[dm-devel] [PATCH v2 04/37] libmultipath: never allocate an alias that's already taken

[mwilck at suse.com]

From: Martin Wilck <mwilck at suse.com>

If the bindings file is changed in a way that multipathd can't handle
(e.g. by swapping the aliases of two maps), multipathd must not try
to re-use an alias that is already used by another map. Creating
or renaming a map with such an alias will fail. We already avoid
this for some cases, but not for all. Fix it.

Signed-off-by: Martin Wilck <mwilck at suse.com>
Cc: David Bond <dbond at suse.com>
---
 libmultipath/alias.c | 33 ++++++++++++++++++++++++---------
 tests/alias.c        |  2 +-
 2 files changed, 25 insertions(+), 10 deletions(-)

diff --git a/libmultipath/alias.c b/libmultipath/alias.c
index 68f5d84..b5248f2 100644
--- a/libmultipath/alias.c
+++ b/libmultipath/alias.c
@@ -120,7 +120,7 @@ static bool alias_already_taken(const char *alias, const char *map_wwid)
 		if (dm_get_uuid(alias, wwid, sizeof(wwid)) == 0 &&
 		    strncmp(map_wwid, wwid, sizeof(wwid)) == 0)
 			return false;
-		condlog(3, "%s: alias '%s' already taken, but not in bindings file. reselecting alias",
+		condlog(3, "%s: alias '%s' already taken, reselecting alias",
 			map_wwid, alias);
 		return true;
 	}
@@ -359,32 +359,47 @@ char *get_user_friendly_alias(const char *wwid, const char *file, const char *al
 	rlookup_binding(f, buff, alias_old);
 
 	if (strlen(buff) > 0) {
-		/* if buff is our wwid, it's already
-		 * allocated correctly
-		 */
+		/* If buff is our wwid, it's already allocated correctly. */
 		if (strcmp(buff, wwid) == 0) {
 			alias = strdup(alias_old);
 			goto out;
+
 		} else {
 			condlog(0, "alias %s already bound to wwid %s, cannot reuse",
 				alias_old, buff);
-			goto new_alias;
+			goto new_alias;		     ;
 		}
 	}
 
-	id = lookup_binding(f, wwid, &alias, NULL, 0);
+	/*
+	 * Look for an existing alias in the bindings file.
+	 * Pass prefix = NULL, so lookup_binding() won't try to allocate a new id.
+	 */
+	lookup_binding(f, wwid, &alias, NULL, 0);
 	if (alias) {
-		condlog(3, "Use existing binding [%s] for WWID [%s]",
-			alias, wwid);
+		if (alias_already_taken(alias, wwid)) {
+			free(alias);
+			alias = NULL;
+		} else
+			condlog(3, "Use existing binding [%s] for WWID [%s]",
+				alias, wwid);
 		goto out;
 	}
 
-	/* allocate the existing alias in the bindings file */
+	/* alias_old is already taken by our WWID, update bindings file. */
 	id = scan_devname(alias_old, prefix);
 
 new_alias:
 	if (id <= 0) {
+		/*
+		 * no existing alias was provided, or allocating it
+		 * failed. Try a new one.
+		 */
 		id = lookup_binding(f, wwid, &alias, prefix, 1);
+		if (id == 0 && alias_already_taken(alias, wwid)) {
+			free(alias);
+			alias = NULL;
+		}
 		if (id <= 0)
 			goto out;
 		else
diff --git a/tests/alias.c b/tests/alias.c
index 3ca6c28..11f209e 100644
--- a/tests/alias.c
+++ b/tests/alias.c
@@ -398,7 +398,7 @@ static void mock_self_alias(const char *alias, const char *wwid)
 	will_return(__wrap_dm_get_uuid, wwid);
 }
 
-#define USED_STR(alias_str, wwid_str) wwid_str ": alias '" alias_str "' already taken, but not in bindings file. reselecting alias\n"
+#define USED_STR(alias_str, wwid_str) wwid_str ": alias '" alias_str "' already taken, reselecting alias\n"
 
 static void mock_failed_alias(const char *alias, char *msg)
 {
-- 
2.42.0