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Re: [Qemu-devel] [PATCH 00/12] nbd improvements

From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH 00/12] nbd improvements
Date: Fri, 09 Sep 2011 12:29:29 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:6.0) Gecko/20110816 Thunderbird/6.0

On 09/09/2011 11:00 AM, Kevin Wolf wrote:
There is anonther patch enabling AIO for NBD on the list [1], by
Nicholas Thomas (CCed), that lacked review so far. Can you guys please
review each others approach and then converge on a solution? I guess
Paolo's patches 1-7 can be applied in any case, probably causing minor
conflicts, but for the rest we need to decide which one to pick.

Stefan also pointed me to Nicholas's patches yesterday. I would go with mine, if only because his work predates coroutines (at least the older versions) and are much more complex.

On the other hand, Nicholas's work includes timeout and reconnect. I'm not sure how complicated it is to include it in my series, but probably not much. With coroutines, preserving the list of outstanding I/O requests is done implicitly by the CoMutex, so you basically have to check errno for ECONNRESET and similar errors, reconnect, and retry issuing the current request only.

Timeout can be done with a QEMUTimer that shuts down the socket (shutdown(2) I mean). This triggers an EPIPE when writing, or a zero-sized read when reading. The timeout can be set every time the coroutine is (re)entered, and reset before exiting nbd_co_readv/writev.

What do you think?


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