Re: [Qemu-devel] No error report when using the qemu-img.exetoconvert a disk to vmdk format which is saved on a disk that has nomorespace

["Guangmu Zhu" <guangmuzhu@gmail.com>]

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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:

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