block monitor: freeze spare assignment for external arrays

In order to support reshape and atomic removal of spares from containers
we need to prevent mdmon from activating spares.  In the reshape case we
additionally need to freeze sync_action while the reshape transaction is
initiated with the kernel and recorded in the metadata.

When reshaping a raid0 array we need to freeze the array *before* it is
transitioned to a redundant raid level.  Since sync_action does not exist
at this point we extend the '-' prefix of a subarray string to flag
mdmon not to activate spares.

Mdadm needs to be reasonably certain that the version of mdmon in the
system honors this 'freeze' indication.  If mdmon is not already active
then we assume the version that gets started is the same as the mdadm
version.  Otherwise, we check the version of mdmon as returned by the
extended ping_monitor() operation.  This is to catch cases where mdadm
is upgraded in the filesystem, but mdmon started in the initramfs is
from a previous release.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 193 insertions, 2 deletions

diff --git a/msg.c b/msg.c
index aabfa8f..bfeadb3 100644
--- a/msg.c
+++ b/msg.c
@@ -135,7 +135,15 @@ int ack(int fd, int tmo)
 int wait_reply(int fd, int tmo)
 {
 	struct metadata_update msg;
-	return receive_message(fd, &msg, tmo);
+	int err = receive_message(fd, &msg, tmo);
+
+	/* mdmon sent extra data, but caller only cares that we got a
+	 * successful reply
+	 */
+	if (err == 0 && msg.len > 0)
+		free(msg.buf);
+
+	return err;
 }
 
 int connect_monitor(char *devname)
@@ -195,7 +203,6 @@ int fping_monitor(int sfd)
 	return err;
 }
 
-
 /* give the monitor a chance to update the metadata */
 int ping_monitor(char *devname)
 {
@@ -206,6 +213,190 @@ int ping_monitor(char *devname)
 	return err;
 }
 
