X-Git-Url: https://git.carlh.net/gitweb/?a=blobdiff_plain;f=lwext4%2Fext4_journal.c;h=033f3a49fd5d6fda28b86881279d75433af438e9;hb=2357dfc97f58c458e110b239b5d147996864ecb5;hp=61926ae973104fb8253bb3f91d90d1866a3b3312;hpb=696059627084945d5b51f1a161731b4bc581ee58;p=lwext4.git

diff --git a/lwext4/ext4_journal.c b/lwext4/ext4_journal.c
index 61926ae..033f3a4 100644
--- a/lwext4/ext4_journal.c
+++ b/lwext4/ext4_journal.c
@@ -1,12 +1,45 @@
+/*
+ * Copyright (c) 2015 Grzegorz Kostka (kostka.grzegorz@gmail.com)
+ * Copyright (c) 2015 Kaho Ng (ngkaho1234@gmail.com)
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ * - Redistributions in binary form must reproduce the above copyright
+ *   notice, this list of conditions and the following disclaimer in the
+ *   documentation and/or other materials provided with the distribution.
+ * - The name of the author may not be used to endorse or promote products
+ *   derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/** @addtogroup lwext4
+ * @{
+ */
 /**
  * @file  ext4_journal.c
- * @brief Journalling
+ * @brief Journal handle functions
  */
 
 #include "ext4_config.h"
 #include "ext4_types.h"
 #include "ext4_fs.h"
 #include "ext4_super.h"
+#include "ext4_journal.h"
 #include "ext4_errno.h"
 #include "ext4_blockdev.h"
 #include "ext4_crc32c.h"
@@ -14,24 +47,47 @@
 #include "tree.h"
 
 #include <string.h>
-#include <malloc.h>
+#include <stdlib.h>
 
+/**@brief  Revoke entry during journal replay.*/
 struct revoke_entry {
+	/**@brief  Block number not to be replayed.*/
 	ext4_fsblk_t block;
+
+	/**@brief  For any transaction id smaller
+	 *         than trans_id, records of @block
+	 *         in those transactions should not
+	 *         be replayed.*/
 	uint32_t trans_id;
+
+	/**@brief  Revoke tree node.*/
 	RB_ENTRY(revoke_entry) revoke_node;
 };
 
+/**@brief  Valid journal replay information.*/
 struct recover_info {
+	/**@brief  Starting transaction id.*/
 	uint32_t start_trans_id;
+
+	/**@brief  Ending transaction id.*/
 	uint32_t last_trans_id;
+
+	/**@brief  Used as internal argument.*/
 	uint32_t this_trans_id;
+
+	/**@brief  RB-Tree storing revoke entries.*/
 	RB_HEAD(jbd_revoke, revoke_entry) revoke_root;
 };
 
+/**@brief  Journal replay internal arguments.*/
 struct replay_arg {
+	/**@brief  Journal replay information.*/
 	struct recover_info *info;
+
+	/**@brief  Current block we are on.*/
 	uint32_t *this_block;
+
+	/**@brief  Current trans_id we are on.*/
 	uint32_t this_trans_id;
 };
 
@@ -45,17 +101,29 @@ jbd_revoke_entry_cmp(struct revoke_entry *a, struct revoke_entry *b)
 	return 0;
 }
 
+static int
+jbd_block_rec_cmp(struct jbd_block_rec *a, struct jbd_block_rec *b)
+{
+	if (a->lba > b->lba)
+		return 1;
+	else if (a->lba < b->lba)
+		return -1;
+	return 0;
+}
+
 RB_GENERATE_INTERNAL(jbd_revoke, revoke_entry, revoke_node,
 		     jbd_revoke_entry_cmp, static inline)
+RB_GENERATE_INTERNAL(jbd_block, jbd_block_rec, block_rec_node,
+		     jbd_block_rec_cmp, static inline)
 
 #define jbd_alloc_revoke_entry() calloc(1, sizeof(struct revoke_entry))
 #define jbd_free_revoke_entry(addr) free(addr)
 
-int jbd_inode_bmap(struct jbd_fs *jbd_fs,
-		   ext4_lblk_t iblock,
-		   ext4_fsblk_t *fblock);
-
-int jbd_sb_write(struct jbd_fs *jbd_fs, struct jbd_sb *s)
+/**@brief  Write jbd superblock to disk.
+ * @param  jbd_fs jbd filesystem
+ * @param  s jbd superblock
+ * @return standard error code*/
+static int jbd_sb_write(struct jbd_fs *jbd_fs, struct jbd_sb *s)
 {
 	int rc;
 	struct ext4_fs *fs = jbd_fs->inode_ref.fs;
@@ -70,7 +138,11 @@ int jbd_sb_write(struct jbd_fs *jbd_fs, struct jbd_sb *s)
 				     EXT4_SUPERBLOCK_SIZE);
 }
 
-int jbd_sb_read(struct jbd_fs *jbd_fs, struct jbd_sb *s)
+/**@brief  Read jbd superblock from disk.
+ * @param  jbd_fs jbd filesystem
+ * @param  s jbd superblock
+ * @return standard error code*/
+static int jbd_sb_read(struct jbd_fs *jbd_fs, struct jbd_sb *s)
 {
 	int rc;
 	struct ext4_fs *fs = jbd_fs->inode_ref.fs;
@@ -85,6 +157,9 @@ int jbd_sb_read(struct jbd_fs *jbd_fs, struct jbd_sb *s)
 				    EXT4_SUPERBLOCK_SIZE);
 }
 
+/**@brief  Verify jbd superblock.
+ * @param  sb jbd superblock
+ * @return true if jbd superblock is valid */
 static bool jbd_verify_sb(struct jbd_sb *sb)
 {
 	struct jbd_bhdr *header = &sb->header;
@@ -98,6 +173,26 @@ static bool jbd_verify_sb(struct jbd_sb *sb)
 	return true;
 }
 
+/**@brief  Write back dirty jbd superblock to disk.
+ * @param  jbd_fs jbd filesystem
+ * @return standard error code*/
+static int jbd_write_sb(struct jbd_fs *jbd_fs)
+{
+	int rc = EOK;
+	if (jbd_fs->dirty) {
+		rc = jbd_sb_write(jbd_fs, &jbd_fs->sb);
+		if (rc != EOK)
+			return rc;
+
+		jbd_fs->dirty = false;
+	}
+	return rc;
+}
+
+/**@brief  Get reference to jbd filesystem.
+ * @param  fs Filesystem to load journal of
+ * @param  jbd_fs jbd filesystem
+ * @return standard error code*/
 int jbd_get_fs(struct ext4_fs *fs,
 	       struct jbd_fs *jbd_fs)
 {
@@ -105,6 +200,9 @@ int jbd_get_fs(struct ext4_fs *fs,
 	uint32_t journal_ino;
 
 	memset(jbd_fs, 0, sizeof(struct jbd_fs));
+	/* See if there is journal inode on this filesystem.*/
+	/* FIXME: detection on existance ofbkejournal bdev is
+	 *        missing.*/
 	journal_ino = ext4_get32(&fs->sb, journal_inode_number);
 
 	rc = ext4_fs_get_inode_ref(fs,
@@ -118,26 +216,39 @@ int jbd_get_fs(struct ext4_fs *fs,
 	if (rc != EOK) {
 		memset(jbd_fs, 0, sizeof(struct jbd_fs));
 		ext4_fs_put_inode_ref(&jbd_fs->inode_ref);
+		return rc;
+	}
+	if (!jbd_verify_sb(&jbd_fs->sb)) {
+		memset(jbd_fs, 0, sizeof(struct jbd_fs));
+		ext4_fs_put_inode_ref(&jbd_fs->inode_ref);
+		rc = EIO;
 	}
 
 	return rc;
 }
 
+/**@brief  Put reference of jbd filesystem.
+ * @param  jbd_fs jbd filesystem
+ * @return standard error code*/
 int jbd_put_fs(struct jbd_fs *jbd_fs)
 {
-	int rc;
-	if (jbd_fs->dirty)
-		jbd_sb_write(jbd_fs, &jbd_fs->sb);
+	int rc = EOK;
+	rc = jbd_write_sb(jbd_fs);
 
