[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>

1 files changed, 49 insertions, 41 deletions

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,