dm snapshot: add new persistent store option to support overflow

Commit 76c44f6d80 introduced the possibly for "Overflow" to be reported
by the snapshot device's status.  Older userspace (e.g. lvm2) does not
handle the "Overflow" status response.

Fix this incompatibility by requiring newer userspace code, that can
cope with "Overflow", request the persistent store with overflow support
by using "PO" (Persistent with Overflow) for the snapshot store type.

Reported-by: Zdenek Kabelac <zkabelac@redhat.com>
Fixes: 76c44f6d80 ("dm snapshot: don't invalidate on-disk image on snapshot write overflow")
Reviewed-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

diff --git a/Documentation/device-mapper/snapshot.txt b/Documentation/device-mapper/snapshot.txt
index 0d5bc46dc1676869358cd6f36975905031f17f9e..ad6949bff2e392d63e7ddb82391746687ea6235e 100644 (file)
--- a/Documentation/device-mapper/snapshot.txt
+++ b/Documentation/device-mapper/snapshot.txt
@@ -41,9 +41,13 @@ useless and be disabled, returning errors.  So it is important to monitor
 the amount of free space and expand the <COW device> before it fills up.
 
 <persistent?> is P (Persistent) or N (Not persistent - will not survive
-after reboot).
-The difference is that for transient snapshots less metadata must be
-saved on disk - they can be kept in memory by the kernel.
+after reboot).  O (Overflow) can be added as a persistent store option
+to allow userspace to advertise its support for seeing "Overflow" in the
+snapshot status.  So supported store types are "P", "PO" and "N".
+
+The difference between persistent and transient is with transient
+snapshots less metadata must be saved on disk - they can be kept in
+memory by the kernel.
 
 
 * snapshot-merge <origin> <COW device> <persistent> <chunksize>

diff --git a/drivers/md/dm-exception-store.c b/drivers/md/dm-exception-store.c
index ebaa4f803eec3a08a0cd9fcd9a9a1b933618c50c..192bb8beeb6b59e296d9a2e06c0ef8c0a9be8aeb 100644 (file)
--- a/drivers/md/dm-exception-store.c
+++ b/drivers/md/dm-exception-store.c
@@ -203,7 +203,7 @@ int dm_exception_store_create(struct dm_target *ti, int argc, char **argv,
                return -EINVAL;
        }
 
-       tmp_store = kmalloc(sizeof(*tmp_store), GFP_KERNEL);
+       tmp_store = kzalloc(sizeof(*tmp_store), GFP_KERNEL);
        if (!tmp_store) {
                ti->error = "Exception store allocation failed";
                return -ENOMEM;
@@ -215,7 +215,7 @@ int dm_exception_store_create(struct dm_target *ti, int argc, char **argv,
        else if (persistent == 'N')
                type = get_type("N");
        else {
-               ti->error = "Persistent flag is not P or N";
+               ti->error = "Exception store type is not P or N";
                r = -EINVAL;
                goto bad_type;
        }
@@ -233,7 +233,7 @@ int dm_exception_store_create(struct dm_target *ti, int argc, char **argv,
        if (r)
                goto bad;
 
-       r = type->ctr(tmp_store, 0, NULL);
+       r = type->ctr(tmp_store, (strlen(argv[0]) > 1 ? &argv[0][1] : NULL));
        if (r) {
                ti->error = "Exception store type constructor failed";
                goto bad;

diff --git a/drivers/md/dm-exception-store.h b/drivers/md/dm-exception-store.h
index 0b2536247cf55a3215223b8b0c72ff29a629b87a..fae34e7a0b1e4e4d60b5867eff9422e432fba83b 100644 (file)
--- a/drivers/md/dm-exception-store.h
+++ b/drivers/md/dm-exception-store.h
@@ -42,8 +42,7 @@ struct dm_exception_store_type {
        const char *name;
        struct module *module;
 
-       int (*ctr) (struct dm_exception_store *store,
-                   unsigned argc, char **argv);
+       int (*ctr) (struct dm_exception_store *store, char *options);
 
        /*
         * Destroys this object when you've finished with it.
@@ -123,6 +122,8 @@ struct dm_exception_store {
        unsigned chunk_shift;
 
        void *context;
+
+       bool userspace_supports_overflow;
 };
 
 /*

diff --git a/drivers/md/dm-snap-persistent.c b/drivers/md/dm-snap-persistent.c
index bf71583296f732b6b78c71ae67dee5222824b2f8..aeacad9be51dcb1c10c78df1398abddb9e8bc4f1 100644 (file)
--- a/drivers/md/dm-snap-persistent.c
+++ b/drivers/md/dm-snap-persistent.c
@@ -7,6 +7,7 @@
 
