[PATCH] dm snapshot: allow zero chunk_size

The chunk size of snapshots cannot be changed so it is redundant to require it
as a parameter when activating an existing snapshot.  Allow a value of zero in
this case and ignore it.  For a new snapshot, use a default value if zero is
specified.

Signed-off-by: Mark McLoughlin <markmc@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

3 files changed, 120 insertions, 99 deletions

diff --git a/drivers/md/dm-exception-store.c b/drivers/md/dm-exception-store.c
index d12379b5cdb5..8b4cd02f75a8 100644
--- a/drivers/md/dm-exception-store.c
+++ b/drivers/md/dm-exception-store.c
@@ -17,6 +17,7 @@
 #include <linux/slab.h>
 
 #define DM_MSG_PREFIX "snapshots"
+#define DM_CHUNK_SIZE_DEFAULT_SECTORS 32        /* 16KB */
 
 /*-----------------------------------------------------------------
  * Persistent snapshots, by persistent we mean that the snapshot
@@ -150,6 +151,7 @@ static int alloc_area(struct pstore *ps)
 static void free_area(struct pstore *ps)
 {
         vfree(ps->area);
+        ps->area = NULL;
 }
 
 /*
@@ -198,48 +200,79 @@ static int read_header(struct pstore *ps, int *new_snapshot)
         int r;
         struct disk_header *dh;
         chunk_t chunk_size;
+        int chunk_size_supplied = 1;
 
-        r = chunk_io(ps, 0, READ);
+        /*
+         * Use default chunk size (or hardsect_size, if larger) if none supplied
+         */
+        if (!ps->snap->chunk_size) {
+                ps->snap->chunk_size = max(DM_CHUNK_SIZE_DEFAULT_SECTORS,
+                    bdev_hardsect_size(ps->snap->cow->bdev) >> 9);
+                ps->snap->chunk_mask = ps->snap->chunk_size - 1;
+                ps->snap->chunk_shift = ffs(ps->snap->chunk_size) - 1;
+                chunk_size_supplied = 0;
+        }
+
+        r = dm_io_get(sectors_to_pages(ps->snap->chunk_size));
         if (r)
                 return r;
 
+        r = alloc_area(ps);
+        if (r)
+                goto bad1;
+
+        r = chunk_io(ps, 0, READ);
+        if (r)
+                goto bad2;
+
         dh = (struct disk_header *) ps->area;
 
         if (le32_to_cpu(dh->magic) == 0) {
                 *new_snapshot = 1;
+                return 0;
+        }
 
-        } else if (le32_to_cpu(dh->magic) == SNAP_MAGIC) {
-                *new_snapshot = 0;
-                ps->valid = le32_to_cpu(dh->valid);
-                ps->version = le32_to_cpu(dh->version);
-                chunk_size = le32_to_cpu(dh->chunk_size);
-                if (ps->snap->chunk_size != chunk_size) {
-                        DMWARN("chunk size %llu in device metadata overrides "
-                               "table chunk size of %llu.",
-                               (unsigned long long)chunk_size,
-                               (unsigned long long)ps->snap->chunk_size);
-
-                        /* We had a bogus chunk_size. Fix stuff up. */
-                        dm_io_put(sectors_to_pages(ps->snap->chunk_size));
-                        free_area(ps);
-
-                        ps->snap->chunk_size = chunk_size;
-                        ps->snap->chunk_mask = chunk_size - 1;
-                        ps->snap->chunk_shift = ffs(chunk_size) - 1;
-
-                        r = alloc_area(ps);
-                        if (r)
-                                return r;
-
-                        r = dm_io_get(sectors_to_pages(chunk_size));
-                        if (r)
-                                return r;
-                }
-        } else {
-                DMWARN("Invalid/corrupt snapshot");
+        if (le32_to_cpu(dh->magic) != SNAP_MAGIC) {
+                DMWARN("Invalid or corrupt snapshot");
                 r = -ENXIO;
+                goto bad2;
         }
 
