On Tue, Sep 06, 2022 at 03:38:54PM -0400, John Snow 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?
As a reference, libvirt arbitrarily chose 10 MB as the QMP reply limit. It is huge enough it'll be hard to make a QMP reply exceed that, but also still tiny in the context of managing VMs on a host with GB's of RAM. NB, this doesn't mean we allocate 10 MB every time, it is just an upper bound - we only allocate what we actually need. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
