[EXT4 set 8][PATCH 1/1]Add journal checksums

From: Mingming Cao
Date: Sun Jul 01 2007 - 03:42:52 EST

Journal checksum feature has been added to detect corruption of journal.

Signed-off-by: Andreas Dilger <adilger@xxxxxxxxxxxxx>
Signed-off-by: Girish Shilamkar <girish@xxxxxxxxxxxxx>
Signed-off-by: Dave Kleikamp <shaggy@xxxxxxxxxxxxxxxxxx>

diff -Nurp linux024/fs/ext4/super.c linux/fs/ext4/super.c
--- linux024/fs/ext4/super.c 2007-06-25 16:19:24.000000000 -0500
+++ linux/fs/ext4/super.c 2007-06-26 08:35:16.000000000 -0500
@@ -721,6 +721,7 @@ enum {
Opt_user_xattr, Opt_nouser_xattr, Opt_acl, Opt_noacl,
Opt_reservation, Opt_noreservation, Opt_noload, Opt_nobh, Opt_bh,
Opt_commit, Opt_journal_update, Opt_journal_inum, Opt_journal_dev,
+ Opt_journal_checksum, Opt_journal_async_commit,
Opt_abort, Opt_data_journal, Opt_data_ordered, Opt_data_writeback,
Opt_usrjquota, Opt_grpjquota, Opt_offusrjquota, Opt_offgrpjquota,
Opt_jqfmt_vfsold, Opt_jqfmt_vfsv0, Opt_quota, Opt_noquota,
@@ -760,6 +761,8 @@ static match_table_t tokens = {
{Opt_journal_update, "journal=update"},
{Opt_journal_inum, "journal=%u"},
{Opt_journal_dev, "journal_dev=%u"},
+ {Opt_journal_checksum, "journal_checksum"},
+ {Opt_journal_async_commit, "journal_async_commit"},
{Opt_abort, "abort"},
{Opt_data_journal, "data=journal"},
{Opt_data_ordered, "data=ordered"},
@@ -948,6 +951,13 @@ static int parse_options (char *options,
return 0;
*journal_devnum = option;
break;
+ case Opt_journal_checksum:
+ set_opt (sbi->s_mount_opt, JOURNAL_CHECKSUM);
+ break;
+ case Opt_journal_async_commit:
+ set_opt (sbi->s_mount_opt, JOURNAL_ASYNC_COMMIT);
+ set_opt (sbi->s_mount_opt, JOURNAL_CHECKSUM);
+ break;
case Opt_noload:
set_opt (sbi->s_mount_opt, NOLOAD);
break;
@@ -1817,6 +1827,21 @@ static int ext4_fill_super (struct super
goto failed_mount4;
}

+ if (test_opt(sb, JOURNAL_ASYNC_COMMIT)) {
+ jbd2_journal_set_features(sbi->s_journal,
+ JBD2_FEATURE_COMPAT_CHECKSUM, 0,
+ JBD2_FEATURE_INCOMPAT_ASYNC_COMMIT);
+ } else if (test_opt(sb, JOURNAL_CHECKSUM)) {
+ jbd2_journal_set_features(sbi->s_journal,
+ JBD2_FEATURE_COMPAT_CHECKSUM, 0, 0);
+ jbd2_journal_clear_features(sbi->s_journal, 0, 0,
+ JBD2_FEATURE_INCOMPAT_ASYNC_COMMIT);
+ } else {
+ jbd2_journal_clear_features(sbi->s_journal,
+ JBD2_FEATURE_COMPAT_CHECKSUM, 0,
+ JBD2_FEATURE_INCOMPAT_ASYNC_COMMIT);
+ }
+
/* We have now updated the journal if required, so we can
* validate the data journaling mode. */
switch (test_opt(sb, DATA_FLAGS)) {
diff -Nurp linux024/fs/jbd2/commit.c linux/fs/jbd2/commit.c
--- linux024/fs/jbd2/commit.c 2007-06-25 16:19:25.000000000 -0500
+++ linux/fs/jbd2/commit.c 2007-06-26 08:40:03.000000000 -0500
@@ -21,6 +21,7 @@
#include <linux/mm.h>
#include <linux/pagemap.h>
#include <linux/jiffies.h>
+#include <linux/crc32.h>

