[Libguestfs] [RFC nbdkit PATCH] multi-conn: New filter
Eric Blake
eblake at redhat.com
Wed Feb 24 17:40:09 UTC 2021
On 2/24/21 11:33 AM, Eric Blake wrote:
> Implement a TODO item of emulating multi-connection consistency via
> multiple plugin flush calls to allow a client to assume that a flush
> on a single connection is good enough. This also gives us some
> fine-tuning over whether to advertise the bit, including some setups
> that are unsafe but may be useful in timing tests.
>
> Testing is interesting: I used the sh plugin to implement a server
> that intentionally keeps a per-connection cache.
>
> Note that this filter assumes that multiple connections will still
> share the same data (other than caching effects); effects are not
> guaranteed when trying to mix it with more exotic plugins like info
> that violate that premise.
> ---
>
> I'm still working on the test; the sh plugin is good enough that it
> does what I want when playing with it manually, but I still need to
> write up various scenarios in test-multi-conn.sh to match what I've
> played with manually.
>
> I'm open to feedback on the set of options I've exposed during .config
> (too many, not enough, better names?) Right now, it is:
> multi-conn-mode=auto|plugin|disable|emulate|unsafe
> multi-conn-track-dirty=fast|connection|off
Another thing I thought about: should I add a knob that lets multi-conn
know whether export names are significant? When set, it only has to
maintain consistency by flushing on other connections visiting the same
export name, and not all connections.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3226
Virtualization: qemu.org | libvirt.org
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