Add feature check for 'zpool resilver' command

The 'zpool resilver' command requires that the resilver_defer
feature is active on the pool. Unfortunately, the check for
this was left out of the original patch. This commit simply
corrects this so that the command properly returns an error
in this case.

Reviewed by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Igor Kozhukhov <igor@dilos.org>
Signed-off-by: Tom Caputi <tcaputi@datto.com>
Closes #8700

lib/libzfs/libzfs_pool.c

@@ -2354,6 +2354,10 @@ zpool_scan(zpool_handle_t *zhp, pool_scan_func_t func, pool_scrub_cmd_t cmd)
 			(void) snprintf(msg, sizeof (msg), dgettext(TEXT_DOMAIN,
 			    "cannot scrub %s"), zc.zc_name);
 		}
+	} else if (func == POOL_SCAN_RESILVER) {
+		assert(cmd == POOL_SCRUB_NORMAL);
+		(void) snprintf(msg, sizeof (msg), dgettext(TEXT_DOMAIN,
+		    "cannot restart resilver on %s"), zc.zc_name);
 	} else if (func == POOL_SCAN_NONE) {
 		(void) snprintf(msg, sizeof (msg),
 		    dgettext(TEXT_DOMAIN, "cannot cancel scrubbing %s"),
@@ -2381,6 +2385,8 @@ zpool_scan(zpool_handle_t *zhp, pool_scan_func_t func, pool_scrub_cmd_t cmd)
 		}
 	} else if (err == ENOENT) {
 		return (zfs_error(hdl, EZFS_NO_SCRUB, msg));
+	} else if (err == ENOTSUP && func == POOL_SCAN_RESILVER) {
+		return (zfs_error(hdl, EZFS_NO_RESILVER_DEFER, msg));
 	} else {
 		return (zpool_standard_error(hdl, err, msg));
 	}

lib/libzfs/libzfs_util.c

@@ -300,6 +300,9 @@ libzfs_error_description(libzfs_handle_t *hdl)
 	case EZFS_TRIM_NOTSUP:
 		return (dgettext(TEXT_DOMAIN, "trim operations are not "
 		    "supported by this device"));
+	case EZFS_NO_RESILVER_DEFER:
+		return (dgettext(TEXT_DOMAIN, "this action requires the "
+		    "resilver_defer feature"));
 	case EZFS_UNKNOWN:
 		return (dgettext(TEXT_DOMAIN, "unknown error"));
 	default: