bcachefs: Single device mode

This provides a new option for single device mode - which allows
multiple filesystems with the same UUID to be mounted simultaneously.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

6 files changed, 34 insertions, 9 deletions

diff --git a/fs/bcachefs/bcachefs_format.h b/fs/bcachefs/bcachefs_format.h
index a3db328dee31..8a1366aabebd 100644
--- a/fs/bcachefs/bcachefs_format.h
+++ b/fs/bcachefs/bcachefs_format.h
@@ -842,7 +842,7 @@ LE64_BITMASK(BCH_SB_SHARD_INUMS,	struct bch_sb, flags[3], 28, 29);
 LE64_BITMASK(BCH_SB_INODES_USE_KEY_CACHE,struct bch_sb, flags[3], 29, 30);
 LE64_BITMASK(BCH_SB_JOURNAL_FLUSH_DELAY,struct bch_sb, flags[3], 30, 62);
 LE64_BITMASK(BCH_SB_JOURNAL_FLUSH_DISABLED,struct bch_sb, flags[3], 62, 63);
-/* one free bit */
+LE64_BITMASK(BCH_SB_SINGLE_DEVICE,	struct bch_sb,	flags[3], 63, 64);
 LE64_BITMASK(BCH_SB_JOURNAL_RECLAIM_DELAY,struct bch_sb, flags[4], 0, 32);
 LE64_BITMASK(BCH_SB_JOURNAL_TRANSACTION_NAMES,struct bch_sb, flags[4], 32, 33);
 LE64_BITMASK(BCH_SB_NOCOW,		struct bch_sb, flags[4], 33, 34);
diff --git a/fs/bcachefs/debug.c b/fs/bcachefs/debug.c
index f4b7877c0843..09b672799ca9 100644
--- a/fs/bcachefs/debug.c
+++ b/fs/bcachefs/debug.c
@@ -933,7 +933,11 @@ void bch2_fs_debug_init(struct bch_fs *c)
 	if (IS_ERR_OR_NULL(bch_debug))
 		return;
 
-	snprintf(name, sizeof(name), "%pU", c->sb.user_uuid.b);
+	if (!c->opts.single_device)
+		snprintf(name, sizeof(name), "%pU", c->sb.user_uuid.b);
+	else
+		strscpy(name, c->name, sizeof(name));
+
 	c->fs_debug_dir = debugfs_create_dir(name, bch_debug);
 	if (IS_ERR_OR_NULL(c->fs_debug_dir))
 		return;
diff --git a/fs/bcachefs/errcode.h b/fs/bcachefs/errcode.h
index c8696f01eb14..c4eb0ed9838d 100644
--- a/fs/bcachefs/errcode.h
+++ b/fs/bcachefs/errcode.h
@@ -192,6 +192,8 @@
 	x(BCH_ERR_data_update_done,	data_update_done_no_rw_devs)		\
 	x(EINVAL,			device_state_not_allowed)		\
 	x(EINVAL,			member_info_missing)			\
+	x(EINVAL,			single_device_filesystem)		\
+	x(EINVAL,			not_single_device_filesystem)		\
 	x(EINVAL,			mismatched_block_size)			\
 	x(EINVAL,			block_size_too_small)			\
 	x(EINVAL,			bucket_size_too_small)			\
diff --git a/fs/bcachefs/opts.c b/fs/bcachefs/opts.c
index af3258814822..e64777ecf44f 100644
--- a/fs/bcachefs/opts.c
+++ b/fs/bcachefs/opts.c
@@ -498,6 +498,14 @@ int bch2_opt_check_may_set(struct bch_fs *c, struct bch_dev *ca, int id, u64 v)
 		if (v)
 			bch2_check_set_feature(c, BCH_FEATURE_ec);
 		break;
+	case Opt_single_device:
+		if (v) {
+			mutex_lock(&c->sb_lock);
+			if (bch2_sb_nr_devices(c->disk_sb.sb) > 1)
+				ret = -BCH_ERR_not_single_device_filesystem;
+			mutex_unlock(&c->sb_lock);
+		}
+		break;
 	}
 
