Allow an externally managed array to be marked readonly

If the metadata_version is
    -mdXXX/whatever
rather than
    /mdXXX/whatever

then the array is readonly and should be left alone by mdmon.

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

Manage.c

@@ -45,11 +45,54 @@ int Manage_ro(char *devname, int fd, int readonly)
 	 *
 	 */
 	mdu_array_info_t array;
+	struct mdinfo *mdi;
 
 	if (md_get_version(fd) < 9000) {
 		fprintf(stderr, Name ": need md driver version 0.90.0 or later\n");
 		return 1;
 	}
+	/* If this is an externally-manage array, we need to modify the
+	 * metadata_version so that mdmon doesn't undo our change.
+	 */
+	mdi = sysfs_read(fd, -1, GET_LEVEL|GET_VERSION);
+	if (mdi &&
+	    mdi->array.major_version == -1 &&
+	    mdi->array.level > 0 &&
+	    is_subarray(mdi->text_version)) {
+		char vers[64];
+		strcpy(vers, "external:");
+		strcat(vers, mdi->text_version);
+		if (readonly > 0) {
+			int rv;
+			/* We set readonly ourselves. */
+			vers[9] = '-';
+			sysfs_set_str(mdi, NULL, "metadata_version", vers);
+
+			close(fd);
+			rv = sysfs_set_str(mdi, NULL, "array_state", "readonly");
+
+			if (rv < 0) {
+				fprintf(stderr, Name ": failed to set readonly for %s: %s\n",
+					devname, strerror(errno));
+
+				vers[9] = mdi->text_version[0];
+				sysfs_set_str(mdi, NULL, "metadata_version", vers);
+				return 1;
+			}
+		} else {
+			char *cp;
+			/* We cannot set read/write - must signal mdmon */
+			vers[9] = '/';
+			sysfs_set_str(mdi, NULL, "metadata_version", vers);
+
+			cp = strchr(vers+10, '/');
+			if (*cp)
+				*cp = 0;
+			ping_monitor(vers+10);
+		}
+		return 0;
+	}
+
 	if (ioctl(fd, GET_ARRAY_INFO, &array)) {
 		fprintf(stderr, Name ": %s does not appear to be active.\n",
 			devname);

managemon.c

@@ -460,6 +460,7 @@ static void manage_new(struct mdstat_ent *mdstat,
 	new->action_fd = sysfs_open(new->devnum, NULL, "sync_action");
 	new->info.state_fd = sysfs_open(new->devnum, NULL, "array_state");
 	new->resync_start_fd = sysfs_open(new->devnum, NULL, "resync_start");
+	new->metadata_fd = sysfs_open(new->devnum, NULL, "metadata_version");
 	get_resync_start(new);
 	dprintf("%s: inst: %d action: %d state: %d\n", __func__, atoi(inst),
 		new->action_fd, new->info.state_fd);

mdadm.h

@@ -807,7 +807,14 @@ static inline int ROUND_UP(int a, int base)
 
 static inline int is_subarray(char *vers)
 {
-	return (*vers == '/');
+	/* The version string for a 'subarray' (an array in a container)
+	 * is 
+	 *    /containername/componentname    for normal read-write arrays
+	 *    -containername/componentname    for read-only arrays.
+	 * containername is e.g. md0, md_d1
+	 * componentname is dependant on the metadata. e.g. '1' 'S1' ...
+	 */
+	return (*vers == '/' || *vers == '-');
 }
 
 #define	LEVEL_MULTIPATH		(-4)

mdmon.h

@@ -19,6 +19,7 @@ struct active_array {
 
 	int action_fd;
 	int resync_start_fd;
+	int metadata_fd; /* for monitoring rw/ro status */
 
 	enum array_state prev_state, curr_state, next_state;
 	enum sync_action prev_action, curr_action, next_action;

monitor.c

@@ -238,15 +238,21 @@ static int read_and_act(struct active_array *a)
 	}
 
 	if (a->curr_state == readonly) {
-		/* Well, I'm ready to handle things, so
-		 * read-auto is OK. FIXME what if we really want
-		 * readonly ???
+		/* Well, I'm ready to handle things.  If readonly
+		 * wasn't requested, transition to read-auto.
 		 */
-		get_resync_start(a);
-		if (a->container->ss->set_array_state(a, 2))
-			a->next_state = read_auto; /* array is clean */
-		else
-			a->next_state = active; /* Now active for recovery etc */
+		char buf[64];
+		read_attr(buf, sizeof(buf), a->metadata_fd);
+		if (strncmp(buf, "external:-", 10) == 0) {
+			/* explicit request for readonly array.  Leave it alone */
+			;
+		} else {
+			get_resync_start(a);
+			if (a->container->ss->set_array_state(a, 2))
+				a->next_state = read_auto; /* array is clean */
+			else
+				a->next_state = active; /* Now active for recovery etc */
+		}
 	}
 
 	if (!deactivate &&