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Re: [Libguestfs] [RFC nbdkit PATCH] multi-conn: New filter



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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