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    Subject[PATCH] Support large blocksize up to PAGESIZE (max 64KB) for ext4
    From: Takashi Sato <>

    This patch set supports large block size(>4k, <=64k) in ext4,
    just enlarging the block size limit. But it is NOT possible to have 64kB
    blocksize on ext4 without some changes to the directory handling
    code. The reason is that an empty 64kB directory block would have a
    rec_len == (__u16)2^16 == 0, and this would cause an error to be hit in
    the filesystem. The proposed solution is treat 64k rec_len
    with a an impossible value like rec_len = 0xffff to handle this.

    The Patch-set consists of the following 2 patches.
    [1/2] ext4: enlarge blocksize
    - Allow blocksize up to pagesize

    [2/2] ext4: fix rec_len overflow
    - prevent rec_len from overflow with 64KB blocksize

    Now on 64k page ppc64 box runs with this patch set we could create a 64k
    block size ext4dev, and able to handle empty directory block.

    Signed-off-by: Takashi Sato <>
    Signed-off-by: Mingming Cao <>
    fs/ext4/super.c | 5 +++++
    include/linux/ext4_fs.h | 4 ++--
    2 files changed, 7 insertions(+), 2 deletions(-)

    diff --git a/fs/ext4/super.c b/fs/ext4/super.c
    index 619db84..d8bb279 100644
    --- a/fs/ext4/super.c
    +++ b/fs/ext4/super.c
    @@ -1548,6 +1548,11 @@ static int ext4_fill_super (struct super_block *sb, void *data, int silent)
    goto out_fail;

    + if (!sb_set_blocksize(sb, blocksize)) {
    + printk(KERN_ERR "EXT4-fs: bad blocksize %d.\n", blocksize);
    + goto out_fail;
    + }
    * The ext4 superblock will not be buffer aligned for other than 1kB
    * block sizes. We need to calculate the offset from buffer start.
    diff --git a/include/linux/ext4_fs.h b/include/linux/ext4_fs.h
    index 46b304d..5d90616 100644
    --- a/include/linux/ext4_fs.h
    +++ b/include/linux/ext4_fs.h
    @@ -73,8 +73,8 @@
    * Macro-instructions used to manage several block sizes
    #define EXT4_MIN_BLOCK_SIZE 1024
    -#define EXT4_MAX_BLOCK_SIZE 4096
    -#define EXT4_MIN_BLOCK_LOG_SIZE 10
    +#define EXT4_MAX_BLOCK_SIZE 65536
    +#define EXT4_MIN_BLOCK_LOG_SIZE 10
    #ifdef __KERNEL__
    # define EXT4_BLOCK_SIZE(s) ((s)->s_blocksize)
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      Last update: 2007-10-04 08:01    [W:0.026 / U:31.600 seconds]
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