[2.6.23 PATCH 09/18] dm snapshot: permit invalid activation

[Alasdair G Kergon <agk@redhat.com>]

From: Milan Broz <mbroz@redhat.com>

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.

Signed-off-by: Milan Broz <mbroz@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

---
 drivers/md/dm-exception-store.c |   11 ++++++-----
 drivers/md/dm-snap.c            |    5 ++++-
 2 files changed, 10 insertions(+), 6 deletions(-)

Index: linux/drivers/md/dm-exception-store.c
===================================================================
--- linux.orig/drivers/md/dm-exception-store.c	2007-07-11 21:37:44.000000000 +0100
+++ linux/drivers/md/dm-exception-store.c	2007-07-11 21:37:45.000000000 +0100
@@ -489,11 +489,6 @@ static int persistent_read_metadata(stru
 		/*
 		 * 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(stru
 		}
 
 		/*
+		 * Metadata are valid, but snapshot is invalidated
+		 */
+		if (!ps->valid)
+			return 1;
+
+		/*
 		 * Read the metadata.
 		 */
 		r = read_exceptions(ps);
Index: linux/drivers/md/dm-snap.c
===================================================================
--- linux.orig/drivers/md/dm-snap.c	2007-07-11 21:37:38.000000000 +0100
+++ linux/drivers/md/dm-snap.c	2007-07-11 21:37:45.000000000 +0100
@@ -523,9 +523,12 @@ static int snapshot_ctr(struct dm_target
 
 	/* 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);