if (EXT4_HAS_RO_COMPAT_FEATURE(sb,
                                       EXT4_FEATURE_RO_COMPAT_METADATA_CSUM)) {
-               /* journal checksum v2 */
+               /* journal checksum v3 */
                compat = 0;
-               incompat = JBD2_FEATURE_INCOMPAT_CSUM_V2;
+               incompat = JBD2_FEATURE_INCOMPAT_CSUM_V3;
        } else {
                /* journal checksum v1 */
                compat = JBD2_FEATURE_COMPAT_CHECKSUM;
                jbd2_journal_clear_features(sbi->s_journal,
                                JBD2_FEATURE_COMPAT_CHECKSUM, 0,
                                JBD2_FEATURE_INCOMPAT_ASYNC_COMMIT |
+                               JBD2_FEATURE_INCOMPAT_CSUM_V3 |
                                JBD2_FEATURE_INCOMPAT_CSUM_V2);
        }
 
 
        struct commit_header *h;
        __u32 csum;
 
-       if (!JBD2_HAS_INCOMPAT_FEATURE(j, JBD2_FEATURE_INCOMPAT_CSUM_V2))
+       if (!jbd2_journal_has_csum_v2or3(j))
                return;
 
        h = (struct commit_header *)(bh->b_data);
        return checksum;
 }
 
-static void write_tag_block(int tag_bytes, journal_block_tag_t *tag,
+static void write_tag_block(journal_t *j, journal_block_tag_t *tag,
                                   unsigned long long block)
 {
        tag->t_blocknr = cpu_to_be32(block & (u32)~0);
-       if (tag_bytes > JBD2_TAG_SIZE32)
+       if (JBD2_HAS_INCOMPAT_FEATURE(j, JBD2_FEATURE_INCOMPAT_64BIT))
                tag->t_blocknr_high = cpu_to_be32((block >> 31) >> 1);
 }
 
        struct jbd2_journal_block_tail *tail;
        __u32 csum;
 
-       if (!JBD2_HAS_INCOMPAT_FEATURE(j, JBD2_FEATURE_INCOMPAT_CSUM_V2))
+       if (!jbd2_journal_has_csum_v2or3(j))
                return;
 
        tail = (struct jbd2_journal_block_tail *)(bh->b_data + j->j_blocksize -
 static void jbd2_block_tag_csum_set(journal_t *j, journal_block_tag_t *tag,
                                    struct buffer_head *bh, __u32 sequence)
 {
+       journal_block_tag3_t *tag3 = (journal_block_tag3_t *)tag;
        struct page *page = bh->b_page;
        __u8 *addr;
        __u32 csum32;
        __be32 seq;
 
-       if (!JBD2_HAS_INCOMPAT_FEATURE(j, JBD2_FEATURE_INCOMPAT_CSUM_V2))
+       if (!jbd2_journal_has_csum_v2or3(j))
                return;
 
        seq = cpu_to_be32(sequence);
                             bh->b_size);
        kunmap_atomic(addr);
 
-       /* We only have space to store the lower 16 bits of the crc32c. */
-       tag->t_checksum = cpu_to_be16(csum32);
+       if (JBD2_HAS_INCOMPAT_FEATURE(j, JBD2_FEATURE_INCOMPAT_CSUM_V3))
+               tag3->t_checksum = cpu_to_be32(csum32);
+       else
+               tag->t_checksum = cpu_to_be16(csum32);
 }
 /*
  * jbd2_journal_commit_transaction
        LIST_HEAD(io_bufs);
        LIST_HEAD(log_bufs);
 
-       if (JBD2_HAS_INCOMPAT_FEATURE(journal, JBD2_FEATURE_INCOMPAT_CSUM_V2))
+       if (jbd2_journal_has_csum_v2or3(journal))
                csum_size = sizeof(struct jbd2_journal_block_tail);
 
