[PATCH v4 00/13] snapshot-merge target
Mike Snitzer
snapshot's origin device.
One expected use of snapshot merging is the rollback of a root
filesystem after system upgrades (e.g.: yum update). snapshot-merge
enables "system rollback" support for any filesystem that is using the
associated DM/LVM devices.
* "[PATCH v4 05/13] dm snapshot: add snapshot-merge target" adds further
documentation to: Documentation/device-mapper/snapshot.txt
* All patch headers have been revised/audited for added clarity.
* Both the latest handover (v10) and origin-write patch have been
included in this series.
* Aside from snapshot-merge specific testing these patches have
survived 75+ iterations of lvm2's testsuite without any failures.
The test kernel was 2.6.32-rc8 and lvm2 was 2.0.55 (with udev_sync
enabled and dmeventd disabled).
The snapshot-merge quilt tree is maintained here:
http://people.redhat.com/msnitzer/patches/snapshot-merge/kernel/2.6.33/
For LVM2 support please see:
http://people.redhat.com/msnitzer/patches/snapshot-merge/lvm2/LVM2-2.02.55/
Mike Snitzer (3):
dm snapshot: allow live exception store handover between tables
dm exception store: snapshot-merge usage accounting
dm snapshot: merge a linear region of chunks using one large IO
Mikulas Patocka (10):
dm snapshot: rework writing to snapshot origin
dm exception store: add snapshot-merge specific methods
dm snapshot: add snapshot-merge target
dm snapshot: merge target should not allocate new exceptions
dm snapshot: do not allow more than one merging snapshot.
dm snapshot: the merge procedure
dm snapshot: queue writes to an area that is actively being merged
dm snapshot: do not merge a chunk until active writes to it finish
dm snapshot: make exceptions in other snapshots when merging
dm snapshot: redirect accesses to origin if merging snap invalidated
Documentation/device-mapper/snapshot.txt | 52 ++-
drivers/md/dm-exception-store.h | 27 +
drivers/md/dm-snap-persistent.c | 91 ++++-
drivers/md/dm-snap.c | 827 ++++++++++++++++++++++++------
4 files changed, 839 insertions(+), 158 deletions(-)
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Mike Snitzer
progress. Care is taken to preserve the established kernel<->userspace
interface.
Signed-off-by: Mike Snitzer <sni...@redhat.com>
Cc: Mikulas Patocka <mpat...@redhat.com>
---
drivers/md/dm-snap-persistent.c | 21 ++++++++++++++++++++-
1 files changed, 20 insertions(+), 1 deletions(-)
diff --git a/drivers/md/dm-snap-persistent.c b/drivers/md/dm-snap-persistent.c
index 1f5752e..3cb609b 100644
--- a/drivers/md/dm-snap-persistent.c
+++ b/drivers/md/dm-snap-persistent.c
@@ -91,6 +91,7 @@ struct pstore {
struct dm_exception_store *store;
int version;
int valid;
+ int merging; /* 1 if there is merging going on */
uint32_t exceptions_per_area;
/*
@@ -506,7 +507,20 @@ static void persistent_usage(struct dm_exception_store *store,
{
struct pstore *ps = get_info(store);
- *sectors_allocated = ps->next_free * store->chunk_size;
+ /*
+ * Must maintain the fact that DM reports all metadata chunks
+ * in 'sectors_allocated'
+ * - preserves the established kernel<->userspace interface
+ * - snapshot-merge must account for the first two metadata
+ * chunks in its 'sectors_allocated'
+ */
+ if (!ps->merging) {
+ *sectors_allocated = ps->next_free * store->chunk_size;
+ } else {
+ *sectors_allocated =
+ (area_location(ps, ps->current_area) - 1 +
+ ps->current_committed + 2) * store->chunk_size;
+ }
*total_sectors = get_dev_size(dm_snap_cow(store->snap)->bdev);
/*
@@ -608,6 +622,8 @@ static int persistent_prepare_exception(struct dm_exception_store *store,
chunk_t next_free;
sector_t size = get_dev_size(dm_snap_cow(store->snap)->bdev);
+ ps->merging = 0;
+
/* Is there enough room ? */
if (size < ((ps->next_free + 1) * store->chunk_size))
return -ENOSPC;
@@ -696,6 +712,8 @@ static int persistent_prepare_merge(struct dm_exception_store *store,
struct pstore *ps = get_info(store);
struct disk_exception de;
+ ps->merging = 1;
+
if (!ps->current_committed) {
if (!ps->current_area)
return 0;
@@ -767,6 +785,7 @@ static int persistent_ctr(struct dm_exception_store *store,
ps->store = store;
ps->valid = 1;
+ ps->merging = 0;
ps->version = SNAPSHOT_DISK_VERSION;
ps->area = NULL;
ps->zero_area = NULL;
--
1.6.5.2
Mike Snitzer
The snapshot-merge target allows a snapshot to be merged back into the
snapshot's origin device.
One expected use of snapshot merging is the rollback of a root
filesystem after system upgrades (e.g.: yum update). snapshot-merge
enables "system rollback" support for any filesystem that is using the
associated DM devices.
Add snapshot-merge target management to both dm_snapshot_init() and
dm_snapshot_exit(). As an initial place-holder, snapshot-merge is
identical to the snapshot target.
Add "snapshot-merge" to Documentation/device-mapper/snapshot.txt
Signed-off-by: Mikulas Patocka <mpat...@redhat.com>
Signed-off-by: Mike Snitzer <sni...@redhat.com>
---
Documentation/device-mapper/snapshot.txt | 52 +++++++++++++++++++++++++++---
drivers/md/dm-snap.c | 48 ++++++++++++++++++++-------
2 files changed, 83 insertions(+), 17 deletions(-)
diff --git a/Documentation/device-mapper/snapshot.txt b/Documentation/device-mapper/snapshot.txt
index a5009c8..ec6c883 100644
--- a/Documentation/device-mapper/snapshot.txt
+++ b/Documentation/device-mapper/snapshot.txt
@@ -8,13 +8,19 @@ the block device which are also writable without interfering with the
original content;
*) To create device "forks", i.e. multiple different versions of the
same data stream.
+*) To merge a snapshot of a block device back into the snapshot's origin
+device.
+In the first two cases, dm copies only the chunks of data that get
+changed and uses a separate copy-on-write (COW) block device for
+storage.
-In both cases, dm copies only the chunks of data that get changed and
-uses a separate copy-on-write (COW) block device for storage.
+For snapshot merge the contents of the COW storage are merged back into
+the origin device.
-There are two dm targets available: snapshot and snapshot-origin.
+There are three dm targets available:
+snapshot, snapshot-origin, and snapshot-merge.
*) snapshot-origin <origin>
@@ -40,8 +46,17 @@ The difference is that for transient snapshots less metadata must be
saved on disk - they can be kept in memory by the kernel.
-How this is used by LVM2
-========================
+* snapshot-merge <origin> <COW device> <persistent> <chunksize>
+
+takes the same table arguments as the snapshot target except it only
+works with persistent snapshots. Creates a merging snapshot that takes
+control of the changed chunks stored in the <COW device> of an existing
+snapshot, through a handover procedure, and merges these chunks back
+into the <origin>.
+
+
+How snapshot is used by LVM2
+============================
When you create the first LVM2 snapshot of a volume, four dm devices are used:
1) a device containing the original mapping table of the source volume;
@@ -72,3 +87,30 @@ brw------- 1 root root 254, 12 29 ago 18:15 /dev/mapper/volumeGroup-snap-cow
brw------- 1 root root 254, 13 29 ago 18:15 /dev/mapper/volumeGroup-snap
brw------- 1 root root 254, 10 29 ago 18:14 /dev/mapper/volumeGroup-base
+
+How snapshot-merge is used by LVM2
+==================================
+A merging snapshot assumes the role of the "snapshot-origin" while
+merging. As such the "snapshot-origin" is replaced with
+"snapshot-merge". The "-real" device is not changed and the "-cow"
+device is renamed to aid LVM2's cleanup of the merging snapshot after it
+completes. The "snapshot" that hands over its COW device to the
+"snapshot-merge" is generally deactivated; but if it is left active it
+will simply return I/O errors.