 	return ret;
diff --git a/fs/bcachefs/opts.h b/fs/bcachefs/opts.h
index 4d06313076ff..45b393f83776 100644
--- a/fs/bcachefs/opts.h
+++ b/fs/bcachefs/opts.h
@@ -517,7 +517,7 @@ enum fsck_err_opts {
 	  BCH_MEMBER_DATA_ALLOWED,	BIT(BCH_DATA_journal)|BIT(BCH_DATA_btree)|BIT(BCH_DATA_user),\
 	  "types",	"Allowed data types for this device: journal, btree, and/or user")\
 	x(discard,			u8,				\
-	  OPT_MOUNT|OPT_DEVICE|OPT_RUNTIME,				\
+	  OPT_MOUNT|OPT_FS|OPT_DEVICE|OPT_RUNTIME,			\
 	  OPT_BOOL(),							\
 	  BCH_MEMBER_DISCARD,		true,				\
 	  NULL,		"Enable discard/TRIM support")			\
@@ -525,8 +525,13 @@ enum fsck_err_opts {
 	  OPT_FS|OPT_MOUNT|OPT_RUNTIME,					\
 	  OPT_BOOL(),							\
 	  BCH2_NO_SB_OPT,		true,				\
-	  NULL,		"BTREE_ITER_prefetch casuse btree nodes to be\n"\
-	  " prefetched sequentially")
+	  NULL,		"BTREE_ITER_prefetch causes btree nodes to be\n"\
+	  " prefetched sequentially")					\
+	x(single_device,		u8,				\
+	  OPT_FS|OPT_MOUNT|OPT_RUNTIME,					\
+	  OPT_BOOL(),							\
+	  BCH_SB_SINGLE_DEVICE,		false,				\
+	  NULL,		"Devices with the same UUID may be mounted simultaneously")
 
 struct bch_opts {
 #define x(_name, _bits, ...)	unsigned _name##_defined:1;
diff --git a/fs/bcachefs/super.c b/fs/bcachefs/super.c
index 07c8149c6712..f868bc5cd19a 100644
--- a/fs/bcachefs/super.c
+++ b/fs/bcachefs/super.c
@@ -708,7 +708,8 @@ static int bch2_fs_online(struct bch_fs *c)
 
 	lockdep_assert_held(&bch_fs_list_lock);
 
-	if (__bch2_uuid_to_fs(c->sb.uuid)) {
+	if (!c->opts.single_device &&
+	    __bch2_uuid_to_fs(c->sb.uuid)) {
 		bch_err(c, "filesystem UUID already open");
 		return -EINVAL;
 	}
@@ -721,7 +722,9 @@ static int bch2_fs_online(struct bch_fs *c)
 
 	bch2_fs_debug_init(c);
 
-	ret = kobject_add(&c->kobj, NULL, "%pU", c->sb.user_uuid.b) ?:
+	ret = (!c->opts.single_device
+	       ? kobject_add(&c->kobj, NULL, "%pU", c->sb.user_uuid.b)
+	       : kobject_add(&c->kobj, NULL, "%s", c->name)) ?:
 	    kobject_add(&c->internal, &c->kobj, "internal") ?:
 	    kobject_add(&c->opts_dir, &c->kobj, "options") ?:
 #ifndef CONFIG_BCACHEFS_NO_LATENCY_ACCT
@@ -897,7 +900,7 @@ static struct bch_fs *bch2_fs_alloc(struct bch_sb *sb, struct bch_opts opts,
 		goto err;
 	}
 
-	if (sbs->nr != 1)
+	if (sbs->nr != 1 && !c->opts.single_device)
 		pr_uuid(&name, c->sb.user_uuid.b);
 	else
 		prt_bdevname(&name, sbs->data[0].bdev);
@@ -1114,6 +1117,9 @@ static int bch2_dev_may_add(struct bch_sb *sb, struct bch_fs *c)
 {
 	struct bch_member m = bch2_sb_member_get(sb, sb->dev_idx);
 
+	if (c->opts.single_device)
+		return -BCH_ERR_single_device_filesystem;
+
 	if (le16_to_cpu(sb->block_size) != block_sectors(c))
 		return -BCH_ERR_mismatched_block_size;
 
@@ -1781,7 +1787,7 @@ err:
 int bch2_dev_add(struct bch_fs *c, const char *path)
 {
 	struct bch_opts opts = bch2_opts_empty();
-	struct bch_sb_handle sb;
+	struct bch_sb_handle sb = {};
 	struct bch_dev *ca = NULL;
 	struct printbuf errbuf = PRINTBUF;
 	struct printbuf label = PRINTBUF;