        /*
                        tag_flag |= JBD2_FLAG_SAME_UUID;
 
                tag = (journal_block_tag_t *) tagp;
-               write_tag_block(tag_bytes, tag, jh2bh(jh)->b_blocknr);
+               write_tag_block(journal, tag, jh2bh(jh)->b_blocknr);
                tag->t_flags = cpu_to_be16(tag_flag);
                jbd2_block_tag_csum_set(journal, tag, wbuf[bufs],
                                        commit_transaction->t_tid);
 
 /* Checksumming functions */
 static int jbd2_verify_csum_type(journal_t *j, journal_superblock_t *sb)
 {
-       if (!JBD2_HAS_INCOMPAT_FEATURE(j, JBD2_FEATURE_INCOMPAT_CSUM_V2))
+       if (!jbd2_journal_has_csum_v2or3(j))
                return 1;
 
        return sb->s_checksum_type == JBD2_CRC32C_CHKSUM;
 
 static int jbd2_superblock_csum_verify(journal_t *j, journal_superblock_t *sb)
 {
-       if (!JBD2_HAS_INCOMPAT_FEATURE(j, JBD2_FEATURE_INCOMPAT_CSUM_V2))
+       if (!jbd2_journal_has_csum_v2or3(j))
                return 1;
 
        return sb->s_checksum == jbd2_superblock_csum(j, sb);
 
 static void jbd2_superblock_csum_set(journal_t *j, journal_superblock_t *sb)
 {
-       if (!JBD2_HAS_INCOMPAT_FEATURE(j, JBD2_FEATURE_INCOMPAT_CSUM_V2))
+       if (!jbd2_journal_has_csum_v2or3(j))
                return;
 
        sb->s_checksum = jbd2_superblock_csum(j, sb);
                goto out;
        }
 
-       if (JBD2_HAS_COMPAT_FEATURE(journal, JBD2_FEATURE_COMPAT_CHECKSUM) &&
-           JBD2_HAS_INCOMPAT_FEATURE(journal, JBD2_FEATURE_INCOMPAT_CSUM_V2)) {
+       if (jbd2_journal_has_csum_v2or3(journal) &&
+           JBD2_HAS_COMPAT_FEATURE(journal, JBD2_FEATURE_COMPAT_CHECKSUM)) {
                /* Can't have checksum v1 and v2 on at the same time! */
                printk(KERN_ERR "JBD2: Can't enable checksumming v1 and v2 "
                       "at the same time!\n");
                goto out;
        }
 
+       if (JBD2_HAS_INCOMPAT_FEATURE(journal, JBD2_FEATURE_INCOMPAT_CSUM_V2) &&
+           JBD2_HAS_INCOMPAT_FEATURE(journal, JBD2_FEATURE_INCOMPAT_CSUM_V3)) {
+               /* Can't have checksum v2 and v3 at the same time! */
+               printk(KERN_ERR "JBD2: Can't enable checksumming v2 and v3 "
+                      "at the same time!\n");
+               goto out;
+       }
+
        if (!jbd2_verify_csum_type(journal, sb)) {
                printk(KERN_ERR "JBD2: Unknown checksum type\n");
                goto out;
        }
 
        /* Load the checksum driver */
-       if (JBD2_HAS_INCOMPAT_FEATURE(journal, JBD2_FEATURE_INCOMPAT_CSUM_V2)) {
+       if (jbd2_journal_has_csum_v2or3(journal)) {
                journal->j_chksum_driver = crypto_alloc_shash("crc32c", 0, 0);
                if (IS_ERR(journal->j_chksum_driver)) {
                        printk(KERN_ERR "JBD2: Cannot load crc32c driver.\n");
        }
 
        /* Precompute checksum seed for all metadata */
-       if (JBD2_HAS_INCOMPAT_FEATURE(journal, JBD2_FEATURE_INCOMPAT_CSUM_V2))
+       if (jbd2_journal_has_csum_v2or3(journal))
                journal->j_csum_seed = jbd2_chksum(journal, ~0, sb->s_uuid,
                                                   sizeof(sb->s_uuid));
 
        if (!jbd2_journal_check_available_features(journal, compat, ro, incompat))
                return 0;
 