-	rc = ext4_fs_put_inode_ref(&jbd_fs->inode_ref);
+	ext4_fs_put_inode_ref(&jbd_fs->inode_ref);
 	return rc;
 }
 
+/**@brief  Data block lookup helper.
+ * @param  jbd_fs jbd filesystem
+ * @param  iblock block index
+ * @param  fblock logical block address
+ * @return standard error code*/
 int jbd_inode_bmap(struct jbd_fs *jbd_fs,
 		   ext4_lblk_t iblock,
 		   ext4_fsblk_t *fblock)
 {
-	int rc = ext4_fs_get_inode_data_block_index(
+	int rc = ext4_fs_get_inode_dblk_idx(
 			&jbd_fs->inode_ref,
 			iblock,
 			fblock,
@@ -145,13 +256,21 @@ int jbd_inode_bmap(struct jbd_fs *jbd_fs,
 	return rc;
 }
 
-int jbd_block_get(struct jbd_fs *jbd_fs,
+/**@brief   jbd block get function (through cache).
+ * @param   jbd_fs jbd filesystem
+ * @param   block block descriptor
+ * @param   fblock jbd logical block address
+ * @return  standard error code*/
+static int jbd_block_get(struct jbd_fs *jbd_fs,
 		  struct ext4_block *block,
 		  ext4_fsblk_t fblock)
 {
 	/* TODO: journal device. */
 	int rc;
 	ext4_lblk_t iblock = (ext4_lblk_t)fblock;
+
+	/* Lookup the logical block address of
+	 * fblock.*/
 	rc = jbd_inode_bmap(jbd_fs, iblock,
 			    &fblock);
 	if (rc != EOK)
@@ -159,10 +278,21 @@ int jbd_block_get(struct jbd_fs *jbd_fs,
 
 	struct ext4_blockdev *bdev = jbd_fs->inode_ref.fs->bdev;
 	rc = ext4_block_get(bdev, block, fblock);
+
+	/* If succeeded, mark buffer as BC_FLUSH to indicate
+	 * that data should be written to disk immediately.*/
+	if (rc == EOK)
+		ext4_bcache_set_flag(block->buf, BC_FLUSH);
+
 	return rc;
 }
 
-int jbd_block_get_noread(struct jbd_fs *jbd_fs,
+/**@brief   jbd block get function (through cache, don't read).
+ * @param   jbd_fs jbd filesystem
+ * @param   block block descriptor
+ * @param   fblock jbd logical block address
+ * @return  standard error code*/
+static int jbd_block_get_noread(struct jbd_fs *jbd_fs,
 			 struct ext4_block *block,
 			 ext4_fsblk_t fblock)
 {
@@ -176,29 +306,41 @@ int jbd_block_get_noread(struct jbd_fs *jbd_fs,
 
 	struct ext4_blockdev *bdev = jbd_fs->inode_ref.fs->bdev;
 	rc = ext4_block_get_noread(bdev, block, fblock);
+	if (rc == EOK)
+		ext4_bcache_set_flag(block->buf, BC_FLUSH);
+
 	return rc;
 }
 
-int jbd_block_set(struct jbd_fs *jbd_fs,
+/**@brief   jbd block set procedure (through cache).
+ * @param   jbd_fs jbd filesystem
+ * @param   block block descriptor
+ * @return  standard error code*/
+static int jbd_block_set(struct jbd_fs *jbd_fs,
 		  struct ext4_block *block)
 {
 	return ext4_block_set(jbd_fs->inode_ref.fs->bdev,
 			      block);
 }
 
-/*
- * helper functions to deal with 32 or 64bit block numbers.
- */
-int jbd_tag_bytes(struct jbd_fs *jbd_fs)
+/**@brief  helper functions to calculate
+ *         block tag size, not including UUID part.
+ * @param  jbd_fs jbd filesystem
+ * @return tag size in bytes*/
+static int jbd_tag_bytes(struct jbd_fs *jbd_fs)
 {
 	int size;
 
+	/* It is very easy to deal with the case which
+	 * JBD_FEATURE_INCOMPAT_CSUM_V3 is enabled.*/
 	if (JBD_HAS_INCOMPAT_FEATURE(&jbd_fs->sb,
 				     JBD_FEATURE_INCOMPAT_CSUM_V3))
 		return sizeof(struct jbd_block_tag3);
 
 	size = sizeof(struct jbd_block_tag);
 
+	/* If JBD_FEATURE_INCOMPAT_CSUM_V2 is enabled,
+	 * add 2 bytes to size.*/
 	if (JBD_HAS_INCOMPAT_FEATURE(&jbd_fs->sb,
 				     JBD_FEATURE_INCOMPAT_CSUM_V2))
 		size += sizeof(uint16_t);
@@ -207,106 +349,227 @@ int jbd_tag_bytes(struct jbd_fs *jbd_fs)
 				     JBD_FEATURE_INCOMPAT_64BIT))
 		return size;
 
+	/* If block number is 4 bytes in size,
+	 * minus 4 bytes from size */
 	return size - sizeof(uint32_t);
 }
 
-static void
+/**@brief  Tag information. */
+struct tag_info {
+	/**@brief  Tag size in bytes, including UUID part.*/
+	int tag_bytes;
+
+	/**@brief  block number stored in this tag.*/
+	ext4_fsblk_t block;
+
+	/**@brief  whether UUID part exists or not.*/
+	bool uuid_exist;
+
+	/**@brief  UUID content if UUID part exists.*/
+	uint8_t uuid[UUID_SIZE];
+
+	/**@brief  Is this the last tag? */
+	bool last_tag;
+};
+
+/**@brief  Extract information from a block tag.
+ * @param  __tag pointer to the block tag
+ * @param  tag_bytes block tag size of this jbd filesystem
+ * @param  remaining size in buffer containing the block tag
+ * @param  tag_info information of this tag.
+ * @return  EOK when succeed, otherwise return EINVAL.*/
+static int
 jbd_extract_block_tag(struct jbd_fs *jbd_fs,
-		      uint32_t tag_bytes,
 		      void *__tag,
-		      ext4_fsblk_t *block,
-		      bool *uuid_exist,
-		      uint8_t *uuid,
-		      bool *last_tag)
+		      int tag_bytes,
+		      int32_t remain_buf_size,
+		      struct tag_info *tag_info)
 {
 	char *uuid_start;
-	*uuid_exist = false;
-	*last_tag = false;
+	tag_info->tag_bytes = tag_bytes;
+	tag_info->uuid_exist = false;
+	tag_info->last_tag = false;
+
+	/* See whether it is possible to hold a valid block tag.*/
+	if (remain_buf_size - tag_bytes < 0)
+		return EINVAL;
+
 	if (JBD_HAS_INCOMPAT_FEATURE(&jbd_fs->sb,
 				     JBD_FEATURE_INCOMPAT_CSUM_V3)) {
 		struct jbd_block_tag3 *tag = __tag;
-		*block = jbd_get32(tag, blocknr);
+		tag_info->block = jbd_get32(tag, blocknr);
 		if (JBD_HAS_INCOMPAT_FEATURE(&jbd_fs->sb,
 					     JBD_FEATURE_INCOMPAT_64BIT))
-			 *block |= (uint64_t)jbd_get32(tag, blocknr_high) << 32;
+			 tag_info->block |=
+				 (uint64_t)jbd_get32(tag, blocknr_high) << 32;
 
 		if (jbd_get32(tag, flags) & JBD_FLAG_ESCAPE)
-			*block = 0;
+			tag_info->block = 0;
 
 		if (!(jbd_get32(tag, flags) & JBD_FLAG_SAME_UUID)) {
+			/* See whether it is possible to hold UUID part.*/
+			if (remain_buf_size - tag_bytes < UUID_SIZE)
+				return EINVAL;
+
 			uuid_start = (char *)tag + tag_bytes;
-			*uuid_exist = true;
-			memcpy(uuid, uuid_start, UUID_SIZE);
+			tag_info->uuid_exist = true;
+			tag_info->tag_bytes += UUID_SIZE;
+			memcpy(tag_info->uuid, uuid_start, UUID_SIZE);
 		}
 
 		if (jbd_get32(tag, flags) & JBD_FLAG_LAST_TAG)
-			*last_tag = true;
+			tag_info->last_tag = true;
 
