| Message ID | 1266000136.4310.36.camel@michlmayr |
|---|---|
| State | Superseded, archived |
| Headers | show |
On 2010-02-12, at 11:42, Leonard Michlmayr wrote: > fs/ext4/extents.c:ext4_fiemap rounds the length of the requested range > down to blocksize. This 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. > > Solution: > Calculate the last byte of the region and round to blocksize. Then get > the number of blocks by subtracting last_blk - start_blk and adding 1 > for the first block. (The variable last_blk is introduced just for > easier reading.) This patch will fix this. > > I already suggested this patch some time ago, this is the same patch > for > a more recent kernel version. > > Signed-off-by: Leonard Michlmayr <leonard.michlmayr@gmail.com> > > diff -rup linux-2.6.32.7/fs/ext4/extents.c linux-2.6.32.7-lm/fs/ext4/ > extents.c > --- linux-2.6.32.7/fs/ext4/extents.c 2010-01-29 00:06:20.000000000 > +0100 > +++ linux-2.6.32.7-lm/fs/ext4/extents.c 2010-02-11 > 21:26:40.000000000 +0100 > @@ -3711,6 +3711,7 @@ int ext4_fiemap(struct inode *inode, str > __u64 start, __u64 len) > { > ext4_lblk_t start_blk; > + ext4_lblk_t last_blk; > ext4_lblk_t len_blks; > int error = 0; > > @@ -3726,7 +3727,9 @@ int ext4_fiemap(struct inode *inode, str > error = ext4_xattr_fiemap(inode, fieinfo); > } else { > start_blk = start >> inode->i_sb->s_blocksize_bits; > - len_blks = len >> inode->i_sb->s_blocksize_bits; > + /* the last byte in the range is (start + len - 1) */ > + last_blk = (start + len - 1) >> inode->i_sb->s_blocksize_bits; > + len_blks = last_blk - start_blk + 1; If "last_blk" is only used in this one place, please put the declaration inside the scope of the "else" clause. Looks fine otherwise. Cheers, Andreas -- Andreas Dilger Sr. Staff Engineer, Lustre Group Sun Microsystems of Canada, Inc. -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff -rup linux-2.6.32.7/fs/ext4/extents.c linux-2.6.32.7-lm/fs/ext4/extents.c --- linux-2.6.32.7/fs/ext4/extents.c 2010-01-29 00:06:20.000000000 +0100 +++ linux-2.6.32.7-lm/fs/ext4/extents.c 2010-02-11 21:26:40.000000000 +0100 @@ -3711,6 +3711,7 @@ int ext4_fiemap(struct inode *inode, str __u64 start, __u64 len) { ext4_lblk_t start_blk; + ext4_lblk_t last_blk; ext4_lblk_t len_blks; int error = 0; @@ -3726,7 +3727,9 @@ int ext4_fiemap(struct inode *inode, str error = ext4_xattr_fiemap(inode, fieinfo); } else { start_blk = start >> inode->i_sb->s_blocksize_bits; - len_blks = len >> inode->i_sb->s_blocksize_bits; + /* the last byte in the range is (start + len - 1) */ + 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.
Problem: fs/ext4/extents.c:ext4_fiemap rounds the length of the requested range down to blocksize. This 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. Solution: Calculate the last byte of the region and round to blocksize. Then get the number of blocks by subtracting last_blk - start_blk and adding 1 for the first block. (The variable last_blk is introduced just for easier reading.) This patch will fix this. I already suggested this patch some time ago, this is the same patch for a more recent kernel version. Signed-off-by: Leonard Michlmayr <leonard.michlmayr@gmail.com> -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html