bcachefs: BCH_SB_VERSION_INCOMPAT

We've been getting away from feature bits: they don't have any kind of
ordering, and thus it's possible for people to enable weird combinations
of features that were never tested or intended to be run.

Much better to just give every new feature, compatible or incompatible,
a version number.

Additionally, we probably won't ever rev the major version number: major
version numbers represent incompatible versions, but that doesn't really
fit with how we actually roll out incompatible features - we need a
better way of rolling out incompatible features.

So, this patch adds two new superblock fields:
- BCH_SB_VERSION_INCOMPAT
- BCH_SB_VERSION_INCOMPAT_ALLOWED

BCH_SB_VERSION_INCOMPAT_ALLOWED indicates that incompatible features up
to version number x are allowed to be used without user prompting, but
it does not by itself deny old versions from mounting.

BCH_SB_VERSION_INCOMPAT does deny old versions from mounting, and must
be <= BCH_SB_VERSION_INCOMPAT_ALLOWED.

BCH_SB_VERSION_INCOMPAT will only be set when a codepath attempts to use
an incompatible feature, so as to not unnecessarily break compatibility
with old versions.

bch2_request_incompat_feature() is the new interface to check if an
incompatible feature may be used.

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

1 files changed, 51 insertions, 3 deletions

diff --git a/fs/bcachefs/super-io.c b/fs/bcachefs/super-io.c
index 6a086c1c4b14..b0d52b6ccad4 100644
--- a/fs/bcachefs/super-io.c
+++ b/fs/bcachefs/super-io.c
@@ -42,7 +42,7 @@ static const struct bch2_metadata_version bch2_metadata_versions[] = {
 #undef x
 };
 
-void bch2_version_to_text(struct printbuf *out, unsigned v)
+void bch2_version_to_text(struct printbuf *out, enum bcachefs_metadata_version v)
 {
 	const char *str = "(unknown version)";
 
@@ -55,7 +55,7 @@ void bch2_version_to_text(struct printbuf *out, unsigned v)
 	prt_printf(out, "%u.%u: %s", BCH_VERSION_MAJOR(v), BCH_VERSION_MINOR(v), str);
 }
 
-unsigned bch2_latest_compatible_version(unsigned v)
+enum bcachefs_metadata_version bch2_latest_compatible_version(enum bcachefs_metadata_version v)
 {
 	if (!BCH_VERSION_MAJOR(v))
 		return v;
@@ -69,6 +69,16 @@ unsigned bch2_latest_compatible_version(unsigned v)
 	return v;
 }
 
+void bch2_set_version_incompat(struct bch_fs *c, enum bcachefs_metadata_version version)
+{
+	mutex_lock(&c->sb_lock);
+	SET_BCH_SB_VERSION_INCOMPAT(c->disk_sb.sb,
+		max(BCH_SB_VERSION_INCOMPAT(c->disk_sb.sb), version));
+	c->disk_sb.sb->features[0] |= cpu_to_le64(BCH_FEATURE_incompat_version_field);
+	bch2_write_super(c);
+	mutex_unlock(&c->sb_lock);
+}
+
 const char * const bch2_sb_fields[] = {
 #define x(name, nr)	#name,
 	BCH_SB_FIELDS()
@@ -369,6 +379,12 @@ static int bch2_sb_validate(struct bch_sb_handle *disk_sb,
 		return -BCH_ERR_invalid_sb_features;
 	}
 
+	if (BCH_VERSION_MAJOR(le16_to_cpu(sb->version)) > BCH_VERSION_MAJOR(bcachefs_metadata_version_current) ||
+	    BCH_SB_VERSION_INCOMPAT(sb) > bcachefs_metadata_version_current) {
+		prt_printf(out, "Filesystem has incompatible version");
+		return -BCH_ERR_invalid_sb_features;
+	}
+
 	block_size = le16_to_cpu(sb->block_size);
 
 	if (block_size > PAGE_SECTORS) {
@@ -407,6 +423,21 @@ static int bch2_sb_validate(struct bch_sb_handle *disk_sb,
 		return -BCH_ERR_invalid_sb_time_precision;
 	}
 