 	} else {
 		struct jbd_block_tag *tag = __tag;
-		*block = jbd_get32(tag, blocknr);
+		tag_info->block = jbd_get32(tag, blocknr);
 		if (JBD_HAS_INCOMPAT_FEATURE(&jbd_fs->sb,
 					     JBD_FEATURE_INCOMPAT_64BIT))
-			 *block |= (uint64_t)jbd_get32(tag, blocknr_high) << 32;
+			 tag_info->block |=
+				 (uint64_t)jbd_get32(tag, blocknr_high) << 32;
 
 		if (jbd_get16(tag, flags) & JBD_FLAG_ESCAPE)
-			*block = 0;
+			tag_info->block = 0;
 
 		if (!(jbd_get16(tag, flags) & JBD_FLAG_SAME_UUID)) {
+			/* See whether it is possible to hold UUID part.*/
+			if (remain_buf_size - tag_bytes < UUID_SIZE)
+				return EINVAL;
+
 			uuid_start = (char *)tag + tag_bytes;
-			*uuid_exist = true;
-			memcpy(uuid, uuid_start, UUID_SIZE);
+			tag_info->uuid_exist = true;
+			tag_info->tag_bytes += UUID_SIZE;
+			memcpy(tag_info->uuid, uuid_start, UUID_SIZE);
 		}
 
 		if (jbd_get16(tag, flags) & JBD_FLAG_LAST_TAG)
-			*last_tag = true;
+			tag_info->last_tag = true;
 
 	}
+	return EOK;
 }
 
+/**@brief  Write information to a block tag.
+ * @param  __tag pointer to the block tag
+ * @param  remaining size in buffer containing the block tag
+ * @param  tag_info information of this tag.
+ * @return  EOK when succeed, otherwise return EINVAL.*/
+static int
+jbd_write_block_tag(struct jbd_fs *jbd_fs,
+		    void *__tag,
+		    int32_t remain_buf_size,
+		    struct tag_info *tag_info)
+{
+	char *uuid_start;
+	int tag_bytes = jbd_tag_bytes(jbd_fs);
+
+	tag_info->tag_bytes = tag_bytes;
+
+	/* See whether it is possible to hold a valid block tag.*/
+	if (remain_buf_size - tag_bytes < 0)
+		return EINVAL;
+
+	if (JBD_HAS_INCOMPAT_FEATURE(&jbd_fs->sb,
+				     JBD_FEATURE_INCOMPAT_CSUM_V3)) {
+		struct jbd_block_tag3 *tag = __tag;
+		memset(tag, 0, sizeof(struct jbd_block_tag3));
+		jbd_set32(tag, blocknr, tag_info->block);
+		if (JBD_HAS_INCOMPAT_FEATURE(&jbd_fs->sb,
+					     JBD_FEATURE_INCOMPAT_64BIT))
+			jbd_set32(tag, blocknr_high, tag_info->block >> 32);
+
+		if (tag_info->uuid_exist) {
+			/* See whether it is possible to hold UUID part.*/
+			if (remain_buf_size - tag_bytes < UUID_SIZE)
+				return EINVAL;
+
+			uuid_start = (char *)tag + tag_bytes;
+			tag_info->tag_bytes += UUID_SIZE;
+			memcpy(uuid_start, tag_info->uuid, UUID_SIZE);
+		} else
+			jbd_set32(tag, flags,
+				  jbd_get32(tag, flags) | JBD_FLAG_SAME_UUID);
+
+		if (tag_info->last_tag)
+			jbd_set32(tag, flags,
+				  jbd_get32(tag, flags) | JBD_FLAG_LAST_TAG);
+
+	} else {
+		struct jbd_block_tag *tag = __tag;
+		memset(tag, 0, sizeof(struct jbd_block_tag));
+		jbd_set32(tag, blocknr, tag_info->block);
+		if (JBD_HAS_INCOMPAT_FEATURE(&jbd_fs->sb,
+					     JBD_FEATURE_INCOMPAT_64BIT))
+			jbd_set32(tag, blocknr_high, tag_info->block >> 32);
+
+		if (tag_info->uuid_exist) {
+			/* See whether it is possible to hold UUID part.*/
+			if (remain_buf_size - tag_bytes < UUID_SIZE)
+				return EINVAL;
+
+			uuid_start = (char *)tag + tag_bytes;
+			tag_info->tag_bytes += UUID_SIZE;
+			memcpy(uuid_start, tag_info->uuid, UUID_SIZE);
+		} else
+			jbd_set16(tag, flags,
+				  jbd_get16(tag, flags) | JBD_FLAG_SAME_UUID);
+
+		if (tag_info->last_tag)
+			jbd_set16(tag, flags,
+				  jbd_get16(tag, flags) | JBD_FLAG_LAST_TAG);
+
+	}
+	return EOK;
+}
+
+/**@brief  Iterate all block tags in a block.
+ * @param  jbd_fs jbd filesystem
+ * @param  __tag_start pointer to the block
+ * @param  tag_tbl_size size of the block
+ * @param  func callback routine to indicate that
+ *         a block tag is found
+ * @param  arg additional argument to be passed to func */
 static void
 jbd_iterate_block_table(struct jbd_fs *jbd_fs,
 			void *__tag_start,
-			uint32_t tag_tbl_size,
+			int32_t tag_tbl_size,
 			void (*func)(struct jbd_fs * jbd_fs,
 					ext4_fsblk_t block,
 					uint8_t *uuid,
 					void *arg),
 			void *arg)
 {
-	ext4_fsblk_t block = 0;
-	uint8_t uuid[UUID_SIZE];
 	char *tag_start, *tag_ptr;
-	uint32_t tag_bytes = jbd_tag_bytes(jbd_fs);
+	int tag_bytes = jbd_tag_bytes(jbd_fs);
 	tag_start = __tag_start;
 	tag_ptr = tag_start;
 
+	/* Cut off the size of block tail storing checksum. */
 	if (JBD_HAS_INCOMPAT_FEATURE(&jbd_fs->sb,
 				     JBD_FEATURE_INCOMPAT_CSUM_V2) ||
 	    JBD_HAS_INCOMPAT_FEATURE(&jbd_fs->sb,
 				     JBD_FEATURE_INCOMPAT_CSUM_V3))
 		tag_tbl_size -= sizeof(struct jbd_block_tail);
 
-	while (tag_ptr - tag_start + tag_bytes <= tag_tbl_size) {
-		bool uuid_exist;
-		bool last_tag;
-		jbd_extract_block_tag(jbd_fs,
-				      tag_bytes,
+	while (tag_tbl_size) {
+		struct tag_info tag_info;
+		int rc = jbd_extract_block_tag(jbd_fs,
 				      tag_ptr,
-				      &block,
-				      &uuid_exist,
-				      uuid,
-				      &last_tag);
+				      tag_bytes,
+				      tag_tbl_size,
+				      &tag_info);
+		if (rc != EOK)
+			break;
+
 		if (func)
-			func(jbd_fs, block, uuid, arg);
+			func(jbd_fs, tag_info.block, tag_info.uuid, arg);
 
