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[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>
This commit is contained in:
Jeff Moyer 2006-02-03 03:04:27 -08:00 committed by Linus Torvalds
parent 835417967c
commit 35dc8161d0
1 changed files with 8 additions and 1 deletions
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9
fs/direct-io.c
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@ -857,6 +857,7 @@ do_holes:
/* Handle holes */
if (!buffer_mapped(map_bh)) {
char *kaddr;
loff_t i_size_aligned;
/* AKPM: eargh, -ENOTBLK is a hack */
if (dio->rw == WRITE) {
@ -864,8 +865,14 @@ do_holes:
return -ENOTBLK;
}
/*
* Be sure to account for a partial block as the
* last block in the file
*/
i_size_aligned = ALIGN(i_size_read(dio->inode),
1 << blkbits);
if (dio->block_in_file >=
i_size_read(dio->inode)>>blkbits) {
i_size_aligned >> blkbits) {
/* We hit eof */
page_cache_release(page);
goto out;