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Subject[PATCH] 2.6.10 - direct-io async short read bug
From
Date
 Hi,

When reading a file in async mode (using kernel AIO), and the file
size is lower than the requested size (short read), the direct IO
layer reports an incorrect number of bytes read (transferred).

That case is handled for the sync path in 'direct_io_worker'
(fs/direct-io.c) where a check is made against the file size.

This patch does the same thing for the async path. It applies to
a vanilla 2.6.10 kernel.

Please CC: me any comments and/or suggestions.

Sébastien.

------------------------------------------------------

Sébastien Dugué BULL/FREC:B1-247
phone: (+33) 476 29 77 70 Bullcom: 229-7770

mailto:sebastien.dugue@bull.net

Linux POSIX AIO: http://www.bullopensource.org/posix

------------------------------------------------------
--- linux-2.6.10/fs/direct-io.c.orig 2005-03-03 12:41:05.541074051 +0100
+++ linux-2.6.10/fs/direct-io.c 2005-03-03 12:01:46.206210808 +0100
@@ -230,17 +230,30 @@ static void finished_one_bio(struct dio
spin_lock_irqsave(&dio->bio_lock, flags);
if (dio->bio_count == 1) {
if (dio->is_async) {
+ ssize_t transferred;
+ ssize_t i_size;
+ loff_t offset;
+
/*
* Last reference to the dio is going away.
* Drop spinlock and complete the DIO.
*/
spin_unlock_irqrestore(&dio->bio_lock, flags);
- dio_complete(dio, dio->block_in_file << dio->blkbits,
- dio->result);
+
+ /* Check for short read case */
+ transferred = dio->result;
+ i_size = i_size_read (dio->inode);
+ offset = dio->iocb->ki_pos;
+
+ if ((dio->rw == READ) && ((offset + transferred) > i_size))
+ transferred = i_size - offset;
+
+ dio_complete(dio, offset, transferred);
+
/* Complete AIO later if falling back to buffered i/o */
if (dio->result == dio->size ||
((dio->rw == READ) && dio->result)) {
- aio_complete(dio->iocb, dio->result, 0);
+ aio_complete(dio->iocb, transferred, 0);
kfree(dio);
return;
} else {
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