Fix 'zpool import' detection issues

This patch addresses multiple 'zpool import' block device
indentification problems which are most likely to occur on a
system configured to use blkid, by_vdev paths, multipath and
failover.  The symptom most commonly observed is the import
uses different path names to import the pool than would
normally be expected.

* When using blkid to identify vdevs the listed devices may
be added to the cache in any order.  In order to apply the
preferred search order heuristic a zfs_path_order() function
was added to calculate the order given full path names.

* Since it's possible to have multiple block devices with
different vdev guids which refer to the same ZPOOL_CONFIG_PATH
the slice cache must be indexed by guid and name.  By avoiding
collisions the preferred ordering can be maintaining even
when multiple block devices claim the same ZPOOL_CONFIG_PATH.
The preferred sorting by partition was never benefitial for
a Linux system and was removed as part of this change.

* When adding entries to the blkid cache avl_find/avl_insert
are used instead of avl_add because collisions are possible
and must be handled gracefully.

* For pools using multipath devices there are, at a minimum,
three devices where a vdev label may be read.  They are the
dm-* device and each underlying /dev/sd* device.  Due to the
way the block cache is implemented each of these devices may
have a different cached copy of the vdev label.  This can
result in "ghost pools" which appear to persist even after
a 'zpool labelclear' has been done to the dm-* device.  In
order to prevent this the vdev label is read with O_DIRECT
in order to bypass any caching to get the on-disk version.

* When opening a block device verify that vdev guid read from
the disk matches the expected vdev guid.  This allows for bad
labels to be filtered out.

Reviewed-by: Tony Hutter <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes #5359 

1 files changed, 39 insertions, 0 deletions

diff --git a/lib/libzfs/libzfs_util.c b/lib/libzfs/libzfs_util.c
index 6f5dae6c3..95ec0b49d 100644
--- a/lib/libzfs/libzfs_util.c
+++ b/lib/libzfs/libzfs_util.c
@@ -1137,6 +1137,45 @@ zfs_strcmp_pathname(char *name, char *cmp, int wholedisk)
 }
 
 /*
+ * Given a full path to a device determine if that device appears in the
+ * import search path.  If it does return the first match and store the
+ * index in the passed 'order' variable, otherwise return an error.
+ */
+int
+zfs_path_order(char *name, int *order)
+{
+	int i = 0, error = ENOENT;
+	char *dir, *env, *envdup;
+
+	env = getenv("ZPOOL_IMPORT_PATH");
+	if (env) {
+		envdup = strdup(env);
+		dir = strtok(envdup, ":");
+		while (dir) {
+			if (strncmp(name, dir, strlen(dir)) == 0) {
+				*order = i;
+				error = 0;
+				break;
+			}
+			dir = strtok(NULL, ":");
+			i++;
+		}
+		free(envdup);
+	} else {
+		for (i = 0; i < DEFAULT_IMPORT_PATH_SIZE; i++) {
+			if (strncmp(name, zpool_default_import_path[i],
+			    strlen(zpool_default_import_path[i])) == 0) {
+				*order = i;
+				error = 0;
+				break;
+			}
+		}
+	}
+
+	return (error);
+}
+
+/*
  * Initialize the zc_nvlist_dst member to prepare for receiving an nvlist from
  * an ioctl().
  */