Add zgenhostid utility script

Turning the multihost property on requires that a hostid be set to allow
ZFS to determine when a foreign system is attemping to import a pool.
The error message instructing the user to set a hostid refers to
genhostid(1).

Genhostid(1) is not available on SUSE Linux.  This commit adds a script
modeled after genhostid(1) for those users.

Zgenhostid checks for an /etc/hostid file; if it does not exist, it
creates one and stores a value.  If the user has provided a hostid as an
argument, that value is used.  Otherwise, a random hostid is generated
and stored.

This differs from the CENTOS 6/7 versions of genhostid, which overwrite
the /etc/hostid file even though their manpages state otherwise.

A man page for zgenhostid is added. The one for genhostid is in (1), but
I put zgenhostid in (8) because I believe it's more appropriate.

The mmp tests are modified to use zgenhostid to set the hostid instead
of using the spl_hostid module parameter.  zgenhostid will not replace
an existing /etc/hostid file, so new mmp_clear_hostid calls are
required.

Reviewed-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Olaf Faaland <faaland1@llnl.gov>
Closes #6358
Closes #6379

tests/zfs-tests/include/commands.cfg

@@ -141,6 +141,7 @@ export ZFS_FILES='zdb
     arcstat.py
     dbufstat.py
     zed
+    zgenhostid
     zstreamdump'
 
 export ZFSTEST_FILES='chg_usr_exec

tests/zfs-tests/tests/functional/mmp/mmp.kshlib

@@ -79,12 +79,7 @@ function mmp_set_hostid
 {
 	typeset hostid=$1
 
-	a=${hostid:6:2}
-	b=${hostid:4:2}
-	c=${hostid:2:2}
-	d=${hostid:0:2}
-
-	printf "\\x$a\\x$b\\x$c\\x$d" >$HOSTID_FILE
+	zgenhostid $1
 
 	if [ $(hostid) != "$hostid" ]; then
 		return 1
@@ -107,10 +102,12 @@ function mmp_pool_create # pool dir
 	log_must mkdir -p $dir
 	log_must truncate -s $MINVDEVSIZE $dir/vdev1 $dir/vdev2
 
+	log_must mmp_clear_hostid
 	log_must mmp_set_hostid $HOSTID1
 	log_must zpool create -f $pool mirror $dir/vdev1 $dir/vdev2
 	log_must zpool set multihost=on $pool
 	log_must zpool export $pool
+	log_must mmp_clear_hostid
 	log_must mmp_set_hostid $HOSTID2
 
 	log_note "Starting ztest in the background as hostid $HOSTID1"
@@ -146,6 +143,7 @@ function mmp_pool_set_hostid # pool hostid
 	typeset pool=$1
 	typeset hostid=$2
 
+	log_must mmp_clear_hostid
 	log_must mmp_set_hostid $hostid
 	log_must zpool export $pool
 	log_must zpool import $pool

tests/zfs-tests/tests/functional/mmp/mmp_active_import.ksh

@@ -86,6 +86,7 @@ log_must mmp_set_hostid $HOSTID1
 MMP_IMPORTED_MSG="The pool can be imported"
 log_must check_pool_import $MMP_POOL "-d $MMP_DIR" "action" $MMP_IMPORTED_MSG
 
+log_must mmp_clear_hostid
 log_must mmp_set_hostid $HOSTID2
 MMP_IMPORTED_MSG="The pool was last accessed by another system."
 log_must check_pool_import $MMP_POOL "-d $MMP_DIR" "status" $MMP_IMPORTED_MSG

tests/zfs-tests/tests/functional/mmp/mmp_exported_import.ksh

@@ -62,6 +62,7 @@ done
 for opt in "" "-f"; do
 	log_must mmp_pool_set_hostid $TESTPOOL $HOSTID1
 	log_must zpool export $TESTPOOL
+	log_must mmp_clear_hostid
 	log_must mmp_set_hostid $HOSTID2
 	log_must import_no_activity_check $TESTPOOL $opt
 done
@@ -87,6 +88,7 @@ done
 for opt in "" "-f"; do
 	log_must mmp_pool_set_hostid $TESTPOOL $HOSTID1
 	log_must zpool export $TESTPOOL
+	log_must mmp_clear_hostid
 	log_must mmp_set_hostid $HOSTID2
 	log_must import_no_activity_check $TESTPOOL $opt
 done

tests/zfs-tests/tests/functional/mmp/mmp_inactive_import.ksh

@@ -60,6 +60,7 @@ done
 
 # 3. Verify multihost=off and hostids differ (no activity check)
 log_must zpool export -F $TESTPOOL
+log_must mmp_clear_hostid
 log_must mmp_set_hostid $HOSTID2
 log_mustnot import_no_activity_check $TESTPOOL ""
 log_must import_no_activity_check $TESTPOOL "-f"
@@ -81,6 +82,7 @@ done
 
 # 6. Verify multihost=on and hostids differ (activity check)
 log_must zpool export -F $TESTPOOL
+log_must mmp_clear_hostid
 log_must mmp_set_hostid $HOSTID2
 log_mustnot import_activity_check $TESTPOOL ""
 log_must import_activity_check $TESTPOOL "-f"