/*
* Default IO end handler for temporary BJ_IO buffer_heads.
@@ -93,15 +94,18 @@ static int inverted_lock(journal_t *jour
return 1;
}

-/* Done it all: now write the commit record. We should have
+/*
+ * Done it all: now submit the commit record. We should have
* cleaned up our previous buffers by now, so if we are in abort
* mode we can now just skip the rest of the journal write
* entirely.
*
* Returns 1 if the journal needs to be aborted or 0 on success
*/
-static int journal_write_commit_record(journal_t *journal,
- transaction_t *commit_transaction)
+static int journal_submit_commit_record(journal_t *journal,
+ transaction_t *commit_transaction,
+ struct buffer_head **cbh,
+ __u32 crc32_sum)
{
struct journal_head *descriptor;
struct buffer_head *bh;
@@ -117,21 +121,36 @@ static int journal_write_commit_record(j

bh = jh2bh(descriptor);

- /* AKPM: buglet - add `i' to tmp! */
for (i = 0; i < bh->b_size; i += 512) {
- journal_header_t *tmp = (journal_header_t*)bh->b_data;
+ struct commit_header *tmp =
+ (struct commit_header *)(bh->b_data + i);
tmp->h_magic = cpu_to_be32(JBD2_MAGIC_NUMBER);
tmp->h_blocktype = cpu_to_be32(JBD2_COMMIT_BLOCK);
tmp->h_sequence = cpu_to_be32(commit_transaction->t_tid);
+
+ if (JBD2_HAS_COMPAT_FEATURE(journal,
+ JBD2_FEATURE_COMPAT_CHECKSUM)) {
+ tmp->h_chksum_type = JBD2_CRC32_CHKSUM;
+ tmp->h_chksum_size = JBD2_CRC32_CHKSUM_SIZE;
+ tmp->h_chksum[0] = cpu_to_be32(crc32_sum);
+ }
}

- JBUFFER_TRACE(descriptor, "write commit block");
+ JBUFFER_TRACE(descriptor, "submit commit block");
+ lock_buffer(bh);
+
set_buffer_dirty(bh);
- if (journal->j_flags & JBD2_BARRIER) {
+ set_buffer_uptodate(bh);
+ bh->b_end_io = journal_end_buffer_io_sync;
+
+ if (journal->j_flags & JBD2_BARRIER &&
+ !JBD2_HAS_COMPAT_FEATURE(journal,
+ JBD2_FEATURE_INCOMPAT_ASYNC_COMMIT)) {
set_buffer_ordered(bh);
barrier_done = 1;
}
- ret = sync_dirty_buffer(bh);
+ ret = submit_bh(WRITE, bh);
+
/* is it possible for another commit to fail at roughly
* the same time as this one? If so, we don't want to
* trust the barrier flag in the super, but instead want
@@ -152,14 +171,72 @@ static int journal_write_commit_record(j
clear_buffer_ordered(bh);
set_buffer_uptodate(bh);
set_buffer_dirty(bh);
- ret = sync_dirty_buffer(bh);
+ ret = submit_bh(WRITE, bh);
}
- put_bh(bh); /* One for getblk() */
- jbd2_journal_put_journal_head(descriptor);
+ *cbh = bh;
+ return ret;
+}
+
+/*
+ * This function along with journal_submit_commit_record
+ * allows to write the commit record asynchronously.
+ */
+static int journal_wait_on_commit_record(struct buffer_head *bh)
+{
+ int ret = 0;

- return (ret == -EIO);
+ if (buffer_locked(bh))
+ wait_on_buffer(bh);
+
+ if (unlikely(!buffer_uptodate(bh)))
+ ret = -EIO;
+ put_bh(bh); /* One for getblk() */
+ jbd2_journal_put_journal_head(bh2jh(bh));
+
+ return ret;
}

