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    Subject[PATCH 3/4] vfs: change sb->s_maxbytes to a loff_t
    sb->s_maxbytes is supposed to indicate the maximum size of a file that
    can exist on the filesystem. It's declared as an unsigned long long.

    Even if a filesystem has no inherent limit that prevents it from using
    every bit in that unsigned long long, it's still problematic to set it
    to anything larger than MAX_LFS_FILESIZE. A lot of places implicitly
    cast s_maxbytes to a signed value when doing comparisons against it
    (usually using loff_t on the other side of the comparison). If it's
    set too large then this cast makes it a negative number and generally
    breaks the comparison.

    Change s_maxbytes to be loff_t instead. That should help eliminate the
    temptation to set it too large by making it a signed value.

    Signed-off-by: Jeff Layton <>
    fs/super.c | 10 ++++++++++
    include/linux/fs.h | 2 +-
    2 files changed, 11 insertions(+), 1 deletions(-)

    diff --git a/fs/super.c b/fs/super.c
    index 2761d3e..929d55d 100644
    --- a/fs/super.c
    +++ b/fs/super.c
    @@ -889,6 +889,16 @@ vfs_kern_mount(struct file_system_type *type, int flags, const char *name, void
    if (error)
    goto out_sb;

    + /*
    + * filesystems should never set s_maxbytes larger than MAX_LFS_FILESIZE
    + * but s_maxbytes was an unsigned long long for many releases. Throw
    + * this warning for a little while to try and catch filesystems that
    + * violate this rule. This warning can be removed in 2.6.34.
    + */
    + WARN(((unsigned long long) mnt->mnt_sb->s_maxbytes > MAX_LFS_FILESIZE),
    + "WARNING: %s sets sb->s_maxbytes too large (%llu)", type->name,
    + (unsigned long long) mnt->mnt_sb->s_maxbytes);
    mnt->mnt_mountpoint = mnt->mnt_root;
    mnt->mnt_parent = mnt;
    diff --git a/include/linux/fs.h b/include/linux/fs.h
    index a36ffa5..25d9743 100644
    --- a/include/linux/fs.h
    +++ b/include/linux/fs.h
    @@ -1316,7 +1316,7 @@ struct super_block {
    unsigned long s_blocksize;
    unsigned char s_blocksize_bits;
    unsigned char s_dirt;
    - unsigned long long s_maxbytes; /* Max file size */
    + loff_t s_maxbytes; /* Max file size */
    struct file_system_type *s_type;
    const struct super_operations *s_op;
    struct dquot_operations *dq_op;

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      Last update: 2009-08-07 21:03    [W:0.020 / U:15.796 seconds]
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