[libvirt] [PATCH v2] iohelper: fix reading with O_DIRECT

[Nikolay Shirokovskiy]

On 20.09.2017 16:30, Daniel P. Berrange wrote:
> On Wed, Sep 20, 2017 at 02:58:55PM +0300, Nikolay Shirokovskiy wrote:
>> saferead is not suitable for direct reads. If file size is not multiple
>> of align size then we get EINVAL on the read(2) that is supposed to
>> return 0 because read buffer will not be aligned at this point.
>>
>> Let's not read again after partial read and check that we read
>> everything by comparing the number of total bytes read against file size.
> 
> What scenario did you actually hit this problem in ?    IIUC, we should
> only be using O_DIRECT against block devices or plain files, and in both
> those cases we should never see short-read unless we hit EOF.

Yes. But saferead is generic function and rereads file after short read.
Here we got EINVAL because of misalignement.

Nikolay