+
+A snapshot will merge into its origin with the following command:
+
+lvconvert --merge volumeGroup/snap
+
+we'll now have this situation:
+
+# dmsetup table|grep volumeGroup
+
+volumeGroup-base-real: 0 2097152 linear 8:19 384
+volumeGroup-base-cow: 0 204800 linear 8:19 2097536
+volumeGroup-base: 0 2097152 snapshot-merge 254:11 254:12 P 16
+
+# ls -lL /dev/mapper/volumeGroup-*
+brw------- 1 root root 254, 11 29 ago 18:15 /dev/mapper/volumeGroup-base-real
+brw------- 1 root root 254, 12 29 ago 18:16 /dev/mapper/volumeGroup-base-cow
+brw------- 1 root root 254, 10 29 ago 18:16 /dev/mapper/volumeGroup-base
diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index ad95039..e8a1107 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -1664,6 +1664,21 @@ static struct target_type snapshot_target = {
.iterate_devices = snapshot_iterate_devices,
};
+static struct target_type merge_target = {
+ .name = "snapshot-merge",
+ .version = {1, 9, 0},
+ .module = THIS_MODULE,
+ .ctr = snapshot_ctr,
+ .dtr = snapshot_dtr,
+ .map = snapshot_map,
+ .end_io = snapshot_end_io,
+ .postsuspend = snapshot_postsuspend,
+ .preresume = snapshot_preresume,
+ .resume = snapshot_resume,
+ .status = snapshot_status,
+ .iterate_devices = snapshot_iterate_devices,
+};
+
static int __init dm_snapshot_init(void)
{
int r;
@@ -1675,7 +1690,7 @@ static int __init dm_snapshot_init(void)
}
r = dm_register_target(&snapshot_target);
- if (r) {
+ if (r < 0) {
DMERR("snapshot target register failed %d", r);
goto bad_register_snapshot_target;
}
@@ -1683,34 +1698,40 @@ static int __init dm_snapshot_init(void)
r = dm_register_target(&origin_target);
if (r < 0) {
DMERR("Origin target register failed %d", r);
- goto bad1;
+ goto bad_register_origin_target;
+ }
+
+ r = dm_register_target(&merge_target);
+ if (r < 0) {
+ DMERR("Merge target register failed %d", r);
+ goto bad_register_merge_target;
}
r = init_origin_hash();
if (r) {
DMERR("init_origin_hash failed.");
- goto bad2;
+ goto bad_origin_hash;
}
exception_cache = KMEM_CACHE(dm_exception, 0);
if (!exception_cache) {
DMERR("Couldn't create exception cache.");
r = -ENOMEM;
- goto bad3;
+ goto bad_exception_cache;
}
pending_cache = KMEM_CACHE(dm_snap_pending_exception, 0);
if (!pending_cache) {
DMERR("Couldn't create pending cache.");
r = -ENOMEM;
- goto bad4;
+ goto bad_pending_cache;
}
tracked_chunk_cache = KMEM_CACHE(dm_snap_tracked_chunk, 0);
if (!tracked_chunk_cache) {
DMERR("Couldn't create cache to track chunks in use.");
r = -ENOMEM;
- goto bad5;
+ goto bad_tracked_chunk_cache;
}
ksnapd = create_singlethread_workqueue("ksnapd");
@@ -1724,19 +1745,21 @@ static int __init dm_snapshot_init(void)
bad_pending_pool:
kmem_cache_destroy(tracked_chunk_cache);
-bad5:
+bad_tracked_chunk_cache:
kmem_cache_destroy(pending_cache);
-bad4:
+bad_pending_cache:
kmem_cache_destroy(exception_cache);
-bad3:
+bad_exception_cache:
exit_origin_hash();
-bad2:
+bad_origin_hash:
+ dm_unregister_target(&merge_target);
+bad_register_merge_target:
dm_unregister_target(&origin_target);
-bad1:
+bad_register_origin_target:
dm_unregister_target(&snapshot_target);
-
bad_register_snapshot_target:
dm_exception_store_exit();
+
return r;
}
@@ -1746,6 +1769,7 @@ static void __exit dm_snapshot_exit(void)
dm_unregister_target(&snapshot_target);
dm_unregister_target(&origin_target);
+ dm_unregister_target(&merge_target);
exit_origin_hash();
kmem_cache_destroy(pending_cache);
--
1.6.5.2
Mike Snitzer
Use new variables, 'merge_write_interlock' and 'merge_write_interlock_n',
to determine the chunk number (on the origin device) and number of chunks
that are being merged. Writes to this area are held on the
'merge_write_list' queue.
Signed-off-by: Mikulas Patocka <mpat...@redhat.com>
Signed-off-by: Mike Snitzer <sni...@redhat.com>
---
drivers/md/dm-snap.c | 120 ++++++++++++++++++++++++++++++++++++-------------
1 files changed, 88 insertions(+), 32 deletions(-)
diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index 87c9033..e1ec4c4 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -108,6 +108,16 @@ struct dm_snapshot {
/* It is requested to shut down merging */
/* Cleared back to 0 when the merging is stopped */
int merge_shutdown;
+
+ /* Merging this area --- block any writes */
+ chunk_t merge_write_interlock;
+ int merge_write_interlock_n;
+
+ /*
+ * A list of requests that were delayed because
+ * of racing with merge
+ */
+ struct bio_list merge_write_list;
};
struct dm_dev *dm_snap_cow(struct dm_snapshot *s)
@@ -729,6 +739,9 @@ static int init_hash_tables(struct dm_snapshot *s)
return 0;
}
+static void flush_bios(struct bio *bio);
+static void error_bios(struct bio *bio);
+
static void merge_callback(int read_err, unsigned long write_err,
void *context);
@@ -736,7 +749,6 @@ static void snapshot_merge_process(struct dm_snapshot *s)
{
int r;
chunk_t old_chunk, new_chunk;
- struct dm_exception *e;
struct dm_io_region src, dest;
BUG_ON(!s->merge_running);
@@ -758,32 +770,6 @@ static void snapshot_merge_process(struct dm_snapshot *s)
/* TODO: use larger I/O size once we verify that kcopyd handles it */
- /* !!! FIXME: intelock writes to this chunk */
- down_write(&s->lock);
- e = dm_lookup_exception(&s->complete, old_chunk);
- if (!e) {
- DMERR("exception for block %llu is on disk but not in memory",
- (unsigned long long)old_chunk);
- up_write(&s->lock);
- goto shut;
- }
- if (dm_consecutive_chunk_count(e)) {
- if (old_chunk == e->old_chunk) {
- e->old_chunk++;
- e->new_chunk++;
- } else if (old_chunk != e->old_chunk +
- dm_consecutive_chunk_count(e)) {
- DMERR("merge from the middle of a chunk range");
- up_write(&s->lock);
- goto shut;
- }
- dm_consecutive_chunk_count_dec(e);
- } else {
- dm_remove_exception(e);
- free_completed_exception(e);
- }
- up_write(&s->lock);
-
dest.bdev = s->origin->bdev;
dest.sector = chunk_to_sector(s->store, old_chunk);
dest.count = min((sector_t)s->store->chunk_size,
@@ -793,6 +779,13 @@ static void snapshot_merge_process(struct dm_snapshot *s)
src.sector = chunk_to_sector(s->store, new_chunk);
src.count = dest.count;
+ down_write(&s->lock);
+ s->merge_write_interlock = old_chunk;
+ s->merge_write_interlock_n = 1;
+ up_write(&s->lock);
+
+ /* !!! FIXME: wait until writes to this chunk drain */
+
dm_kcopyd_copy(s->kcopyd_client, &src, 1, &dest, 0, merge_callback, s);
return;
@@ -800,10 +793,25 @@ shut:
s->merge_running = 0;
}
+/* This function drops s->lock */
+static inline void release_write_interlock(struct dm_snapshot *s, int err)
+{
+ struct bio *b;
+ s->merge_write_interlock = 0;
+ s->merge_write_interlock_n = 0;
+ b = bio_list_get(&s->merge_write_list);
+ up_write(&s->lock);
+ if (!err)
+ flush_bios(b);
+ else
+ error_bios(b);
+}
+
static void merge_callback(int read_err, unsigned long write_err, void *context)
{
- int r;
+ int r, i;
struct dm_snapshot *s = context;
+ struct dm_exception *e;
if (read_err || write_err) {
if (read_err)
@@ -813,16 +821,51 @@ static void merge_callback(int read_err, unsigned long write_err, void *context)
goto shut;
}
- r = s->store->type->commit_merge(s->store, 1);
+ r = s->store->type->commit_merge(s->store, s->merge_write_interlock_n);
if (r < 0) {
DMERR("Write error in exception store, shutting down merge");
goto shut;
}
+ down_write(&s->lock);
+ /*
+ * Must process chunks (and associated exceptions) in reverse
+ * so that dm_consecutive_chunk_count_dec() accounting works
+ */
+ for (i = s->merge_write_interlock_n - 1; i >= 0; i--) {
+ chunk_t old_chunk = s->merge_write_interlock + i;
+ e = dm_lookup_exception(&s->complete, old_chunk);
+ if (!e) {
+ DMERR("exception for block %llu is on "
+ "disk but not in memory",
+ (unsigned long long)old_chunk);
+ up_write(&s->lock);
+ goto shut;
+ }
+ if (dm_consecutive_chunk_count(e)) {
+ if (old_chunk == e->old_chunk) {
+ e->old_chunk++;
+ e->new_chunk++;
+ } else if (old_chunk != e->old_chunk +
+ dm_consecutive_chunk_count(e)) {
+ DMERR("merge from the middle of a chunk range");
+ up_write(&s->lock);
+ goto shut;
+ }
+ dm_consecutive_chunk_count_dec(e);
+ } else {
+ dm_remove_exception(e);
+ free_completed_exception(e);
+ }
+ }
+ release_write_interlock(s, 0);
+
snapshot_merge_process(s);
return;
shut:
+ down_write(&s->lock);
+ release_write_interlock(s, 1);
s->merge_running = 0;
}
@@ -912,6 +955,9 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
spin_lock_init(&s->pe_lock);
s->merge_running = 0;
s->merge_shutdown = 0;
+ s->merge_write_interlock = 0;
+ s->merge_write_interlock_n = 0;
+ bio_list_init(&s->merge_write_list);
/* Allocate hash table for COW data */
if (init_hash_tables(s)) {
@@ -1475,7 +1521,7 @@ static int snapshot_merge_map(struct dm_target *ti, struct bio *bio,
chunk = sector_to_chunk(s->store, bio->bi_sector);
- down_read(&s->lock);
+ down_write(&s->lock);
/* Full snapshots are not usable */
if (!s->valid) {
@@ -1486,6 +1532,16 @@ static int snapshot_merge_map(struct dm_target *ti, struct bio *bio,
/* If the block is already remapped - use that */
e = dm_lookup_exception(&s->complete, chunk);
if (e) {
+ /* We are copying this area --- so don't write to it */
+ if (bio_rw(bio) == WRITE &&
+ chunk >= s->merge_write_interlock &&
+ chunk < (s->merge_write_interlock +
+ s->merge_write_interlock_n)) {
+ bio->bi_bdev = s->origin->bdev;
+ bio_list_add(&s->merge_write_list, bio);
+ r = DM_MAPIO_SUBMITTED;
+ goto out_unlock;
+ }
remap_exception(s, e, bio, chunk);
goto out_unlock;
}
@@ -1493,12 +1549,12 @@ static int snapshot_merge_map(struct dm_target *ti, struct bio *bio,
bio->bi_bdev = s->origin->bdev;
if (bio_rw(bio) == WRITE) {
- up_read(&s->lock);
+ up_write(&s->lock);
return do_origin(s->origin, bio);
}
out_unlock:
- up_read(&s->lock);
+ up_write(&s->lock);
return r;
}
--
1.6.5.2
Mike Snitzer
linearly copied starting from the returned chunk number backward (but
the caller is allowed to copy less, and the caller passes the number of
copied chunks to s->store->type->commit_merge).
