lvm2/avoid_reading_failed_dev_in_mirrored_log.diff

commit b248ba0a396d7fc9a459eea02cfdc70b33ce3441
Author: Jonathan Brassow <jbrassow@redhat.com>
Date:   Thu Oct 25 00:42:45 2012 -0500

    mirror:  Avoid reading mirrors with failed devices in mirrored log
    
    Commit 9fd7ac7d035f0b2f8dcc3cb19935eb181816bd76 did not handle mirrors
    that contained mirrored logs.  This is because the status line of the
    mirror does not give an indication of the health of the mirrored log,
    as you can see here:
            [root@bp-01 lvm2]# dmsetup status vg-lv vg-lv_mlog
            vg-lv: 0 409600 mirror 2 253:6 253:7 400/400 1 AA 3 disk 253:5 A
            vg-lv_mlog: 0 8192 mirror 2 253:3 253:4 7/8 1 AD 1 core
    Thus, the possibility for LVM commands to hang still persists when mirror
    have mirrored logs.  I discovered this while performing some testing that
    does polling with 'pvs' while doing I/O and killing devices.  The 'pvs'
    managed to get between the mirrored log device failure and the attempt
    by dmeventd to repair it.  The result was a very nasty block in LVM
    commands that is very difficult to remove - even for someone who knows
    what is going on.  Thus, it is absolutely essential that the log of a
    mirror be recursively checked for mirror devices which may be failed
    as well.
    
    Despite what the code comment says in the aforementioned commit...
    + * _mirrored_transient_status().  FIXME: It is unable to handle mirrors
    + * with mirrored logs because it does not have a way to get the status of
    + * the mirror that forms the log, which could be blocked.
    ... it is possible to get the status of the log because the log device
    major/minor is given to us by the status output of the top-level mirror.
    We can use that to query the log device for any DM status and see if it
    is a mirror that needs to be bypassed.  This patch does just that and is
    now able to avoid reading from mirrors that have failed devices in a
    mirrored log.

diff --git a/lib/activate/dev_manager.c b/lib/activate/dev_manager.c
index 6cc57d0..40f719e 100644
--- a/lib/activate/dev_manager.c
+++ b/lib/activate/dev_manager.c
@@ -139,6 +139,7 @@ static int _info_run(const char *name, const char *dlid, struct dm_info *info,
  * _parse_mirror_status
  * @mirror_status_string
  * @image_health:  return for allocated copy of image health characters
+ * @log_device: return for 'dev_t' of log device
  * @log_health: NULL if corelog, otherwise alloc'ed log health char
  *
  * This function takes the mirror status string, breaks it up and returns
@@ -149,8 +150,10 @@ static int _info_run(const char *name, const char *dlid, struct dm_info *info,
  * Returns: 1 on success, 0 on failure
  */
 static int _parse_mirror_status(char *mirror_status_str,
-				char **images_health, char **log_health)
+				char **images_health,
+				dev_t *log_dev, char **log_health)
 {
+	int major, minor;
 	char *p = NULL;
 	char **args, **log_args;
 	unsigned num_devs, log_argc;
@@ -174,10 +177,14 @@ static int _parse_mirror_status(char *mirror_status_str,
 		return_0;
 
 	*log_health = NULL;
-	if (!strcmp(log_args[0], "disk") &&
-	    !(*log_health = dm_strdup(log_args[2])))
-		return_0;
-
+	*log_dev = 0;
+	if (!strcmp(log_args[0], "disk")) {
+		if (!(*log_health = dm_strdup(log_args[2])))
+			return_0;
+		if (sscanf(log_args[1], "%d:%d", &major, &minor) != 2)
+			return_0;
+		*log_dev = MKDEV((dev_t)major, minor);
+	}
 	if (!(*images_health = dm_strdup(args[2 + num_devs])))
 		return_0;
 
@@ -199,9 +206,7 @@ static int _parse_mirror_status(char *mirror_status_str,
  * attempting to read a mirror, a circular dependency would be created.)
  *
  * This function is a slimmed-down version of lib/mirror/mirrored.c:
- * _mirrored_transient_status().  FIXME: It is unable to handle mirrors
- * with mirrored logs because it does not have a way to get the status of
- * the mirror that forms the log, which could be blocked.
+ * _mirrored_transient_status().
  *
  * If a failed device is detected in the status string, then it must be
  * determined if 'block_on_error' or 'handle_errors' was used when
@@ -217,23 +222,17 @@ static int _ignore_blocked_mirror_devices(struct device *dev,
 					  char *mirror_status_str)
 {
 	unsigned i, check_for_blocking = 0;
+	dev_t log_dev;
 	char *images_health, *log_health;
-
 	uint64_t s,l;
 	char *params, *target_type = NULL;
 	void *next = NULL;
 	struct dm_task *dmt;
 
 	if (!_parse_mirror_status(mirror_status_str,
-				  &images_health, &log_health))
+				  &images_health, &log_dev, &log_health))
 		goto_out;
 
-	if (log_health && (log_health[0] != 'A')) {
-		log_debug("%s: Mirror log device marked as failed",
-			  dev_name(dev));
-		check_for_blocking = 1;
-	}
-
 	for (i = 0; images_health[i]; i++)
 		if (images_health[i] != 'A') {
 			log_debug("%s: Mirror image %d marked as failed",
@@ -241,6 +240,29 @@ static int _ignore_blocked_mirror_devices(struct device *dev,
 			check_for_blocking = 1;
 		}
 
+	if (!check_for_blocking && log_dev) {
+		if (log_health[0] != 'A') {
+			log_debug("%s: Mirror log device marked as failed",
+				  dev_name(dev));
+			check_for_blocking = 1;
+		} else {
+			struct device *tmp_dev;
+			char buf[16];
+
+			if (dm_snprintf(buf, sizeof(buf), "%d:%d",
+					(int)MAJOR(log_dev),
+					(int)MINOR(log_dev)) < 0)
+				goto_out;
+
+			if (!(tmp_dev = dev_create_file(buf, NULL, NULL, 1)))
+				goto_out;
+
+			tmp_dev->dev = log_dev;
+			if (!device_is_usable(tmp_dev))
+				goto_out;
+		}
+	}
+
 	if (!check_for_blocking)
 		return 0;