Merge tag 'ext4_for_linus_fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4

Pull ext4 fixes from Ted Ts'o:
 "Bug fixes for the new ext4 fast commit feature, plus a fix for the
  'data=journal' bug fix.

  Also use the generic casefolding support which has now landed in
  fs/libfs.c for 5.10"

* tag 'ext4_for_linus_fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4:
  ext4: indicate that fast_commit is available via /sys/fs/ext4/feature/...
  ext4: use generic casefolding support
  ext4: do not use extent after put_bh
  ext4: use IS_ERR() for error checking of path
  ext4: fix mmap write protection for data=journal mode
  jbd2: fix a kernel-doc markup
  ext4: use s_mount_flags instead of s_mount_state for fast commit state
  ext4: make num of fast commit blocks configurable
  ext4: properly check for dirty state in ext4_inode_datasync_dirty()
  ext4: fix double locking in ext4_fc_commit_dentry_updates()

fs/ext4/dir.c

@@ -669,68 +669,8 @@ const struct file_operations ext4_dir_operations = {
 };
 
 #ifdef CONFIG_UNICODE
-static int ext4_d_compare(const struct dentry *dentry, unsigned int len,
-			  const char *str, const struct qstr *name)
-{
-	struct qstr qstr = {.name = str, .len = len };
-	const struct dentry *parent = READ_ONCE(dentry->d_parent);
-	const struct inode *inode = d_inode_rcu(parent);
-	char strbuf[DNAME_INLINE_LEN];
-
-	if (!inode || !IS_CASEFOLDED(inode) ||
-	    !EXT4_SB(inode->i_sb)->s_encoding) {
-		if (len != name->len)
-			return -1;
-		return memcmp(str, name->name, len);
-	}
-
-	/*
-	 * If the dentry name is stored in-line, then it may be concurrently
-	 * modified by a rename.  If this happens, the VFS will eventually retry
-	 * the lookup, so it doesn't matter what ->d_compare() returns.
-	 * However, it's unsafe to call utf8_strncasecmp() with an unstable
-	 * string.  Therefore, we have to copy the name into a temporary buffer.
-	 */
-	if (len <= DNAME_INLINE_LEN - 1) {
-		memcpy(strbuf, str, len);
-		strbuf[len] = 0;
-		qstr.name = strbuf;
-		/* prevent compiler from optimizing out the temporary buffer */
-		barrier();
-	}
-
-	return ext4_ci_compare(inode, name, &qstr, false);
-}
-
-static int ext4_d_hash(const struct dentry *dentry, struct qstr *str)
-{
-	const struct ext4_sb_info *sbi = EXT4_SB(dentry->d_sb);
-	const struct unicode_map *um = sbi->s_encoding;
-	const struct inode *inode = d_inode_rcu(dentry);
-	unsigned char *norm;
-	int len, ret = 0;
-
-	if (!inode || !IS_CASEFOLDED(inode) || !um)
-		return 0;
-
-	norm = kmalloc(PATH_MAX, GFP_ATOMIC);
-	if (!norm)
-		return -ENOMEM;
-
-	len = utf8_casefold(um, str, norm, PATH_MAX);
-	if (len < 0) {
-		if (ext4_has_strict_mode(sbi))
-			ret = -EINVAL;
-		goto out;
-	}
-	str->hash = full_name_hash(dentry, norm, len);
-out:
-	kfree(norm);
-	return ret;
-}
-
 const struct dentry_operations ext4_dentry_ops = {
-	.d_hash = ext4_d_hash,
-	.d_compare = ext4_d_compare,
+	.d_hash = generic_ci_d_hash,
+	.d_compare = generic_ci_d_compare,
 };
 #endif

fs/ext4/ext4.h

@@ -1166,10 +1166,6 @@ struct ext4_inode_info {
 #define	EXT4_VALID_FS			0x0001	/* Unmounted cleanly */
 #define	EXT4_ERROR_FS			0x0002	/* Errors detected */
 #define	EXT4_ORPHAN_FS			0x0004	/* Orphans being recovered */
-#define EXT4_FC_INELIGIBLE		0x0008	/* Fast commit ineligible */
-#define EXT4_FC_COMMITTING		0x0010	/* File system underoing a fast
-						 * commit.
-						 */
 #define EXT4_FC_REPLAY			0x0020	/* Fast commit replay ongoing */
 