I.e. if returned chunk numbers are old_chunk == 10 and new_chunk == 20
and returned value is 3, then chunk 20 can be copied to 10, chunk 19 to
9 and 18 to 8.
s->merge_write_interlock_n has been increased up to the full range of
chunks returned from s->store->type->prepare_merge. Until now kcopyd
was only ever allowed to copy one chunk at a time; as a result
snapshot-merge performance was extremely slow.
Relative to the snapshot target, snapshot-merge's performance is now
comparable.
Also, snapshot_merge_process() needs to delay the merging of _all_
chunks that have in-progress writes; not just the first chunk in the
region that is to be merged.
Signed-off-by: Mike Snitzer <sni...@redhat.com>
---
drivers/md/dm-snap.c | 35 +++++++++++++++++++++++------------
1 files changed, 23 insertions(+), 12 deletions(-)
diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index 74f7f38..4d6387e 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -752,11 +752,12 @@ static void merge_callback(int read_err, unsigned long write_err,
static void snapshot_merge_process(struct dm_snapshot *s)
{
- int r;
+ int r, i, linear_chunks;
chunk_t old_chunk, new_chunk, n;
struct origin *o;
int must_wait;
struct dm_io_region src, dest;
+ sector_t io_size;
BUG_ON(!s->merge_running);
if (s->merge_shutdown)
@@ -767,27 +768,34 @@ static void snapshot_merge_process(struct dm_snapshot *s)
goto shut;
}
- r = s->store->type->prepare_merge(s->store, &old_chunk, &new_chunk);
- if (r <= 0) {
- if (r < 0)
+ linear_chunks = s->store->type->prepare_merge(s->store,
+ &old_chunk, &new_chunk);
+ if (linear_chunks <= 0) {
+ if (linear_chunks < 0)
DMERR("Read error in exception store, "
"shutting down merge");
goto shut;
}
+ /* Adjust old_chunk and new_chunk to reflect start of linear region */
+ old_chunk = old_chunk + 1 - linear_chunks;
+ new_chunk = new_chunk + 1 - linear_chunks;
- /* TODO: use larger I/O size once we verify that kcopyd handles it */
+ /*
+ * Use one (potentially large) I/O to copy all 'linear_chunks'
+ * from the exception store to the origin
+ */
+ io_size = linear_chunks * s->store->chunk_size;
dest.bdev = s->origin->bdev;
dest.sector = chunk_to_sector(s->store, old_chunk);
- dest.count = min((sector_t)s->store->chunk_size,
- get_dev_size(dest.bdev) - dest.sector);
+ dest.count = min(io_size, get_dev_size(dest.bdev) - dest.sector);
src.bdev = s->cow->bdev;
src.sector = chunk_to_sector(s->store, new_chunk);
src.count = dest.count;
test_again:
- /* Reallocate other snapshots */
+ /* Reallocate other snapshots; must account for all 'linear_chunks' */
must_wait = 0;
/*
* Merging snapshot already has the origin's __minimum_chunk_size()
@@ -796,7 +804,7 @@ test_again:
BUG_ON(!s->ti->split_io);
down_read(&_origins_lock);
o = __lookup_origin(s->origin->bdev);
- for (n = 0; n < s->store->chunk_size; n += s->ti->split_io) {
+ for (n = 0; n < io_size; n += s->ti->split_io) {
r = __origin_write(&o->snapshots, dest.sector + n, NULL);
if (r == DM_MAPIO_SUBMITTED)
must_wait = 1;
@@ -809,11 +817,14 @@ test_again:
down_write(&s->lock);
s->merge_write_interlock = old_chunk;
- s->merge_write_interlock_n = 1;
+ s->merge_write_interlock_n = linear_chunks;
up_write(&s->lock);
- while (__chunk_is_tracked(s, old_chunk))
- msleep(1);
+ /* Wait until writes to all 'linear_chunks' drain */
+ for (i = 0; i < linear_chunks; i++) {
+ while (__chunk_is_tracked(s, old_chunk + i))
+ msleep(1);
+ }
dm_kcopyd_copy(s->kcopyd_client, &src, 1, &dest, 0, merge_callback, s);
return;
--
1.6.5.2
Mike Snitzer
Merging is started when origin is resumed and it is stopped when
origin is suspended or when the merging snapshot is destoyed.
We don't need a separate thread, kcopyd does the job just fine
(provided that we have a private kcopyd).
Merging is not yet interlocked with writes, so there is a race condition
with concurrent access. It will be fixed in further patches.
Adds a supporting function to decrement consecutive chunk counter.
Care is taken to increment the exception's old_chunk and new_chunk,
prior to the dm_consecutive_chunk_count_dec() call, if the chunk is at
the start of an exception's consecutive chunk range. This allows for
snapshot-merge to support chunks that are added to the 'complete'
exception hash table before existing chunks.