+/*
+ * Wait for all submitted IO to complete.
+ */
+static int journal_wait_on_locked_list(journal_t *journal,
+ transaction_t *commit_transaction)
+{
+ int ret = 0;
+ struct journal_head *jh;
+
+ while (commit_transaction->t_locked_list) {
+ struct buffer_head *bh;
+
+ jh = commit_transaction->t_locked_list->b_tprev;
+ bh = jh2bh(jh);
+ get_bh(bh);
+ if (buffer_locked(bh)) {
+ spin_unlock(&journal->j_list_lock);
+ wait_on_buffer(bh);
+ if (unlikely(!buffer_uptodate(bh)))
+ ret = -EIO;
+ spin_lock(&journal->j_list_lock);
+ }
+ if (!inverted_lock(journal, bh)) {
+ put_bh(bh);
+ spin_lock(&journal->j_list_lock);
+ continue;
+ }
+ if (buffer_jbd(bh) && jh->b_jlist == BJ_Locked) {
+ __jbd2_journal_unfile_buffer(jh);
+ jbd_unlock_bh_state(bh);
+ jbd2_journal_remove_journal_head(bh);
+ put_bh(bh);
+ } else {
+ jbd_unlock_bh_state(bh);
+ }
+ put_bh(bh);
+ cond_resched_lock(&journal->j_list_lock);
+ }
+ return ret;
+ }
+
static void journal_do_submit_data(struct buffer_head **wbuf, int bufs)
{
int i;
@@ -307,6 +384,8 @@ void jbd2_journal_commit_transaction(jou
int tag_flag;
int i;
int tag_bytes = journal_tag_bytes(journal);
+ struct buffer_head *cbh = NULL; /* For transactional checksums */
+ __u32 crc32_sum = ~0;

/*
* First job: lock down the current transaction and wait for
@@ -450,38 +529,15 @@ void jbd2_journal_commit_transaction(jou
journal_submit_data_buffers(journal, commit_transaction);

/*
- * Wait for all previously submitted IO to complete.
+ * Wait for all previously submitted IO to complete if commit
+ * record is to be written synchronously.
*/
spin_lock(&journal->j_list_lock);
- while (commit_transaction->t_locked_list) {
- struct buffer_head *bh;
+ if (!JBD2_HAS_INCOMPAT_FEATURE(journal,
+ JBD2_FEATURE_INCOMPAT_ASYNC_COMMIT))
+ err = journal_wait_on_locked_list(journal,
+ commit_transaction);

- jh = commit_transaction->t_locked_list->b_tprev;
- bh = jh2bh(jh);
- get_bh(bh);
- if (buffer_locked(bh)) {
- spin_unlock(&journal->j_list_lock);
- wait_on_buffer(bh);
- if (unlikely(!buffer_uptodate(bh)))
- err = -EIO;
- spin_lock(&journal->j_list_lock);
- }
- if (!inverted_lock(journal, bh)) {
- put_bh(bh);
- spin_lock(&journal->j_list_lock);
- continue;
- }
- if (buffer_jbd(bh) && jh->b_jlist == BJ_Locked) {
- __jbd2_journal_unfile_buffer(jh);
- jbd_unlock_bh_state(bh);
- jbd2_journal_remove_journal_head(bh);
- put_bh(bh);
- } else {
- jbd_unlock_bh_state(bh);
- }
- put_bh(bh);
- cond_resched_lock(&journal->j_list_lock);
- }
spin_unlock(&journal->j_list_lock);

if (err)
@@ -654,6 +710,16 @@ void jbd2_journal_commit_transaction(jou
start_journal_io:
for (i = 0; i < bufs; i++) {
struct buffer_head *bh = wbuf[i];
+ /*
+ * Compute checksum.
+ */
+ if (JBD2_HAS_COMPAT_FEATURE(journal,
+ JBD2_FEATURE_COMPAT_CHECKSUM)) {
+ crc32_sum = crc32_be(crc32_sum,
+ (void *)bh->b_data,
+ bh->b_size);
+ }
+
lock_buffer(bh);
clear_buffer_dirty(bh);
set_buffer_uptodate(bh);
@@ -670,6 +736,23 @@ start_journal_io:
}
}

+ /* Done it all: now write the commit record asynchronously. */
+
+ if (JBD2_HAS_INCOMPAT_FEATURE(journal,
+ JBD2_FEATURE_INCOMPAT_ASYNC_COMMIT)) {
+ err = journal_submit_commit_record(journal, commit_transaction,
+ &cbh, crc32_sum);
+ if (err)
+ __jbd2_journal_abort_hard(journal);
+
+ spin_lock(&journal->j_list_lock);
+ err = journal_wait_on_locked_list(journal,
+ commit_transaction);
+ spin_unlock(&journal->j_list_lock);
+ if (err)
+ __jbd2_journal_abort_hard(journal);
+ }
+
/* Lo and behold: we have just managed to send a transaction to
the log. Before we can commit it, wait for the IO so far to
complete. Control buffers being written are on the
@@ -769,8 +852,14 @@ wait_for_iobuf:

jbd_debug(3, "JBD: commit phase 6\n");

