btrfs-progs: balance: add stripes filter

Add new balance filter 'stripes=<range>' to process only chunks that are
spread accross given number of chunks.

The range minimum and maximum are inclusive.

Signed-off-by: Gabríel Arthúr Pétursson <gabriel@system.is>
[ reworked a bit to use the range helpers, dropped the single value
  for stripes ]
Signed-off-by: David Sterba <dsterba@suse.com>

Documentation/btrfs-balance.asciidoc

@@ -137,6 +137,12 @@ only the single value format.
 +
 The range minimum and maximum are inclusive.
 
+*stripes*::
+Balances only block groups which have the given number of stripes. The
+parameter is a range specified as <start..end>.
++
+The range minimum and maximum are inclusive.
+
 *soft*::
 Takes no parameters. Only has meaning when converting between profiles.
 When doing convert from one profile to another and soft mode is on,

cmds-balance.c

@@ -319,6 +319,18 @@ static int parse_filters(char *filters, struct btrfs_balance_args *args)
 				args->flags &= ~BTRFS_BALANCE_ARGS_LIMIT_RANGE;
 				args->flags |= BTRFS_BALANCE_ARGS_LIMIT;
 			}
+		} else if (!strcmp(this_char, "stripes")) {
+			if (!value || !*value) {
+				fprintf(stderr,
+					"the stripes filter requires an argument\n");
+				return 1;
+			}
+			if (parse_range_u32(value, &args->stripes_min,
+					    &args->stripes_max)) {
+				fprintf(stderr, "Invalid stripes argument\n");
+				return 1;
+			}
+			args->flags |= BTRFS_BALANCE_ARGS_STRIPES_RANGE;
 		} else {
 			fprintf(stderr, "Unrecognized balance option '%s'\n",
 				this_char);
@@ -359,6 +371,10 @@ static void dump_balance_args(struct btrfs_balance_args *args)
 		printf(", limit=");
 		print_range_u32(args->limit_min, args->limit_max);
 	}
+	if (args->flags & BTRFS_BALANCE_ARGS_STRIPES_RANGE) {
+		printf(", stripes=");
+		print_range_u32(args->stripes_min, args->stripes_max);
+	}
 
 	printf("\n");
 }

ioctl.h

@@ -239,7 +239,9 @@ struct btrfs_balance_args {
 			__u32 limit_max;
 		};
 	};
-	__u64 unused[7];
+	__u32 stripes_min;
+	__u32 stripes_max;
+	__u64 unused[6];
 } __attribute__ ((__packed__));
 
 /* report balance progress to userspace */

volumes.h

@@ -137,6 +137,7 @@ struct map_lookup {
 #define BTRFS_BALANCE_ARGS_VRANGE	(1ULL << 4)
 #define BTRFS_BALANCE_ARGS_LIMIT	(1ULL << 5)
 #define BTRFS_BALANCE_ARGS_LIMIT_RANGE	(1ULL << 6)
+#define BTRFS_BALANCE_ARGS_STRIPES_RANGE (1ULL << 7)
 
 /*
  * Profile changing flags.  When SOFT is set we won't relocate chunk if