Signed-off-by: Mikulas Patocka <mpat...@redhat.com>
Signed-off-by: Mike Snitzer <sni...@redhat.com>
---
drivers/md/dm-exception-store.h | 11 +++
drivers/md/dm-snap.c | 179 +++++++++++++++++++++++++++++++++++++--
2 files changed, 184 insertions(+), 6 deletions(-)
diff --git a/drivers/md/dm-exception-store.h b/drivers/md/dm-exception-store.h
index 534427f..7b83002 100644
--- a/drivers/md/dm-exception-store.h
+++ b/drivers/md/dm-exception-store.h
@@ -153,6 +153,13 @@ static inline void dm_consecutive_chunk_count_inc(struct dm_exception *e)
BUG_ON(!dm_consecutive_chunk_count(e));
}
+static inline void dm_consecutive_chunk_count_dec(struct dm_exception *e)
+{
+ BUG_ON(!dm_consecutive_chunk_count(e));
+
+ e->new_chunk -= (1ULL << DM_CHUNK_NUMBER_BITS);
+}
+
# else
# define DM_CHUNK_CONSECUTIVE_BITS 0
@@ -170,6 +177,10 @@ static inline void dm_consecutive_chunk_count_inc(struct dm_exception *e)
{
}
+static inline void dm_consecutive_chunk_count_dec(struct dm_exception *e)
+{
+}
+
# endif
/*
diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index f4e9aa6..87c9033 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -101,6 +101,13 @@ struct dm_snapshot {
mempool_t *tracked_chunk_pool;
spinlock_t tracked_chunk_lock;
struct hlist_head tracked_chunk_hash[DM_TRACKED_CHUNK_HASH_SIZE];
+
+ /* Merge operation is in progress */
+ int merge_running;
+
+ /* It is requested to shut down merging */
+ /* Cleared back to 0 when the merging is stopped */
+ int merge_shutdown;
};
struct dm_dev *dm_snap_cow(struct dm_snapshot *s)
@@ -375,6 +382,14 @@ static int __validate_exception_handover(struct dm_snapshot *snap)
r = -EINVAL;
goto out;
}
+
+ if (!snap_src->store->type->prepare_merge ||
+ !snap_src->store->type->commit_merge) {
+ snap->ti->error = "Merging snapshot store must "
+ "support snapshot-merge";
+ r = -EINVAL;
+ goto out;
+ }
}
r = 1;
@@ -714,6 +729,123 @@ static int init_hash_tables(struct dm_snapshot *s)
return 0;
}
+static void merge_callback(int read_err, unsigned long write_err,
+ void *context);
+
+static void snapshot_merge_process(struct dm_snapshot *s)
+{
+ int r;
+ chunk_t old_chunk, new_chunk;
+ struct dm_exception *e;
+ struct dm_io_region src, dest;
+
+ BUG_ON(!s->merge_running);
+ if (s->merge_shutdown)
+ goto shut;
+
+ if (!s->valid) {
+ DMERR("snapshot is invalid, can't merge");
+ goto shut;
+ }
+
+ r = s->store->type->prepare_merge(s->store, &old_chunk, &new_chunk);
+ if (r <= 0) {
+ if (r < 0)
+ DMERR("Read error in exception store, "
+ "shutting down merge");
+ goto shut;
+ }
+
+ /* TODO: use larger I/O size once we verify that kcopyd handles it */
+
+ /* !!! FIXME: intelock writes to this chunk */
+ down_write(&s->lock);
+ e = dm_lookup_exception(&s->complete, old_chunk);
+ if (!e) {
+ DMERR("exception for block %llu is on disk but not in memory",
+ (unsigned long long)old_chunk);
+ up_write(&s->lock);
+ goto shut;
+ }
+ if (dm_consecutive_chunk_count(e)) {
+ if (old_chunk == e->old_chunk) {
+ e->old_chunk++;
+ e->new_chunk++;
+ } else if (old_chunk != e->old_chunk +
+ dm_consecutive_chunk_count(e)) {
+ DMERR("merge from the middle of a chunk range");
+ up_write(&s->lock);
+ goto shut;
+ }
+ dm_consecutive_chunk_count_dec(e);
+ } else {
+ dm_remove_exception(e);
+ free_completed_exception(e);
+ }
+ up_write(&s->lock);
+
+ dest.bdev = s->origin->bdev;
+ dest.sector = chunk_to_sector(s->store, old_chunk);
+ dest.count = min((sector_t)s->store->chunk_size,
+ get_dev_size(dest.bdev) - dest.sector);
+
+ src.bdev = s->cow->bdev;
+ src.sector = chunk_to_sector(s->store, new_chunk);
+ src.count = dest.count;
+
+ dm_kcopyd_copy(s->kcopyd_client, &src, 1, &dest, 0, merge_callback, s);
+ return;
+
+shut:
+ s->merge_running = 0;
+}
+
+static void merge_callback(int read_err, unsigned long write_err, void *context)
+{
+ int r;
+ struct dm_snapshot *s = context;
+
+ if (read_err || write_err) {
+ if (read_err)
+ DMERR("Read error in data, shutting down merge");
+ else
+ DMERR("Write error in data, shutting down merge");
+ goto shut;
+ }
+
+ r = s->store->type->commit_merge(s->store, 1);
+ if (r < 0) {
+ DMERR("Write error in exception store, shutting down merge");
+ goto shut;
+ }
+
+ snapshot_merge_process(s);
+ return;
+
+shut:
+ s->merge_running = 0;
+}
+
+static void start_merge(struct dm_snapshot *s)
+{
+ if (!s->merge_running && !s->merge_shutdown) {
+ s->merge_running = 1;
+ snapshot_merge_process(s);
+ }
+}
+
+/*
+ * Stop the merging process and wait until it finishes.
+ */
+static void stop_merge(struct dm_snapshot *s)
+{
+ while (s->merge_running) {
+ s->merge_shutdown = 1;
+ msleep(1);
+ }
+ s->merge_shutdown = 0;
+}
+
/*
* Construct a snapshot mapping: <origin_dev> <COW-dev> <p/n> <chunk-size>
*/
@@ -778,6 +910,8 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
init_rwsem(&s->lock);
INIT_LIST_HEAD(&s->list);
spin_lock_init(&s->pe_lock);
+ s->merge_running = 0;
+ s->merge_shutdown = 0;
/* Allocate hash table for COW data */
if (init_hash_tables(s)) {
@@ -950,6 +1084,9 @@ static void snapshot_dtr(struct dm_target *ti)
}
up_read(&_origins_lock);
+ if (is_merge(ti))
+ stop_merge(s);
+
/* Prevent further origin writes from using this snapshot. */
/* After this returns there can be no new kcopyd jobs. */
unregister_snapshot(s);
@@ -1378,6 +1515,13 @@ static int snapshot_end_io(struct dm_target *ti, struct bio *bio,
return 0;
}
+static void snapshot_merge_presuspend(struct dm_target *ti)
+{
+ struct dm_snapshot *s = ti->private;
+
+ stop_merge(s);
+}
+
static void snapshot_postsuspend(struct dm_target *ti)
{
struct dm_snapshot *s = ti->private;
@@ -1438,6 +1582,32 @@ static void snapshot_resume(struct dm_target *ti)
up_write(&s->lock);
}
+static chunk_t get_origin_minimum_chunksize(struct block_device *bdev)
+{
+ chunk_t min_chunksize;
+
+ down_read(&_origins_lock);
+
+ min_chunksize = __minimum_chunk_size(__lookup_origin(bdev));
+
+ up_read(&_origins_lock);
+
+ return min_chunksize;
+}
+
+static void snapshot_merge_resume(struct dm_target *ti)
+{
+ struct dm_snapshot *s = ti->private;
+
+ snapshot_resume(ti);
+ /*
+ * snapshot-merge can take on the role of the origin too
+ * - must adjust snapshot-merge's ti->split_io accordingly
+ */
+ ti->split_io = get_origin_minimum_chunksize(s->origin->bdev);
+ start_merge(s);
+}
+
static int snapshot_status(struct dm_target *ti, status_type_t type,
char *result, unsigned int maxlen)
{
@@ -1682,11 +1852,7 @@ static void origin_resume(struct dm_target *ti)
{
struct dm_dev *dev = ti->private;
- down_read(&_origins_lock);
-
- ti->split_io = __minimum_chunk_size(__lookup_origin(dev->bdev));
-
- up_read(&_origins_lock);
+ ti->split_io = get_origin_minimum_chunksize(dev->bdev);
}
static int origin_status(struct dm_target *ti, status_type_t type, char *result,
@@ -1750,9 +1916,10 @@ static struct target_type merge_target = {
.dtr = snapshot_dtr,
.map = snapshot_merge_map,
.end_io = snapshot_end_io,
+ .presuspend = snapshot_merge_presuspend,
.postsuspend = snapshot_postsuspend,
.preresume = snapshot_preresume,
- .resume = snapshot_resume,
+ .resume = snapshot_merge_resume,
.status = snapshot_status,
.iterate_devices = snapshot_iterate_devices,
};
--
1.6.5.2
Mike Snitzer
If we are merging an invalidated snapshot, redirect all accesses to the
origin device. This is safe because snapshot_merge_process() will
stop_merge() if the merging snapshot becomes invalid.
Allowing the origin device to remain functional is important because it
may contain the root filesystem.
Signed-off-by: Mikulas Patocka <mpat...@redhat.com>
Reviewed-by: Mike Snitzer <sni...@redhat.com>
---
drivers/md/dm-snap.c | 9 ++++-----
1 files changed, 4 insertions(+), 5 deletions(-)
diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index 2b5b083..74f7f38 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -1554,11 +1554,9 @@ static int snapshot_merge_map(struct dm_target *ti, struct bio *bio,
down_write(&s->lock);
- /* Full snapshots are not usable */
- if (!s->valid) {
- r = -EIO;
- goto out_unlock;
- }
+ /* Full merging snapshots are redirected to the origin */
+ if (!s->valid)
+ goto redirect_to_origin;
/* If the block is already remapped - use that */
e = dm_lookup_exception(&s->complete, chunk);
@@ -1581,6 +1579,7 @@ static int snapshot_merge_map(struct dm_target *ti, struct bio *bio,
goto out_unlock;
}
+ redirect_to_origin:
bio->bi_bdev = s->origin->bdev;
if (bio_rw(bio) == WRITE) {
--
1.6.5.2
Mike Snitzer
When there is one merging snapshot and other non-merging snapshots,
snapshot_merge_process() must make exceptions in the non-merging
snapshots.