- if (journal_write_commit_record(journal, commit_transaction))
- err = -EIO;
+ if (!JBD2_HAS_INCOMPAT_FEATURE(journal,
+ JBD2_FEATURE_INCOMPAT_ASYNC_COMMIT)) {
+ err = journal_submit_commit_record(journal, commit_transaction,
+ &cbh, crc32_sum);
+ if (err)
+ __jbd2_journal_abort_hard(journal);
+ }
+ err = journal_wait_on_commit_record(cbh);

if (err)
__jbd2_journal_abort_hard(journal);
diff -Nurp linux024/fs/jbd2/journal.c linux/fs/jbd2/journal.c
--- linux024/fs/jbd2/journal.c 2007-06-25 16:19:25.000000000 -0500
+++ linux/fs/jbd2/journal.c 2007-06-26 08:35:16.000000000 -0500
@@ -66,6 +66,7 @@ EXPORT_SYMBOL(jbd2_journal_update_format
EXPORT_SYMBOL(jbd2_journal_check_used_features);
EXPORT_SYMBOL(jbd2_journal_check_available_features);
EXPORT_SYMBOL(jbd2_journal_set_features);
+EXPORT_SYMBOL(jbd2_journal_clear_features);
EXPORT_SYMBOL(jbd2_journal_create);
EXPORT_SYMBOL(jbd2_journal_load);
EXPORT_SYMBOL(jbd2_journal_destroy);
@@ -1581,6 +1582,33 @@ int jbd2_journal_set_features (journal_t
return 1;
}

+/**
+ * int jbd2_journal_clear_features () - Clear a given journal feature in the superblock
+ * @journal: Journal to act on.
+ * @compat: bitmask of compatible features
+ * @ro: bitmask of features that force read-only mount
+ * @incompat: bitmask of incompatible features
+ *
+ * Clear a given journal feature as present on the
+ * superblock. Returns true if the requested features could be reset.
+ *
+ */
+int jbd2_journal_clear_features (journal_t *journal, unsigned long compat,
+ unsigned long ro, unsigned long incompat)
+{
+ journal_superblock_t *sb;
+
+ jbd_debug(1, "Clear features 0x%lx/0x%lx/0x%lx\n",
+ compat, ro, incompat);
+
+ sb = journal->j_superblock;
+
+ sb->s_feature_compat &= ~cpu_to_be32(compat);
+ sb->s_feature_ro_compat &= ~cpu_to_be32(ro);
+ sb->s_feature_incompat &= ~cpu_to_be32(incompat);
+
+ return 1;
+}

/**
* int jbd2_journal_update_format () - Update on-disk journal structure.
diff -Nurp linux024/fs/jbd2/recovery.c linux/fs/jbd2/recovery.c
--- linux024/fs/jbd2/recovery.c 2007-06-25 16:19:22.000000000 -0500
+++ linux/fs/jbd2/recovery.c 2007-06-26 08:35:16.000000000 -0500
@@ -21,6 +21,7 @@
#include <linux/jbd2.h>
#include <linux/errno.h>
#include <linux/slab.h>
+#include <linux/crc32.h>
#endif

/*
@@ -316,6 +317,37 @@ static inline unsigned long long read_ta
return block;
}

+/*
+ * cal_chksums calculates the checksums for the blocks described in the
+ * descriptor block.
+ */
+static int cal_chksums(journal_t *journal, struct buffer_head *bh,
+ unsigned long *next_log_block, __u32 *crc32_sum)
+{
+ int i, num_blks, err;
+ unsigned long io_block;
+ struct buffer_head *obh;
+
+ num_blks = count_tags(journal, bh);
+ /* Calculate checksum of the descriptor block. */
+ *crc32_sum = crc32_be(*crc32_sum, (void *)bh->b_data, bh->b_size);
+
+ for (i = 0; i < num_blks; i++) {
+ io_block = (*next_log_block)++;
+ wrap(journal, *next_log_block);
+ err = jread(&obh, journal, io_block);
+ if (err) {
+ printk(KERN_ERR "JBD: IO error %d recovering block "
+ "%ld in log\n", err, io_block);
+ return 1;
+ } else {
+ *crc32_sum = crc32_be(*crc32_sum, (void *)obh->b_data,
+ obh->b_size);
+ }
+ }
+ return 0;
+}
+
static int do_one_pass(journal_t *journal,
struct recovery_info *info, enum passtype pass)
{
@@ -328,6 +360,7 @@ static int do_one_pass(journal_t *journa
unsigned int sequence;
int blocktype;
int tag_bytes = journal_tag_bytes(journal);
+ __u32 crc32_sum = ~0; /* Transactional Checksums */

