Hi
I think that the patch is valid as it is.
<snip>
> > start_blk = start>> inode->i_sb->s_blocksize_bits;
> > - len_blks = len>> inode->i_sb->s_blocksize_bits;
> > + last_blk = (start + len - 1)>> inode->i_sb->s_blocksize_bits;
> > + len_blks = last_blk - start_blk + 1;
>
> In 1KB block size, the overflow occurs at above line.
> Since last_blk is set 0xffffffff when len is equal to s_maxbytes.
> Therefore ext4_fiemap() can not get correct extent information
> with 0 length. How about adding this change?
>
I have considered this possibility, but len == 0 is an invalid request
and would be sorted out by fs/ioctl.c:fiemap_check_ranges. If you want
to make sure that everything is correct even if len == 0 slips through
consider Andreas Dilger's solution which does not introduce a new branch
to the code:
(Here end_blk is one more than the last block)
end_blk = (start + len + inode->i_sb->s_blocksize - 1) >> inode->i_sb->s_blocksize_bits;
len_blks = end_blk - start_blk;
I think we don't need to copy the functionality of fiemap_check_ranges.
At least if there a no danger that len == 0 will be allowed in the
specification in future?
> Signed-off-by: Akira Fujita <a-fujita@xxxxxxxxxxxxx>
> ---
> extents.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
> --- linux-2.6.33-rc8-a/fs/ext4/extents.c 2010-03-03 14:53:49.000000000 +0900
> +++ linux-2.6.33-rc8-b/fs/ext4/extents.c 2010-03-03 15:31:57.000000000 +0900
> @@ -3912,7 +3912,8 @@ int ext4_fiemap(struct inode *inode, str
>
> start_blk = start >> inode->i_sb->s_blocksize_bits;
> last_blk = (start + len - 1) >> inode->i_sb->s_blocksize_bits;
> - len_blks = last_blk - start_blk + 1;
> + len_blks = (loff_t)last_blk - start_blk + 1 < EXT_MAX_BLOCK ?
> + last_blk - start_blk + 1 : EXT_MAX_BLOCK;
>
> /*
> * Walk the extent tree gathering extent information.
>
>
> (2010/03/03 3:18), Theodore Ts'o wrote:
> > From: Leonard Michlmayr<leonard.michlmayr@xxxxxxxxx>
> >
> > ext4_fiemap() rounds the length of the requested range down to
> > blocksize, which is is not the true number of blocks that cover the
> > requested region. This problem is especially impressive if the user
> > requests only the first byte of a file: not a single extent will be
> > reported.
> >
> > We fix this by calculating the last block of the region and then
> > subtract to find the number of blocks in the extents.
> >
> > Signed-off-by: Leonard Michlmayr<leonard.michlmayr@xxxxxxxxx>
> > Signed-off-by: "Theodore Ts'o"<tytso@xxxxxxx>
> > ---
> > fs/ext4/extents.c | 6 ++++--
> > 1 files changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> > index bd80891..bc9860f 100644
> > --- a/fs/ext4/extents.c
> > +++ b/fs/ext4/extents.c
> > @@ -3768,7 +3768,6 @@ int ext4_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
> > __u64 start, __u64 len)
> > {
> > ext4_lblk_t start_blk;
> > - ext4_lblk_t len_blks;
> > int error = 0;
> >
> > /* fallback to generic here if not in extents fmt */
> > @@ -3782,8 +3781,11 @@ int ext4_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
> > if (fieinfo->fi_flags& FIEMAP_FLAG_XATTR) {
> > error = ext4_xattr_fiemap(inode, fieinfo);
> > } else {
> > + ext4_lblk_t last_blk, len_blks;
> > +
> > start_blk = start>> inode->i_sb->s_blocksize_bits;
> > - len_blks = len>> inode->i_sb->s_blocksize_bits;
> > + last_blk = (start + len - 1)>> inode->i_sb->s_blocksize_bits;
> > + len_blks = last_blk - start_blk + 1;
> >
> > /*
> > * Walk the extent tree gathering extent information.
>
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