+	/* old versions didn't know to downgrade this field */
+	if (BCH_SB_VERSION_INCOMPAT_ALLOWED(sb) > le16_to_cpu(sb->version))
+		SET_BCH_SB_VERSION_INCOMPAT_ALLOWED(sb, le16_to_cpu(sb->version));
+
+	if (BCH_SB_VERSION_INCOMPAT(sb) > BCH_SB_VERSION_INCOMPAT_ALLOWED(sb)) {
+		prt_printf(out, "Invalid version_incompat ");
+		bch2_version_to_text(out, BCH_SB_VERSION_INCOMPAT(sb));
+		prt_str(out, " > incompat_allowed ");
+		bch2_version_to_text(out, BCH_SB_VERSION_INCOMPAT_ALLOWED(sb));
+		if (flags & BCH_VALIDATE_write)
+			return -BCH_ERR_invalid_sb_version;
+		else
+			SET_BCH_SB_VERSION_INCOMPAT_ALLOWED(sb, BCH_SB_VERSION_INCOMPAT(sb));
+	}
+
 	if (!flags) {
 		/*
 		 * Been seeing a bug where these are getting inexplicably
@@ -520,6 +551,9 @@ static void bch2_sb_update(struct bch_fs *c)
 	c->sb.uuid		= src->uuid;
 	c->sb.user_uuid		= src->user_uuid;
 	c->sb.version		= le16_to_cpu(src->version);
+	c->sb.version_incompat	= BCH_SB_VERSION_INCOMPAT(src);
+	c->sb.version_incompat_allowed
+				= BCH_SB_VERSION_INCOMPAT_ALLOWED(src);
 	c->sb.version_min	= le16_to_cpu(src->version_min);
 	c->sb.version_upgrade_complete = BCH_SB_VERSION_UPGRADE_COMPLETE(src);
 	c->sb.nr_devices	= src->nr_devices;
@@ -1152,6 +1186,8 @@ bool bch2_check_version_downgrade(struct bch_fs *c)
 	 */
 	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 (BCH_SB_VERSION_INCOMPAT_ALLOWED(c->disk_sb.sb) > bcachefs_metadata_version_current)
+		SET_BCH_SB_VERSION_INCOMPAT_ALLOWED(c->disk_sb.sb, 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 (c->sb.version_min > bcachefs_metadata_version_current)
@@ -1160,7 +1196,7 @@ bool bch2_check_version_downgrade(struct bch_fs *c)
 	return ret;
 }
 
-void bch2_sb_upgrade(struct bch_fs *c, unsigned new_version)
+void bch2_sb_upgrade(struct bch_fs *c, unsigned new_version, bool incompat)
 {
 	lockdep_assert_held(&c->sb_lock);
 
@@ -1170,6 +1206,10 @@ void bch2_sb_upgrade(struct bch_fs *c, unsigned new_version)
 
 	c->disk_sb.sb->version = cpu_to_le16(new_version);
 	c->disk_sb.sb->features[0] |= cpu_to_le64(BCH_SB_FEATURES_ALL);
+
+	if (incompat)
+		SET_BCH_SB_VERSION_INCOMPAT_ALLOWED(c->disk_sb.sb,
+			max(BCH_SB_VERSION_INCOMPAT_ALLOWED(c->disk_sb.sb), new_version));
 }
 
 static int bch2_sb_ext_validate(struct bch_sb *sb, struct bch_sb_field *f,
@@ -1334,6 +1374,14 @@ void bch2_sb_to_text(struct printbuf *out, struct bch_sb *sb,
 	bch2_version_to_text(out, le16_to_cpu(sb->version));
 	prt_newline(out);
 
+	prt_printf(out, "Incompatible features allowed:\t");
+	bch2_version_to_text(out, BCH_SB_VERSION_INCOMPAT_ALLOWED(sb));
+	prt_newline(out);
+
+	prt_printf(out, "Incompatible features in use:\t");
+	bch2_version_to_text(out, BCH_SB_VERSION_INCOMPAT(sb));
+	prt_newline(out);
+
 	prt_printf(out, "Version upgrade complete:\t");
 	bch2_version_to_text(out, BCH_SB_VERSION_UPGRADE_COMPLETE(sb));
 	prt_newline(out);