/* Precompute the maximum metadata descriptors in a descriptor block */
int MAX_BLOCKS_PER_DESC;
@@ -419,9 +452,23 @@ static int do_one_pass(journal_t *journa
switch(blocktype) {
case JBD2_DESCRIPTOR_BLOCK:
/* If it is a valid descriptor block, replay it
- * in pass REPLAY; otherwise, just skip over the
- * blocks it describes. */
+ * in pass REPLAY; if journal_checksums enabled, then
+ * calculate checksums in PASS_SCAN, otherwise,
+ * just skip over the blocks it describes. */
if (pass != PASS_REPLAY) {
+ if (pass == PASS_SCAN &&
+ JBD2_HAS_COMPAT_FEATURE(journal,
+ JBD2_FEATURE_COMPAT_CHECKSUM) &&
+ !info->end_transaction) {
+ if (cal_chksums(journal, bh,
+ &next_log_block,
+ &crc32_sum)) {
+ brelse(bh);
+ break;
+ }
+ brelse(bh);
+ continue;
+ }
next_log_block += count_tags(journal, bh);
wrap(journal, next_log_block);
brelse(bh);
@@ -516,9 +563,72 @@ static int do_one_pass(journal_t *journa
continue;

case JBD2_COMMIT_BLOCK:
- /* Found an expected commit block: not much to
- * do other than move on to the next sequence
+ /* How to differentiate between interrupted commit
+ * and journal corruption ?
+ *
+ * {nth transaction}
+ * Checksum Verification Failed
+ * |
+ * ____________________
+ * | |
+ * async_commit sync_commit
+ * | |
+ * | GO TO NEXT "Journal Corruption"
+ * | TRANSACTION
+ * |
+ * {(n+1)th transanction}
+ * |
+ * _______|______________
+ * | |
+ * Commit block found Commit block not found
+ * | |
+ * "Journal Corruption" |
+ * _____________|_________
+ * | |
+ * nth trans corrupt OR nth trans
+ * and (n+1)th interrupted interrupted
+ * before commit block
+ * could reach the disk.
+ * (Cannot find the difference in above
+ * mentioned conditions. Hence assume
+ * "Interrupted Commit".)
+ */
+
+ /* Found an expected commit block: if checksums
+ * are present verify them in PASS_SCAN; else not
+ * much to do other than move on to the next sequence
* number. */
+ if (pass == PASS_SCAN &&
+ JBD2_HAS_COMPAT_FEATURE(journal,
+ JBD2_FEATURE_COMPAT_CHECKSUM)) {
+ struct commit_header *cbh =
+ (struct commit_header *)bh->b_data;
+ unsigned found_chksum =
+ be32_to_cpu(cbh->h_chksum[0]);
+
+ if (info->end_transaction) {
+ printk(KERN_ERR "JBD: Transaction %u "
+ "found to be corrupt.\n",
+ next_commit_ID - 1);
+ brelse(bh);
+ break;
+ }
+
+ if (crc32_sum != found_chksum) {
+ info->end_transaction = next_commit_ID;
+
+ if (!JBD2_HAS_COMPAT_FEATURE(journal,
+ JBD2_FEATURE_INCOMPAT_ASYNC_COMMIT)){
+ printk(KERN_ERR
+ "JBD: Transaction %u "
+ "found to be corrupt.\n",
+ next_commit_ID);
+ brelse(bh);
+ break;
+ }
+ }
+ crc32_sum = ~0;
+ }
brelse(bh);
next_commit_ID++;
continue;
@@ -554,9 +664,10 @@ static int do_one_pass(journal_t *journa
* transaction marks the end of the valid log.
*/

