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

[Daniel P. Berrange]

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
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