-		if (last_tag)
+		/* Stop the iteration when we reach the last tag. */
+		if (tag_info.last_tag)
 			break;
 
-		tag_ptr += tag_bytes;
-		if (uuid_exist)
-			tag_ptr += UUID_SIZE;
-
+		tag_ptr += tag_info.tag_bytes;
+		tag_tbl_size -= tag_info.tag_bytes;
 	}
 }
 
@@ -333,6 +596,9 @@ jbd_revoke_entry_lookup(struct recover_info *info, ext4_fsblk_t block)
 	return RB_FIND(jbd_revoke, &info->revoke_root, &tmp);
 }
 
+/**@brief  Replay a block in a transaction.
+ * @param  jbd_fs jbd filesystem
+ * @param  block  block address to be replayed.*/
 static void jbd_replay_block_tags(struct jbd_fs *jbd_fs,
 				  ext4_fsblk_t block,
 				  uint8_t *uuid __unused,
@@ -346,20 +612,24 @@ static void jbd_replay_block_tags(struct jbd_fs *jbd_fs,
 	struct ext4_block journal_block, ext4_block;
 	struct ext4_fs *fs = jbd_fs->inode_ref.fs;
 
-	ext4_dbg(DEBUG_JBD,
-		 "Replaying block in block_tag: %" PRIu64 "\n",
-		 block);
 	(*this_block)++;
 
+	/* We replay this block only if the current transaction id
+	 * is equal or greater than that in revoke entry.*/
 	revoke_entry = jbd_revoke_entry_lookup(info, block);
 	if (revoke_entry &&
 	    arg->this_trans_id < revoke_entry->trans_id)
 		return;
 
+	ext4_dbg(DEBUG_JBD,
+		 "Replaying block in block_tag: %" PRIu64 "\n",
+		 block);
+
 	r = jbd_block_get(jbd_fs, &journal_block, *this_block);
 	if (r != EOK)
 		return;
 
+	/* We need special treatment for ext4 superblock. */
 	if (block) {
 		r = ext4_block_get_noread(fs->bdev, &ext4_block, block);
 		if (r != EOK) {
@@ -371,7 +641,7 @@ static void jbd_replay_block_tags(struct jbd_fs *jbd_fs,
 			journal_block.data,
 			jbd_get32(&jbd_fs->sb, blocksize));
 
-		ext4_block.dirty = true;
+		ext4_bcache_set_dirty(ext4_block.buf);
 		ext4_block_set(fs->bdev, &ext4_block);
 	} else {
 		uint16_t mount_count, state;
@@ -397,12 +667,18 @@ static void jbd_replay_block_tags(struct jbd_fs *jbd_fs,
 	return;
 }
 
+/**@brief  Add block address to revoke tree, along with
+ *         its transaction id.
+ * @param  info  journal replay info
+ * @param  block  block address to be replayed.*/
 static void jbd_add_revoke_block_tags(struct recover_info *info,
 				      ext4_fsblk_t block)
 {
 	struct revoke_entry *revoke_entry;
 
 	ext4_dbg(DEBUG_JBD, "Add block %" PRIu64 " to revoke tree\n", block);
+	/* If the revoke entry with respect to the block address
+	 * exists already, update its transaction id.*/
 	revoke_entry = jbd_revoke_entry_lookup(info, block);
 	if (revoke_entry) {
 		revoke_entry->trans_id = info->this_trans_id;
@@ -440,7 +716,10 @@ do {									\
 #define ACTION_REVOKE 1
 #define ACTION_RECOVER 2
 
-
+/**@brief  Add entries in a revoke block to revoke tree.
+ * @param  jbd_fs jbd filesystem
+ * @param  header revoke block header
+ * @param  recover_info  journal replay info*/
 static void jbd_build_revoke_tree(struct jbd_fs *jbd_fs,
 				  struct jbd_bhdr *header,
 				  struct recover_info *info)
@@ -449,11 +728,13 @@ static void jbd_build_revoke_tree(struct jbd_fs *jbd_fs,
 	struct jbd_revoke_header *revoke_hdr =
 		(struct jbd_revoke_header *)header;
 	uint32_t i, nr_entries, record_len = 4;
+
+	/* If we are working on a 64bit jbd filesystem, */
 	if (JBD_HAS_INCOMPAT_FEATURE(&jbd_fs->sb,
 				     JBD_FEATURE_INCOMPAT_64BIT))
 		record_len = 8;
 
-	nr_entries = (revoke_hdr->count -
+	nr_entries = (jbd_get32(revoke_hdr, count) -
 			sizeof(struct jbd_revoke_header)) /
 			record_len;
 
@@ -463,11 +744,11 @@ static void jbd_build_revoke_tree(struct jbd_fs *jbd_fs,
 		if (record_len == 8) {
 			uint64_t *blocks =
 				(uint64_t *)blocks_entry;
-			jbd_add_revoke_block_tags(info, *blocks);
+			jbd_add_revoke_block_tags(info, to_be64(*blocks));
 		} else {
 			uint32_t *blocks =
 				(uint32_t *)blocks_entry;
-			jbd_add_revoke_block_tags(info, *blocks);
+			jbd_add_revoke_block_tags(info, to_be32(*blocks));
 		}
 		blocks_entry += record_len;
 	}
@@ -497,9 +778,14 @@ static void jbd_replay_descriptor_block(struct jbd_fs *jbd_fs,
 				arg);
 }
 
-int jbd_iterate_log(struct jbd_fs *jbd_fs,
-		    struct recover_info *info,
-		    int action)
+/**@brief  The core routine of journal replay.
+ * @param  jbd_fs jbd filesystem
+ * @param  recover_info  journal replay info
+ * @param  action action needed to be taken
+ * @return standard error code*/
+static int jbd_iterate_log(struct jbd_fs *jbd_fs,
+			   struct recover_info *info,
+			   int action)
 {
 	int r = EOK;
 	bool log_end = false;
@@ -507,6 +793,7 @@ int jbd_iterate_log(struct jbd_fs *jbd_fs,
 	uint32_t start_trans_id, this_trans_id;
 	uint32_t start_block, this_block;
 
+	/* We start iterating valid blocks in the whole journal.*/
 	start_trans_id = this_trans_id = jbd_get32(sb, sequence);
 	start_block = this_block = jbd_get32(sb, start);
 
@@ -516,6 +803,10 @@ int jbd_iterate_log(struct jbd_fs *jbd_fs,
 	while (!log_end) {
 		struct ext4_block block;
 		struct jbd_bhdr *header;
+		/* If we are not scanning for the last
+		 * valid transaction in the journal,
+		 * we will stop when we reach the end of
+		 * the journal.*/
 		if (action != ACTION_SCAN)
 			if (this_trans_id > info->last_trans_id) {
 				log_end = true;
@@ -527,12 +818,19 @@ int jbd_iterate_log(struct jbd_fs *jbd_fs,
 			break;
 
 		header = (struct jbd_bhdr *)block.data;
+		/* This block does not have a valid magic number,
+		 * so we have reached the end of the journal.*/
 		if (jbd_get32(header, magic) != JBD_MAGIC_NUMBER) {
 			jbd_block_set(jbd_fs, &block);
 			log_end = true;
 			continue;
 		}
 
