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

On Wed, Jan 16, 2013 at 07:39:53PM +0100, Michal Privoznik wrote: > 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. >> > In that case I think we have to note it explicitly in the comments. BTW, what code did you encounter that was using this with non-blocking fds ? Daniel