dm snapshot: report merge failure in status

Set 'merge_failed' flag if a snapshot fails to merge.  Update
snapshot_status() to report "Merge failed" if 'merge_failed' is set.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index bb4b733697b30c1c257e1267bd98ff2d8de7dc43..4c80e82f941c92e59442e15f1c2a6c22032b96a2 100644 (file)
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -71,7 +71,10 @@ struct dm_snapshot {
        /* List of snapshots per Origin */
        struct list_head list;
 
-       /* You can't use a snapshot if this is 0 (e.g. if full) */
+       /*
+        * You can't use a snapshot if this is 0 (e.g. if full).
+        * A snapshot-merge target never clears this.
+        */
        int valid;
 
        /* Origin writes don't trigger exceptions until this is set */
@@ -107,6 +110,21 @@ struct dm_snapshot {
        spinlock_t tracked_chunk_lock;
        struct hlist_head tracked_chunk_hash[DM_TRACKED_CHUNK_HASH_SIZE];
 
+       /*
+        * The merge operation failed if this flag is set.
+        * Failure modes are handled as follows:
+        * - I/O error reading the header
+        *      => don't load the target; abort.
+        * - Header does not have "valid" flag set
+        *      => use the origin; forget about the snapshot.
+        * - I/O error when reading exceptions
+        *      => don't load the target; abort.
+        *         (We can't use the intermediate origin state.)
+        * - I/O error while merging
+        *      => stop merging; set merge_failed; process I/O normally.
+        */
+       int merge_failed;
+
        /* Wait for events based on state_bits */
        unsigned long state_bits;
 
@@ -900,9 +918,13 @@ static void snapshot_merge_next_chunks(struct dm_snapshot *s)
        linear_chunks = s->store->type->prepare_merge(s->store, &old_chunk,
                                                      &new_chunk);
        if (linear_chunks <= 0) {
-               if (linear_chunks < 0)
+               if (linear_chunks < 0) {
                        DMERR("Read error in exception store: "
                              "shutting down merge");
+                       down_write(&s->lock);
+                       s->merge_failed = 1;
+                       up_write(&s->lock);
+               }
                goto shut;
        }
 
@@ -988,6 +1010,7 @@ static void merge_callback(int read_err, unsigned long write_err, void *context)
 
 shut:
        down_write(&s->lock);
+       s->merge_failed = 1;
        b = __release_queued_bios_after_merge(s);
        up_write(&s->lock);
        error_bios(b);
@@ -1090,6 +1113,7 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
        INIT_LIST_HEAD(&s->list);
        spin_lock_init(&s->pe_lock);
        s->state_bits = 0;
+       s->merge_failed = 0;
        s->first_merging_chunk = 0;
        s->num_merging_chunks = 0;
        bio_list_init(&s->bios_queued_during_merge);
@@ -1835,6 +1859,8 @@ static int snapshot_status(struct dm_target *ti, status_type_t type,
 
                if (!snap->valid)
                        DMEMIT("Invalid");
+               else if (snap->merge_failed)
+                       DMEMIT("Merge failed");
                else {
                        if (snap->store->type->usage) {
                                sector_t total_sectors, sectors_allocated,