Re: [Qemu-devel] [PATCH/RFC 0/7] Screendump to UNIX socket & in PNG format

[Luiz Capitulino <lcapitulino@redhat.com>]

On Wed, 14 Mar 2012 07:28:44 -0600
Eric Blake <eblake@redhat.com> wrote:

> On 03/14/2012 07:19 AM, Alon Levy wrote:
> 
> >> Also, when returning the image via fd, we could offload its writing to
> >> a bh. This would give us a poor man's async support, where the biggest
> >> drawback would the lack of error detection (can this operation fail anyway?).
> >>
> > 
> > It leaves detection of completion up to the user, so inotify / parsing
> > the file to see if it's complete (header says size X, but file is still
> > Y<X, not done..), which looks like as big a drawback.
> 
> Notification on a pipe is easy - the reader gets EOF when the writer
> closes the fd, with no need to use inotify. 

Oh, so I was right, it's a pipe. Alon confused me for a few seconds :-)

> The only remaining issue is
> whether the writer closes the fd early on error, so that the reader gets
> an incomplete file.  But then the client can tell after getting EOF
> whether the image file is complete (read the header, final file size is
> too small), without having to have the intermediate management app
> parsing headers during the streaming, although it would be a bonus if
> there were a way to tell the management app that an error occurred and
> qemu closed the write end early.

This is async support. Anything other than that is going to be a hack
(which can or can not be accepted).