+        *new_snapshot = 0;
+        ps->valid = le32_to_cpu(dh->valid);
+        ps->version = le32_to_cpu(dh->version);
+        chunk_size = le32_to_cpu(dh->chunk_size);
+
+        if (!chunk_size_supplied || ps->snap->chunk_size == chunk_size)
+                return 0;
+
+        DMWARN("chunk size %llu in device metadata overrides "
+               "table chunk size of %llu.",
+               (unsigned long long)chunk_size,
+               (unsigned long long)ps->snap->chunk_size);
+
+        /* We had a bogus chunk_size. Fix stuff up. */
+        dm_io_put(sectors_to_pages(ps->snap->chunk_size));
+        free_area(ps);
+
+        ps->snap->chunk_size = chunk_size;
+        ps->snap->chunk_mask = chunk_size - 1;
+        ps->snap->chunk_shift = ffs(chunk_size) - 1;
+
+        r = dm_io_get(sectors_to_pages(chunk_size));
+        if (r)
+                return r;
+
+        r = alloc_area(ps);
+        if (r)
+                goto bad1;
+
+        return 0;
+
+bad2:
+        free_area(ps);
+bad1:
+        dm_io_put(sectors_to_pages(ps->snap->chunk_size));
         return r;
 }
 
@@ -547,32 +580,22 @@ static void persistent_drop(struct exception_store *store)
                 DMWARN("write header failed");
 }
 
-int dm_create_persistent(struct exception_store *store, uint32_t chunk_size)
+int dm_create_persistent(struct exception_store *store)
 {
-        int r;
         struct pstore *ps;
 
-        r = dm_io_get(sectors_to_pages(chunk_size));
-        if (r)
-                return r;
-
         /* allocate the pstore */
         ps = kmalloc(sizeof(*ps), GFP_KERNEL);
-        if (!ps) {
-                r = -ENOMEM;
-                goto bad;
-        }
+        if (!ps)
+                return -ENOMEM;
 
         ps->snap = store->snap;
         ps->valid = 1;
         ps->version = SNAPSHOT_DISK_VERSION;
+        ps->area = NULL;
         ps->next_free = 2;      /* skipping the header and first area */
         ps->current_committed = 0;
 
-        r = alloc_area(ps);
-        if (r)
-                goto bad;
-
         ps->callback_count = 0;
         atomic_set(&ps->pending_count, 0);
         ps->callbacks = NULL;
@@ -586,13 +609,6 @@ int dm_create_persistent(struct exception_store *store, uint32_t chunk_size)
         store->context = ps;
 
         return 0;
-
-      bad:
-        dm_io_put(sectors_to_pages(chunk_size));
-        if (ps && ps->area)
-                free_area(ps);
-        kfree(ps);
-        return r;
 }
 
 /*-----------------------------------------------------------------
@@ -642,18 +658,16 @@ static void transient_fraction_full(struct exception_store *store,
         *denominator = get_dev_size(store->snap->cow->bdev);
 }
 
-int dm_create_transient(struct exception_store *store,
-                        struct dm_snapshot *s, int blocksize)
+int dm_create_transient(struct exception_store *store)
 {
         struct transient_c *tc;
 
-        memset(store, 0, sizeof(*store));
         store->destroy = transient_destroy;
         store->read_metadata = transient_read_metadata;
         store->prepare_exception = transient_prepare;
         store->commit_exception = transient_commit;
+        store->drop_snapshot = NULL;
         store->fraction_full = transient_fraction_full;
-        store->snap = s;
 
         tc = kmalloc(sizeof(struct transient_c), GFP_KERNEL);
         if (!tc)
diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index 7c14867b5903..89f8dd1bfaa0 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -398,21 +398,60 @@ static void read_snapshot_metadata(struct dm_snapshot *s)
         }
 }
 
+static int set_chunk_size(struct dm_snapshot *s, const char *chunk_size_arg,
+                          char **error)
+{
+        unsigned long chunk_size;
+        char *value;
+
+        chunk_size = simple_strtoul(chunk_size_arg, &value, 10);
+        if (*chunk_size_arg == '\0' || *value != '\0') {
+                *error = "Invalid chunk size";
+                return -EINVAL;
+        }
+
+        if (!chunk_size) {
+                s->chunk_size = s->chunk_mask = s->chunk_shift = 0;
+                return 0;
+        }
+
+        /*
+         * Chunk size must be multiple of page size.  Silently
+         * round up if it's not.
+         */
+        chunk_size = round_up(chunk_size, PAGE_SIZE >> 9);
+
+        /* Check chunk_size is a power of 2 */
+        if (chunk_size & (chunk_size - 1)) {
+                *error = "Chunk size is not a power of 2";
+                return -EINVAL;
+        }
+
+        /* Validate the chunk size against the device block size */
+        if (chunk_size % (bdev_hardsect_size(s->cow->bdev) >> 9)) {
+                *error = "Chunk size is not a multiple of device blocksize";
+                return -EINVAL;
+        }
+
+        s->chunk_size = chunk_size;
+        s->chunk_mask = chunk_size - 1;
+        s->chunk_shift = ffs(chunk_size) - 1;
+
+        return 0;
+}
+
 /*
  * Construct a snapshot mapping: <origin_dev> <COW-dev> <p/n> <chunk-size>
  */
 static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 {
         struct dm_snapshot *s;
-        unsigned long chunk_size;
         int r = -EINVAL;
         char persistent;
         char *origin_path;
         char *cow_path;
-        char *value;
-        int blocksize;
 
