I'll try the patch and report in a week for I'm too busy these days. And if I
could, I would like to help to maintain the Windows backend.
Sincerely.
Guangmu Zhu
-------------------------------------------------
Am 23.09.2015 um 13:30 hat Guangmu Zhu geschrieben:
> If the "BlockDriver" is "bdrv_vmdk", the function "vmdk_co_write" will be
> called instead. In function "vmdk_write_extent" I see "ret = bdrv_pwrite
> (extent->file, write_offset, write_buf, write_len);". So the "extend->file" is
> "bdrv_file", is it?
Yes, exactly. You'll go through bdrv_vmdk first, and then the nested
call goes to bdrv_file.
> -------------------------------------------------
>
> Correct a mistake:
> So though the "count" would be "-EINVAL" if error occurred while writing some
> file, the return value will always be zero. Maybe I missed something?
I think you're right. Instead of setting count = 0/-EINVAL in
aio_worker, we should be setting ret.
Can you try the patch below and report back?
> 3. The "bs->drv->bdrv_aio_writev" is function "raw_aio_writev" in file
> "raw-win32.c" and the quemu-img uses synchronous IO always, so the function
> "paio_submit" in the same file will be called. This function submits the "aio"
> to "worker_thread" with the callback "aio_worker". There are some codes in
> "aio_worker":
>
> ssize_t ret = 0;
> ......
> case QEMU_AIO_WRITE:
> count = handle_aiocb_rw(aiocb);
> if (count == aiocb->aio_nbytes) {
> count = 0;
> } else {
> count = -EINVAL;
> }
> break;
> ......
> return ret;
Independently of your problem, the code in aio_worker() looks a bit
fishy, because handle_aiocb_rw() can't distinguish between an error
and 0 bytes transferred.
For writes, that probably doesn't matter, but for reads, I think we
return a successful read of zeroes instead of signalling an error. This
might need another patch.
Generally, the Windows backend is not getting a lot of attention and
could use someone who checks it, cleans it up and fixes bugs.
Kevin
diff --git a/block/raw-win32.c b/block/raw-win32.c
index 68f2338..b562c94 100644
--- a/block/raw-win32.c
+++ b/block/raw-win32.c
@@ -119,9 +119,9 @@ static int aio_worker(void *arg)
case QEMU_AIO_WRITE:
count = handle_aiocb_rw(aiocb);
if (count == aiocb->aio_nbytes) {
- count = 0;
+ ret = 0;
} else {
- count = -EINVAL;
+ ret = -EINVAL;
}
break;
case QEMU_AIO_FLUSH:
