[dm-devel] [PATCH v4 3/3] multipathd: skip spurious event message for blacklisted paths

[Mauricio Faria de Oliveira]

Currently, multipath still prints the 'spurious uevent, path not found'
message if a path is blacklisted by something different than a devnode
in the 'change' uevent handling. (uev_trigger() calls filter_devnode()).

Thus blacklisting by vendor/product, wwid, and udev property still get
that message in the system log for paths that are explicitly marked to
be ignored (since it's verbosity level 0).

This problem happens on common scenarios such as creating filesystems
on a blacklisted device (e.g., mkfs.* /dev/sdX), which is usually run
several times on test environments, and the error message may mislead
the error checker/monitor tools with false negatives.

This patch resolves it by checking alloc_path_with_pathinfo()/pathinfo()
for PATHINFO_SKIPPED with just enough device information flags for
blacklist verification -- and it prints a debug message (verbosity
level 3) instead of an error message since this case is not an error.

Even though this introduces a bit of overhead (to get the path info),
it only happens in a corner case of an error path; so, not a problem.

Test-cases (on QEMU):
----------

Several versions of /etc/multipath.conf:

  blacklist {
      devnode "sdb"
  }

  blacklist {
      property "ID_SERIAL"
  }

  blacklist {
      wwid "0QEMU_QEMU_HARDDISK_drive-scsi0-0-0-1"
  }

  blacklist {
      device {
          vendor "QEMU"
      }
  }

Either command can be used to generate a 'change' uevent:

  # echo change > /sys/block/sdb/uevent

  # mkfs.ext3 -F /dev/sdb

The output of multipathd is monitored with:

  # multipathd -d -s
  ...

Without the patch, only the devnode blacklisting is silent;
all other cases (property, wwid, device) print the message:

  sdb: spurious uevent, path not found

With the patch applied, no message is printed by default
(that is, verbosity level 2) in any case.

With verbosity level 3 (debug), the following messages
are printed, according to the performed test-case:

  uevent 'change' from '/devices/.../block/sdb'
  Forwarding 1 uevents
  < and either of >

  sdb: device node name blacklisted

  sdb: udev property ID_SERIAL blacklisted
  sdb: spurious uevent, path is blacklisted

  sdb: wwid 0QEMU_QEMU_HARDDISK_drive-scsi0-0-0-1 blacklisted
  sdb: spurious uevent, path is blacklisted

  (null): (QEMU:QEMU HARDDISK) vendor/product blacklisted
  sdb: spurious uevent, path is blacklisted

Signed-off-by: Mauricio Faria de Oliveira <mauricfo at linux.vnet.ibm.com>
Reported-by: Yueh Chyong (Ida) Jackson <idaj at us.ibm.com>
Reviewed-by: Hannes Reinecke <hare at suse.com>
---
 multipathd/main.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/multipathd/main.c b/multipathd/main.c
index d6f081f2f83a..adc325898c76 100644
--- a/multipathd/main.c
+++ b/multipathd/main.c
@@ -1010,8 +1010,23 @@ uev_update_path (struct uevent *uev, struct vectors * vecs)
 	}
 out:
 	lock_cleanup_pop(vecs->lock);
-	if (!pp)
+	if (!pp) {
+		/* If the path is blacklisted, print a debug/non-default verbosity message. */
+		if (uev->udev) {
+			int flag = DI_SYSFS | DI_WWID;
+
+			conf = get_multipath_config();
+			retval = alloc_path_with_pathinfo(conf, uev->udev, flag, NULL);
+			put_multipath_config(conf);
+
+			if (retval == PATHINFO_SKIPPED) {
+				condlog(3, "%s: spurious uevent, path is blacklisted", uev->kernel);
+				return 0;
+			}
+		}
+
 		condlog(0, "%s: spurious uevent, path not found", uev->kernel);
+	}
 
 	return retval;
 }
-- 
1.8.3.1