- if (pass == PASS_SCAN)
- info->end_transaction = next_commit_ID;
- else {
+ if (pass == PASS_SCAN) {
+ if (!info->end_transaction)
+ info->end_transaction = next_commit_ID;
+ } else {
/* It's really bad news if different passes end up at
* different places (but possible due to IO errors). */
if (info->end_transaction != next_commit_ID) {
diff -Nurp linux024/include/linux/ext4_fs.h linux/include/linux/ext4_fs.h
--- linux024/include/linux/ext4_fs.h 2007-06-25 16:19:25.000000000 -0500
+++ linux/include/linux/ext4_fs.h 2007-06-26 08:37:30.000000000 -0500
@@ -475,6 +475,8 @@ do { \
#define EXT4_MOUNT_GRPQUOTA 0x200000 /* "old" group quota */
#define EXT4_MOUNT_EXTENTS 0x400000 /* Extents support */
#define EXT4_MOUNT_NOVERSION 0x800000 /* No inode version updates */
+#define EXT4_MOUNT_JOURNAL_CHECKSUM 0x1000000 /* Journal checksums */
+#define EXT4_MOUNT_JOURNAL_ASYNC_COMMIT 0x2000000 /* Journal Async Commit */

/* Compatibility, for having both ext2_fs.h and ext4_fs.h included at once */
#ifndef _LINUX_EXT2_FS_H
diff -Nurp linux024/include/linux/jbd2.h linux/include/linux/jbd2.h
--- linux024/include/linux/jbd2.h 2007-06-25 16:19:25.000000000 -0500
+++ linux/include/linux/jbd2.h 2007-06-26 08:35:16.000000000 -0500
@@ -148,6 +148,29 @@ typedef struct journal_header_s
__be32 h_sequence;
} journal_header_t;

+/*
+ * Checksum types.
+ */
+#define JBD2_CRC32_CHKSUM 1
+#define JBD2_MD5_CHKSUM 2
+#define JBD2_SHA1_CHKSUM 3
+
+#define JBD2_CRC32_CHKSUM_SIZE 4
+
+#define JBD2_CHECKSUM_BYTES (32 / sizeof(u32))
+/*
+ * Commit block header for storing transactional checksums:
+ */
+struct commit_header
+{
+ __be32 h_magic;
+ __be32 h_blocktype;
+ __be32 h_sequence;
+ unsigned char h_chksum_type;
+ unsigned char h_chksum_size;
+ unsigned char h_padding[2];
+ __be32 h_chksum[JBD2_CHECKSUM_BYTES];
+};

/*
* The block tag: used to describe a single buffer in the journal.
@@ -241,14 +264,18 @@ typedef struct journal_superblock_s
((j)->j_format_version >= 2 && \
((j)->j_superblock->s_feature_incompat & cpu_to_be32((mask))))

-#define JBD2_FEATURE_INCOMPAT_REVOKE 0x00000001
-#define JBD2_FEATURE_INCOMPAT_64BIT 0x00000002
+#define JBD2_FEATURE_COMPAT_CHECKSUM 0x00000001
+
+#define JBD2_FEATURE_INCOMPAT_REVOKE 0x00000001
+#define JBD2_FEATURE_INCOMPAT_64BIT 0x00000002
+#define JBD2_FEATURE_INCOMPAT_ASYNC_COMMIT 0x00000004

/* Features known to this kernel version: */
-#define JBD2_KNOWN_COMPAT_FEATURES 0
+#define JBD2_KNOWN_COMPAT_FEATURES JBD2_FEATURE_COMPAT_CHECKSUM
#define JBD2_KNOWN_ROCOMPAT_FEATURES 0
#define JBD2_KNOWN_INCOMPAT_FEATURES (JBD2_FEATURE_INCOMPAT_REVOKE | \
- JBD2_FEATURE_INCOMPAT_64BIT)
+ JBD2_FEATURE_INCOMPAT_64BIT | \
+ JBD2_FEATURE_INCOMPAT_ASYNC_COMMIT)

#ifdef __KERNEL__

@@ -1023,6 +1050,8 @@ extern int jbd2_journal_check_availab
(journal_t *, unsigned long, unsigned long, unsigned long);
extern int jbd2_journal_set_features
(journal_t *, unsigned long, unsigned long, unsigned long);
+extern int jbd2_journal_clear_features
+ (journal_t *, unsigned long, unsigned long, unsigned long);
extern int jbd2_journal_create (journal_t *);
extern int jbd2_journal_load (journal_t *journal);
extern void jbd2_journal_destroy (journal_t *);


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