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[Qemu-devel] [PULL 24/29] raw-posix: fix O_DIRECT short reads


From: Kevin Wolf
Subject: [Qemu-devel] [PULL 24/29] raw-posix: fix O_DIRECT short reads
Date: Fri, 22 Aug 2014 16:51:48 +0200

From: Stefan Hajnoczi <address@hidden>

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.

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

diff --git a/block/raw-posix.c b/block/raw-posix.c
index 5c745b9..d737f3a 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;
-- 
1.8.3.1




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