pvmove: disallow tag args

pvmove began processing tags unintentionally from commit,
6d7dc87cb pvmove: use toollib

pvmove works on a single PV, but tags can match multiple PVs.
If we allowed tags, but processed only the first matching PV,
then the resulting PV would be unpredictable.

Also, the current processing code does not allow us to simply
report an error and do nothing if more than one PV matches the tag,
because the command starts processing PVs as they are found,
so it's too late to do nothing if a second PV matches.

tools/commands.h

@@ -874,9 +874,11 @@ xx(pvdisplay,
    select_ARG, separator_ARG, shared_ARG, short_ARG, sort_ARG, unbuffered_ARG,
    units_ARG)
 
+/* ALL_VGS_IS_DEFAULT is for polldaemon to find pvmoves in-progress using process_each_vg. */
+
 xx(pvmove,
    "Move extents from one physical volume to another",
-   ALL_VGS_IS_DEFAULT,	/* For polldaemon to find pvmoves in-progress using process_each_vg. */
+   ALL_VGS_IS_DEFAULT | DISALLOW_TAG_ARGS,
    "pvmove\n"
    "\t[--abort]\n"
    "\t[--alloc AllocationPolicy]\n"

tools/toollib.c

@@ -3375,6 +3375,11 @@ int process_each_pv(struct cmd_context *cmd,
 		return ret;
 	}
 
+	if ((cmd->command->flags & DISALLOW_TAG_ARGS) && !dm_list_empty(&arg_tags)) {
+		log_error("Tags cannot be used with this command.");
+		return ECMD_FAILED;
+	}
+
 	orphans_locked = lvmcache_vgname_is_locked(VG_ORPHANS);
 
 	process_all_pvs = dm_list_empty(&arg_pvnames) && dm_list_empty(&arg_tags);

tools/tools.h

@@ -114,6 +114,8 @@ struct arg_value_group_list {
 #define NO_LVMETAD_AUTOSCAN      0x00000200
 /* Command should process unused duplicate devices. */
 #define ENABLE_DUPLICATE_DEVS    0x00000400
+/* Command does not accept tags as args. */
+#define DISALLOW_TAG_ARGS        0x00000800
  
 /* a register of the lvm commands */
 struct command {