[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: Maximum QMP reply size
From: |
Dr. David Alan Gilbert |
Subject: |
Re: Maximum QMP reply size |
Date: |
Thu, 15 Sep 2022 16:21:44 +0100 |
User-agent: |
Mutt/2.2.7 (2022-08-07) |
* Peter Maydell (peter.maydell@linaro.org) wrote:
> On Tue, 6 Sept 2022 at 20:41, John Snow <jsnow@redhat.com> wrote:
> > Hi, I suspect I have asked this before, but I didn't write it down in
> > a comment, so I forget my justification...
> >
> > In the QMP lib, we need to set a buffering limit for how big a QMP
> > message can be -- In practice, I found that the largest possible
> > response was the QAPI schema reply, and I set the code to this:
> >
> > # Maximum allowable size of read buffer
> > _limit = (64 * 1024)
> >
> > However, I didn't document if this was a reasonable limit or just a
> > "worksforme" one. I assume that there's no hard limit for the protocol
> > or the implementation thereof in QEMU. Is there any kind of value here
> > that would be more sensible than another?
> >
> > I'm worried that if replies get bigger in the future (possibly in some
> > degenerate case I am presently unaware of) that the library default
> > will become nonsensical.
>
> There are some QMP commands which return lists of things
> where we put no inherent limit on how many things there
> are in the list, like qom-list-types. We'd have to be getting
> a bit enthusiastic about defining types for that to get
> up towards 64K's worth of response, but it's not inherently
> impossible. I think using human-monitor-command to send
> an 'xp' HMP command is also a way to get back an arbitrarily
> large string (just ask for a lot of memory to be dumped).
We could put size limits on xp; most Humans will only dump a few kB
maximum like that, any larger and you can dump to file.
Dave
> -- PMM
>
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
Re: Maximum QMP reply size, Daniel P . Berrangé, 2022/09/07
Re: Maximum QMP reply size, Daniel P . Berrangé, 2022/09/07
Re: Maximum QMP reply size, Markus Armbruster, 2022/09/07