It's not enough to check for the kernel module in the case of cluster

mirrors, we must also check that the log daemon (cmirrord) is running.
The log module can be auto-loaded, but the daemon cannot be
"auto-started".  Failing to check for the daemon produces cryptic
messages that customers have a hard time deciphering.  (The system
messages do report that the log daemon is not running, but people
don't seem to find this message easily.)

Here are examples of what is printed when the module is available,
but the log daemon has not been started.

[root@bp-01 LVM2]# lvcreate -m1 -l1 -n lv vg
  Shared cluster mirrors are not available.

[root@bp-01 LVM2]# lvcreate -m1 -l1 -n lv vg -v
    Setting logging type to disk
    Finding volume group "vg"
    Archiving volume group "vg" metadata (seqno 3).
    Creating logical volume lv
    Executing: /sbin/modprobe dm-log-userspace
    Cluster mirror log daemon is not running
  Shared cluster mirrors are not available.
    Creating volume group backup "/etc/lvm/backup/vg" (seqno 4).

1 files changed, 26 insertions, 0 deletions

diff --git a/libdm/libdm-file.c b/libdm/libdm-file.c
index ae2da76d..8dbf099c 100644
--- a/libdm/libdm-file.c
+++ b/libdm/libdm-file.c
@@ -166,3 +166,29 @@ fail:
 
 	return 0;
 }
+
+int dm_daemon_is_running(const char* lockfile)
+{
+       int fd;
+       struct flock lock;
+
+       if((fd = open(lockfile, O_RDONLY)) < 0)
+               return 0;
+
+       lock.l_type = F_WRLCK;
+       lock.l_start = 0;
+       lock.l_whence = SEEK_SET;
+       lock.l_len = 0;
+       if (fcntl(fd, F_GETLK, &lock) < 0) {
+               log_error("Cannot check lock status of lockfile [%s], error was [%s]",
+                         lockfile, strerror(errno));
+               if (close(fd))
+                       stack;
+               return 0;
+       }
+
+       if (close(fd))
+               stack;
+
+       return (lock.l_type == F_UNLCK) ? 0 : 1;
+}