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

[Amit Shah]

On (Tue) Apr 06 2010 [10:34:29], Paul Brook wrote:
> > On (Mon) Apr 05 2010 [17:33:38], Paul Brook wrote:
> > > > There might be cases where a few bytes would have been sent out to char
> > > > devices and some not. Currently the return values from qemu_chr_write()
> > > > to char devs are only -1, indicating an error, or the complete length
> > > > of the string passed.
> > > >
> > > > Make 'len' a pointer instead, and indicate how much of the string was
> > > > written. The return value will either be the same as 'len' or a
> > > > negative number indicating an error condition.
> > >
> > > This seems wrong. We should not be getting recoverable errors.
> > 
> > I was thinking of adding a bool to CharDriverState to indicate if EAGAIN
> > should be reported to the writer. This can be conveyed at the time of
> > doing qemu_chr_add_handlers().
> > 
> > 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?

                Amit