-       /* Asking for checksumming v2 and v1?  Only give them v2. */
-       if (incompat & JBD2_FEATURE_INCOMPAT_CSUM_V2 &&
+       /* If enabling v2 checksums, turn on v3 instead */
+       if (incompat & JBD2_FEATURE_INCOMPAT_CSUM_V2) {
+               incompat &= ~JBD2_FEATURE_INCOMPAT_CSUM_V2;
+               incompat |= JBD2_FEATURE_INCOMPAT_CSUM_V3;
+       }
+
+       /* Asking for checksumming v3 and v1?  Only give them v3. */
+       if (incompat & JBD2_FEATURE_INCOMPAT_CSUM_V3 &&
            compat & JBD2_FEATURE_COMPAT_CHECKSUM)
                compat &= ~JBD2_FEATURE_COMPAT_CHECKSUM;
 
 
        sb = journal->j_superblock;
 
-       /* If enabling v2 checksums, update superblock */
-       if (INCOMPAT_FEATURE_ON(JBD2_FEATURE_INCOMPAT_CSUM_V2)) {
+       /* If enabling v3 checksums, update superblock */
+       if (INCOMPAT_FEATURE_ON(JBD2_FEATURE_INCOMPAT_CSUM_V3)) {
                sb->s_checksum_type = JBD2_CRC32C_CHKSUM;
                sb->s_feature_compat &=
                        ~cpu_to_be32(JBD2_FEATURE_COMPAT_CHECKSUM);
                }
 
                /* Precompute checksum seed for all metadata */
-               if (JBD2_HAS_INCOMPAT_FEATURE(journal,
-                                             JBD2_FEATURE_INCOMPAT_CSUM_V2))
+               if (jbd2_journal_has_csum_v2or3(journal))
                        journal->j_csum_seed = jbd2_chksum(journal, ~0,
                                                           sb->s_uuid,
                                                           sizeof(sb->s_uuid));
        /* If enabling v1 checksums, downgrade superblock */
        if (COMPAT_FEATURE_ON(JBD2_FEATURE_COMPAT_CHECKSUM))
                sb->s_feature_incompat &=
-                       ~cpu_to_be32(JBD2_FEATURE_INCOMPAT_CSUM_V2);
+                       ~cpu_to_be32(JBD2_FEATURE_INCOMPAT_CSUM_V2 |
+                                    JBD2_FEATURE_INCOMPAT_CSUM_V3);
 
        sb->s_feature_compat    |= cpu_to_be32(compat);
        sb->s_feature_ro_compat |= cpu_to_be32(ro);
  */
 size_t journal_tag_bytes(journal_t *journal)
 {
-       journal_block_tag_t tag;
-       size_t x = 0;
+       size_t sz;
+
+       if (JBD2_HAS_INCOMPAT_FEATURE(journal, JBD2_FEATURE_INCOMPAT_CSUM_V3))
+               return sizeof(journal_block_tag3_t);
+
+       sz = sizeof(journal_block_tag_t);
 
        if (JBD2_HAS_INCOMPAT_FEATURE(journal, JBD2_FEATURE_INCOMPAT_CSUM_V2))
-               x += sizeof(tag.t_checksum);
+               sz += sizeof(__u16);
 
        if (JBD2_HAS_INCOMPAT_FEATURE(journal, JBD2_FEATURE_INCOMPAT_64BIT))
-               return x + JBD2_TAG_SIZE64;
+               return sz;
        else
-               return x + JBD2_TAG_SIZE32;
+               return sz - sizeof(__u32);
 }
 
 /*
 
        __be32 provided;
        __u32 calculated;
 
-       if (!JBD2_HAS_INCOMPAT_FEATURE(j, JBD2_FEATURE_INCOMPAT_CSUM_V2))
+       if (!jbd2_journal_has_csum_v2or3(j))
                return 1;
 
        tail = (struct jbd2_journal_block_tail *)(buf + j->j_blocksize -
        int                     nr = 0, size = journal->j_blocksize;
        int                     tag_bytes = journal_tag_bytes(journal);
 
