dm snapshot: track snapshot reads
Whenever a snapshot read gets mapped through to the origin, track it in
a per-snapshot hash table indexed by chunk number, using memory allocated
from a new per-snapshot mempool.
We need to track these reads to avoid race conditions which will be fixed
by patches that follow.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
diff --git a/drivers/md/dm-snap.h b/drivers/md/dm-snap.h
index 24f9fb7..70dc961 100644
--- a/drivers/md/dm-snap.h
+++ b/drivers/md/dm-snap.h
@@ -130,6 +130,10 @@
void *context;
};
+#define DM_TRACKED_CHUNK_HASH_SIZE 16
+#define DM_TRACKED_CHUNK_HASH(x) ((unsigned long)(x) & \
+ (DM_TRACKED_CHUNK_HASH_SIZE - 1))
+
struct dm_snapshot {
struct rw_semaphore lock;
struct dm_target *ti;
@@ -174,6 +178,11 @@
/* Queue of snapshot writes for ksnapd to flush */
struct bio_list queued_bios;
struct work_struct queued_bios_work;
+
+ /* Chunks with outstanding reads */
+ mempool_t *tracked_chunk_pool;
+ spinlock_t tracked_chunk_lock;
+ struct hlist_head tracked_chunk_hash[DM_TRACKED_CHUNK_HASH_SIZE];
};
/*