 /*
@@ -1431,6 +1427,10 @@ struct ext4_super_block {
  */
 #define EXT4_MF_MNTDIR_SAMPLED		0x0001
 #define EXT4_MF_FS_ABORTED		0x0002	/* Fatal error detected */
+#define EXT4_MF_FC_INELIGIBLE		0x0004	/* Fast commit ineligible */
+#define EXT4_MF_FC_COMMITTING		0x0008	/* File system underoing a fast
+						 * commit.
+						 */
 
 #ifdef CONFIG_FS_ENCRYPTION
 #define DUMMY_ENCRYPTION_ENABLED(sbi) ((sbi)->s_dummy_enc_policy.policy != NULL)
@@ -1443,14 +1443,6 @@ struct ext4_super_block {
 
 #define EXT4_ENC_UTF8_12_1	1
 
-/*
- * Flags for ext4_sb_info.s_encoding_flags.
- */
-#define EXT4_ENC_STRICT_MODE_FL	(1 << 0)
-
-#define ext4_has_strict_mode(sbi) \
-	(sbi->s_encoding_flags & EXT4_ENC_STRICT_MODE_FL)
-
 /*
  * fourth extended-fs super-block data in memory
  */
@@ -1500,10 +1492,6 @@ struct ext4_sb_info {
 	struct kobject s_kobj;
 	struct completion s_kobj_unregister;
 	struct super_block *s_sb;
-#ifdef CONFIG_UNICODE
-	struct unicode_map *s_encoding;
-	__u16 s_encoding_flags;
-#endif
 
 	/* Journaling */
 	struct journal_s *s_journal;

fs/ext4/extents.c

@@ -1471,16 +1471,16 @@ static int ext4_ext_search_left(struct inode *inode,
 }
 
 /*
- * search the closest allocated block to the right for *logical
- * and returns it at @logical + it's physical address at @phys
- * if *logical is the largest allocated block, the function
- * returns 0 at @phys
- * return value contains 0 (success) or error code
+ * Search the closest allocated block to the right for *logical
+ * and returns it at @logical + it's physical address at @phys.
+ * If not exists, return 0 and @phys is set to 0. We will return
+ * 1 which means we found an allocated block and ret_ex is valid.
+ * Or return a (< 0) error code.
  */
 static int ext4_ext_search_right(struct inode *inode,
 				 struct ext4_ext_path *path,
 				 ext4_lblk_t *logical, ext4_fsblk_t *phys,
-				 struct ext4_extent **ret_ex)
+				 struct ext4_extent *ret_ex)
 {
 	struct buffer_head *bh = NULL;
 	struct ext4_extent_header *eh;
@@ -1574,10 +1574,11 @@ static int ext4_ext_search_right(struct inode *inode,
 found_extent:
 	*logical = le32_to_cpu(ex->ee_block);
 	*phys = ext4_ext_pblock(ex);
-	*ret_ex = ex;
+	if (ret_ex)
+		*ret_ex = *ex;
 	if (bh)
 		put_bh(bh);
-	return 0;
+	return 1;
 }
 
 /*
@@ -2868,8 +2869,8 @@ int ext4_ext_remove_space(struct inode *inode, ext4_lblk_t start,
 			 */
 			lblk = ex_end + 1;
 			err = ext4_ext_search_right(inode, path, &lblk, &pblk,
-						    &ex);
-			if (err)
+						    NULL);
+			if (err < 0)
 				goto out;
 			if (pblk) {
 				partial.pclu = EXT4_B2C(sbi, pblk);
@@ -4039,7 +4040,7 @@ int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,
 			struct ext4_map_blocks *map, int flags)
 {
 	struct ext4_ext_path *path = NULL;
-	struct ext4_extent newex, *ex, *ex2;
+	struct ext4_extent newex, *ex, ex2;
 	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
 	ext4_fsblk_t newblock = 0, pblk;
 	int err = 0, depth, ret;
@@ -4175,15 +4176,14 @@ int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,
 	if (err)
 		goto out;
 	ar.lright = map->m_lblk;
-	ex2 = NULL;
 	err = ext4_ext_search_right(inode, path, &ar.lright, &ar.pright, &ex2);
-	if (err)
+	if (err < 0)
 		goto out;
 