+		/* If the transaction id we found is not expected,
+		 * we may have reached the end of the journal.
+		 *
+		 * If we are not scanning the journal, something
+		 * bad might have taken place. :-( */
 		if (jbd_get32(header, sequence) != this_trans_id) {
 			if (action != ACTION_SCAN)
 				r = EIO;
@@ -547,10 +845,7 @@ int jbd_iterate_log(struct jbd_fs *jbd_fs,
 			ext4_dbg(DEBUG_JBD, "Descriptor block: %" PRIu32", "
 					    "trans_id: %" PRIu32"\n",
 					    this_block, this_trans_id);
-			if (action == ACTION_SCAN)
-				jbd_debug_descriptor_block(jbd_fs,
-						header, &this_block);
-			else if (action == ACTION_RECOVER) {
+			if (action == ACTION_RECOVER) {
 				struct replay_arg replay_arg;
 				replay_arg.info = info;
 				replay_arg.this_block = &this_block;
@@ -558,13 +853,18 @@ int jbd_iterate_log(struct jbd_fs *jbd_fs,
 
 				jbd_replay_descriptor_block(jbd_fs,
 						header, &replay_arg);
-			}
+			} else
+				jbd_debug_descriptor_block(jbd_fs,
+						header, &this_block);
 
 			break;
 		case JBD_COMMIT_BLOCK:
 			ext4_dbg(DEBUG_JBD, "Commit block: %" PRIu32", "
 					    "trans_id: %" PRIu32"\n",
 					    this_block, this_trans_id);
+			/* This is the end of a transaction,
+			 * we may now proceed to the next transaction.
+			 */
 			this_trans_id++;
 			break;
 		case JBD_REVOKE_BLOCK:
@@ -590,6 +890,7 @@ int jbd_iterate_log(struct jbd_fs *jbd_fs,
 	}
 	ext4_dbg(DEBUG_JBD, "End of journal.\n");
 	if (r == EOK && action == ACTION_SCAN) {
+		/* We have finished scanning the journal. */
 		info->start_trans_id = start_trans_id;
 		if (this_trans_id > start_trans_id)
 			info->last_trans_id = this_trans_id - 1;
@@ -600,6 +901,9 @@ int jbd_iterate_log(struct jbd_fs *jbd_fs,
 	return r;
 }
 
+/**@brief  Replay journal.
+ * @param  jbd_fs jbd filesystem
+ * @return standard error code*/
 int jbd_recover(struct jbd_fs *jbd_fs)
 {
 	int r;
@@ -620,9 +924,783 @@ int jbd_recover(struct jbd_fs *jbd_fs)
 
