Re: [PATCH] Use qemu_memalign instead of qemu_malloc

[Kevin Wolf <kwolf@suse.de>]

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
    }

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.

Kevin