bcachefs: bcachefs_metadata_version_major_minor

This introduces major/minor versioning to the superblock version number.
Major version number changes indicate incompatible releases; we can move
forward to a new major version number, but not backwards. Minor version
numbers indicate compatible changes - these add features, but can still
be mounted and used by old versions.

With the recent patches that make it possible to roll out new btrees and
key types without breaking compatibility, we should be able to roll out
most new features without incompatible changes.

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

1 files changed, 40 insertions, 18 deletions

diff --git a/fs/bcachefs/super-io.c b/fs/bcachefs/super-io.c
index 1437c363a4ab..23e25af001f0 100644
--- a/fs/bcachefs/super-io.c
+++ b/fs/bcachefs/super-io.c
@@ -26,19 +26,42 @@
 static const struct blk_holder_ops bch2_sb_handle_bdev_ops = {
 };
 
-static const char * const bch2_metadata_versions[] = {
-#define x(t, n) [n] = #t,
+struct bch2_metadata_version_str {
+	u16		version;
+	const char	*name;
+};
+
+static const struct bch2_metadata_version_str bch2_metadata_versions[] = {
+#define x(n, v) { .version = v, .name = #n },
 	BCH_METADATA_VERSIONS()
 #undef x
 };
 
 void bch2_version_to_text(struct printbuf *out, unsigned v)
 {
-	const char *str = v < ARRAY_SIZE(bch2_metadata_versions)
-		? bch2_metadata_versions[v]
-		: "(unknown version)";
+	const char *str = "(unknown version)";
+
+	for (unsigned i = 0; i < ARRAY_SIZE(bch2_metadata_versions); i++)
+		if (bch2_metadata_versions[i].version == v) {
+			str = bch2_metadata_versions[i].name;
+			break;
+		}
+
+	prt_printf(out, "%u.%u: %s", BCH_VERSION_MAJOR(v), BCH_VERSION_MINOR(v), str);
+}
+
+unsigned bch2_latest_compatible_version(unsigned v)
+{
+	if (!BCH_VERSION_MAJOR(v))
+		return v;
+
+	for (unsigned i = 0; i < ARRAY_SIZE(bch2_metadata_versions); i++)
+		if (bch2_metadata_versions[i].version > v &&
+		    BCH_VERSION_MAJOR(bch2_metadata_versions[i].version) ==
+		    BCH_VERSION_MAJOR(v))
+			v = bch2_metadata_versions[i].version;
 
-	prt_printf(out, "%u: %s", v, str);
+	return v;
 }
 
 const char * const bch2_sb_fields[] = {
@@ -816,10 +839,9 @@ int bch2_write_super(struct bch_fs *c)
 	closure_init_stack(cl);
 	memset(&sb_written, 0, sizeof(sb_written));
 
-	if (test_bit(BCH_FS_VERSION_UPGRADE, &c->flags)) {
-		c->disk_sb.sb->magic = BCHFS_MAGIC;
-		c->disk_sb.sb->layout.magic = BCHFS_MAGIC;
-	}
+	/* Make sure we're using the new magic numbers: */
+	c->disk_sb.sb->magic = BCHFS_MAGIC;
+	c->disk_sb.sb->layout.magic = BCHFS_MAGIC;
 
 	le64_add_cpu(&c->disk_sb.sb->seq, 1);
 
@@ -1194,19 +1216,19 @@ int bch2_fs_mark_dirty(struct bch_fs *c)
 	mutex_lock(&c->sb_lock);
 	SET_BCH_SB_CLEAN(c->disk_sb.sb, false);
 
+	/*
+	 * Downgrade, if superblock is at a higher version than currently
+	 * supported:
+	 */
 	if (BCH_SB_VERSION_UPGRADE_COMPLETE(c->disk_sb.sb) > bcachefs_metadata_version_current)
 		SET_BCH_SB_VERSION_UPGRADE_COMPLETE(c->disk_sb.sb, bcachefs_metadata_version_current);
-
-	if (test_bit(BCH_FS_VERSION_UPGRADE, &c->flags) ||
-	    c->sb.version > bcachefs_metadata_version_current)
+	if (c->sb.version > bcachefs_metadata_version_current)
 		c->disk_sb.sb->version = cpu_to_le16(bcachefs_metadata_version_current);
-
-	if (test_bit(BCH_FS_VERSION_UPGRADE, &c->flags))
-		c->disk_sb.sb->features[0] |= cpu_to_le64(BCH_SB_FEATURES_ALL);
+	if (c->sb.version_min > bcachefs_metadata_version_current)
+		c->disk_sb.sb->version_min = cpu_to_le16(bcachefs_metadata_version_current);
+	c->disk_sb.sb->compat[0] &= cpu_to_le64((1ULL << BCH_COMPAT_NR) - 1);
 
 	c->disk_sb.sb->features[0] |= cpu_to_le64(BCH_SB_FEATURES_ALWAYS);
-
-	c->disk_sb.sb->compat[0] &= cpu_to_le64((1ULL << BCH_COMPAT_NR) - 1);
 	ret = bch2_write_super(c);
 	mutex_unlock(&c->sb_lock);