Signed-off-by: Mikulas Patocka <mpat...@redhat.com>
Signed-off-by: Mike Snitzer <sni...@redhat.com>
---
drivers/md/dm-snap.c | 32 +++++++++++++++++++++++++++++++-
1 files changed, 31 insertions(+), 1 deletions(-)
diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index e41be70..2b5b083 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -255,6 +255,8 @@ struct origin {
static struct list_head *_origins;
static struct rw_semaphore _origins_lock;
+static DECLARE_WAIT_QUEUE_HEAD(_pending_exception_done);
+
static int init_origin_hash(void)
{
int i;
@@ -742,13 +744,18 @@ static int init_hash_tables(struct dm_snapshot *s)
static void flush_bios(struct bio *bio);
static void error_bios(struct bio *bio);
+static int __origin_write(struct list_head *snapshots,
+ sector_t sector, struct bio *bio);
+
static void merge_callback(int read_err, unsigned long write_err,
void *context);
static void snapshot_merge_process(struct dm_snapshot *s)
{
int r;
- chunk_t old_chunk, new_chunk;
+ chunk_t old_chunk, new_chunk, n;
+ struct origin *o;
+ int must_wait;
struct dm_io_region src, dest;
BUG_ON(!s->merge_running);
@@ -779,6 +786,27 @@ static void snapshot_merge_process(struct dm_snapshot *s)
src.sector = chunk_to_sector(s->store, new_chunk);
src.count = dest.count;
+test_again:
+ /* Reallocate other snapshots */
+ must_wait = 0;
+ /*
+ * Merging snapshot already has the origin's __minimum_chunk_size()
+ * stored in split_io (see: snapshot_merge_resume); avoid rediscovery
+ */
+ BUG_ON(!s->ti->split_io);
+ down_read(&_origins_lock);
+ o = __lookup_origin(s->origin->bdev);
+ for (n = 0; n < s->store->chunk_size; n += s->ti->split_io) {
+ r = __origin_write(&o->snapshots, dest.sector + n, NULL);
+ if (r == DM_MAPIO_SUBMITTED)
+ must_wait = 1;
+ }
+ up_read(&_origins_lock);
+ if (must_wait) {
+ sleep_on_timeout(&_pending_exception_done, HZ / 100 + 1);
+ goto test_again;
+ }
+
down_write(&s->lock);
s->merge_write_interlock = old_chunk;
s->merge_write_interlock_n = 1;
@@ -1301,6 +1329,8 @@ static void pending_complete(struct dm_snap_pending_exception *pe, int success)
origin_bios = bio_list_get(&pe->origin_bios);
free_pending_exception(pe);
+ wake_up_all(&_pending_exception_done);
+
up_write(&s->lock);
/* Submit any pending write bios */
--
1.6.5.2
Mike Snitzer
Track merging snapshot device's in-progress writes, to chunks that
were already remapped, and delay merging a chunk until all writes to
that chunk finish.
Signed-off-by: Mikulas Patocka <mpat...@redhat.com>
Reviewed-by: Mike Snitzer <sni...@redhat.com>
---
drivers/md/dm-snap.c | 7 ++++++-
1 files changed, 6 insertions(+), 1 deletions(-)
diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index e1ec4c4..e41be70 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -784,7 +784,8 @@ static void snapshot_merge_process(struct dm_snapshot *s)
s->merge_write_interlock_n = 1;
up_write(&s->lock);
- /* !!! FIXME: wait until writes to this chunk drain */
+ while (__chunk_is_tracked(s, old_chunk))
+ msleep(1);
dm_kcopyd_copy(s->kcopyd_client, &src, 1, &dest, 0, merge_callback, s);
return;
@@ -1542,7 +1543,11 @@ static int snapshot_merge_map(struct dm_target *ti, struct bio *bio,
r = DM_MAPIO_SUBMITTED;
goto out_unlock;
}
+
remap_exception(s, e, bio, chunk);
+
+ if (bio_rw(bio) == WRITE)
+ map_context->ptr = track_chunk(s, chunk);
goto out_unlock;
}
--
1.6.5.2
Mike Snitzer
Merging more than one snapshot is not supported.
__find_merging_snapshot() will find the merging snapshot for a given
origin device.
Signed-off-by: Mikulas Patocka <mpat...@redhat.com>
Signed-off-by: Mike Snitzer <sni...@redhat.com>
---
drivers/md/dm-snap.c | 35 +++++++++++++++++++++++++++++++++--
1 files changed, 33 insertions(+), 2 deletions(-)
diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index b8838e7..f4e9aa6 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -332,9 +332,29 @@ out:
return count;
}
+static struct dm_snapshot *__find_merging_snapshot(struct block_device *origin)
+{
+ struct dm_snapshot *s, *merging_snap;
+ struct origin *o;
+
+ o = __lookup_origin(origin);
+ if (!o)
+ return NULL;
+
+ list_for_each_entry(s, &o->snapshots, list) {
+ if (is_merge(s->ti)) {
+ merging_snap = s;
+ break;
+ }
+ }
+
+ return merging_snap;
+}
+
static int __validate_exception_handover(struct dm_snapshot *snap)
{
struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
+ struct block_device *bdev = snap->origin->bdev;
int r = 0;
/* Does snapshot need exceptions handed over to it? */
@@ -346,8 +366,19 @@ static int __validate_exception_handover(struct dm_snapshot *snap)
goto out;
}
- if (snap_src)
+ if (snap_src) {
+ if (is_merge(snap->ti)) {
+ /* Do not allow more than one merging snapshot */
+ if (__find_merging_snapshot(bdev)) {
+ snap->ti->error = "A snapshot is already "
+ "merging.";
+ r = -EINVAL;
+ goto out;
+ }
+ }
+
r = 1;
+ }
out:
return r;
@@ -1325,7 +1356,7 @@ static int snapshot_merge_map(struct dm_target *ti, struct bio *bio,
bio->bi_bdev = s->origin->bdev;
if (bio_rw(bio) == WRITE) {
- up_write(&s->lock);
+ up_read(&s->lock);
return do_origin(s->origin, bio);
}
--
1.6.5.2
Mike Snitzer
The snapshot-merge target should not allocate new exceptions because the
intent is to merge all of its exceptions as quickly and safely as
possible.
Introduce new method, snapshot_merge_map(), that won't allocate
exceptions. Modify __origin_write() so that it doesn't allocate
exceptions in merging snapshots.
If a write request to a merging snapshot device is to be dispatched
directly to the origin (because the chunk is not remapped or was already
merged), snapshot_merge_map() must make exceptions in other snapshots.
Signed-off-by: Mikulas Patocka <mpat...@redhat.com>
Signed-off-by: Mike Snitzer <sni...@redhat.com>
---
drivers/md/dm-snap.c | 49 ++++++++++++++++++++++++++++++++++++++++++++++++-
1 files changed, 48 insertions(+), 1 deletions(-)
diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index e8a1107..b8838e7 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -127,6 +127,11 @@ static int bdev_equal(struct block_device *lhs, struct block_device *rhs)
return lhs == rhs;
}
+static int snapshot_merge_map(struct dm_target *ti, struct bio *bio,
+ union map_info *map_context);
+
+#define is_merge(ti) ((ti)->type->map == snapshot_merge_map)
+
struct dm_snap_pending_exception {
struct dm_exception e;
@@ -1292,6 +1297,44 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio,
return r;
}
+static int snapshot_merge_map(struct dm_target *ti, struct bio *bio,
+ union map_info *map_context)
+{
+ struct dm_exception *e;
+ struct dm_snapshot *s = ti->private;
+ int r = DM_MAPIO_REMAPPED;
+ chunk_t chunk;
+
+ chunk = sector_to_chunk(s->store, bio->bi_sector);
+
+ down_read(&s->lock);
+
+ /* Full snapshots are not usable */
+ if (!s->valid) {
+ r = -EIO;
+ goto out_unlock;
+ }
+
+ /* If the block is already remapped - use that */
+ e = dm_lookup_exception(&s->complete, chunk);
+ if (e) {
+ remap_exception(s, e, bio, chunk);
+ goto out_unlock;
+ }
+
+ bio->bi_bdev = s->origin->bdev;
+
+ if (bio_rw(bio) == WRITE) {
+ up_write(&s->lock);
+ return do_origin(s->origin, bio);
+ }
+
+ out_unlock:
+ up_read(&s->lock);
+
+ return r;
+}
+
static int snapshot_end_io(struct dm_target *ti, struct bio *bio,
int error, union map_info *map_context)
{
@@ -1442,6 +1485,10 @@ static int __origin_write(struct list_head *snapshots,
/* Do all the snapshots on this origin */
list_for_each_entry (snap, snapshots, list) {
+ /* Don't make new exceptions in a merging snapshot */
+ if (is_merge(snap->ti))
+ continue;
+
down_write(&snap->lock);
/* Only deal with valid and active snapshots */
@@ -1670,7 +1717,7 @@ static struct target_type merge_target = {
.module = THIS_MODULE,
.ctr = snapshot_ctr,
.dtr = snapshot_dtr,
- .map = snapshot_map,
+ .map = snapshot_merge_map,
.end_io = snapshot_end_io,
.postsuspend = snapshot_postsuspend,
.preresume = snapshot_preresume,
--
1.6.5.2
Mike Snitzer
prepare_merge: returns the last chunk in the variables passed by reference.
The return value is the number of consecutive chunks.
commit_merge: permanently removes 'n' chunks from the exception store.
'n' is less or equal that the number returned by prepare_merge.
If the caller wishes, it can do the optimization of merging several consecutive
chunks at once. If it doesn't want to do this optimization, it just calls
commit_merge with n == 1.
Signed-off-by: Mikulas Patocka <mpat...@redhat.com>
Reviewed-by: Mike Snitzer <sni...@redhat.com>
---
drivers/md/dm-exception-store.h | 16 +++++++++
drivers/md/dm-snap-persistent.c | 70 +++++++++++++++++++++++++++++++++++++++
2 files changed, 86 insertions(+), 0 deletions(-)
diff --git a/drivers/md/dm-exception-store.h b/drivers/md/dm-exception-store.h
index bb88746..534427f 100644
--- a/drivers/md/dm-exception-store.h
+++ b/drivers/md/dm-exception-store.h
@@ -75,6 +75,22 @@ struct dm_exception_store_type {
void *callback_context);
/*
+ * Returns the last chunk in the pointers. (TODO: -ENOPARSE)
+ * > 0: the number of consecutive chunks that can
+ * be copied in one shot.
