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Re: [Qemu-devel] chardev's and fd's in monitors
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] chardev's and fd's in monitors |
Date: |
Tue, 18 Oct 2016 12:32:02 +0100 |
User-agent: |
Mutt/1.7.1 (2016-10-04) |
* Daniel P. Berrange (address@hidden) wrote:
> On Wed, Oct 12, 2016 at 08:15:02PM +0100, Dr. David Alan Gilbert wrote:
> > Hi,
> > I had a look at a couple of readline like libraries;
> > editline and linenoise. A difficulty with using them is that
> > they both want fd's or FILE*'s; editline takes either but
> > from a brief look I think it's expecting to extract the fd.
> > That makes them tricky to integrate into qemu, where
> > the chardev's hide a whole bunch of non-fd things; in particular
> > tls, mux, ringbuffers etc.
> >
> > If we could get away with just a FILE* then we could use fopencookie,
> > but that's GNU only.
> >
> > Is there any sane way of shepherding all chardev's into having an
> > fd?
>
> The entire chardev abstraction model exists precisely because we cannot
> make all chardevs look like a single fd. Even those which are fd based
> may have separate FDs for input and output.
Note that editline takes separate in/out streams, but it does want those streams
to be FILE*'s.
> IMHO the only viable approach would be to enhance linenoise/editline to
> not assume use of fd* or FILE * abstractions.
I think if it came to that then we'd probably end up sticking with what we
had for a very long time; I'd assume it would take a long time before
any mods we made to the libraries would come around to be generally useful.
> BTW, what is the actual thread issue you are facing ? Chardevs at least
> ought to be usable from a separate thread, as long as each distinct
> chardev object instance was only used from one thread at a time ?
Marc-André pointed that out; I hadn't realised they were thread safe.
But what are the rules? You say 'only used from one thread at a time' -
what happens if we have a mux and the different streams to the mux come
from different threads?
My actual thoughts for threads came from a few sides:
a) Maybe I could have a shim thread that fed the editline fd from a chardev
b) I'd eventually like multiple monitor threads.
Dave
> Regards,
> Daniel
> --
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--
Dr. David Alan Gilbert / address@hidden / Manchester, UK
- [Qemu-devel] chardev's and fd's in monitors, Dr. David Alan Gilbert, 2016/10/12
- Re: [Qemu-devel] chardev's and fd's in monitors, Marc-André Lureau, 2016/10/12
- Re: [Qemu-devel] chardev's and fd's in monitors, Daniel P. Berrange, 2016/10/18
- Re: [Qemu-devel] chardev's and fd's in monitors,
Dr. David Alan Gilbert <=
- Re: [Qemu-devel] chardev's and fd's in monitors, Daniel P. Berrange, 2016/10/18
- Re: [Qemu-devel] chardev's and fd's in monitors, Dr. David Alan Gilbert, 2016/10/18
- Re: [Qemu-devel] chardev's and fd's in monitors, Daniel P. Berrange, 2016/10/18
- Re: [Qemu-devel] chardev's and fd's in monitors, Dr. David Alan Gilbert, 2016/10/18
- Re: [Qemu-devel] chardev's and fd's in monitors, Daniel P. Berrange, 2016/10/18
- Re: [Qemu-devel] chardev's and fd's in monitors, Dr. David Alan Gilbert, 2016/10/18
- Re: [Qemu-devel] chardev's and fd's in monitors, Daniel P. Berrange, 2016/10/19
- Re: [Qemu-devel] chardev's and fd's in monitors, Markus Armbruster, 2016/10/19