+static char *ping_monitor_version(char *devname)
+{
+	int sfd = connect_monitor(devname);
+	struct metadata_update msg;
+	int err = 0;
+
+	if (sfd < 0)
+		return NULL;
+
+	if (ack(sfd, 20) != 0)
+		err = -1;
+
+	if (!err && receive_message(sfd, &msg, 20) != 0)
+		err = -1;
+
+	close(sfd);
+
+	if (err || !msg.len || !msg.buf)
+		return NULL;
+	return msg.buf;
+}
+
+static int unblock_subarray(struct mdinfo *sra, const int unfreeze)
+{
+	char buf[64];
+	int rc = 0;
+
+	if (sra) {
+		sprintf(buf, "external:%s\n", sra->text_version);
+		buf[9] = '/';
+	} else
+		buf[9] = '-';
+
+	if (buf[9] == '-' ||
+	    sysfs_set_str(sra, NULL, "metadata_version", buf) ||
+	    (unfreeze &&
+	     sysfs_attribute_available(sra, NULL, "sync_action") &&
+	     sysfs_set_str(sra, NULL, "sync_action", "idle")))
+		rc = -1;
+	return rc;
+}
+
+/**
+ * block_monitor - prevent mdmon spare assignment
+ * @container - container to block
+ * @freeze - flag to additionally freeze sync_action
+ *
+ * This is used by the reshape code to freeze the container, and the
+ * auto-rebuild implementation to atomically move spares.  For reshape
+ * we need to freeze sync_action in the auto-rebuild we only need to
+ * block new spare assignment, existing rebuilds can continue
+ */
+int block_monitor(char *container, const int freeze)
+{
+	int devnum = devname2devnum(container);
+	struct mdstat_ent *ent, *e, *e2;
+	struct mdinfo *sra = NULL;
+	char *version = NULL;
+	char buf[64];
+	int rv = 0;
+
+	if (!mdmon_running(devnum)) {
+		/* if mdmon is not active we assume that any instance that is
+		 * later started will match the current mdadm version, if this
+		 * assumption is violated we may inadvertantly rebuild an array
+		 * that was meant for reshape, or start rebuild on a spare that
+		 * was to be moved to another container
+		 */
+		/* pass */;
+	} else {
+		int ver;
+
+		version = ping_monitor_version(container);
+		ver = version ? mdadm_version(version) : -1;
+		free(version);
+		if (ver < 3002000) {
+			fprintf(stderr, Name
+				": mdmon instance for %s cannot be disabled\n",
+				container);
+			return -1;
+		}
+	}
+
+	ent = mdstat_read(0, 0);
+	if (!ent) {
+		fprintf(stderr, Name
+			": failed to read /proc/mdstat while disabling mdmon\n");
+		return -1;
+	}
+
+	/* freeze container contents */
+	for (e = ent; e; e = e->next) {
+		if (!is_container_member(e, container))
+			continue;
+		sysfs_free(sra);
+		sra = sysfs_read(-1, e->devnum, GET_VERSION);
+		if (!sra) {
+			fprintf(stderr, Name
+				": failed to read sysfs for subarray%s\n",
+				to_subarray(e, container));
+			break;
+		}
+		/* can't reshape an array that we can't monitor */
+		if (sra->text_version[0] == '-')
+			break;
+
+		if (freeze && sysfs_freeze_array(sra) < 1)
+			break;
+		/* flag this array to not be modified by mdmon (close race with
+		 * takeover in reshape case and spare reassignment in the
+		 * auto-rebuild case)
+		 */
+		sprintf(buf, "external:%s\n", sra->text_version);
+		buf[9] = '-';
+		if (sysfs_set_str(sra, NULL, "metadata_version", buf))
+			break;
+		ping_monitor(container);
+
+		/* check that we did not race with recovery */
+		if ((freeze &&
+		     !sysfs_attribute_available(sra, NULL, "sync_action")) ||
+		    (freeze &&
+		     sysfs_attribute_available(sra, NULL, "sync_action") &&
+		     sysfs_get_str(sra, NULL, "sync_action", buf, 20) > 0 &&
+		     strcmp(buf, "frozen\n") == 0))
+			/* pass */;
+		else
+			break;
+	}
+
+	if (e) {
+		fprintf(stderr, Name ": failed to freeze subarray%s\n",
+			to_subarray(e, container));
+
+		/* thaw the partially frozen container */
+		for (e2 = ent; e2 && e2 != e; e2 = e2->next) {
+			if (!is_container_member(e2, container))
+				continue;
+			sysfs_free(sra);
+			sra = sysfs_read(-1, e2->devnum, GET_VERSION);
+			if (unblock_subarray(sra, freeze))
+				fprintf(stderr, Name ": Failed to unfreeze %s\n", e2->dev);
+		}
+
+		ping_monitor(container); /* cleared frozen */
+		rv = -1;
+	}
+
+	sysfs_free(sra);
+	free_mdstat(ent);
+	free(container);
+
+	return rv;
+}
+
+void unblock_monitor(char *container, const int unfreeze)
+{
+	struct mdstat_ent *ent, *e;
+	struct mdinfo *sra = NULL;
+
+	ent = mdstat_read(0, 0);
+	if (!ent) {
+		fprintf(stderr, Name
+			": failed to read /proc/mdstat while unblocking container\n");
+		return;
+	}
+
+	/* unfreeze container contents */
+	for (e = ent; e; e = e->next) {
+		if (!is_container_member(e, container))
+			continue;
+		sysfs_free(sra);
+		sra = sysfs_read(-1, e->devnum, GET_VERSION);
+		if (unblock_subarray(sra, unfreeze))
+			fprintf(stderr, Name ": Failed to unfreeze %s\n", e->dev);
+	}
+	ping_monitor(container);
+
+	sysfs_free(sra);
+	free_mdstat(ent);
+}
+
+
+
 /* give the manager a chance to view the updated container state.  This
  * would naturally happen due to the manager noticing a change in
  * /proc/mdstat; however, pinging encourages this detection to happen