+ * == 0: the exception store is empty.
+ * < 0: error.
+ */
+ int (*prepare_merge) (struct dm_exception_store *store,
+ chunk_t *old_chunk, chunk_t *new_chunk);
+
+ /*
+ * Clear the last n exceptions.
+ * n must be <= the value returned by prepare_merge.
+ */
+ int (*commit_merge) (struct dm_exception_store *store, int n);
+
+ /*
* The snapshot is invalid, note this in the metadata.
*/
void (*drop_snapshot) (struct dm_exception_store *store);
diff --git a/drivers/md/dm-snap-persistent.c b/drivers/md/dm-snap-persistent.c
index 157999e..1f5752e 100644
--- a/drivers/md/dm-snap-persistent.c
+++ b/drivers/md/dm-snap-persistent.c
@@ -409,6 +409,15 @@ 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
@@ -680,6 +689,63 @@ 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 *old_chunk, chunk_t *new_chunk)
+{
+ int r, i;
+ struct pstore *ps = get_info(store);
+ struct disk_exception de;
+
+ if (!ps->current_committed) {
+ 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);
+ *old_chunk = de.old_chunk;
+ *new_chunk = de.new_chunk;
+
+ for (i = 1; i < ps->current_committed; i++) {
+ read_exception(ps, ps->current_committed - 1 - i, &de);
+ if (de.old_chunk != *old_chunk - i ||
+ de.new_chunk != *new_chunk - i)
+ break;
+ }
+
+ return i;
+}
+
+static int persistent_commit_merge(struct dm_exception_store *store, int n)
+{
+ int r, i;
+ struct pstore *ps = get_info(store);
+
+ BUG_ON(n > ps->current_committed);
+
+ for (i = 0; i < n; i++)
+ clear_exception(ps, ps->current_committed - 1 - i);
+
+ r = area_io(ps, WRITE);
+ if (r < 0)
+ return r;
+
+ ps->current_committed -= i;
+
+ /*
+ * ps->next_free cannot really be reliably decreased here (because of
+ * misordered chunks), so don't do it. We don't even need it, because
+ * there is no situation where merging snapshot would become
+ * non-merging.
+ */
+
+ return 0;
+}
+
static void persistent_drop_snapshot(struct dm_exception_store *store)
{
struct pstore *ps = get_info(store);
@@ -748,6 +814,8 @@ 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 +829,8 @@ 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,
--
1.6.5.2
Mike Snitzer
The previous code selected one exception as "primary_pe", linked all
other exceptions to it and used reference counting to wait until all
exceptions were reallocated.
All the complexity with exceptions linking and reference counting has
been removed. Now, a bio is linked to one exception and when that
exception is reallocated, the bio is retried to possibly wait for other
exceptions.
The new __origin_write() interface affords the snapshot-merge support
the ability to trigger exceptions in other snapshots without having a
need for an associated bio (which snapshot-merge does not generate). As
such this patch is a prerequisite for snapshot-merge.
Signed-off-by: Mikulas Patocka <mpat...@redhat.com>
Signed-off-by: Mike Snitzer <sni...@redhat.com>
---
drivers/md/dm-snap.c | 165 +++++++++++++++++--------------------------------
1 files changed, 57 insertions(+), 108 deletions(-)
diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index 60bfefb..ad95039 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -137,28 +137,6 @@ struct dm_snap_pending_exception {
struct bio_list origin_bios;
struct bio_list snapshot_bios;
- /*
- * Short-term queue of pending exceptions prior to submission.
- */
- struct list_head list;
-
- /*
- * The primary pending_exception is the one that holds
- * the ref_count and the list of origin_bios for a
- * group of pending_exceptions. It is always last to get freed.
- * These fields get set up when writing to the origin.
- */
- struct dm_snap_pending_exception *primary_pe;
-
- /*
- * Number of pending_exceptions processing this chunk.
- * When this drops to zero we must complete the origin bios.
- * If incrementing or decrementing this, hold pe->snap->lock for
- * the sibling concerned and not pe->primary_pe->snap->lock unless
- * they are the same.
- */
- atomic_t ref_count;
-
/* Pointer back to snapshot context */
struct dm_snapshot *snap;
@@ -997,6 +975,28 @@ static void flush_queued_bios(struct work_struct *work)
flush_bios(queued_bios);
}
+static int do_origin(struct dm_dev *origin, struct bio *bio);
+
+/*
+ * Flush a list of buffers.
+ */
+static void retry_origin_bios(struct dm_snapshot *s, struct bio *bio)
+{
+ struct bio *n;
+ int r;
+
+ while (bio) {
+ n = bio->bi_next;
+ bio->bi_next = NULL;
+ r = do_origin(s->origin, bio);
+ if (r == DM_MAPIO_REMAPPED)
+ generic_make_request(bio);
+ else
+ BUG_ON(r != DM_MAPIO_SUBMITTED);
+ bio = n;
+ }
+}
+
/*
* Error a list of buffers.
*/
@@ -1030,39 +1030,6 @@ static void __invalidate_snapshot(struct dm_snapshot *s, int err)
dm_table_event(s->ti->table);
}
-static void get_pending_exception(struct dm_snap_pending_exception *pe)
-{
- atomic_inc(&pe->ref_count);
-}
-
-static struct bio *put_pending_exception(struct dm_snap_pending_exception *pe)
-{
- struct dm_snap_pending_exception *primary_pe;
- struct bio *origin_bios = NULL;
-
- primary_pe = pe->primary_pe;
-
- /*
- * If this pe is involved in a write to the origin and
- * it is the last sibling to complete then release
- * the bios for the original write to the origin.
- */
- if (primary_pe &&
- atomic_dec_and_test(&primary_pe->ref_count)) {
- origin_bios = bio_list_get(&primary_pe->origin_bios);
- free_pending_exception(primary_pe);
- }
-
- /*
- * Free the pe if it's not linked to an origin write or if
- * it's not itself a primary pe.
- */
- if (!primary_pe || primary_pe != pe)
- free_pending_exception(pe);
-
- return origin_bios;
-}
-
static void pending_complete(struct dm_snap_pending_exception *pe, int success)
{
struct dm_exception *e;
@@ -1111,7 +1078,8 @@ static void pending_complete(struct dm_snap_pending_exception *pe, int success)
out:
dm_remove_exception(&pe->e);
snapshot_bios = bio_list_get(&pe->snapshot_bios);
- origin_bios = put_pending_exception(pe);
+ origin_bios = bio_list_get(&pe->origin_bios);
+ free_pending_exception(pe);
up_write(&s->lock);
@@ -1121,7 +1089,7 @@ static void pending_complete(struct dm_snap_pending_exception *pe, int success)
else
flush_bios(snapshot_bios);
- flush_bios(origin_bios);
+ retry_origin_bios(s, origin_bios);
}
static void commit_callback(void *context, int success)
@@ -1208,8 +1176,6 @@ __find_pending_exception(struct dm_snapshot *s,
pe->e.old_chunk = chunk;
bio_list_init(&pe->origin_bios);
bio_list_init(&pe->snapshot_bios);
- pe->primary_pe = NULL;
- atomic_set(&pe->ref_count, 0);
pe->started = 0;
if (s->store->type->prepare_exception(s->store, &pe->e)) {
@@ -1217,7 +1183,6 @@ __find_pending_exception(struct dm_snapshot *s,
return NULL;
}
- get_pending_exception(pe);
dm_insert_exception(&s->pending, &pe->e);
return pe;
@@ -1458,14 +1423,21 @@ static int snapshot_iterate_devices(struct dm_target *ti,
/*-----------------------------------------------------------------
* Origin methods
*---------------------------------------------------------------*/
-static int __origin_write(struct list_head *snapshots, struct bio *bio)
+
+/*
+ * Returns:
+ * DM_MAPIO_REMAPPED: bio may be submitted to origin device
+ * DM_MAPIO_SUBMITTED: bio was queued on queue on one of exceptions
+ */
+
+static int __origin_write(struct list_head *snapshots,
+ sector_t sector, struct bio *bio)
{
- int r = DM_MAPIO_REMAPPED, first = 0;
+ int r = DM_MAPIO_REMAPPED;
struct dm_snapshot *snap;
struct dm_exception *e;
- struct dm_snap_pending_exception *pe, *next_pe, *primary_pe = NULL;
+ struct dm_snap_pending_exception *pe, *pe_to_start = NULL;
chunk_t chunk;
- LIST_HEAD(pe_queue);
/* Do all the snapshots on this origin */
list_for_each_entry (snap, snapshots, list) {
@@ -1477,22 +1449,19 @@ static int __origin_write(struct list_head *snapshots, struct bio *bio)
goto next_snapshot;
/* Nothing to do if writing beyond end of snapshot */
- if (bio->bi_sector >= dm_table_get_size(snap->ti->table))
+ if (sector >= dm_table_get_size(snap->ti->table))
goto next_snapshot;
/*
* Remember, different snapshots can have
* different chunk sizes.
