dm exception store: add merge specific methods

Add functions that decide how many consecutive chunks of snapshot to
merge back into the origin next and to update the metadata afterwards.

prepare_merge provides a pointer to the most recent still-to-be-merged
chunk and returns how many previous ones are consecutive and can be
processed together.

commit_merge removes the nr_merged most-recent chunks permanently from
the exception store.  The number must not exceed that returned by
prepare_merge.

Introduce NUM_SNAPSHOT_HDR_CHUNKS to show where the snapshot header
chunk is accounted for.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Reviewed-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
This commit is contained in:
Mikulas Patocka 2009-12-10 23:52:29 +00:00 committed by Alasdair G Kergon
parent 615d1eb9ca
commit 4454a6216f
2 changed files with 129 additions and 2 deletions

View File

@ -74,6 +74,23 @@ struct dm_exception_store_type {
void (*callback) (void *, int success),
void *callback_context);
/*
* Returns 0 if the exception store is empty.
*
* If there are exceptions still to be merged, sets
* *last_old_chunk and *last_new_chunk to the most recent
* still-to-be-merged chunk and returns the number of
* consecutive previous ones.
*/
int (*prepare_merge) (struct dm_exception_store *store,
chunk_t *last_old_chunk, chunk_t *last_new_chunk);
/*
* Clear the last n exceptions.
* nr_merged must be <= the value returned by prepare_merge.
*/
int (*commit_merge) (struct dm_exception_store *store, int nr_merged);
/*
* The snapshot is invalid, note this in the metadata.
*/

View File

@ -55,6 +55,8 @@
*/
#define SNAPSHOT_DISK_VERSION 1
#define NUM_SNAPSHOT_HDR_CHUNKS 1
struct disk_header {
uint32_t magic;
@ -120,7 +122,22 @@ struct pstore {
/*
* The next free chunk for an exception.
*
* When creating exceptions, all the chunks here and above are
* free. It holds the next chunk to be allocated. On rare
* occasions (e.g. after a system crash) holes can be left in
* the exception store because chunks can be committed out of
* order.
*
* When merging exceptions, it does not necessarily mean all the
* chunks here and above are free. It holds the value it would
* have held if all chunks had been committed in order of
* allocation. Consequently the value may occasionally be
* slightly too low, but since it's only used for 'status' and
* it can never reach its minimum value too early this doesn't
* matter.
*/
chunk_t next_free;
/*
@ -409,6 +426,15 @@ static void write_exception(struct pstore *ps,
e->new_chunk = cpu_to_le64(de->new_chunk);
}
static void clear_exception(struct pstore *ps, uint32_t index)
{
struct disk_exception *e = get_exception(ps, index);
/* clear it */
e->old_chunk = 0;
e->new_chunk = 0;
}
/*
* Registers the exceptions that are present in the current area.
* 'full' is filled in to indicate if the area has been
@ -505,7 +531,8 @@ static void persistent_usage(struct dm_exception_store *store,
* Then there are (ps->current_area + 1) metadata chunks, each one
* separated from the next by ps->exceptions_per_area data chunks.
*/
*metadata_sectors = (ps->current_area + 2) * store->chunk_size;
*metadata_sectors = (ps->current_area + 1 + NUM_SNAPSHOT_HDR_CHUNKS) *
store->chunk_size;
}
static void persistent_dtr(struct dm_exception_store *store)
@ -680,6 +707,85 @@ static void persistent_commit_exception(struct dm_exception_store *store,
ps->callback_count = 0;
}
static int persistent_prepare_merge(struct dm_exception_store *store,
chunk_t *last_old_chunk,
chunk_t *last_new_chunk)
{
struct pstore *ps = get_info(store);
struct disk_exception de;
int nr_consecutive;
int r;
/*
* When current area is empty, move back to preceding area.
*/
if (!ps->current_committed) {
/*
* Have we finished?
*/
if (!ps->current_area)
return 0;
ps->current_area--;
r = area_io(ps, READ);
if (r < 0)
return r;
ps->current_committed = ps->exceptions_per_area;
}
read_exception(ps, ps->current_committed - 1, &de);
*last_old_chunk = de.old_chunk;
*last_new_chunk = de.new_chunk;
/*
* Find number of consecutive chunks within the current area,
* working backwards.
*/
for (nr_consecutive = 1; nr_consecutive < ps->current_committed;
nr_consecutive++) {
read_exception(ps, ps->current_committed - 1 - nr_consecutive,
&de);
if (de.old_chunk != *last_old_chunk - nr_consecutive ||
de.new_chunk != *last_new_chunk - nr_consecutive)
break;
}
return nr_consecutive;
}
static int persistent_commit_merge(struct dm_exception_store *store,
int nr_merged)
{
int r, i;
struct pstore *ps = get_info(store);
BUG_ON(nr_merged > ps->current_committed);
for (i = 0; i < nr_merged; i++)
clear_exception(ps, ps->current_committed - 1 - i);
r = area_io(ps, WRITE);
if (r < 0)
return r;
ps->current_committed -= nr_merged;
/*
* At this stage, only persistent_usage() uses ps->next_free, so
* we make no attempt to keep ps->next_free strictly accurate
* as exceptions may have been committed out-of-order originally.
* Once a snapshot has become merging, we set it to the value it
* would have held had all the exceptions been committed in order.
*
* ps->current_area does not get reduced by prepare_merge() until
* after commit_merge() has removed the nr_merged previous exceptions.
*/
ps->next_free = (area_location(ps, ps->current_area) - 1) +
(ps->current_committed + 1) + NUM_SNAPSHOT_HDR_CHUNKS;
return 0;
}
static void persistent_drop_snapshot(struct dm_exception_store *store)
{
struct pstore *ps = get_info(store);
@ -705,7 +811,7 @@ static int persistent_ctr(struct dm_exception_store *store,
ps->area = NULL;
ps->zero_area = NULL;
ps->header_area = NULL;
ps->next_free = 2; /* skipping the header and first area */
ps->next_free = NUM_SNAPSHOT_HDR_CHUNKS + 1; /* header and 1st area */
ps->current_committed = 0;
ps->callback_count = 0;
@ -748,6 +854,8 @@ static struct dm_exception_store_type _persistent_type = {
.read_metadata = persistent_read_metadata,
.prepare_exception = persistent_prepare_exception,
.commit_exception = persistent_commit_exception,
.prepare_merge = persistent_prepare_merge,
.commit_merge = persistent_commit_merge,
.drop_snapshot = persistent_drop_snapshot,
.usage = persistent_usage,
.status = persistent_status,
@ -761,6 +869,8 @@ static struct dm_exception_store_type _persistent_compat_type = {
.read_metadata = persistent_read_metadata,
.prepare_exception = persistent_prepare_exception,
.commit_exception = persistent_commit_exception,
.prepare_merge = persistent_prepare_merge,
.commit_merge = persistent_commit_merge,
.drop_snapshot = persistent_drop_snapshot,
.usage = persistent_usage,
.status = persistent_status,