 	/* Check if the extent after searching to the right implies a
 	 * cluster we can use. */
-	if ((sbi->s_cluster_ratio > 1) && ex2 &&
-	    get_implied_cluster_alloc(inode->i_sb, map, ex2, path)) {
+	if ((sbi->s_cluster_ratio > 1) && err &&
+	    get_implied_cluster_alloc(inode->i_sb, map, &ex2, path)) {
 		ar.len = allocated = map->m_len;
 		newblock = map->m_pblk;
 		goto got_allocated_blocks;

fs/ext4/fast_commit.c

@@ -269,7 +269,7 @@ void ext4_fc_mark_ineligible(struct super_block *sb, int reason)
 	    (EXT4_SB(sb)->s_mount_state & EXT4_FC_REPLAY))
 		return;
 
-	sbi->s_mount_state |= EXT4_FC_INELIGIBLE;
+	sbi->s_mount_flags |= EXT4_MF_FC_INELIGIBLE;
 	WARN_ON(reason >= EXT4_FC_REASON_MAX);
 	sbi->s_fc_stats.fc_ineligible_reason_count[reason]++;
 }
@@ -292,7 +292,7 @@ void ext4_fc_start_ineligible(struct super_block *sb, int reason)
 }
 
 /*
- * Stop a fast commit ineligible update. We set EXT4_FC_INELIGIBLE flag here
+ * Stop a fast commit ineligible update. We set EXT4_MF_FC_INELIGIBLE flag here
  * to ensure that after stopping the ineligible update, at least one full
  * commit takes place.
  */
@@ -302,13 +302,13 @@ void ext4_fc_stop_ineligible(struct super_block *sb)
 	    (EXT4_SB(sb)->s_mount_state & EXT4_FC_REPLAY))
 		return;
 
-	EXT4_SB(sb)->s_mount_state |= EXT4_FC_INELIGIBLE;
+	EXT4_SB(sb)->s_mount_flags |= EXT4_MF_FC_INELIGIBLE;
 	atomic_dec(&EXT4_SB(sb)->s_fc_ineligible_updates);
 }
 
 static inline int ext4_fc_is_ineligible(struct super_block *sb)
 {
-	return (EXT4_SB(sb)->s_mount_state & EXT4_FC_INELIGIBLE) ||
+	return (EXT4_SB(sb)->s_mount_flags & EXT4_MF_FC_INELIGIBLE) ||
 		atomic_read(&EXT4_SB(sb)->s_fc_ineligible_updates);
 }
 
@@ -358,7 +358,7 @@ static int ext4_fc_track_template(
 	spin_lock(&sbi->s_fc_lock);
 	if (list_empty(&EXT4_I(inode)->i_fc_list))
 		list_add_tail(&EXT4_I(inode)->i_fc_list,
-				(sbi->s_mount_state & EXT4_FC_COMMITTING) ?
+				(sbi->s_mount_flags & EXT4_MF_FC_COMMITTING) ?
 				&sbi->s_fc_q[FC_Q_STAGING] :
 				&sbi->s_fc_q[FC_Q_MAIN]);
 	spin_unlock(&sbi->s_fc_lock);
@@ -411,7 +411,7 @@ static int __track_dentry_update(struct inode *inode, void *arg, bool update)
 	node->fcd_name.len = dentry->d_name.len;
 
 	spin_lock(&sbi->s_fc_lock);
-	if (sbi->s_mount_state & EXT4_FC_COMMITTING)
+	if (sbi->s_mount_flags & EXT4_MF_FC_COMMITTING)
 		list_add_tail(&node->fcd_list,
 				&sbi->s_fc_dentry_q[FC_Q_STAGING]);
 	else
@@ -846,7 +846,7 @@ static int ext4_fc_submit_inode_data_all(journal_t *journal)
 	int ret = 0;
 
 	spin_lock(&sbi->s_fc_lock);
-	sbi->s_mount_state |= EXT4_FC_COMMITTING;
+	sbi->s_mount_flags |= EXT4_MF_FC_COMMITTING;
 	list_for_each(pos, &sbi->s_fc_q[FC_Q_MAIN]) {
 		ei = list_entry(pos, struct ext4_inode_info, i_fc_list);
 		ext4_set_inode_state(&ei->vfs_inode, EXT4_STATE_FC_COMMITTING);
@@ -964,7 +964,6 @@ static int ext4_fc_commit_dentry_updates(journal_t *journal, u32 *crc)
 			fc_dentry->fcd_parent, fc_dentry->fcd_ino,
 			fc_dentry->fcd_name.len,
 			fc_dentry->fcd_name.name, crc)) {
-			spin_lock(&sbi->s_fc_lock);
 			ret = -ENOSPC;
 			goto lock_and_exit;
 		}
@@ -1191,8 +1190,8 @@ static void ext4_fc_cleanup(journal_t *journal, int full)
 	list_splice_init(&sbi->s_fc_q[FC_Q_STAGING],
 				&sbi->s_fc_q[FC_Q_STAGING]);
 
