[libvirt] [PATCH] safe{read, write}: Don't lie on nonblocking FD

[Michal Privoznik]

On 16.01.2013 19:31, Daniel P. Berrange wrote:
> On Wed, Jan 16, 2013 at 07:27:46PM +0100, Michal Privoznik wrote:
>> Currently, whenever somebody calls saferead() on nonblocking FD
>> (safewrite() is totally interchangeable for purpose of this
>> message) he might get wrong return value. For instance, in the
>> first iteration some data is read. The number of bytes read is
>> stored into local variable 'nread'. However, in next iterations
>> we can get -1 from read() with errno == EAGAIN, in which case the
>> -1 is returned despite fact some data has already been read. So
>> the caller gets confused.
>>
>> Moreover, the comment just above the functions says, they act
>> like regular read() with nicer handling of EINTR. Well, they
>> don't now.
> 
> I think that it is correct that these APIs return -1 on EAGAIN.
> These APIs should *not* be used on non-blocking FDs.
> 
> Daniel
> 

In that case I think we have to note it explicitly in the comments.

Michal