->store->type->read_metadata(s->store, dm_add_exception,
(void *)s);
@@ -741,15 +777,49 @@ static void __free_exceptions(struct dm_
exit_exception_table(&s->complete, exception_cache);
}
+static void handover_exceptions(struct dm_snapshot *old,
+ struct dm_snapshot *new)
+{
+ union {
+ struct exception_table table_swap;
+ struct dm_exception_store *store_swap;
+ } u;
+
+ u.table_swap = new->complete;
+ new->complete = old->complete;
+ old->complete = u.table_swap;
+ u.store_swap = new->store;
+ new->store = old->store;
+ old->store = u.store_swap;
+
+ new->store->snap = new;
+ old->store->snap = old;
+
+ old->active = 0;
+ new->handover = 0;
+}
+
static void snapshot_dtr(struct dm_target *ti)
{
#ifdef CONFIG_DM_DEBUG
int i;
#endif
struct dm_snapshot *s = ti->private;
+ struct dm_snapshot *dup;
flush_workqueue(ksnapd);
+ down_write(&_origins_lock);
+ down_write(&s->lock);
+ dup = __find_duplicate(s);
+ if (dup && dup->handover) {
+ down_write_nested(&dup->lock, SINGLE_DEPTH_NESTING);
+ handover_exceptions(s, dup);
+ up_write(&dup->lock);
+ }
+ up_write(&s->lock);
+ up_write(&_origins_lock);
+
/* Prevent further origin writes from using this snapshot. */
/* After this returns there can be no new kcopyd jobs. */
unregister_snapshot(s);
@@ -1144,9 +1214,24 @@ static void snapshot_resume(struct dm_ta
{
struct dm_snapshot *s = ti->private;
+ down_write(&_origins_lock);
down_write(&s->lock);
+ if (s->handover) {
+ struct dm_snapshot *dup;
+ dup = __find_duplicate(s);
+ if (!dup) {
+ DMERR("duplicate not found");
+ s->valid = 0;
+ goto ret;
+ }
+ down_write_nested(&dup->lock, SINGLE_DEPTH_NESTING);
+ handover_exceptions(dup, s);
+ up_write(&dup->lock);
+ }
s->active = 1;
+ ret:
up_write(&s->lock);
+ up_write(&_origins_lock);
}
static int snapshot_status(struct dm_target *ti, status_type_t type,
--
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