dm snapshot: permit invalid activation

Allow invalid snapshots to be activated instead of failing.

This allows userspace to reinstate any given snapshot state - for
example after an unscheduled reboot - and clean up the invalid snapshot
at its leisure.

Cc: stable@kernel.org
Signed-off-by: Milan Broz <mbroz@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 10 insertions, 6 deletions

diff --git a/drivers/md/dm-exception-store.c b/drivers/md/dm-exception-store.c
index 8c25c2ff724a..3d65917a1bbb 100644
--- a/drivers/md/dm-exception-store.c
+++ b/drivers/md/dm-exception-store.c
@@ -489,11 +489,6 @@ static int persistent_read_metadata(struct exception_store *store)
                 /*
                  * Sanity checks.
                  */
-                if (!ps->valid) {
-                        DMWARN("snapshot is marked invalid");
-                        return -EINVAL;
-                }
-
                 if (ps->version != SNAPSHOT_DISK_VERSION) {
                         DMWARN("unable to handle snapshot disk version %d",
                                ps->version);
@@ -501,6 +496,12 @@ static int persistent_read_metadata(struct exception_store *store)
                 }
 
                 /*
+                 * Metadata are valid, but snapshot is invalidated
+                 */
+                if (!ps->valid)
+                        return 1;
+
+                /*
                  * Read the metadata.
                  */
                 r = read_exceptions(ps);
diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index 1da41229fbf2..854891d07b59 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -523,9 +523,12 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 
         /* Metadata must only be loaded into one table at once */
         r = s->store.read_metadata(&s->store);
-        if (r) {
+        if (r < 0) {
                 ti->error = "Failed to read snapshot metadata";
                 goto bad6;
+        } else if (r > 0) {
+                s->valid = 0;
+                DMWARN("Snapshot is marked invalid.");
         }
 
         bio_list_init(&s->queued_bios);