-        if (argc < 4) {
+        if (argc != 4) {
                 ti->error = "requires exactly 4 arguments";
                 r = -EINVAL;
                 goto bad1;
@@ -428,13 +467,6 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
                 goto bad1;
         }
 
-        chunk_size = simple_strtoul(argv[3], &value, 10);
-        if (chunk_size == 0 || value == NULL) {
-                ti->error = "Invalid chunk size";
-                r = -EINVAL;
-                goto bad1;
-        }
-
         s = kmalloc(sizeof(*s), GFP_KERNEL);
         if (s == NULL) {
                 ti->error = "Cannot allocate snapshot context private "
@@ -457,31 +489,11 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
                 goto bad2;
         }
 
-        /*
-         * Chunk size must be multiple of page size.  Silently
-         * round up if it's not.
-         */
-        chunk_size = round_up(chunk_size, PAGE_SIZE >> 9);
-
-        /* Validate the chunk size against the device block size */
-        blocksize = s->cow->bdev->bd_disk->queue->hardsect_size;
-        if (chunk_size % (blocksize >> 9)) {
-                ti->error = "Chunk size is not a multiple of device blocksize";
-                r = -EINVAL;
-                goto bad3;
-        }
-
-        /* Check chunk_size is a power of 2 */
-        if (chunk_size & (chunk_size - 1)) {
-                ti->error = "Chunk size is not a power of 2";
-                r = -EINVAL;
+        r = set_chunk_size(s, argv[3], &ti->error);
+        if (r)
                 goto bad3;
-        }
 
-        s->chunk_size = chunk_size;
-        s->chunk_mask = chunk_size - 1;
         s->type = persistent;
-        s->chunk_shift = ffs(chunk_size) - 1;
 
         s->valid = 1;
         s->active = 0;
@@ -496,16 +508,12 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
                 goto bad3;
         }
 
-        /*
-         * Check the persistent flag - done here because we need the iobuf
-         * to check the LV header
-         */
         s->store.snap = s;
 
         if (persistent == 'P')
-                r = dm_create_persistent(&s->store, chunk_size);
+                r = dm_create_persistent(&s->store);
         else
-                r = dm_create_transient(&s->store, s, blocksize);
+                r = dm_create_transient(&s->store);
 
         if (r) {
                 ti->error = "Couldn't create exception store";
@@ -1205,7 +1213,7 @@ static int origin_status(struct dm_target *ti, status_type_t type, char *result,
 
 static struct target_type origin_target = {
         .name    = "snapshot-origin",
-        .version = {1, 4, 0},
+        .version = {1, 5, 0},
         .module  = THIS_MODULE,
         .ctr     = origin_ctr,
         .dtr     = origin_dtr,
@@ -1216,7 +1224,7 @@ static struct target_type origin_target = {
 
 static struct target_type snapshot_target = {
         .name    = "snapshot",
-        .version = {1, 4, 0},
+        .version = {1, 5, 0},
         .module  = THIS_MODULE,
         .ctr     = snapshot_ctr,
         .dtr     = snapshot_dtr,
diff --git a/drivers/md/dm-snap.h b/drivers/md/dm-snap.h
index fdec1e2dc871..221eb8880c80 100644
--- a/drivers/md/dm-snap.h
+++ b/drivers/md/dm-snap.h
@@ -128,10 +128,9 @@ int dm_add_exception(struct dm_snapshot *s, chunk_t old, chunk_t new);
  * Constructor and destructor for the default persistent
  * store.
  */
-int dm_create_persistent(struct exception_store *store, uint32_t chunk_size);
+int dm_create_persistent(struct exception_store *store);
 
-int dm_create_transient(struct exception_store *store,
-                        struct dm_snapshot *s, int blocksize);
+int dm_create_transient(struct exception_store *store);
 
 /*
  * Return the number of sectors in the device.