 	r = jbd_iterate_log(jbd_fs, &info, ACTION_RECOVER);
 	if (r == EOK) {
+		/* If we successfully replay the journal,
+		 * clear EXT4_FINCOM_RECOVER flag on the
+		 * ext4 superblock, and set the start of
+		 * journal to 0.*/
+		uint32_t features_incompatible =
+			ext4_get32(&jbd_fs->inode_ref.fs->sb,
+				   features_incompatible);
 		jbd_set32(&jbd_fs->sb, start, 0);
+		features_incompatible &= ~EXT4_FINCOM_RECOVER;
+		ext4_set32(&jbd_fs->inode_ref.fs->sb,
+			   features_incompatible,
+			   features_incompatible);
 		jbd_fs->dirty = true;
+		r = ext4_sb_write(jbd_fs->inode_ref.fs->bdev,
+				  &jbd_fs->inode_ref.fs->sb);
 	}
 	jbd_destroy_revoke_tree(&info);
 	return r;
 }
+
+static void jbd_journal_write_sb(struct jbd_journal *journal)
+{
+	struct jbd_fs *jbd_fs = journal->jbd_fs;
+	jbd_set32(&jbd_fs->sb, start, journal->start);
+	jbd_set32(&jbd_fs->sb, sequence, journal->trans_id);
+	jbd_fs->dirty = true;
+}
+
+/**@brief  Start accessing the journal.
+ * @param  jbd_fs jbd filesystem
+ * @param  journal current journal session
+ * @return standard error code*/
+int jbd_journal_start(struct jbd_fs *jbd_fs,
+		      struct jbd_journal *journal)
+{
+	int r;
+	uint32_t features_incompatible =
+			ext4_get32(&jbd_fs->inode_ref.fs->sb,
+				   features_incompatible);
+	features_incompatible |= EXT4_FINCOM_RECOVER;
+	ext4_set32(&jbd_fs->inode_ref.fs->sb,
+			features_incompatible,
+			features_incompatible);
+	r = ext4_sb_write(jbd_fs->inode_ref.fs->bdev,
+			&jbd_fs->inode_ref.fs->sb);
+	if (r != EOK)
+		return r;
+
+	journal->first = jbd_get32(&jbd_fs->sb, first);
+	journal->start = journal->first;
+	journal->last = journal->first;
+	journal->trans_id = 1;
+	journal->alloc_trans_id = 1;
+
+	journal->block_size = jbd_get32(&jbd_fs->sb, blocksize);
+
+	TAILQ_INIT(&journal->trans_queue);
+	TAILQ_INIT(&journal->cp_queue);
+	RB_INIT(&journal->block_rec_root);
+	journal->jbd_fs = jbd_fs;
+	jbd_journal_write_sb(journal);
+	return jbd_write_sb(jbd_fs);
+}
+
+static void jbd_journal_flush_trans(struct jbd_trans *trans)
+{
+	struct jbd_buf *jbd_buf, *tmp;
+	struct jbd_journal *journal = trans->journal;
+	struct ext4_fs *fs = journal->jbd_fs->inode_ref.fs;
+	LIST_FOREACH_SAFE(jbd_buf, &trans->buf_list, buf_node,
+			tmp) {
+		struct ext4_block block = jbd_buf->block;
+		ext4_block_flush_buf(fs->bdev, block.buf);
+	}
+}
+
+static void
+jbd_journal_skip_pure_revoke(struct jbd_journal *journal,
+			     struct jbd_trans *trans)
+{
+	journal->start = trans->start_iblock +
+		trans->alloc_blocks;
+	wrap(&journal->jbd_fs->sb, journal->start);
+	journal->trans_id = trans->trans_id + 1;
+	jbd_journal_free_trans(journal,
+			trans, false);
+	jbd_journal_write_sb(journal);
+}
+
+static void jbd_journal_flush_all_trans(struct jbd_journal *journal)
+{
+	struct jbd_trans *trans;
+	while ((trans = TAILQ_FIRST(&journal->cp_queue))) {
+		if (!trans->data_cnt) {
+			TAILQ_REMOVE(&journal->cp_queue,
+					trans,
+					trans_node);
+			jbd_journal_skip_pure_revoke(journal, trans);
+		} else
+			jbd_journal_flush_trans(trans);
+
+	}
+}
+
+/**@brief  Stop accessing the journal.
+ * @param  journal current journal session
+ * @return standard error code*/
+int jbd_journal_stop(struct jbd_journal *journal)
+{
+	int r;
+	struct jbd_fs *jbd_fs = journal->jbd_fs;
+	uint32_t features_incompatible;
+
+	/* Commit all the transactions to the journal.*/
+	jbd_journal_commit_all(journal);
+
+	/* Make sure that journalled content have reached
+	 * the disk.*/
+	jbd_journal_flush_all_trans(journal);
+
+	/* There should be no block record in this journal
+	 * session. */
+	if (!RB_EMPTY(&journal->block_rec_root))
+		ext4_dbg(DEBUG_JBD,
+			 DBG_WARN "There are still block records "
+			 	  "in this journal session!\n");
+
+	features_incompatible =
+		ext4_get32(&jbd_fs->inode_ref.fs->sb,
+			   features_incompatible);
+	features_incompatible &= ~EXT4_FINCOM_RECOVER;
+	ext4_set32(&jbd_fs->inode_ref.fs->sb,
+			features_incompatible,
+			features_incompatible);
+	r = ext4_sb_write(jbd_fs->inode_ref.fs->bdev,
+			&jbd_fs->inode_ref.fs->sb);
+	if (r != EOK)
+		return r;
+
+	journal->start = 0;
+	journal->trans_id = 0;
+	jbd_journal_write_sb(journal);
+	return jbd_write_sb(journal->jbd_fs);
+}
+
+/**@brief  Allocate a block in the journal.
+ * @param  journal current journal session
+ * @param  trans transaction
+ * @return allocated block address*/
+static uint32_t jbd_journal_alloc_block(struct jbd_journal *journal,
+					struct jbd_trans *trans)
+{
+	uint32_t start_block;
+
+	start_block = journal->last++;
+	trans->alloc_blocks++;
+	wrap(&journal->jbd_fs->sb, journal->last);
+	
+	/* If there is no space left, flush all journalled
+	 * blocks to disk first.*/
+	if (journal->last == journal->start)
+		jbd_journal_flush_all_trans(journal);
+
+	return start_block;
+}
+
+/**@brief  Allocate a new transaction
+ * @param  journal current journal session
+ * @return transaction allocated*/
+struct jbd_trans *
+jbd_journal_new_trans(struct jbd_journal *journal)
+{
+	struct jbd_trans *trans = calloc(1, sizeof(struct jbd_trans));
+	if (!trans)
+		return NULL;
+
+	/* We will assign a trans_id to this transaction,
+	 * once it has been committed.*/
+	trans->journal = journal;
+	trans->error = EOK;
+	return trans;
+}
+
+static void jbd_trans_end_write(struct ext4_bcache *bc __unused,
+			  struct ext4_buf *buf __unused,
+			  int res,
+			  void *arg);
+
+/**@brief  gain access to it before making any modications.
+ * @param  journal current journal session
+ * @param  trans transaction
+ * @param  block descriptor
+ * @return standard error code.*/
+int jbd_trans_get_access(struct jbd_journal *journal,
+			 struct jbd_trans *trans,
+			 struct ext4_block *block)
+{
+	int r = EOK;
+	struct ext4_fs *fs = journal->jbd_fs->inode_ref.fs;
+	struct jbd_buf *jbd_buf = block->buf->end_write_arg;
+
+	/* If the buffer has already been modified, we should
+	 * flush dirty data in this buffer to disk.*/
+	if (ext4_bcache_test_flag(block->buf, BC_DIRTY) &&
+	    block->buf->end_write == jbd_trans_end_write) {
+		ext4_assert(jbd_buf);
+		if (jbd_buf->trans != trans)
+			r = ext4_block_flush_buf(fs->bdev, block->buf);
+
+	}
+	return r;
+}
+
+static struct jbd_block_rec *
+jbd_trans_block_rec_lookup(struct jbd_journal *journal,
+			   ext4_fsblk_t lba)
+{
+	struct jbd_block_rec tmp = {
+		.lba = lba
+	};
+
+	return RB_FIND(jbd_block,
+		       &journal->block_rec_root,
+		       &tmp);
+}
+
+static inline struct jbd_block_rec *
+jbd_trans_insert_block_rec(struct jbd_trans *trans,
+			   ext4_fsblk_t lba,
+			   struct ext4_buf *buf)
+{
+	struct jbd_block_rec *block_rec;
+	block_rec = jbd_trans_block_rec_lookup(trans->journal, lba);
+	if (block_rec) {
+		/* Data should be flushed to disk already. */
+		ext4_assert(!block_rec->buf);
+		/* Now this block record belongs to this transaction. */
+		block_rec->trans = trans;
+		return block_rec;
+	}
+	block_rec = calloc(1, sizeof(struct jbd_block_rec));
+	if (!block_rec)
+		return NULL;
+
+	block_rec->lba = lba;
+	block_rec->buf = buf;
+	block_rec->trans = trans;
+	RB_INSERT(jbd_block, &trans->journal->block_rec_root, block_rec);
+	return block_rec;
+}
+
+static inline void
+jbd_trans_remove_block_rec(struct jbd_journal *journal,
