raw-posix: Remove O_RDWR when attempting to open a file read-only

When we open a file, we first attempt to open it read-write, then fall back
to read-only.  Unfortunately we reuse the flags from the previous attempt,
so both attempts try to open the file with write permissions, and fail.

Fix by clearing the O_RDWR flag from the previous attempt.

Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

block/raw-posix.c

@@ -133,6 +133,7 @@ static int raw_open_common(BlockDriverState *bs, const char *filename,
     s->lseek_err_cnt = 0;
 
     s->open_flags |= O_BINARY;
+    s->open_flags &= ~O_ACCMODE;
     if ((flags & BDRV_O_ACCESS) == BDRV_O_RDWR) {
         s->open_flags |= O_RDWR;
     } else {