-	sbi->s_mount_state &= ~EXT4_FC_COMMITTING;
-	sbi->s_mount_state &= ~EXT4_FC_INELIGIBLE;
+	sbi->s_mount_flags &= ~EXT4_MF_FC_COMMITTING;
+	sbi->s_mount_flags &= ~EXT4_MF_FC_INELIGIBLE;
 
 	if (full)
 		sbi->s_fc_bytes = 0;
@@ -1617,8 +1616,10 @@ static int ext4_fc_replay_add_range(struct super_block *sb,
 		if (ret == 0) {
 			/* Range is not mapped */
 			path = ext4_find_extent(inode, cur, NULL, 0);
-			if (!path)
-				continue;
+			if (IS_ERR(path)) {
+				iput(inode);
+				return 0;
+			}
 			memset(&newex, 0, sizeof(newex));
 			newex.ee_block = cpu_to_le32(cur);
 			ext4_ext_store_pblock(
@@ -2078,6 +2079,8 @@ static int ext4_fc_replay(journal_t *journal, struct buffer_head *bh,
 
 void ext4_fc_init(struct super_block *sb, journal_t *journal)
 {
+	int num_fc_blocks;
+
 	/*
 	 * We set replay callback even if fast commit disabled because we may
 	 * could still have fast commit blocks that need to be replayed even if
@@ -2087,7 +2090,15 @@ void ext4_fc_init(struct super_block *sb, journal_t *journal)
 	if (!test_opt2(sb, JOURNAL_FAST_COMMIT))
 		return;
 	journal->j_fc_cleanup_callback = ext4_fc_cleanup;
-	if (jbd2_fc_init(journal, EXT4_NUM_FC_BLKS)) {
+	if (!buffer_uptodate(journal->j_sb_buffer)
+		&& ext4_read_bh_lock(journal->j_sb_buffer, REQ_META | REQ_PRIO,
+					true)) {
+		ext4_msg(sb, KERN_ERR, "I/O error on journal");
+		return;
+	}
+	num_fc_blocks = be32_to_cpu(journal->j_superblock->s_num_fc_blks);
+	if (jbd2_fc_init(journal, num_fc_blocks ? num_fc_blocks :
+					EXT4_NUM_FC_BLKS)) {
 		pr_warn("Error while enabling fast commits, turning off.");
 		ext4_clear_feature_fast_commit(sb);
 	}

fs/ext4/hash.c

@@ -275,7 +275,7 @@ int ext4fs_dirhash(const struct inode *dir, const char *name, int len,
 		   struct dx_hash_info *hinfo)
 {
 #ifdef CONFIG_UNICODE
-	const struct unicode_map *um = EXT4_SB(dir->i_sb)->s_encoding;
+	const struct unicode_map *um = dir->i_sb->s_encoding;
 	int r, dlen;
 	unsigned char *buff;
 	struct qstr qstr = {.name = name, .len = len };

fs/ext4/inode.c

@@ -1918,7 +1918,7 @@ static int __ext4_journalled_writepage(struct page *page,
 	}
 	if (ret == 0)
 		ret = err;
-	err = ext4_jbd2_inode_add_write(handle, inode, 0, len);
+	err = ext4_jbd2_inode_add_write(handle, inode, page_offset(page), len);
 	if (ret == 0)
 		ret = err;
 	EXT4_I(inode)->i_datasync_tid = handle->h_transaction->t_tid;
@@ -3307,10 +3307,12 @@ static bool ext4_inode_datasync_dirty(struct inode *inode)
 
 	if (journal) {
 		if (jbd2_transaction_committed(journal,
-					EXT4_I(inode)->i_datasync_tid))
-			return true;
-		return atomic_read(&EXT4_SB(inode->i_sb)->s_fc_subtid) >=
-			EXT4_I(inode)->i_fc_committed_subtid;
+			EXT4_I(inode)->i_datasync_tid))
+			return false;
+		if (test_opt2(inode->i_sb, JOURNAL_FAST_COMMIT))
+			return atomic_read(&EXT4_SB(inode->i_sb)->s_fc_subtid) <
+				EXT4_I(inode)->i_fc_committed_subtid;
+		return true;
 	}
 