+			   struct jbd_buf *jbd_buf)
+{
+	struct jbd_block_rec *block_rec = jbd_buf->block_rec;
+	/* If this block record doesn't belong to this transaction,
+	 * give up.*/
+	if (block_rec->trans == jbd_buf->trans) {
+		RB_REMOVE(jbd_block,
+				&journal->block_rec_root,
+				block_rec);
+		free(block_rec);
+	}
+}
+
+/**@brief  Add block to a transaction and mark it dirty.
+ * @param  trans transaction
+ * @param  block block descriptor
+ * @return standard error code*/
+int jbd_trans_set_block_dirty(struct jbd_trans *trans,
+			      struct ext4_block *block)
+{
+	struct jbd_buf *buf;
+
+	if (!ext4_bcache_test_flag(block->buf, BC_DIRTY) &&
+	    block->buf->end_write != jbd_trans_end_write) {
+		struct jbd_block_rec *block_rec;
+		buf = calloc(1, sizeof(struct jbd_buf));
+		if (!buf)
+			return ENOMEM;
+
+		if ((block_rec = jbd_trans_insert_block_rec(trans,
+					block->lb_id,
+					block->buf)) == NULL) {
+			free(buf);
+			return ENOMEM;
+		}
+
+		buf->block_rec = block_rec;
+		buf->trans = trans;
+		buf->block = *block;
+		ext4_bcache_inc_ref(block->buf);
+
+		/* If the content reach the disk, notify us
+		 * so that we may do a checkpoint. */
+		block->buf->end_write = jbd_trans_end_write;
+		block->buf->end_write_arg = buf;
+
+		trans->data_cnt++;
+		LIST_INSERT_HEAD(&trans->buf_list, buf, buf_node);
+
+		ext4_bcache_set_dirty(block->buf);
+	}
+	return EOK;
+}
+
+/**@brief  Add block to be revoked to a transaction
+ * @param  trans transaction
+ * @param  lba logical block address
+ * @return standard error code*/
+int jbd_trans_revoke_block(struct jbd_trans *trans,
+			   ext4_fsblk_t lba)
+{
+	struct jbd_revoke_rec *rec =
+		calloc(1, sizeof(struct jbd_revoke_rec));
+	if (!rec)
+		return ENOMEM;
+
+	rec->lba = lba;
+	LIST_INSERT_HEAD(&trans->revoke_list, rec, revoke_node);
+	return EOK;
+}
+
+/**@brief  Try to add block to be revoked to a transaction.
+ *         If @lba still remains in an transaction on checkpoint
+ *         queue, add @lba as a revoked block to the transaction.
+ * @param  trans transaction
+ * @param  lba logical block address
+ * @return standard error code*/
+int jbd_trans_try_revoke_block(struct jbd_trans *trans,
+			       ext4_fsblk_t lba)
+{
+	int r = EOK;
+	struct jbd_journal *journal = trans->journal;
+	struct ext4_fs *fs = journal->jbd_fs->inode_ref.fs;
+	struct jbd_block_rec *block_rec =
+		jbd_trans_block_rec_lookup(journal, lba);
+
+	/* Make sure we don't flush any buffers belong to this transaction. */
+	if (block_rec && block_rec->trans != trans) {
+		/* If the buffer has not been flushed yet, flush it now. */
+		if (block_rec->buf) {
+			r = ext4_block_flush_buf(fs->bdev, block_rec->buf);
+			if (r != EOK)
+				return r;
+
+		}
+
+		jbd_trans_revoke_block(trans, lba);
+	}
+
+	return EOK;
+}
+
+/**@brief  Free a transaction
+ * @param  journal current journal session
+ * @param  trans transaction
+ * @param  abort discard all the modifications on the block?
+ * @return standard error code*/
+void jbd_journal_free_trans(struct jbd_journal *journal,
+			    struct jbd_trans *trans,
+			    bool abort)
+{
+	struct jbd_buf *jbd_buf, *tmp;
+	struct jbd_revoke_rec *rec, *tmp2;
+	struct ext4_fs *fs = journal->jbd_fs->inode_ref.fs;
+	LIST_FOREACH_SAFE(jbd_buf, &trans->buf_list, buf_node,
+			  tmp) {
+		if (abort) {
+			jbd_buf->block.buf->end_write = NULL;
+			jbd_buf->block.buf->end_write_arg = NULL;
+			ext4_bcache_clear_dirty(jbd_buf->block.buf);
+			ext4_block_set(fs->bdev, &jbd_buf->block);
+		}
+
+		jbd_trans_remove_block_rec(journal, jbd_buf);
+		LIST_REMOVE(jbd_buf, buf_node);
+		free(jbd_buf);
+	}
+	LIST_FOREACH_SAFE(rec, &trans->revoke_list, revoke_node,
+			  tmp2) {
+		LIST_REMOVE(rec, revoke_node);
+		free(rec);
+	}
+
+	free(trans);
+}
+
+/**@brief  Write commit block for a transaction
+ * @param  trans transaction
+ * @return standard error code*/
+static int jbd_trans_write_commit_block(struct jbd_trans *trans)
+{
+	int rc;
+	struct jbd_commit_header *header;
+	uint32_t commit_iblock = 0;
+	struct ext4_block commit_block;
+	struct jbd_journal *journal = trans->journal;
+
+	commit_iblock = jbd_journal_alloc_block(journal, trans);
+	rc = jbd_block_get_noread(journal->jbd_fs,
+			&commit_block, commit_iblock);
+	if (rc != EOK)
+		return rc;
+
+	header = (struct jbd_commit_header *)commit_block.data;
+	jbd_set32(&header->header, magic, JBD_MAGIC_NUMBER);
+	jbd_set32(&header->header, blocktype, JBD_COMMIT_BLOCK);
+	jbd_set32(&header->header, sequence, trans->trans_id);
+
+	ext4_bcache_set_dirty(commit_block.buf);
+	rc = jbd_block_set(journal->jbd_fs, &commit_block);
+	if (rc != EOK)
+		return rc;
+
+	return EOK;
+}
+
+/**@brief  Write descriptor block for a transaction
+ * @param  journal current journal session
+ * @param  trans transaction
+ * @return standard error code*/
+static int jbd_journal_prepare(struct jbd_journal *journal,
+			       struct jbd_trans *trans)
+{
+	int rc = EOK, i = 0;
+	int32_t tag_tbl_size;
+	uint32_t desc_iblock = 0;
+	uint32_t data_iblock = 0;
+	char *tag_start = NULL, *tag_ptr = NULL;
+	struct jbd_buf *jbd_buf, *tmp;
+	struct ext4_block desc_block, data_block;
+	struct ext4_fs *fs = journal->jbd_fs->inode_ref.fs;
+
+	LIST_FOREACH_SAFE(jbd_buf, &trans->buf_list, buf_node, tmp) {
+		struct tag_info tag_info;
+		bool uuid_exist = false;
+		if (!ext4_bcache_test_flag(jbd_buf->block.buf,
+					   BC_DIRTY)) {
+			/* The buffer has not been modified, just release
+			 * that jbd_buf. */
+			jbd_buf->block.buf->end_write = NULL;
+			jbd_buf->block.buf->end_write_arg = NULL;
+			ext4_block_set(fs->bdev, &jbd_buf->block);
+			LIST_REMOVE(jbd_buf, buf_node);
+			free(jbd_buf);
+			continue;
+		}
+again:
+		if (!desc_iblock) {
+			struct jbd_bhdr *bhdr;
+			desc_iblock = jbd_journal_alloc_block(journal, trans);
+			rc = jbd_block_get_noread(journal->jbd_fs,
+					   &desc_block, desc_iblock);
+			if (rc != EOK)
+				break;
+
+			ext4_bcache_set_dirty(desc_block.buf);
+
+			bhdr = (struct jbd_bhdr *)desc_block.data;
+			jbd_set32(bhdr, magic, JBD_MAGIC_NUMBER);
+			jbd_set32(bhdr, blocktype, JBD_DESCRIPTOR_BLOCK);
+			jbd_set32(bhdr, sequence, trans->trans_id);
+
+			tag_start = (char *)(bhdr + 1);
+			tag_ptr = tag_start;
+			uuid_exist = true;
+			tag_tbl_size = journal->block_size -
+				sizeof(struct jbd_bhdr);
+
+			if (!trans->start_iblock)
+				trans->start_iblock = desc_iblock;
+
+		}
+		tag_info.block = jbd_buf->block.lb_id;
+		tag_info.uuid_exist = uuid_exist;
+		if (i == trans->data_cnt - 1)
+			tag_info.last_tag = true;
+		else
+			tag_info.last_tag = false;
+
+		if (uuid_exist)
+			memcpy(tag_info.uuid, journal->jbd_fs->sb.uuid,
+					UUID_SIZE);
+
+		rc = jbd_write_block_tag(journal->jbd_fs,
+				tag_ptr,
+				tag_tbl_size,
+				&tag_info);
+		if (rc != EOK) {
+			jbd_block_set(journal->jbd_fs, &desc_block);
+			desc_iblock = 0;
+			goto again;
+		}
+
+		data_iblock = jbd_journal_alloc_block(journal, trans);
+		rc = jbd_block_get_noread(journal->jbd_fs,
+				&data_block, data_iblock);
+		if (rc != EOK)
+			break;
+
+		ext4_bcache_set_dirty(data_block.buf);
+
+		memcpy(data_block.data, jbd_buf->block.data,
+			journal->block_size);
+
+		rc = jbd_block_set(journal->jbd_fs, &data_block);
+		if (rc != EOK)
+			break;
+
+		tag_ptr += tag_info.tag_bytes;
