diff --git a/Documentation/device-mapper/snapshot.txt b/Documentation/device-mapper/snapshot.txt
index b8bbb516f9894a86f2f94b93c7a056633c45f85c..1810833f6dc6489c695d4dc40f0127a51476dc62 100644
--- a/Documentation/device-mapper/snapshot.txt
+++ b/Documentation/device-mapper/snapshot.txt
@@ -31,6 +31,7 @@ its visible content unchanged, at least until the <COW device> fills up.
*) snapshot <origin> <COW device> <persistent?> <chunksize>
+ [<# feature args> [<arg>]*]
A snapshot of the <origin> block device is created. Changed chunks of
<chunksize> sectors will be stored on the <COW device>. Writes will
@@ -53,8 +54,23 @@ When loading or unloading the snapshot target, the corresponding
snapshot-origin or snapshot-merge target must be suspended. A failure to
suspend the origin target could result in data corruption.
+Optional features:
+
+ discard_zeroes_cow - a discard issued to the snapshot device that
+ maps to entire chunks to will zero the corresponding exception(s) in
+ the snapshot's exception store.
+
+ discard_passdown_origin - a discard to the snapshot device is passed
+ down to the snapshot-origin's underlying device. This doesn't cause
+ copy-out to the snapshot exception store because the snapshot-origin
+ target is bypassed.
+
+ The discard_passdown_origin feature depends on the discard_zeroes_cow
+ feature being enabled.
+
* snapshot-merge <origin> <COW device> <persistent> <chunksize>
+ [<# feature args> [<arg>]*]
takes the same table arguments as the snapshot target except it only
works with persistent snapshots. This target assumes the role of the
diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index 3107f2b1988b35f3b22f8324becb48bdffe3bc13..63916e1dc569caf1ddc2e09fe85e1b06803ada88 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -1,6 +1,4 @@
/*
- * dm-snapshot.c
- *
* Copyright (C) 2001-2002 Sistina Software (UK) Limited.
*
* This file is released under the GPL.
@@ -134,7 +132,10 @@ struct dm_snapshot {
* - I/O error while merging
* => stop merging; set merge_failed; process I/O normally.
*/
- int merge_failed;
+ bool merge_failed:1;
+
+ bool discard_zeroes_cow:1;
+ bool discard_passdown_origin:1;
/*
* Incoming bios that overlap with chunks being merged must wait
@@ -1173,12 +1174,64 @@ static void stop_merge(struct dm_snapshot *s)
clear_bit(SHUTDOWN_MERGE, &s->state_bits);
}
+static int parse_snapshot_features(struct dm_arg_set *as, struct dm_snapshot *s,
+ struct dm_target *ti)
+{
+ int r;
+ unsigned argc;
+ const char *arg_name;
+
+ static const struct dm_arg _args[] = {
+ {0, 2, "Invalid number of feature arguments"},
+ };
+
+ /*
+ * No feature arguments supplied.
+ */
+ if (!as->argc)
+ return 0;
+
+ r = dm_read_arg_group(_args, as, &argc, &ti->error);
+ if (r)
+ return -EINVAL;
+
+ while (argc && !r) {
+ arg_name = dm_shift_arg(as);
+ argc--;
+
+ if (!strcasecmp(arg_name, "discard_zeroes_cow"))
+ s->discard_zeroes_cow = true;
+
+ else if (!strcasecmp(arg_name, "discard_passdown_origin"))
+ s->discard_passdown_origin = true;
+
+ else {
+ ti->error = "Unrecognised feature requested";
+ r = -EINVAL;
+ break;
+ }
+ }
+
+ if (!s->discard_zeroes_cow && s->discard_passdown_origin) {
+ /*
+ * TODO: really these are disjoint.. but ti->num_discard_bios
+ * and dm_bio_get_target_bio_nr() require rigid constraints.