*/
- chunk = sector_to_chunk(snap->store, bio->bi_sector);
+ chunk = sector_to_chunk(snap->store, sector);
/*
* Check exception table to see if block
* is already remapped in this snapshot
* and trigger an exception if not.
- *
- * ref_count is initialised to 1 so pending_complete()
- * won't destroy the primary_pe while we're inside this loop.
*/
e = dm_lookup_exception(&snap->complete, chunk);
if (e)
@@ -1522,59 +1491,39 @@ static int __origin_write(struct list_head *snapshots, struct bio *bio)
}
}
- if (!primary_pe) {
- /*
- * Either every pe here has same
- * primary_pe or none has one yet.
- */
- if (pe->primary_pe)
- primary_pe = pe->primary_pe;
- else {
- primary_pe = pe;
- first = 1;
- }
-
- bio_list_add(&primary_pe->origin_bios, bio);
+ r = DM_MAPIO_SUBMITTED;
- r = DM_MAPIO_SUBMITTED;
- }
+ if (bio) {
+ bio_list_add(&pe->origin_bios, bio);
+ bio = NULL;
- if (!pe->primary_pe) {
- pe->primary_pe = primary_pe;
- get_pending_exception(primary_pe);
+ if (!pe->started) {
+ pe->started = 1;
+ pe_to_start = pe;
+ }
}
if (!pe->started) {
pe->started = 1;
- list_add_tail(&pe->list, &pe_queue);
+ start_copy(pe);
}
next_snapshot:
up_write(&snap->lock);
}
- if (!primary_pe)
- return r;
-
/*
- * If this is the first time we're processing this chunk and
- * ref_count is now 1 it means all the pending exceptions
- * got completed while we were in the loop above, so it falls to
- * us here to remove the primary_pe and submit any origin_bios.
+ * pe_to_start is a small performance improvement:
+ * To avoid calling __origin_write N times for N snapshots, we start
+ * the snapshot where we queued the bio as the last one.
+ *
+ * If we start it as the last one, it finishes most likely as the last
+ * one and exceptions in other snapshots will be already finished when
+ * the bio will be retried.
*/
- if (first && atomic_dec_and_test(&primary_pe->ref_count)) {
- flush_bios(bio_list_get(&primary_pe->origin_bios));
- free_pending_exception(primary_pe);
- /* If we got here, pe_queue is necessarily empty. */
- return r;
- }
-
- /*
- * Now that we have a complete pe list we can start the copying.
- */
- list_for_each_entry_safe(pe, next_pe, &pe_queue, list)
- start_copy(pe);
+ if (pe_to_start)
+ start_copy(pe_to_start);
return r;
}
@@ -1590,7 +1539,7 @@ static int do_origin(struct dm_dev *origin, struct bio *bio)
down_read(&_origins_lock);
o = __lookup_origin(origin->bdev);
if (o)
- r = __origin_write(&o->snapshots, bio);
+ r = __origin_write(&o->snapshots, bio->bi_sector, bio);
up_read(&_origins_lock);
return r;
--
1.6.5.2
Mike Snitzer
snapshot instance to another. This is a pre-requisite for patches
that allow the changes made in a snapshot device to be merged back into
its origin device and also allows device resizing.
The basic call sequence is:
dmsetup load new_snapshot (referencing the existing in-use cow device)
- the ctr code detects that the cow is already in use and allows the
two snapshot target instances to be linked together
dmsetup suspend original_snapshot
dmsetup resume new_snapshot
- the new_snapshot becomes live, and if anything now tries to access
the original one it will receive -EIO
dmsetup remove original_snapshot
(There can only be two snapshot targets referencing the same cow device
simultaneously.)
Signed-off-by: Mike Snitzer <sni...@redhat.com>
Signed-off-by: Mikulas Patocka <mpat...@redhat.com>
---
drivers/md/dm-snap.c | 258 ++++++++++++++++++++++++++++++++++++++++++++-----
1 files changed, 231 insertions(+), 27 deletions(-)
diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index c6c26a3..60bfefb 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -303,22 +303,111 @@ static void __insert_origin(struct origin *o)
}
/*
+ * _origins_lock must be held when calling this function.
+ * Returns number of snapshots registered using the supplied cow device, plus:
+ * snap_src - a snapshot suitable for use as a source of exception handover
+ * snap_dest - a snapshot capable of receiving exception handover.
+ *
+ * Possible return values and states:
+ * 0: NULL, NULL - first new snapshot
+ * 1: snap_src, NULL - normal snapshot
+ * 2: snap_src, snap_dest - waiting for handover
+ * 2: snap_src, NULL - handed over, waiting for old to be deleted
+ * 1: NULL, snap_dest - source got destroyed without handover
+ */
+static int __find_snapshots_sharing_cow(struct dm_snapshot *snap,
+ struct dm_snapshot **snap_src,
+ struct dm_snapshot **snap_dest)
+{
+ struct dm_snapshot *s;
+ struct origin *o;
+ int count = 0;
+ int active;
+
+ o = __lookup_origin(snap->origin->bdev);
+ if (!o)
+ goto out;
+
+ list_for_each_entry(s, &o->snapshots, list) {
+ if (!bdev_equal(s->cow->bdev, snap->cow->bdev))
+ continue;
+
+ down_read(&s->lock);
+ active = s->active;
+ up_read(&s->lock);
+
+ if (active) {
+ if (snap_src)
+ *snap_src = s;
+ } else if (snap_dest)
+ *snap_dest = s;
+
+ count++;
+ }
+
+out:
+ return count;
+}
+
+static int __validate_exception_handover(struct dm_snapshot *snap)
+{
+ struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
+ int r = 0;
+
+ /* Does snapshot need exceptions handed over to it? */
+ if ((__find_snapshots_sharing_cow(snap, &snap_src, &snap_dest) == 2) ||
+ snap_dest) {
+ snap->ti->error = "Snapshot cow pairing for exception "
+ "table handover failed";
+ r = -EINVAL;
+ goto out;
+ }
+
+ if (snap_src)
+ r = 1;
+
+out:
+ return r;
+}
+
+static void __insert_snapshot(struct origin *o, struct dm_snapshot *s)
+{
+ struct dm_snapshot *l;
+
+ /* Sort the list according to chunk size, largest-first smallest-last */
+ list_for_each_entry(l, &o->snapshots, list)
+ if (l->store->chunk_size < s->store->chunk_size)
+ break;
+ list_add_tail(&s->list, &l->list);
+}
+
+/*
* Make a note of the snapshot and its origin so we can look it
* up when the origin has a write on it.
+ *
+ * Also validate snapshot exception store handovers.
+ * On success, returns 1 if this registration is a handover destination,
+ * otherwise returns 0.
*/
static int register_snapshot(struct dm_snapshot *snap)
{
- struct dm_snapshot *l;
- struct origin *o, *new_o;
+ struct origin *o, *new_o = NULL;
struct block_device *bdev = snap->origin->bdev;
+ int r = 0;
new_o = kmalloc(sizeof(*new_o), GFP_KERNEL);
if (!new_o)
return -ENOMEM;
down_write(&_origins_lock);
- o = __lookup_origin(bdev);
+ r = __validate_exception_handover(snap);
+ if (r < 0) {
+ kfree(new_o);
+ goto out;
+ }
+
+ o = __lookup_origin(bdev);
if (o)
kfree(new_o);
else {
@@ -332,14 +421,27 @@ static int register_snapshot(struct dm_snapshot *snap)
__insert_origin(o);
}
- /* Sort the list according to chunk size, largest-first smallest-last */
- list_for_each_entry(l, &o->snapshots, list)
- if (l->store->chunk_size < snap->store->chunk_size)
- break;
- list_add_tail(&snap->list, &l->list);
+ __insert_snapshot(o, snap);
+
+out:
+ up_write(&_origins_lock);
+
+ return r;
+}
+
+/*
+ * Move snapshot to correct place in list according to chunk size.
+ */
+static void reregister_snapshot(struct dm_snapshot *s)
+{
+ struct block_device *bdev = s->origin->bdev;
+
+ down_write(&_origins_lock);
+
+ list_del(&s->list);
+ __insert_snapshot(__lookup_origin(bdev), s);
up_write(&_origins_lock);
- return 0;
}
static void unregister_snapshot(struct dm_snapshot *s)
@@ -350,7 +452,7 @@ static void unregister_snapshot(struct dm_snapshot *s)
o = __lookup_origin(s->origin->bdev);
list_del(&s->list);
- if (list_empty(&o->snapshots)) {
+ if (o && list_empty(&o->snapshots)) {
list_del(&o->hash_list);
kfree(o);
}
@@ -660,6 +762,7 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
s->suspended = 0;
atomic_set(&s->pending_exceptions_count, 0);
init_rwsem(&s->lock);
+ INIT_LIST_HEAD(&s->list);
spin_lock_init(&s->pe_lock);
/* Allocate hash table for COW data */
@@ -694,39 +797,55 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
spin_lock_init(&s->tracked_chunk_lock);
- /* Metadata must only be loaded into one table at once */
+ bio_list_init(&s->queued_bios);
+ INIT_WORK(&s->queued_bios_work, flush_queued_bios);
+
+ ti->private = s;
+ ti->num_flush_requests = 1;
+
+ /* Add snapshot to the list of snapshots for this origin */
+ /* Exceptions aren't triggered till snapshot_resume() is called */
+ r = register_snapshot(s);
+ if (r == -ENOMEM) {
+ ti->error = "Snapshot origin struct allocation failed";
+ goto bad_load_and_register;
+ } else if (r < 0) {
+ /* invalid handover, register_snapshot has set ti->error */
+ goto bad_load_and_register;
+ }
+
+ /*
+ * Metadata must only be loaded into one table at once, so skip this
+ * if metadata will be handed over during resume.