+		tag_tbl_size -= tag_info.tag_bytes;
+
+		i++;
+	}
+	if (rc == EOK && desc_iblock)
+		jbd_block_set(journal->jbd_fs, &desc_block);
+
+	return rc;
+}
+
+/**@brief  Write revoke block for a transaction
+ * @param  journal current journal session
+ * @param  trans transaction
+ * @return standard error code*/
+static int
+jbd_journal_prepare_revoke(struct jbd_journal *journal,
+			   struct jbd_trans *trans)
+{
+	int rc = EOK, i = 0;
+	int32_t tag_tbl_size;
+	uint32_t desc_iblock = 0;
+	char *blocks_entry = NULL;
+	struct jbd_revoke_rec *rec, *tmp;
+	struct ext4_block desc_block;
+	struct jbd_revoke_header *header = NULL;
+	int32_t record_len = 4;
+
+	if (JBD_HAS_INCOMPAT_FEATURE(&journal->jbd_fs->sb,
+				     JBD_FEATURE_INCOMPAT_64BIT))
+		record_len = 8;
+
+	LIST_FOREACH_SAFE(rec, &trans->revoke_list, revoke_node,
+			  tmp) {
+again:
+		if (!desc_iblock) {
+			struct jbd_bhdr *bhdr;
+			desc_iblock = jbd_journal_alloc_block(journal, trans);
+			rc = jbd_block_get_noread(journal->jbd_fs,
+					   &desc_block, desc_iblock);
+			if (rc != EOK) {
+				break;
+			}
+
+			ext4_bcache_set_dirty(desc_block.buf);
+
+			bhdr = (struct jbd_bhdr *)desc_block.data;
+			jbd_set32(bhdr, magic, JBD_MAGIC_NUMBER);
+			jbd_set32(bhdr, blocktype, JBD_REVOKE_BLOCK);
+			jbd_set32(bhdr, sequence, trans->trans_id);
+			
+			header = (struct jbd_revoke_header *)bhdr;
+			blocks_entry = (char *)(header + 1);
+			tag_tbl_size = journal->block_size -
+				sizeof(struct jbd_revoke_header);
+
+			if (!trans->start_iblock)
+				trans->start_iblock = desc_iblock;
+
+		}
+
+		if (tag_tbl_size < record_len) {
+			jbd_set32(header, count,
+				  journal->block_size - tag_tbl_size);
+			jbd_block_set(journal->jbd_fs, &desc_block);
+			desc_iblock = 0;
+			header = NULL;
+			goto again;
+		}
+		if (record_len == 8) {
+			uint64_t *blocks =
+				(uint64_t *)blocks_entry;
+			*blocks = to_be64(rec->lba);
+		} else {
+			uint32_t *blocks =
+				(uint32_t *)blocks_entry;
+			*blocks = to_be32(rec->lba);
+		}
+		blocks_entry += record_len;
+		tag_tbl_size -= record_len;
+
+		i++;
+	}
+	if (rc == EOK && desc_iblock) {
+		if (header != NULL)
+			jbd_set32(header, count,
+				  journal->block_size - tag_tbl_size);
+
+		jbd_block_set(journal->jbd_fs, &desc_block);
+	}
+
+	return rc;
+}
+
+/**@brief  Submit the transaction to transaction queue.
+ * @param  journal current journal session
+ * @param  trans transaction*/
+void
+jbd_journal_submit_trans(struct jbd_journal *journal,
+			 struct jbd_trans *trans)
+{
+	TAILQ_INSERT_TAIL(&journal->trans_queue,
+			  trans,
+			  trans_node);
+}
+
+/**@brief  Put references of block descriptors in a transaction.
+ * @param  journal current journal session
+ * @param  trans transaction*/
+void jbd_journal_cp_trans(struct jbd_journal *journal, struct jbd_trans *trans)
+{
+	struct jbd_buf *jbd_buf, *tmp;
+	struct ext4_fs *fs = journal->jbd_fs->inode_ref.fs;
+	LIST_FOREACH_SAFE(jbd_buf, &trans->buf_list, buf_node,
+			tmp) {
+		struct ext4_block block = jbd_buf->block;
+		ext4_block_set(fs->bdev, &block);
+	}
+}
+
+/**@brief  Update the start block of the journal when
+ *         all the contents in a transaction reach the disk.*/
+static void jbd_trans_end_write(struct ext4_bcache *bc __unused,
+			  struct ext4_buf *buf,
+			  int res,
+			  void *arg)
+{
+	struct jbd_buf *jbd_buf = arg;
+	struct jbd_trans *trans = jbd_buf->trans;
+	struct jbd_journal *journal = trans->journal;
+	bool first_in_queue =
+		trans == TAILQ_FIRST(&journal->cp_queue);
+	if (res != EOK)
+		trans->error = res;
+
+	LIST_REMOVE(jbd_buf, buf_node);
+	jbd_buf->block_rec->buf = NULL;
+	jbd_trans_remove_block_rec(journal, jbd_buf);
+	free(jbd_buf);
+
+	/* Clear the end_write and end_write_arg fields. */
+	buf->end_write = NULL;
+	buf->end_write_arg = NULL;
+
+	trans->written_cnt++;
+	if (trans->written_cnt == trans->data_cnt) {
+		TAILQ_REMOVE(&journal->cp_queue, trans, trans_node);
+
+		if (first_in_queue) {
+			journal->start = trans->start_iblock +
+				trans->alloc_blocks;
+			wrap(&journal->jbd_fs->sb, journal->start);
+			journal->trans_id = trans->trans_id + 1;
+		}
+		jbd_journal_free_trans(journal, trans, false);
+
+		if (first_in_queue) {
+			while ((trans = TAILQ_FIRST(&journal->cp_queue))) {
+				if (!trans->data_cnt) {
+					TAILQ_REMOVE(&journal->cp_queue,
+						     trans,
+						     trans_node);
+					jbd_journal_skip_pure_revoke(journal,
+								     trans);
+				} else {
+					journal->start = trans->start_iblock;
+					wrap(&journal->jbd_fs->sb, journal->start);
+					journal->trans_id = trans->trans_id;
+					break;
+				}
+			}
+			jbd_journal_write_sb(journal);
+			jbd_write_sb(journal->jbd_fs);
+		}
+	}
+}
+
+/**@brief  Commit a transaction to the journal immediately.
+ * @param  journal current journal session
+ * @param  trans transaction
+ * @return standard error code*/
+int jbd_journal_commit_trans(struct jbd_journal *journal,
+			     struct jbd_trans *trans)
+{
+	int rc = EOK;
+	uint32_t last = journal->last;
+
+	trans->trans_id = journal->alloc_trans_id;
+	rc = jbd_journal_prepare(journal, trans);
+	if (rc != EOK)
+		goto Finish;
+
+	rc = jbd_journal_prepare_revoke(journal, trans);
+	if (rc != EOK)
+		goto Finish;
+
+	if (LIST_EMPTY(&trans->buf_list) &&
+	    LIST_EMPTY(&trans->revoke_list)) {
+		/* Since there are no entries in both buffer list
+		 * and revoke entry list, we do not consider trans as
+		 * complete transaction and just return EOK.*/
+		jbd_journal_free_trans(journal, trans, false);
+		goto Finish;
+	}
+
+	rc = jbd_trans_write_commit_block(trans);
+	if (rc != EOK)
+		goto Finish;
+
+	journal->alloc_trans_id++;
+	if (TAILQ_EMPTY(&journal->cp_queue)) {
+		if (trans->data_cnt) {
+			journal->start = trans->start_iblock;
+			wrap(&journal->jbd_fs->sb, journal->start);
+			journal->trans_id = trans->trans_id;
+			jbd_journal_write_sb(journal);
+			jbd_write_sb(journal->jbd_fs);
+			TAILQ_INSERT_TAIL(&journal->cp_queue, trans,
+					trans_node);
+			jbd_journal_cp_trans(journal, trans);
+		} else {
+			journal->start = trans->start_iblock +
+				trans->alloc_blocks;
+			wrap(&journal->jbd_fs->sb, journal->start);
+			journal->trans_id = trans->trans_id + 1;
+			jbd_journal_write_sb(journal);
+			jbd_journal_free_trans(journal, trans, false);
+		}
+	} else {
+		TAILQ_INSERT_TAIL(&journal->cp_queue, trans,
+				trans_node);
+		if (trans->data_cnt)
+			jbd_journal_cp_trans(journal, trans);
+
+	}
+Finish:
+	if (rc != EOK) {
+		journal->last = last;
+		jbd_journal_free_trans(journal, trans, true);
+	}
+	return rc;
+}
+
+/**@brief  Commit one transaction on transaction queue
+ *         to the journal.
+ * @param  journal current journal session.*/
+void jbd_journal_commit_one(struct jbd_journal *journal)
+{
+	struct jbd_trans *trans;
+
+	if ((trans = TAILQ_FIRST(&journal->trans_queue))) {
+		TAILQ_REMOVE(&journal->trans_queue, trans, trans_node);
+		jbd_journal_commit_trans(journal, trans);
+	}
+}
+
+/**@brief  Commit all the transactions on transaction queue
+ *         to the journal.
+ * @param  journal current journal session.*/
+void jbd_journal_commit_all(struct jbd_journal *journal)
+{
+	while (!TAILQ_EMPTY(&journal->trans_queue)) {
+		jbd_journal_commit_one(journal);
+	}
+}
+
+/**
+ * @}
+ */