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Re: [Xen-devel] /proc/xen/xenbus supports watch?

To: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] /proc/xen/xenbus supports watch?
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Sun, 25 Sep 2005 12:02:42 +0100
Cc: xen-devel List <xen-devel@xxxxxxxxxxxxxxxxxxx>, Christian Limpach <Christian.Limpach@xxxxxxxxxxxx>
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On 25 Sep 2005, at 04:29, Rusty Russell wrote:


I was assuming per-connection, ie. every time a tool
opens /proc/xen/xenbus we map a new page/event channel, and free on
close.  ie. the drivers in the domU kernel share the store comms page
created with the domain, tools in the domU get a separate page each,
tools in dom0 connect to the unix domain socket each. To the store, one connection, one transport. (Each connection can set up multiple watches
of course, and Christian has been hinting that he wants multiple
transactions too, but that's another argument).

Yeah, I can live with this, although: What about multiple transactions within the kernel? Do you plan to continue serialising them (e.g., on a waitqueue)? An advantage of mux/demux would be that concurrent kernel transactions could easily use the same mechanism. Your scheme places restart mechanisms in user space, so they're out of reach for kernel transactions.

 -- Keir


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