config: restore the possibility of a NULL homehost

As homehost defaults to the system name it is not possible to specify
a NULL homehost.

This patch restored this ability with either --homehost="" or
--homehost="<none>".

This allows the creation of v1.x arrays without a "hostname:"
prefix in the name.

Signed-off-by: NeilBrown <neilb@suse.de>

config.c

@@ -589,9 +589,12 @@ void homehostline(char *line)
 	for (w=dl_next(line); w != line ; w=dl_next(w)) {
 		if (strcasecmp(w, "<ignore>")==0)
 			require_homehost = 0;
-		else if (home_host == NULL)
-			home_host = strdup(w);
-		else
+		else if (home_host == NULL) {
+			if (strcasecmp(w, "<none>")==0)
+				home_host = strdup("");
+			else
+				home_host = strdup(w);
+		}else
 			fprintf(stderr, Name ": excess host name on HOMEHOST line: %s - ignored\n",
 				w);
 	}

mdadm.c

@@ -1167,12 +1167,16 @@ int main(int argc, char *argv[])
 
 	if (homehost == NULL)
 		homehost = conf_get_homehost(&require_homehost);
-	if (homehost == NULL || strcmp(homehost, "<system>")==0) {
+	if (homehost == NULL || strcasecmp(homehost, "<system>")==0) {
 		if (gethostname(sys_hostname, sizeof(sys_hostname)) == 0) {
 			sys_hostname[sizeof(sys_hostname)-1] = 0;
 			homehost = sys_hostname;
 		}
 	}
+	if (homehost && (!homehost[0] || strcasecmp(homehost, "<none>") == 0)) {
+		homehost = NULL;
+		require_homehost = 0;
+	}
 
 	if ((mode != MISC || devmode != 'E') &&
 	    geteuid() != 0) {

mdadm.conf.5

@@ -339,14 +339,15 @@ line gives a default value for the
 .B \-\-homehost=
 option to mdadm.  There should normally be only one other word on the line.
 It should either be a host name, or one of the special words
-.B <system>
+.BR <system>,
+.B <none>
 and
 .BR <ignore> .
 If
 .B <system>
 is given, then the
 .BR gethostname ( 2 )
-systemcall is used to get the host name.
+systemcall is used to get the host name.  This is the default.
 
 If
 .B <ignore>
@@ -362,6 +363,12 @@ more that one other word on the
 .B HOMEHOST
 line.
 
+If
+.B <none>
+is given, then the default of using
+.BR gethostname ( 2 )
+is over-ridden and no homehost name is assumed.
+
 When arrays are created, this host name will be stored in the
 metadata.  When arrays are assembled using auto-assembly, arrays which
 do not record the correct homehost name in their metadata will be

super0.c

@@ -541,7 +541,7 @@ static int update_super0(struct supertype *st, struct mdinfo *info,
 		sb->state &= ~(1<<MD_SB_CLEAN);
 		sb->recovery_cp = 0;
 	} else if (strcmp(update, "homehost") == 0 &&
-	    homehost) {
+		   homehost) {
 		uuid_set = 0;
 		update = "uuid";
 		info->uuid[0] = sb->set_uuid0;

super1.c

@@ -772,7 +772,7 @@ static int update_super1(struct supertype *st, struct mdinfo *info,
 	} else if (strcmp(update, "no-bitmap") == 0) {
 		sb->feature_map &= ~__cpu_to_le32(MD_FEATURE_BITMAP_OFFSET);
 	} else if (strcmp(update, "homehost") == 0 &&
-	    homehost) {
+		   homehost) {
 		char *c;
 		update = "name";
 		c = strchr(sb->set_name, ':');