 #include "dm-exception-store.h"
 
+#include <linux/ctype.h>
 #include <linux/mm.h>
 #include <linux/pagemap.h>
 #include <linux/vmalloc.h>
@@ -843,8 +844,7 @@ static void persistent_drop_snapshot(struct dm_exception_store *store)
                DMWARN("write header failed");
 }
 
-static int persistent_ctr(struct dm_exception_store *store,
-                         unsigned argc, char **argv)
+static int persistent_ctr(struct dm_exception_store *store, char *options)
 {
        struct pstore *ps;
 
@@ -873,6 +873,16 @@ static int persistent_ctr(struct dm_exception_store *store,
                return -ENOMEM;
        }
 
+       if (options) {
+               char overflow = toupper(options[0]);
+               if (overflow == 'O')
+                       store->userspace_supports_overflow = true;
+               else {
+                       DMERR("Unsupported persistent store option: %s", options);
+                       return -EINVAL;
+               }
+       }
+
        store->context = ps;
 
        return 0;
@@ -888,7 +898,8 @@ static unsigned persistent_status(struct dm_exception_store *store,
        case STATUSTYPE_INFO:
                break;
        case STATUSTYPE_TABLE:
-               DMEMIT(" P %llu", (unsigned long long)store->chunk_size);
+               DMEMIT(" %s %llu", store->userspace_supports_overflow ? "PO" : "P",
+                      (unsigned long long)store->chunk_size);
        }
 
        return sz;

diff --git a/drivers/md/dm-snap-transient.c b/drivers/md/dm-snap-transient.c
index 1ce9a2586e4134a79ec3289808f8229e9aaa2080..9b7c8c8049d6186f54bdfec114c43cb3ce4d77fa 100644 (file)
--- a/drivers/md/dm-snap-transient.c
+++ b/drivers/md/dm-snap-transient.c
@@ -70,8 +70,7 @@ static void transient_usage(struct dm_exception_store *store,
        *metadata_sectors = 0;
 }
 
-static int transient_ctr(struct dm_exception_store *store,
-                        unsigned argc, char **argv)
+static int transient_ctr(struct dm_exception_store *store, char *options)
 {
        struct transient_c *tc;
 

diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index c0bcd6516dfe17f8e7a06ec8c66d1e1d5801f133..c06b74e91cd6aeef00ef4eefae9953d4d8c8f91b 100644 (file)
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -1098,7 +1098,7 @@ static void stop_merge(struct dm_snapshot *s)
 }
 
 /*
- * Construct a snapshot mapping: <origin_dev> <COW-dev> <p/n> <chunk-size>
+ * Construct a snapshot mapping: <origin_dev> <COW-dev> <p|po|n> <chunk-size>
  */
 static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 {
@@ -1302,6 +1302,7 @@ static void __handover_exceptions(struct dm_snapshot *snap_src,
 
        u.store_swap = snap_dest->store;
        snap_dest->store = snap_src->store;
+       snap_dest->store->userspace_supports_overflow = u.store_swap->userspace_supports_overflow;
        snap_src->store = u.store_swap;
 
        snap_dest->store->snap = snap_dest;
@@ -1739,8 +1740,11 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio)
 
                        pe = __find_pending_exception(s, pe, chunk);
                        if (!pe) {
-                               s->snapshot_overflowed = 1;
-                               DMERR("Snapshot overflowed: Unable to allocate exception.");
+                               if (s->store->userspace_supports_overflow) {
+                                       s->snapshot_overflowed = 1;
+                                       DMERR("Snapshot overflowed: Unable to allocate exception.");
+                               } else
+                                       __invalidate_snapshot(s, -ENOMEM);
                                r = -EIO;
                                goto out_unlock;
                        }
@@ -2365,7 +2369,7 @@ static struct target_type origin_target = {
 
 static struct target_type snapshot_target = {
        .name    = "snapshot",
-       .version = {1, 14, 0},
+       .version = {1, 15, 0},
        .module  = THIS_MODULE,
        .ctr     = snapshot_ctr,
        .dtr     = snapshot_dtr,
@@ -2379,7 +2383,7 @@ static struct target_type snapshot_target = {
 
 static struct target_type merge_target = {
        .name    = dm_snapshot_merge_target_name,
-       .version = {1, 3, 0},
+       .version = {1, 4, 0},
        .module  = THIS_MODULE,
        .ctr     = snapshot_ctr,
        .dtr     = snapshot_dtr,