From: Milan Broz <mbroz@redhat.com>
Subject: [RHEL 5.1 PATCH] dm: allow invalid snapshots to be activated
Date: Thu, 28 Jun 2007 20:30:29 +0200
Bugzilla: 244215
Message-Id: <4683FE45.9030003@redhat.com>
Changelog: [dm] allow invalid snapshots to be activated


RHEL5.1 device mapper: Allow invalid snapshots to be activated instead of failing.

Resolves:
 rhbz#244215 (exception+) 
	- activating of snapshot marked invalid causes incorrect mapping
 
Patch is currently in -mm tree.

This patch allows userspace to reinstate any given snapshot state - 
for example after an unscheduled reboot.

Currently device mapper does not allow activation of overfilled
(invalid) snapshot and fails.
This can lead to reporting incorrect attributes in userspace 
(e.g. no invalid flag in lvs).

Patch compiled and tested (testcase in bugzilla).

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

Index: linux-2.6.18/drivers/md/dm-exception-store.c
===================================================================
--- linux-2.6.18.orig/drivers/md/dm-exception-store.c	2007-06-28 18:34:08.000000000 +0200
+++ linux-2.6.18/drivers/md/dm-exception-store.c	2007-06-28 18:41:49.000000000 +0200
@@ -456,11 +456,6 @@ 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);
@@ -468,6 +463,12 @@ 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-2.6.18/drivers/md/dm-snap.c
===================================================================
--- linux-2.6.18.orig/drivers/md/dm-snap.c	2007-06-28 18:34:03.000000000 +0200
+++ linux-2.6.18/drivers/md/dm-snap.c	2007-06-28 18:41:49.000000000 +0200
@@ -522,9 +522,12 @@ 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);