 	/* Any metadata buffers to write? */
@@ -6157,7 +6159,8 @@ vm_fault_t ext4_page_mkwrite(struct vm_fault *vmf)
 			if (ext4_walk_page_buffers(handle, page_buffers(page),
 					0, len, NULL, write_end_fn))
 				goto out_error;
-			if (ext4_jbd2_inode_add_write(handle, inode, 0, len))
+			if (ext4_jbd2_inode_add_write(handle, inode,
+						      page_offset(page), len))
 				goto out_error;
 			ext4_set_inode_state(inode, EXT4_STATE_JDATA);
 		} else {

fs/ext4/namei.c

@@ -1285,8 +1285,8 @@ static void dx_insert_block(struct dx_frame *frame, u32 hash, ext4_lblk_t block)
 int ext4_ci_compare(const struct inode *parent, const struct qstr *name,
 		    const struct qstr *entry, bool quick)
 {
-	const struct ext4_sb_info *sbi = EXT4_SB(parent->i_sb);
-	const struct unicode_map *um = sbi->s_encoding;
+	const struct super_block *sb = parent->i_sb;
+	const struct unicode_map *um = sb->s_encoding;
 	int ret;
 
 	if (quick)
@@ -1298,7 +1298,7 @@ int ext4_ci_compare(const struct inode *parent, const struct qstr *name,
 		/* Handle invalid character sequence as either an error
 		 * or as an opaque byte sequence.
 		 */
-		if (ext4_has_strict_mode(sbi))
+		if (sb_has_strict_encoding(sb))
 			return -EINVAL;
 
 		if (name->len != entry->len)
@@ -1315,7 +1315,7 @@ void ext4_fname_setup_ci_filename(struct inode *dir, const struct qstr *iname,
 {
 	int len;
 
-	if (!IS_CASEFOLDED(dir) || !EXT4_SB(dir->i_sb)->s_encoding) {
+	if (!IS_CASEFOLDED(dir) || !dir->i_sb->s_encoding) {
 		cf_name->name = NULL;
 		return;
 	}
@@ -1324,7 +1324,7 @@ void ext4_fname_setup_ci_filename(struct inode *dir, const struct qstr *iname,
 	if (!cf_name->name)
 		return;
 
-	len = utf8_casefold(EXT4_SB(dir->i_sb)->s_encoding,
+	len = utf8_casefold(dir->i_sb->s_encoding,
 			    iname, cf_name->name,
 			    EXT4_NAME_LEN);
 	if (len <= 0) {
@@ -1361,7 +1361,7 @@ static inline bool ext4_match(const struct inode *parent,
 #endif
 
 #ifdef CONFIG_UNICODE
-	if (EXT4_SB(parent->i_sb)->s_encoding && IS_CASEFOLDED(parent)) {
+	if (parent->i_sb->s_encoding && IS_CASEFOLDED(parent)) {
 		if (fname->cf_name.name) {
 			struct qstr cf = {.name = fname->cf_name.name,
 					  .len = fname->cf_name.len};
@@ -2180,9 +2180,6 @@ static int ext4_add_entry(handle_t *handle, struct dentry *dentry,
 	struct buffer_head *bh = NULL;
 	struct ext4_dir_entry_2 *de;
 	struct super_block *sb;
-#ifdef CONFIG_UNICODE
-	struct ext4_sb_info *sbi;
-#endif
 	struct ext4_filename fname;
 	int	retval;
 	int	dx_fallback=0;
@@ -2199,9 +2196,8 @@ static int ext4_add_entry(handle_t *handle, struct dentry *dentry,
 		return -EINVAL;
 
