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Re: [Qemu-devel] [PATCH v2 for 2.10] block/nbd-client: always return EIO


From: Eric Blake
Subject: Re: [Qemu-devel] [PATCH v2 for 2.10] block/nbd-client: always return EIO on and after the first io channel error
Date: Tue, 15 Aug 2017 09:04:24 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1

On 08/15/2017 02:26 AM, Vladimir Sementsov-Ogievskiy wrote:
>>> The only doubt: is it possible to hang on nbd_rwv because some fail in
>>> connection or server?
>> We _already_ have the bug that we are hanging in trying to talk to a
>> broken server, which is a regression introduced in 2.9 and not present
>> in 2.8.  And that's what I'm most worried about getting fixed before
>> 2.10 is released.
>>
>> I don't think that sending any more data to the server is necessarily
>> going to cause a hang, so much as trying to read data that is going to
>> be sent in reply or failing to manipulate the coroutine handlers
>> correctly (that is, our current hang is because even after we detect
>> failure, we are still sending NBD_CMD_FLUSH but no longer have a
>> coroutine in place to read the reply, so we no longer make progress to
>> the point of sending NBD_CMD_DISC and closing the connection).
> 
> but we will not try to read.
> However, I'm convinced, ok, let's send nothing to the broken server.

Can you offer a review on my proposed patch? I'm hoping to send an NBD
pull request in the next couple of hours, to make -rc3.
https://lists.gnu.org/archive/html/qemu-devel/2017-08/msg02593.html

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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