-       if (JBD2_HAS_INCOMPAT_FEATURE(journal, JBD2_FEATURE_INCOMPAT_CSUM_V2))
+       if (jbd2_journal_has_csum_v2or3(journal))
                size -= sizeof(struct jbd2_journal_block_tail);
 
        tagp = &bh->b_data[sizeof(journal_header_t)];
        return err;
 }
 
-static inline unsigned long long read_tag_block(int tag_bytes, journal_block_tag_t *tag)
+static inline unsigned long long read_tag_block(journal_t *journal,
+                                               journal_block_tag_t *tag)
 {
        unsigned long long block = be32_to_cpu(tag->t_blocknr);
-       if (tag_bytes > JBD2_TAG_SIZE32)
+       if (JBD2_HAS_INCOMPAT_FEATURE(journal, JBD2_FEATURE_INCOMPAT_64BIT))
                block |= (u64)be32_to_cpu(tag->t_blocknr_high) << 32;
        return block;
 }
        __be32 provided;
        __u32 calculated;
 
-       if (!JBD2_HAS_INCOMPAT_FEATURE(j, JBD2_FEATURE_INCOMPAT_CSUM_V2))
+       if (!jbd2_journal_has_csum_v2or3(j))
                return 1;
 
        h = buf;
 static int jbd2_block_tag_csum_verify(journal_t *j, journal_block_tag_t *tag,
                                      void *buf, __u32 sequence)
 {
+       journal_block_tag3_t *tag3 = (journal_block_tag3_t *)tag;
        __u32 csum32;
        __be32 seq;
 
-       if (!JBD2_HAS_INCOMPAT_FEATURE(j, JBD2_FEATURE_INCOMPAT_CSUM_V2))
+       if (!jbd2_journal_has_csum_v2or3(j))
                return 1;
 
        seq = cpu_to_be32(sequence);
        csum32 = jbd2_chksum(j, j->j_csum_seed, (__u8 *)&seq, sizeof(seq));
        csum32 = jbd2_chksum(j, csum32, buf, j->j_blocksize);
 
-       return tag->t_checksum == cpu_to_be16(csum32);
+       if (JBD2_HAS_INCOMPAT_FEATURE(j, JBD2_FEATURE_INCOMPAT_CSUM_V3))
+               return tag3->t_checksum == cpu_to_be32(csum32);
+       else
+               return tag->t_checksum == cpu_to_be16(csum32);
 }
 
 static int do_one_pass(journal_t *journal,
                switch(blocktype) {
                case JBD2_DESCRIPTOR_BLOCK:
                        /* Verify checksum first */
-                       if (JBD2_HAS_INCOMPAT_FEATURE(journal,
-                                       JBD2_FEATURE_INCOMPAT_CSUM_V2))
+                       if (jbd2_journal_has_csum_v2or3(journal))
                                descr_csum_size =
                                        sizeof(struct jbd2_journal_block_tail);
                        if (descr_csum_size > 0 &&
                                        unsigned long long blocknr;
 
                                        J_ASSERT(obh != NULL);
-                                       blocknr = read_tag_block(tag_bytes,
+                                       blocknr = read_tag_block(journal,
                                                                 tag);
 
                                        /* If the block has been
        __be32 provided;
        __u32 calculated;
 
-       if (!JBD2_HAS_INCOMPAT_FEATURE(j, JBD2_FEATURE_INCOMPAT_CSUM_V2))
+       if (!jbd2_journal_has_csum_v2or3(j))
                return 1;
 
        tail = (struct jbd2_journal_revoke_tail *)(buf + j->j_blocksize -
 
 #include <linux/list.h>
 #include <linux/init.h>
 #include <linux/bio.h>
-#endif
 #include <linux/log2.h>
+#endif
 
 static struct kmem_cache *jbd2_revoke_record_cache;
 static struct kmem_cache *jbd2_revoke_table_cache;
        offset = *offsetp;
 
        /* Do we need to leave space at the end for a checksum? */
-       if (JBD2_HAS_INCOMPAT_FEATURE(journal, JBD2_FEATURE_INCOMPAT_CSUM_V2))
+       if (jbd2_journal_has_csum_v2or3(journal))
                csum_size = sizeof(struct jbd2_journal_revoke_tail);
 
