forked from Minki/linux
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
Alasdair G Kergon
parent
615d1eb9ca
commit
4454a6216f
@ -74,6 +74,23 @@ struct dm_exception_store_type {
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void (*callback) (void *, int success),
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void *callback_context);
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/*
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* Returns 0 if the exception store is empty.
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*
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* If there are exceptions still to be merged, sets
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* *last_old_chunk and *last_new_chunk to the most recent
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* still-to-be-merged chunk and returns the number of
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* consecutive previous ones.
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*/
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int (*prepare_merge) (struct dm_exception_store *store,
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chunk_t *last_old_chunk, chunk_t *last_new_chunk);
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/*
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* Clear the last n exceptions.
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* nr_merged must be <= the value returned by prepare_merge.
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*/
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int (*commit_merge) (struct dm_exception_store *store, int nr_merged);
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/*
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* The snapshot is invalid, note this in the metadata.
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*/
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@ -55,6 +55,8 @@
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*/
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#define SNAPSHOT_DISK_VERSION 1
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#define NUM_SNAPSHOT_HDR_CHUNKS 1
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struct disk_header {
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uint32_t magic;
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@ -120,7 +122,22 @@ struct pstore {
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/*
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* The next free chunk for an exception.
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*
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* When creating exceptions, all the chunks here and above are
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* free. It holds the next chunk to be allocated. On rare
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* occasions (e.g. after a system crash) holes can be left in
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* the exception store because chunks can be committed out of
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* order.
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*
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* When merging exceptions, it does not necessarily mean all the
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* chunks here and above are free. It holds the value it would
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* have held if all chunks had been committed in order of
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* allocation. Consequently the value may occasionally be
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* slightly too low, but since it's only used for 'status' and
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* it can never reach its minimum value too early this doesn't
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* matter.
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*/
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chunk_t next_free;
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/*
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@ -409,6 +426,15 @@ static void write_exception(struct pstore *ps,
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e->new_chunk = cpu_to_le64(de->new_chunk);
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}
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static void clear_exception(struct pstore *ps, uint32_t index)
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{
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struct disk_exception *e = get_exception(ps, index);
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/* clear it */
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e->old_chunk = 0;
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e->new_chunk = 0;
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}
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/*
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* Registers the exceptions that are present in the current area.
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* 'full' is filled in to indicate if the area has been
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@ -505,7 +531,8 @@ static void persistent_usage(struct dm_exception_store *store,
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* Then there are (ps->current_area + 1) metadata chunks, each one
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* separated from the next by ps->exceptions_per_area data chunks.
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*/
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*metadata_sectors = (ps->current_area + 2) * store->chunk_size;
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*metadata_sectors = (ps->current_area + 1 + NUM_SNAPSHOT_HDR_CHUNKS) *
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store->chunk_size;
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}
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static void persistent_dtr(struct dm_exception_store *store)
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@ -680,6 +707,85 @@ static void persistent_commit_exception(struct dm_exception_store *store,
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ps->callback_count = 0;
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}
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static int persistent_prepare_merge(struct dm_exception_store *store,
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chunk_t *last_old_chunk,
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chunk_t *last_new_chunk)
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{
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struct pstore *ps = get_info(store);
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struct disk_exception de;
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int nr_consecutive;
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int r;
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/*
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* When current area is empty, move back to preceding area.
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*/
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if (!ps->current_committed) {
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/*
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* Have we finished?
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*/
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if (!ps->current_area)
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return 0;
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ps->current_area--;
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r = area_io(ps, READ);
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if (r < 0)
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return r;
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ps->current_committed = ps->exceptions_per_area;
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}
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read_exception(ps, ps->current_committed - 1, &de);
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*last_old_chunk = de.old_chunk;
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*last_new_chunk = de.new_chunk;
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/*
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* Find number of consecutive chunks within the current area,
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* working backwards.
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*/
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for (nr_consecutive = 1; nr_consecutive < ps->current_committed;
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nr_consecutive++) {
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read_exception(ps, ps->current_committed - 1 - nr_consecutive,
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&de);
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if (de.old_chunk != *last_old_chunk - nr_consecutive ||
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de.new_chunk != *last_new_chunk - nr_consecutive)
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break;
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}
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return nr_consecutive;
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}
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static int persistent_commit_merge(struct dm_exception_store *store,
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int nr_merged)
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{
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int r, i;
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struct pstore *ps = get_info(store);
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BUG_ON(nr_merged > ps->current_committed);
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for (i = 0; i < nr_merged; i++)
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clear_exception(ps, ps->current_committed - 1 - i);
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r = area_io(ps, WRITE);
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if (r < 0)
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return r;
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ps->current_committed -= nr_merged;
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/*
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* At this stage, only persistent_usage() uses ps->next_free, so
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* we make no attempt to keep ps->next_free strictly accurate
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* as exceptions may have been committed out-of-order originally.
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* Once a snapshot has become merging, we set it to the value it
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* would have held had all the exceptions been committed in order.
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*
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* ps->current_area does not get reduced by prepare_merge() until
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* after commit_merge() has removed the nr_merged previous exceptions.
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*/
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ps->next_free = (area_location(ps, ps->current_area) - 1) +
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(ps->current_committed + 1) + NUM_SNAPSHOT_HDR_CHUNKS;
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return 0;
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}
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static void persistent_drop_snapshot(struct dm_exception_store *store)
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{
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struct pstore *ps = get_info(store);
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@ -705,7 +811,7 @@ static int persistent_ctr(struct dm_exception_store *store,
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ps->area = NULL;
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ps->zero_area = NULL;
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ps->header_area = NULL;
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ps->next_free = 2; /* skipping the header and first area */
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ps->next_free = NUM_SNAPSHOT_HDR_CHUNKS + 1; /* header and 1st area */
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ps->current_committed = 0;
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ps->callback_count = 0;
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@ -748,6 +854,8 @@ static struct dm_exception_store_type _persistent_type = {
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.read_metadata = persistent_read_metadata,
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.prepare_exception = persistent_prepare_exception,
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.commit_exception = persistent_commit_exception,
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.prepare_merge = persistent_prepare_merge,
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.commit_merge = persistent_commit_merge,
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.drop_snapshot = persistent_drop_snapshot,
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.usage = persistent_usage,
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.status = persistent_status,
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@ -761,6 +869,8 @@ static struct dm_exception_store_type _persistent_compat_type = {
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.read_metadata = persistent_read_metadata,
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.prepare_exception = persistent_prepare_exception,
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.commit_exception = persistent_commit_exception,
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.prepare_merge = persistent_prepare_merge,
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.commit_merge = persistent_commit_merge,
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.drop_snapshot = persistent_drop_snapshot,
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.usage = persistent_usage,
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.status = persistent_status,
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