 #ifdef CONFIG_UNICODE
-	sbi = EXT4_SB(sb);
-	if (ext4_has_strict_mode(sbi) && IS_CASEFOLDED(dir) &&
-	    sbi->s_encoding && utf8_validate(sbi->s_encoding, &dentry->d_name))
+	if (sb_has_strict_encoding(sb) && IS_CASEFOLDED(dir) &&
+	    sb->s_encoding && utf8_validate(sb->s_encoding, &dentry->d_name))
 		return -EINVAL;
 #endif
 

fs/ext4/super.c

@@ -1288,7 +1288,7 @@ static void ext4_put_super(struct super_block *sb)
 	fs_put_dax(sbi->s_daxdev);
 	fscrypt_free_dummy_policy(&sbi->s_dummy_enc_policy);
 #ifdef CONFIG_UNICODE
-	utf8_unload(sbi->s_encoding);
+	utf8_unload(sb->s_encoding);
 #endif
 	kfree(sbi);
 }
@@ -4303,7 +4303,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 		goto failed_mount;
 
 #ifdef CONFIG_UNICODE
-	if (ext4_has_feature_casefold(sb) && !sbi->s_encoding) {
+	if (ext4_has_feature_casefold(sb) && !sb->s_encoding) {
 		const struct ext4_sb_encodings *encoding_info;
 		struct unicode_map *encoding;
 		__u16 encoding_flags;
@@ -4334,8 +4334,8 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 			 "%s-%s with flags 0x%hx", encoding_info->name,
 			 encoding_info->version?:"\b", encoding_flags);
 
-		sbi->s_encoding = encoding;
-		sbi->s_encoding_flags = encoding_flags;
+		sb->s_encoding = encoding;
+		sb->s_encoding_flags = encoding_flags;
 	}
 #endif
 
@@ -4777,8 +4777,8 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 	INIT_LIST_HEAD(&sbi->s_fc_dentry_q[FC_Q_MAIN]);
 	INIT_LIST_HEAD(&sbi->s_fc_dentry_q[FC_Q_STAGING]);
 	sbi->s_fc_bytes = 0;
-	sbi->s_mount_state &= ~EXT4_FC_INELIGIBLE;
-	sbi->s_mount_state &= ~EXT4_FC_COMMITTING;
+	sbi->s_mount_flags &= ~EXT4_MF_FC_INELIGIBLE;
+	sbi->s_mount_flags &= ~EXT4_MF_FC_COMMITTING;
 	spin_lock_init(&sbi->s_fc_lock);
 	memset(&sbi->s_fc_stats, 0, sizeof(sbi->s_fc_stats));
 	sbi->s_fc_replay_state.fc_regions = NULL;
@@ -4975,7 +4975,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 	}
 
 #ifdef CONFIG_UNICODE
-	if (sbi->s_encoding)
+	if (sb->s_encoding)
 		sb->s_d_op = &ext4_dentry_ops;
 #endif
 
@@ -5184,7 +5184,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 		crypto_free_shash(sbi->s_chksum_driver);
 
 #ifdef CONFIG_UNICODE
-	utf8_unload(sbi->s_encoding);
+	utf8_unload(sb->s_encoding);
 #endif
 
 #ifdef CONFIG_QUOTA

fs/ext4/sysfs.c

@@ -315,6 +315,7 @@ EXT4_ATTR_FEATURE(casefold);
 EXT4_ATTR_FEATURE(verity);
 #endif
 EXT4_ATTR_FEATURE(metadata_csum_seed);
+EXT4_ATTR_FEATURE(fast_commit);
 
 static struct attribute *ext4_feat_attrs[] = {
 	ATTR_LIST(lazy_itable_init),
@@ -331,6 +332,7 @@ static struct attribute *ext4_feat_attrs[] = {
 	ATTR_LIST(verity),
 #endif
 	ATTR_LIST(metadata_csum_seed),
+	ATTR_LIST(fast_commit),
 	NULL,
 };
 ATTRIBUTE_GROUPS(ext4_feat);

include/linux/jbd2.h

@@ -263,7 +263,10 @@ typedef struct journal_superblock_s
 /* 0x0050 */
 	__u8	s_checksum_type;	/* checksum type */
 	__u8	s_padding2[3];
-	__u32	s_padding[42];
+/* 0x0054 */
+	__be32	s_num_fc_blks;		/* Number of fast commit blocks */
+/* 0x0058 */
+	__u32	s_padding[41];
 	__be32	s_checksum;		/* crc32c(superblock) */
 
 /* 0x0100 */
@@ -1253,7 +1256,7 @@ struct journal_s
 	 */
 	void (*j_fc_cleanup_callback)(struct journal_s *journal, int);
 
-	/*
+	/**
 	 * @j_fc_replay_callback:
 	 *
 	 * File-system specific function that performs replay of a fast