Increase default superblock size to 1MB

Also - add an option to bcachefs format for specifying it,
--superblock_size

Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>

cmd_format.c

@@ -36,6 +36,7 @@ x(0,	no_passphrase,		no_argument)		\
 x('L',	label,			required_argument)	\
 x('U',	uuid,			required_argument)	\
 x(0,	fs_size,		required_argument)	\
+x(0,	superblock_size,	required_argument)	\
 x(0,	bucket_size,		required_argument)	\
 x('g',	group,			required_argument)	\
 x(0,	discard,		no_argument)		\
@@ -62,6 +63,7 @@ static void usage(void)
 	     "      --no_passphrase         Don't encrypt master encryption key\n"
 	     "  -L, --label=label\n"
 	     "  -U, --uuid=uuid\n"
+	     "      --superblock_size=size\n"
 	     "\n"
 	     "Device specific options:");
 
@@ -164,6 +166,12 @@ int cmd_format(int argc, char *argv[])
 
 			dev_opts.size >>= 9;
 			break;
+		case O_superblock_size:
+			if (bch2_strtouint_h(optarg, &opts.superblock_size))
+				die("invalid filesystem size");
+
+			opts.superblock_size >>= 9;
+			break;
 		case O_bucket_size:
 			dev_opts.bucket_size =
 				hatoi_validate(optarg, "bucket size");

cmd_migrate.c

@@ -599,7 +599,9 @@ static void copy_fs(struct bch_fs *c, int src_fd, const char *src_path,
 	bch2_alloc_write(c, false);
 }
 
-static void find_superblock_space(ranges extents, struct dev_opts *dev)
+static void find_superblock_space(ranges extents,
+				  struct format_opts opts,
+				  struct dev_opts *dev)
 {
 	struct range *i;
 
@@ -609,9 +611,10 @@ static void find_superblock_space(ranges extents, struct dev_opts *dev)
 		u64 end = round_down(i->end,
 				     dev->bucket_size << 9);
 
-		if (start + (128 << 10) <= end) {
+		/* Need space for two superblocks: */
+		if (start + (opts.superblock_size << 9) * 2 <= end) {
 			dev->sb_offset	= start >> 9;
-			dev->sb_end	= dev->sb_offset + 256;
+			dev->sb_end	= dev->sb_offset + opts.superblock_size * 2;
 			return;
 		}
 	}
@@ -673,7 +676,7 @@ static int migrate_fs(const char		*fs_path,
 				get_size(dev.path, dev.fd) / 5,
 				&bcachefs_inum, stat.st_dev, force);
 
-	find_superblock_space(extents, &dev);
+	find_superblock_space(extents, format_opts, &dev);
 
 	struct bch_sb *sb = bch2_format(fs_opt_strs,
 					fs_opts,format_opts, &dev, 1);

libbcachefs.c

@@ -35,52 +35,35 @@ static u64 min_size(unsigned bucket_size)
 	return BCH_MIN_NR_NBUCKETS * bucket_size;
 }
 
-static void init_layout(struct bch_sb_layout *l, unsigned block_size,
+static void init_layout(struct bch_sb_layout *l,
+			unsigned block_size,
+			unsigned sb_size,
 			u64 start, u64 end)
 {
-	unsigned sb_size;
-	u64 backup; /* offset of 2nd sb */
+	unsigned i;
 
 	memset(l, 0, sizeof(*l));
 
-	if (start != BCH_SB_SECTOR)
-		start = round_up(start, block_size);
-	end = round_down(end, block_size);
-
-	if (start >= end)
-		die("insufficient space for superblocks");
-
-	/*
-	 * Create two superblocks in the allowed range: reserve a maximum of 64k
-	 */
-	sb_size = min_t(u64, 128, end - start / 2);
-
-	backup = start + sb_size;
-	backup = round_up(backup, block_size);
-
-	backup = min(backup, end);
-
-	sb_size = min(end - backup, backup- start);
-	sb_size = rounddown_pow_of_two(sb_size);
-
-	if (sb_size < 8)
-		die("insufficient space for superblocks");
-
 	l->magic		= BCACHE_MAGIC;
 	l->layout_type		= 0;
 	l->nr_superblocks	= 2;
 	l->sb_max_size_bits	= ilog2(sb_size);
-	l->sb_offset[0]		= cpu_to_le64(start);
-	l->sb_offset[1]		= cpu_to_le64(backup);
+
+	/* Create two superblocks in the allowed range: */
+	for (i = 0; i < l->nr_superblocks; i++) {
+		if (start != BCH_SB_SECTOR)
+			start = round_up(start, block_size);
+
+		l->sb_offset[i] = cpu_to_le64(start);
+		start += sb_size;
+	}
+
+	if (start >= end)
+		die("insufficient space for superblocks");
 }
 
 void bch2_pick_bucket_size(struct bch_opts opts, struct dev_opts *dev)
 {
-	if (!dev->sb_offset) {
-		dev->sb_offset	= BCH_SB_SECTOR;
-		dev->sb_end	= BCH_SB_SECTOR + 256;
-	}
-
 	if (!dev->size)
 		dev->size = get_size(dev->path, dev->fd) >> 9;
 
@@ -300,7 +283,13 @@ struct bch_sb *bch2_format(struct bch_opt_strs	fs_opt_strs,
 	for (i = devs; i < devs + nr_devs; i++) {
 		sb.sb->dev_idx = i - devs;
 
+		if (!i->sb_offset) {
+			i->sb_offset	= BCH_SB_SECTOR;
+			i->sb_end	= i->size;
+		}
+
 		init_layout(&sb.sb->layout, fs_opts.block_size,
+			    opts.superblock_size,
 			    i->sb_offset, i->sb_end);
 
 		if (i->sb_offset == BCH_SB_SECTOR) {

libbcachefs.h

@@ -12,6 +12,8 @@
 
 /* option parsing */
 
+#define SUPERBLOCK_SIZE_DEFAULT		2048	/* 1 MB */
+
 struct bch_opt_strs {
 union {
 	char			*by_id[bch2_opts_nr];
@@ -31,9 +33,8 @@ struct format_opts {
 	char		*label;
 	uuid_le		uuid;
 	unsigned	version;
-
+	unsigned	superblock_size;
 	unsigned	encoded_extent_max;
-
 	bool		encrypted;
 	char		*passphrase;
 };
@@ -42,6 +43,7 @@ static inline struct format_opts format_opts_default()
 {
 	return (struct format_opts) {
 		.version		= bcachefs_metadata_version_current,
+		.superblock_size	= SUPERBLOCK_SIZE_DEFAULT,
 		.encoded_extent_max	= 128,
 	};
 }