[PATCH] fix O_DIRECT read of last block in a sparse file
commit35dc8161d0a6fa5e654bcb3d6240acc9ecb0a259
authorJeff Moyer <jmoyer@redhat.com>
Fri, 3 Feb 2006 11:04:27 +0000 (3 03:04 -0800)
committerLinus Torvalds <torvalds@g5.osdl.org>
Fri, 3 Feb 2006 16:32:07 +0000 (3 08:32 -0800)
tree0c688ffc3adc127f5cf9f35ff93e6072e1f42438
parent835417967c10b6dfaffdffddba59196196e5d431
[PATCH] fix O_DIRECT read of last block in a sparse file

Currently, if you open a file O_DIRECT, truncate it to a size that is not a
multiple of the disk block size, and then try to read the last block in the
file, the read will return 0.  The problem is in do_direct_IO, here:

        /* Handle holes */
        if (!buffer_mapped(map_bh)) {
                char *kaddr;

...

                if (dio->block_in_file >=
                        i_size_read(dio->inode)>>blkbits) {
                        /* We hit eof */
                        page_cache_release(page);
                        goto out;
                }

We shift off any remaining bytes in the final block of the I/O, resulting
in a 0-sized read.  I've attached a patch that fixes this.  I'm not happy
about how ugly the math is getting, so suggestions are more than welcome.

I've tested this with a simple program that performs the steps outlined for
reproducing the problem above.  Without the patch, we get a 0-sized result
from read.  With the patch, we get the correct return value from the short
read.

Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
Cc: Badari Pulavarty <pbadari@us.ibm.com>
Cc: Suparna Bhattacharya <suparna@in.ibm.com>
Cc: Mingming Cao <cmm@us.ibm.com>
Cc: Joel Becker <Joel.Becker@oracle.com>
Cc: "Chen, Kenneth W" <kenneth.w.chen@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
fs/direct-io.c