Anthony Liguori schrieb:
> Kevin Wolf wrote:
>> Anthony Liguori schrieb:
>>
>>> Kevin Wolf wrote:
>>>
>>>> Anthony Liguori schrieb:
>>>>
>>>> Yes, if it fails, the EINVAL is no surprise. I meant what code path it
>>>> was using. Obviously we missed something in our patch and I'd like to
>>>> fix that. Did the error occur on raw images or something like qcow2?
>>>>
>>> It's a raw image and the calls are being made via
>>> bdrv_aio_read/bdrv_aio_write. It doesn't occur with a qcow2 but then
>>> cache=off doesn't seem to do what it's supposed to with cache=off (I
>>> believe the underlying backing file is not opened O_DIRECT?).
>>>
>>
>> This is really strange. In raw_aio_read/write there is a check like this:
>>
>> if (unlikely(s->aligned_buf != NULL && ((uintptr_t) buf % 512))) {
>> // emulate it using raw_pread/write which uses
>> // s->aligned_buf for the request then
>> }
>>
>
> Something is goofy then.
>
>> For qcow2 I think O_DIRECT actually is in effect. Otherwise it would
>> have worked even without our patch, and it didn't. And indeed, looking
>> at the code, it passes flags to bdrv_file_open when it opens the image
>> file.
>>
>
> Something's broken then. Maybe -snapshot doesn't pick up the
> O_DIRECT'ness? I'll have to check again. I was definitely seeing page
> cache behavior with cache=off.
Right, qemu seems to drop the flags for the backing file when using
BDRV_O_SNAPSHOT (bdrv2_open in block.c opens the file). So O_DIRECT
applies only to new data.
Have you been using -snapshot when you had trouble with the unaligned
buffer, too? I don't think I have tested this one when I made the patch...
Kevin
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