+ */
+ ti->error = "discard_passdown_origin feature depends on discard_zeroes_cow";
+ r = -EINVAL;
+ }
+
+ return r;
+}
+
/*
- * Construct a snapshot mapping: <origin_dev> <COW-dev> <p|po|n> <chunk-size>
+ * Construct a snapshot mapping:
+ * <origin_dev> <COW-dev> <p|po|n> <chunk-size> [<# feature args> [<arg>]*]
*/
static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
{
struct dm_snapshot *s;
+ struct dm_arg_set as;
int i;
int r = -EINVAL;
char *origin_path, *cow_path;
@@ -1186,8 +1239,8 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
unsigned args_used, num_flush_bios = 1;
fmode_t origin_mode = FMODE_READ;
- if (argc != 4) {
- ti->error = "requires exactly 4 arguments";
+ if (argc < 4) {
+ ti->error = "requires 4 or more arguments";
r = -EINVAL;
goto bad;
}
@@ -1204,6 +1257,13 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
goto bad;
}
+ as.argc = argc;
+ as.argv = argv;
+ dm_consume_args(&as, 4);
+ r = parse_snapshot_features(&as, s, ti);
+ if (r)
+ goto bad_features;
+
origin_path = argv[0];
argv++;
argc--;
@@ -1289,6 +1349,8 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
ti->private = s;
ti->num_flush_bios = num_flush_bios;
+ if (s->discard_zeroes_cow)
+ ti->num_discard_bios = (s->discard_passdown_origin ? 2 : 1);
ti->per_io_data_size = sizeof(struct dm_snap_tracked_chunk);
/* Add snapshot to the list of snapshots for this origin */
@@ -1336,29 +1398,22 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
bad_read_metadata:
unregister_snapshot(s);
-
bad_load_and_register:
mempool_exit(&s->pending_pool);
-
bad_pending_pool:
dm_kcopyd_client_destroy(s->kcopyd_client);
-
bad_kcopyd:
dm_exception_table_exit(&s->pending, pending_cache);
dm_exception_table_exit(&s->complete, exception_cache);
-
bad_hash_tables:
dm_exception_store_destroy(s->store);
-
bad_store:
dm_put_device(ti, s->cow);
-
bad_cow:
dm_put_device(ti, s->origin);
-
bad_origin:
+bad_features:
kfree(s);
-
bad:
return r;
}
@@ -1806,6 +1861,37 @@ static void remap_exception(struct dm_snapshot *s, struct dm_exception *e,
(bio->bi_iter.bi_sector & s->store->chunk_mask);
}
+static void zero_callback(int read_err, unsigned long write_err, void *context)
+{
+ struct bio *bio = context;
+ struct dm_snapshot *s = bio->bi_private;
+
+ up(&s->cow_count);
+ bio->bi_status = write_err ? BLK_STS_IOERR : 0;
+ bio_endio(bio);
+}
+
+static void zero_exception(struct dm_snapshot *s, struct dm_exception *e,
+ struct bio *bio, chunk_t chunk)
+{
+ struct dm_io_region dest;
+
+ dest.bdev = s->cow->bdev;
+ dest.sector = bio->bi_iter.bi_sector;
+ dest.count = s->store->chunk_size;
+
+ down(&s->cow_count);
+ WARN_ON_ONCE(bio->bi_private);
+ bio->bi_private = s;
+ dm_kcopyd_zero(s->kcopyd_client, 1, &dest, 0, zero_callback, bio);
+}
+
+static bool io_overlaps_chunk(struct dm_snapshot *s, struct bio *bio)
+{
+ return bio->bi_iter.bi_size ==
+ (s->store->chunk_size << SECTOR_SHIFT);
+}
+
static int snapshot_map(struct dm_target *ti, struct bio *bio)
{
struct dm_exception *e;
@@ -1839,10 +1925,43 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio)
goto out_unlock;
}
+ if (unlikely(bio_op(bio) == REQ_OP_DISCARD)) {
+ if (s->discard_passdown_origin && dm_bio_get_target_bio_nr(bio)) {
+ /*
+ * passdown discard to origin (without triggering
+ * snapshot exceptions via do_origin; doing so would
+ * defeat the goal of freeing space in origin that is
+ * implied by the "discard_passdown_origin" feature)
+ */
+ bio_set_dev(bio, s->origin->bdev);
+ track_chunk(s, bio, chunk);
+ goto out_unlock;
+ }
+ /* discard to snapshot (target_bio_nr == 0) zeroes exceptions */
+ }
+
/* If the block is already remapped - use that, else remap it */
e = dm_lookup_exception(&s->complete, chunk);
if (e) {
remap_exception(s, e, bio, chunk);
+ if (unlikely(bio_op(bio) == REQ_OP_DISCARD) &&
+ io_overlaps_chunk(s, bio)) {
+ dm_exception_table_unlock(&lock);
+ up_read(&s->lock);
+ zero_exception(s, e, bio, chunk);
+ r = DM_MAPIO_SUBMITTED; /* discard is not issued */
+ goto out;
+ }
+ goto out_unlock;
+ }
+
+ if (unlikely(bio_op(bio) == REQ_OP_DISCARD)) {
+ /*
+ * If no exception exists, complete discard immediately
+ * otherwise it'll trigger copy-out.