+ * Chunk size will be set during the handover - set it to zero to
+ * ensure it's ignored.
+ */
+ if (r > 0) {
+ s->store->chunk_size = 0;
+ return 0;
+ }
+
r = s->store->type->read_metadata(s->store, dm_add_exception,
(void *)s);
if (r < 0) {
ti->error = "Failed to read snapshot metadata";
- goto bad_load_and_register;
+ goto bad_read_metadata;
} else if (r > 0) {
s->valid = 0;
DMWARN("Snapshot is marked invalid.");
}
- bio_list_init(&s->queued_bios);
- INIT_WORK(&s->queued_bios_work, flush_queued_bios);
-
if (!s->store->chunk_size) {
ti->error = "Chunk size not set";
- goto bad_load_and_register;
- }
-
- /* Add snapshot to the list of snapshots for this origin */
- /* Exceptions aren't triggered till snapshot_resume() is called */
- if (register_snapshot(s)) {
- r = -EINVAL;
- ti->error = "Cannot register snapshot origin";
- goto bad_load_and_register;
+ goto bad_read_metadata;
}
-
- ti->private = s;
ti->split_io = s->store->chunk_size;
- ti->num_flush_requests = 1;
return 0;
+bad_read_metadata:
+ unregister_snapshot(s);
+
bad_load_and_register:
mempool_destroy(s->tracked_chunk_pool);
@@ -765,15 +884,58 @@ static void __free_exceptions(struct dm_snapshot *s)
dm_exception_table_exit(&s->complete, exception_cache);
}
+static void __handover_exceptions(struct dm_snapshot *snap_src,
+ struct dm_snapshot *snap_dest)
+{
+ union {
+ struct dm_exception_table table_swap;
+ struct dm_exception_store *store_swap;
+ } u;
+
+ /*
+ * Swap all snapshot context information between the two instances.
+ */
+ u.table_swap = snap_dest->complete;
+ snap_dest->complete = snap_src->complete;
+ snap_src->complete = u.table_swap;
+
+ u.store_swap = snap_dest->store;
+ snap_dest->store = snap_src->store;
+ snap_src->store = u.store_swap;
+
+ snap_dest->store->snap = snap_dest;
+ snap_src->store->snap = snap_src;
+
+ snap_dest->ti->split_io = snap_dest->store->chunk_size;
+ snap_dest->valid = snap_src->valid;
+
+ /*
+ * Set source invalid to ensure it receives no further I/O.
+ */
+ snap_src->valid = 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 *snap_src = NULL, *snap_dest = NULL;
flush_workqueue(ksnapd);
+ down_read(&_origins_lock);
+ /* Check whether exception handover must be cancelled */
+ (void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest);
+ if (snap_src && snap_dest && (s == snap_src)) {
+ down_write(&snap_dest->lock);
+ snap_dest->valid = 0;
+ up_write(&snap_dest->lock);
+ DMERR("Cancelling snapshot handover.");
+ }
+ up_read(&_origins_lock);
+
/* Prevent further origin writes from using this snapshot. */
/* After this returns there can be no new kcopyd jobs. */
unregister_snapshot(s);
@@ -1186,9 +1348,50 @@ static void snapshot_postsuspend(struct dm_target *ti)
up_write(&s->lock);
}
+static int snapshot_preresume(struct dm_target *ti)
+{
+ int r = 0;
+ struct dm_snapshot *s = ti->private;
+ struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
+
+ down_read(&_origins_lock);
+ (void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest);
+ if (snap_src && snap_dest) {
+ down_read(&snap_src->lock);
+ if (s == snap_src) {
+ DMERR("Unable to resume snapshot source until "
+ "handover completes.");
+ r = -EINVAL;
+ } else if (!snap_src->suspended) {
+ DMERR("Unable to perform snapshot handover until "
+ "source is suspended.");
+ r = -EINVAL;
+ }
+ up_read(&snap_src->lock);
+ }
+ up_read(&_origins_lock);
+
+ return r;
+}
+
static void snapshot_resume(struct dm_target *ti)
{
struct dm_snapshot *s = ti->private;
+ struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
+
+ down_read(&_origins_lock);
+ (void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest);
+ if (snap_src && snap_dest) {
+ down_write(&snap_src->lock);
+ down_write_nested(&snap_dest->lock, SINGLE_DEPTH_NESTING);
+ __handover_exceptions(snap_src, snap_dest);
+ up_write(&snap_dest->lock);
+ up_write(&snap_src->lock);
+ }
+ up_read(&_origins_lock);
+
+ /* Now we have correct chunk size, reregister */
+ reregister_snapshot(s);
down_write(&s->lock);
s->active = 1;
@@ -1506,6 +1709,7 @@ static struct target_type snapshot_target = {
.map = snapshot_map,
.end_io = snapshot_end_io,
.postsuspend = snapshot_postsuspend,
+ .preresume = snapshot_preresume,
.resume = snapshot_resume,
.status = snapshot_status,
.iterate_devices = snapshot_iterate_devices,
--
1.6.5.2
--
Mike Snitzer
Mike Snitzer <sni...@redhat.com> wrote:
> If a write request to a merging snapshot device is to be dispatched
> directly to the origin (because the chunk is not remapped or was already
> merged), snapshot_merge_map() must make exceptions in other snapshots.
..
OK, I caught this in review but clearly didn't refresh the patch; the
above up_write() should be up_read().
Mike
Mike Snitzer
The snapshot-merge target should not allocate new exceptions because the
intent is to merge all of its exceptions as quickly and safely as
possible.
Introduce new method, snapshot_merge_map(), that won't allocate
exceptions. Modify __origin_write() so that it doesn't allocate
exceptions in merging snapshots.
If a write request to a merging snapshot device is to be dispatched
directly to the origin (because the chunk is not remapped or was already
merged), snapshot_merge_map() must make exceptions in other snapshots.
Signed-off-by: Mikulas Patocka <mpat...@redhat.com>
Signed-off-by: Mike Snitzer <sni...@redhat.com>
---
drivers/md/dm-snap.c | 49 ++++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 48 insertions(+), 1 deletion(-)
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
@@ -127,6 +127,11 @@ static int bdev_equal(struct block_devic
return lhs == rhs;
}
+static int snapshot_merge_map(struct dm_target *ti, struct bio *bio,
+ union map_info *map_context);
+
+#define is_merge(ti) ((ti)->type->map == snapshot_merge_map)
+
struct dm_snap_pending_exception {
struct dm_exception e;
@@ -1292,6 +1297,44 @@ static int snapshot_map(struct dm_target
+ up_read(&s->lock);
+ return do_origin(s->origin, bio);
+ }
+
+ out_unlock:
+ up_read(&s->lock);
+
+ return r;
+}
+
static int snapshot_end_io(struct dm_target *ti, struct bio *bio,
int error, union map_info *map_context)
{
@@ -1442,6 +1485,10 @@ static int __origin_write(struct list_he
/* Do all the snapshots on this origin */
list_for_each_entry (snap, snapshots, list) {
+ /* Don't make new exceptions in a merging snapshot */
+ if (is_merge(snap->ti))
+ continue;
+
down_write(&snap->lock);
/* Only deal with valid and active snapshots */
@@ -1670,7 +1717,7 @@ static struct target_type merge_target =
.module = THIS_MODULE,
.ctr = snapshot_ctr,
.dtr = snapshot_dtr,
- .map = snapshot_map,
+ .map = snapshot_merge_map,
.end_io = snapshot_end_io,
.postsuspend = snapshot_postsuspend,
.preresume = snapshot_preresume,
--
Mike Snitzer
Merging more than one snapshot is not supported.
__find_merging_snapshot() will find the merging snapshot for a given
origin device.
Signed-off-by: Mikulas Patocka <mpat...@redhat.com>
Signed-off-by: Mike Snitzer <sni...@redhat.com>
---
drivers/md/dm-snap.c | 33 ++++++++++++++++++++++++++++++++-
1 file changed, 32 insertions(+), 1 deletion(-)
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
goto out;
}
- if (snap_src)
+ if (snap_src) {
+ if (is_merge(snap->ti)) {
+ /* Do not allow more than one merging snapshot */
+ if (__find_merging_snapshot(bdev)) {
+ snap->ti->error = "A snapshot is already "
+ "merging.";
+ r = -EINVAL;
+ goto out;
+ }
+ }
+
r = 1;
+ }
out:
return r;