Do not allow creating mirrors of more than 8 images.

This is kernel limitation in all kernel versions,
so better detect this early.

WHATS_NEW

@@ -1,5 +1,6 @@
 Version 2.02.57 -
 ====================================
+  Do not allow creating mirrors of more than 8 images.
   Use locking_type 3 (compiled in cluster locking) in lvmconf.
   Remove duplicate dm_list macros and functions.
   Log failure type and recognise type 'F' (flush) in dmeventd mirror plugin.

lib/config/defaults.h

@@ -47,6 +47,7 @@
 #define DEFAULT_MIRRORLOG "disk"
 #define DEFAULT_MIRROR_LOG_FAULT_POLICY "allocate"
 #define DEFAULT_MIRROR_DEV_FAULT_POLICY "remove"
+#define DEFAULT_MIRROR_MAX_IMAGES 8 /* limited by kernel DM_KCOPYD_MAX_REGIONS */
 #define DEFAULT_DMEVENTD_MIRROR_LIB "libdevmapper-event-lvm2mirror.so"
 #define DEFAULT_DMEVENTD_MONITOR 1
 

tools/lvconvert.c

@@ -571,6 +571,12 @@ static int _lvconvert_mirrors(struct cmd_context *cmd, struct logical_volume *lv
 	else
 		lp->mirrors += 1;
 
+	if (lp->mirrors > DEFAULT_MIRROR_MAX_IMAGES) {
+		log_error("Only up to %d images in mirror supported currently.",
+			  DEFAULT_MIRROR_MAX_IMAGES);
+		return 0;
+	}
+
 	if (repair) {
 		cmd->handles_missing_pvs = 1;
 		cmd->partial_activation = 1;

tools/lvcreate.c

@@ -500,6 +500,12 @@ static int _lvcreate_params(struct lvcreate_params *lp,
 		return 0;
 	}
 
+	if (lp->mirrors > DEFAULT_MIRROR_MAX_IMAGES) {
+		log_error("Only up to %d images in mirror supported currently.",
+			  DEFAULT_MIRROR_MAX_IMAGES);
+		return 0;
+	}
+
 	/*
 	 * Read ahead.
 	 */