zed: Fix config_sync autoexpand flood

Users were seeing floods of `config_sync` events when autoexpand was
enabled.  This happened because all "disk status change" udev events
invoke the autoexpand codepath, which calls zpool_relabel_disk(),
which in turn cause another "disk status change" event to happen,
in a feedback loop.  Note that "disk status change" happens every time
a user calls close() on a block device.

This commit breaks the feedback loop by only allowing an autoexpand
to happen if the disk actually changed size.

Fixes: openzfs#7132
Fixes: openzfs#7366

Signed-off-by: Tony Hutter <hutter2@llnl.gov>

cmd/zed/agents/zfs_mod.c

@@ -894,14 +894,55 @@ zfs_deliver_check(nvlist_t *nvl)
 	return (0);
 }
 
+/*
+ * Given a path to a vdev, lookup the vdev's physical size from its
+ * config nvlist.
+ *
+ * Returns the vdev's physical size in bytes on success, 0 on error.
+ */
+static uint64_t
+vdev_size_from_config(zpool_handle_t *zhp, const char *vdev_path)
+{
+	nvlist_t *nvl = NULL;
+	boolean_t avail_spare, l2cache, log;
+	vdev_stat_t *vs = NULL;
+       uint_t c;
+
+	nvl = zpool_find_vdev(zhp, vdev_path, &avail_spare, &l2cache, &log);
+	if (!nvl)
+		return 0;
+
+	verify(nvlist_lookup_uint64_array(nvl, ZPOOL_CONFIG_VDEV_STATS,
+	    (uint64_t **)&vs, &c) == 0);
+	if (!vs) {
+		zed_log_msg(LOG_INFO, "%s: no nvlist for '%s'",
+		    __func__, vdev_path);
+		return 0;
+	}
+
+	return vs->vs_pspace;
+}
+
 static int
 zfsdle_vdev_online(zpool_handle_t *zhp, void *data)
 {
-	char *devname = data;
 	boolean_t avail_spare, l2cache;
+	nvlist_t *udev_nvl = data;
 	nvlist_t *tgt;
 	int error;
 
+	char *tmp_devname, devname[MAXPATHLEN];
+       uint64_t guid;
+
+	if (nvlist_lookup_uint64(udev_nvl, ZFS_EV_VDEV_GUID, &guid) == 0) {
+		sprintf(devname, "%llu", (u_longlong_t)guid);
+	} else if (nvlist_lookup_string(udev_nvl, DEV_PHYS_PATH, &tmp_devname) == 0) {
+		strlcpy(devname, tmp_devname, MAXPATHLEN);
+		zfs_append_partition(devname, MAXPATHLEN);
+	} else {
+		zed_log_msg(LOG_INFO, "%s: no guid or physpath", __func__);
+	}
+
 	zed_log_msg(LOG_INFO, "zfsdle_vdev_online: searching for '%s' in '%s'",
 	    devname, zpool_get_name(zhp));
 
@@ -953,12 +994,44 @@ zfsdle_vdev_online(zpool_handle_t *zhp, void *data)
 			vdev_state_t newstate;
 
 			if (zpool_get_state(zhp) != POOL_STATE_UNAVAIL) {
-				error = zpool_vdev_online(zhp, fullpath, 0,
-				    &newstate);
-				zed_log_msg(LOG_INFO, "zfsdle_vdev_online: "
-				    "setting device '%s' to ONLINE state "
-				    "in pool '%s': %d", fullpath,
-				    zpool_get_name(zhp), error);
+				/*
+				 * If this disk size has not changed, then there's
+				 * no need to do an autoexpand.  To check we look
+				 * at the disk's size in its config, and compare
+				 * it to the disk size that udev is reporting.
+				 */
+				uint64_t udev_size = 0, conf_size = 0;
+
+				/*
+				 * Earlier we put udev's reported disk size
+				 * into a nvlist.  Extract it here.
+				 */
+				if (nvlist_lookup_uint64(udev_nvl, DEV_SIZE,
+				    &udev_size) != 0) {
+					/*
+					 * No DEV_SIZE - set udev_size to 0, which
+					 * will in turn attempt the
+					 * zpool_vdev_online()
+					 */
+					udev_size = 0;
+				}
+
+				conf_size = vdev_size_from_config(zhp, fullpath);
+
+				/*
+				 * Only attempt an autoexpand if the drive size
+				 * changed.
+				 */
+				if (conf_size != udev_size) {
+					error = zpool_vdev_online(zhp, fullpath, 0,
+					    &newstate);
+					zed_log_msg(LOG_INFO, "%s: autoexpand "
+					    "setting '%s' to ONLINE state in pool "
+					    "'%s': %d (was %llu bytes, now %llu "
+					    "bytes)", __func__, fullpath,
+					    zpool_get_name(zhp), error, conf_size,
+					    udev_size);
+				}
 			}
 		}
 		zpool_close(zhp);
@@ -989,7 +1062,7 @@ zfs_deliver_dle(nvlist_t *nvl)
 		zed_log_msg(LOG_INFO, "zfs_deliver_dle: no guid or physpath");
 	}
 
-	if (zpool_iter(g_zfshdl, zfsdle_vdev_online, name) != 1) {
+	if (zpool_iter(g_zfshdl, zfsdle_vdev_online, nvl) != 1) {
 		zed_log_msg(LOG_INFO, "zfs_deliver_dle: device '%s' not "
 		    "found", name);
 		return (1);