+ */
+ bio_endio(bio);
+ r = DM_MAPIO_SUBMITTED;
goto out_unlock;
}
@@ -1890,9 +2009,7 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio)
r = DM_MAPIO_SUBMITTED;
- if (!pe->started &&
- bio->bi_iter.bi_size ==
- (s->store->chunk_size << SECTOR_SHIFT)) {
+ if (!pe->started && io_overlaps_chunk(s, bio)) {
pe->started = 1;
dm_exception_table_unlock(&lock);
@@ -2138,6 +2255,7 @@ static void snapshot_status(struct dm_target *ti, status_type_t type,
{
unsigned sz = 0;
struct dm_snapshot *snap = ti->private;
+ unsigned num_features;
switch (type) {
case STATUSTYPE_INFO:
@@ -2178,8 +2296,16 @@ static void snapshot_status(struct dm_target *ti, status_type_t type,
* make sense.
*/
DMEMIT("%s %s", snap->origin->name, snap->cow->name);
- snap->store->type->status(snap->store, type, result + sz,
- maxlen - sz);
+ sz += snap->store->type->status(snap->store, type, result + sz,
+ maxlen - sz);
+ num_features = snap->discard_zeroes_cow + snap->discard_passdown_origin;
+ if (num_features) {
+ DMEMIT(" %u", num_features);
+ if (snap->discard_zeroes_cow)
+ DMEMIT(" discard_zeroes_cow");
+ if (snap->discard_passdown_origin)
+ DMEMIT(" discard_passdown_origin");
+ }
break;
}
}
@@ -2198,6 +2324,22 @@ static int snapshot_iterate_devices(struct dm_target *ti,
return r;
}
+static void snapshot_io_hints(struct dm_target *ti, struct queue_limits *limits)
+{
+ struct dm_snapshot *snap = ti->private;
+
+ if (snap->discard_zeroes_cow) {
+ struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
+
+ (void) __find_snapshots_sharing_cow(snap, &snap_src, &snap_dest, NULL);
+ if (snap_src && snap_dest)
+ snap = snap_src;
+
+ /* All discards are split on chunk_size boundary */
+ limits->discard_granularity = snap->store->chunk_size;
+ limits->max_discard_sectors = snap->store->chunk_size;
+ }
+}
/*-----------------------------------------------------------------
* Origin methods
@@ -2522,7 +2664,7 @@ static struct target_type origin_target = {
static struct target_type snapshot_target = {
.name = "snapshot",
- .version = {1, 15, 0},
+ .version = {1, 16, 0},
.module = THIS_MODULE,
.ctr = snapshot_ctr,
.dtr = snapshot_dtr,
@@ -2532,11 +2674,12 @@ static struct target_type snapshot_target = {
.resume = snapshot_resume,
.status = snapshot_status,
.iterate_devices = snapshot_iterate_devices,
+ .io_hints = snapshot_io_hints,
};
static struct target_type merge_target = {
.name = dm_snapshot_merge_target_name,
- .version = {1, 4, 0},
+ .version = {1, 5, 0},
.module = THIS_MODULE,
.ctr = snapshot_ctr,
.dtr = snapshot_dtr,
@@ -2547,6 +2690,7 @@ static struct target_type merge_target = {
.resume = snapshot_merge_resume,
.status = snapshot_status,
.iterate_devices = snapshot_iterate_devices,
+ .io_hints = snapshot_io_hints,
};
static int __init dm_snapshot_init(void)