        /* Make sure we have a descriptor with space left for the record */
        struct jbd2_journal_revoke_tail *tail;
        __u32 csum;
 
-       if (!JBD2_HAS_INCOMPAT_FEATURE(j, JBD2_FEATURE_INCOMPAT_CSUM_V2))
+       if (!jbd2_journal_has_csum_v2or3(j))
                return;
 
        tail = (struct jbd2_journal_revoke_tail *)(bh->b_data + j->j_blocksize -
 
  * journal_block_tag (in the descriptor).  The other h_chksum* fields are
  * not used.
  *
- * Checksum v1 and v2 are mutually exclusive features.
+ * If FEATURE_INCOMPAT_CSUM_V3 is set, the descriptor block uses
+ * journal_block_tag3_t to store a full 32-bit checksum.  Everything else
+ * is the same as v2.
+ *
+ * Checksum v1, v2, and v3 are mutually exclusive features.
  */
 struct commit_header {
        __be32          h_magic;
  * raw struct shouldn't be used for pointer math or sizeof() - use
  * journal_tag_bytes(journal) instead to compute this.
  */
+typedef struct journal_block_tag3_s
+{
+       __be32          t_blocknr;      /* The on-disk block number */
+       __be32          t_flags;        /* See below */
+       __be32          t_blocknr_high; /* most-significant high 32bits. */
+       __be32          t_checksum;     /* crc32c(uuid+seq+block) */
+} journal_block_tag3_t;
+
 typedef struct journal_block_tag_s
 {
        __be32          t_blocknr;      /* The on-disk block number */
        __be32          t_blocknr_high; /* most-significant high 32bits. */
 } journal_block_tag_t;
 
-#define JBD2_TAG_SIZE32 (offsetof(journal_block_tag_t, t_blocknr_high))
-#define JBD2_TAG_SIZE64 (sizeof(journal_block_tag_t))
-
 /* Tail of descriptor block, for checksumming */
 struct jbd2_journal_block_tail {
        __be32          t_checksum;     /* crc32c(uuid+descr_block) */
 #define JBD2_FEATURE_INCOMPAT_64BIT            0x00000002
 #define JBD2_FEATURE_INCOMPAT_ASYNC_COMMIT     0x00000004
 #define JBD2_FEATURE_INCOMPAT_CSUM_V2          0x00000008
+#define JBD2_FEATURE_INCOMPAT_CSUM_V3          0x00000010
 
 /* Features known to this kernel version: */
 #define JBD2_KNOWN_COMPAT_FEATURES     JBD2_FEATURE_COMPAT_CHECKSUM
 #define JBD2_KNOWN_INCOMPAT_FEATURES   (JBD2_FEATURE_INCOMPAT_REVOKE | \
                                        JBD2_FEATURE_INCOMPAT_64BIT | \
                                        JBD2_FEATURE_INCOMPAT_ASYNC_COMMIT | \
-                                       JBD2_FEATURE_INCOMPAT_CSUM_V2)
+                                       JBD2_FEATURE_INCOMPAT_CSUM_V2 | \
+                                       JBD2_FEATURE_INCOMPAT_CSUM_V3)
 
 #ifdef __KERNEL__
 
 extern int jbd2_journal_blocks_per_page(struct inode *inode);
 extern size_t journal_tag_bytes(journal_t *journal);
 
+static inline int jbd2_journal_has_csum_v2or3(journal_t *journal)
+{
+       if (JBD2_HAS_INCOMPAT_FEATURE(journal, JBD2_FEATURE_INCOMPAT_CSUM_V2) ||
+           JBD2_HAS_INCOMPAT_FEATURE(journal, JBD2_FEATURE_INCOMPAT_CSUM_V3))
+               return 1;
+
+       return 0;
+}
+
 /*
  * We reserve t_outstanding_credits >> JBD2_CONTROL_BLOCKS_SHIFT for
  * transaction control blocks.