Re: [Qemu-devel] [PATCH 1/5] char: Let the caller know how many bytes were written in case of incomplete writes

[Jamie Lokier]

Gerd Hoffmann wrote:
> On 04/06/10 13:05, Amit Shah wrote:
> >On (Tue) Apr 06 2010 [12:21:52], Gerd Hoffmann wrote:
> >>On 04/06/10 11:58, Amit Shah wrote:
> >>>>>It would certainly be beneficial for consumers of virtio-serial to be
> >>>>>notified of -EAGAIN so that the guest can be throttled till the chardev
> >>>>>catches up with the data being sent.
> >>>>
> >>>>EAGAIN should only ever occur if no bytes are written.
> >>>
> >>>Right. That, or just return 0 and let the caller handle the situation?
> >>
> >>Go with the usual unix semantics instead of creating something new.
> >>
> >>When something was written -- return the number of bytes.  Caller has to
> >>compare with the length passed in to figure whenever it was a partial
> >>write or not.
> >>
> >>When nothing was written -- return the error.
> >
> >Unless Paul wants to never return recoverable error messages as he
> >mentioned in his first mail.
> 
> Return value "0" usually means end-of-file, I would not use that for 
> something else too.  We have to agree on something though ...

Which is why EAGAIN was invented.

-- Jamie