btrfs-progs: extend balance args to take min/max limit filter

Add the overlapping limit and [limit_min, limit_max] members to the
balance args. The min/max values are interpreted iff the corresponding
flag BTRFS_BALANCE_ARGS_LIMIT_RANGE is set.

The minimum and maximum are inclusive.

Note that the values are only 32bit, but this should be enough for the
foreseeable future.

Signed-off-by: David Sterba <dsterba@suse.com>

Documentation/btrfs-balance.asciidoc

@@ -130,6 +130,12 @@ parameters.
 Process only given number of chunks, after all filters are applied. This can be
 used to specifically target a chunk in connection with other filters (drange,
 vrange) or just simply limit the amount of work done by a single balance run.
++
+The argument may be a single value or a range. The single value *N* means *at
+most N chunks*, equivalent to *..N* range syntax. Kernels prior to 4.4 accept
+only the single value format.
++
+The range minimum and maximum are inclusive.
 
 *soft*::
 Takes no parameters. Only has meaning when converting between profiles.

cmds-balance.c

@@ -347,6 +347,10 @@ static void dump_balance_args(struct btrfs_balance_args *args)
 		       (unsigned long long)args->vend);
 	if (args->flags & BTRFS_BALANCE_ARGS_LIMIT)
 		printf(", limit=%llu", (unsigned long long)args->limit);
+	if (args->flags & BTRFS_BALANCE_ARGS_LIMIT_RANGE) {
+		printf(", limit=");
+		print_range_u32(args->limit_min, args->limit_max);
+	}
 
 	printf("\n");
 }

ioctl.h

@@ -227,7 +227,18 @@ struct btrfs_balance_args {
 
 	__u64 flags;
 
-	__u64 limit;		/* limit number of processed chunks */
+	/*
+	 * BTRFS_BALANCE_ARGS_LIMIT with value 'limit'
+	 * BTRFS_BALANCE_ARGS_LIMIT_RANGE - the extend version can use minimum
+	 * and maximum
+	 */
+	union {
+		__u64 limit;		/* limit number of processed chunks */
+		struct {
+			__u32 limit_min;
+			__u32 limit_max;
+		};
+	};
 	__u64 unused[7];
 } __attribute__ ((__packed__));
 

volumes.h

@@ -136,6 +136,7 @@ struct map_lookup {
 #define BTRFS_BALANCE_ARGS_DRANGE	(1ULL << 3)
 #define BTRFS_BALANCE_ARGS_VRANGE	(1ULL << 4)
 #define BTRFS_BALANCE_ARGS_LIMIT	(1ULL << 5)
+#define BTRFS_BALANCE_ARGS_LIMIT_RANGE	(1ULL << 6)
 
 /*
  * Profile changing flags.  When SOFT is set we won't relocate chunk if