[Qemu-devel] [PATCH 1/2] raw-posix: fix O_DIRECT short reads

[Stefan Hajnoczi <stefanha@redhat.com>]

The following O_DIRECT read from a <512 byte file fails:

  $ truncate -s 320 test.img
  $ qemu-io -n -c 'read -P 0 0 512' test.img
  qemu-io: can't open device test.img: Could not read image for determining its format: Invalid argument

Note that qemu-io completes successfully without the -n (O_DIRECT)
option.

This patch fixes qemu-iotests ./check -nocache -vmdk 059.

Suggested-by: Kevin Wolf <kwolf@redhat.com>
Reported-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 block/raw-posix.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/block/raw-posix.c b/block/raw-posix.c
index 1194eb0..a48ce91 100644
--- a/block/raw-posix.c
+++ b/block/raw-posix.c
@@ -747,6 +747,15 @@ static ssize_t handle_aiocb_rw_linear(RawPosixAIOData *aiocb, char *buf)
         }
         if (len == -1 && errno == EINTR) {
             continue;
+        } else if (len == -1 && errno == EINVAL &&
+                   (aiocb->bs->open_flags & BDRV_O_NOCACHE) &&
+                   !(aiocb->aio_type & QEMU_AIO_WRITE) &&
+                   offset > 0) {
+            /* O_DIRECT pread() may fail with EINVAL when offset is unaligned
+             * after a short read.  Assume that O_DIRECT short reads only occur
+             * at EOF.  Therefore this is a short read, not an I/O error.
+             */
+            break;
         } else if (len == -1) {
             offset = -errno;
             break;
-- 
1.9.3