Add stripes filter

["Gabríel Arthúr Pétursson" <gabriel@system.is>]

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Hello everyone!

The attached patches to linux and btrfs-progs add support for filtering
based on the number of strips in a block when balancing.

This is my first attempt at kernel development, I'd love if you could
please point out any mistakes that I've made.

Thanks,
Gabríel

P.S. I could not figure out how to subscribe to this mailing list, so
please remember to include me in your replies.

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diff --git a/Documentation/btrfs-balance.asciidoc b/Documentation/btrfs-balance.asciidoc
index 6d2fd0c..8663855 100644
--- a/Documentation/btrfs-balance.asciidoc
+++ b/Documentation/btrfs-balance.asciidoc
@@ -110,6 +110,10 @@ Process only given number of chunks, after all filters apply. 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.
 
+*stripes*::
+Balances only block groups which have the given number of stripes. The
+parameter is either a range specified as <start..end>, or a single integer.
+
 *soft*::
 Takes no parameters. Only has meaning when converting between profiles.
 When doing convert from one profile to another and soft mode is on,
diff --git a/cmds-balance.c b/cmds-balance.c
index 9af218b..c47f8b7 100644
--- a/cmds-balance.c
+++ b/cmds-balance.c
@@ -226,6 +226,21 @@ static int parse_filters(char *filters, struct btrfs_balance_args *args)
 				return 1;
 			}
 			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_u64(value, &args->sstart)) {
+				if (parse_range(value, &args->sstart, &args->send)) {
+					fprintf(stderr, "Invalid stripes argument\n");
+					return 1;
+				}
+			} else {
+				args->send = args->sstart;
+			}
+			args->flags |= BTRFS_BALANCE_ARGS_STRIPES;
 		} else {
 			fprintf(stderr, "Unrecognized balance option '%s'\n",
 				this_char);
@@ -262,6 +277,15 @@ 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_STRIPES) {
+		if (args->sstart == args->send) {
+			printf(", stripes=%llu", (unsigned long long)args->sstart);
+		} else {
+			printf(", stripes=%llu..%llu",
+			        (unsigned long long)args->sstart,
+			        (unsigned long long)args->send);
+		}
+	}
 
 	printf("\n");
 }
diff --git a/ioctl.h b/ioctl.h
index dff015a..c1f6aec 100644
--- a/ioctl.h
+++ b/ioctl.h
@@ -228,7 +228,11 @@ struct btrfs_balance_args {
 	__u64 flags;
 
 	__u64 limit;		/* limit number of processed chunks */
-	__u64 unused[7];
+
+	__u64 sstart;
+	__u64 send;
+
+	__u64 unused[5];
 } __attribute__ ((__packed__));
 
 /* report balance progress to userspace */
diff --git a/volumes.h b/volumes.h
index 4ecb993..a809a78 100644
--- a/volumes.h
+++ b/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_STRIPES	(1ULL << 6)
 
 /*
  * Profile changing flags.  When SOFT is set we won't relocate chunk if

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diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 938efe3..78573e5 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -849,7 +849,11 @@ struct btrfs_disk_balance_args {
 	/* BTRFS_BALANCE_ARGS_LIMIT value */
 	__le64 limit;
 
-	__le64 unused[7];
+	/* btrfs stripes filter */
+	__le64 sstart;
+	__le64 send;
+
+	__le64 unused[5];
 } __attribute__ ((__packed__));
 
 /*
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 6fc73586..dc65fbb 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -3170,6 +3170,18 @@ static int chunk_vrange_filter(struct extent_buffer *leaf,
 	return 1;
 }
 
+static int chunk_stripes_filter(struct extent_buffer *leaf,
+			       struct btrfs_chunk *chunk,
+			       struct btrfs_balance_args *bargs)
+{
+	int num_stripes = btrfs_chunk_num_stripes(leaf, chunk);
+
+	if (bargs->sstart <= num_stripes && num_stripes <= bargs->send)
+		return 0;
+
+	return 1;
+}
+
 static int chunk_soft_convert_filter(u64 chunk_type,
 				     struct btrfs_balance_args *bargs)
 {
@@ -3236,6 +3248,12 @@ static int should_balance_chunk(struct btrfs_root *root,
 		return 0;
 	}
 
+	/* stripes filter */
+	if ((bargs->flags & BTRFS_BALANCE_ARGS_STRIPES) &&
+	    chunk_stripes_filter(leaf, chunk, bargs)) {
+		return 0;
+	}
+
 	/* soft profile changing mode */
 	if ((bargs->flags & BTRFS_BALANCE_ARGS_SOFT) &&
 	    chunk_soft_convert_filter(chunk_type, bargs)) {
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 2ca784a..fb6b89a 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -375,6 +375,7 @@ 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_STRIPES	(1ULL << 6)
 
 /*
  * Profile changing flags.  When SOFT is set we won't relocate chunk if
diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
index b6dec05..a7819d0 100644
--- a/include/uapi/linux/btrfs.h
+++ b/include/uapi/linux/btrfs.h
@@ -218,7 +218,11 @@ struct btrfs_balance_args {
 	__u64 flags;
 
 	__u64 limit;		/* limit number of processed chunks */
-	__u64 unused[7];
+
+	__u64 sstart;
+	__u64 send;
+
+	__u64 unused[5];
 } __attribute__ ((__packed__));
 
 /* report balance progress to userspace */