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Re: [Qemu-block] [PATCH] file-posix: Cache lseek result for data regions

From: Paolo Bonzini
Subject: Re: [Qemu-block] [PATCH] file-posix: Cache lseek result for data regions
Date: Fri, 25 Jan 2019 11:10:56 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.3.1

On 24/01/19 16:42, Kevin Wolf wrote:
>> Recently Paolo asked me not to add more users of AioContext lock. 
>> Unfortunately
>> I don't understand the whole picture around it.. Doesn't this apply here?
>> https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg03410.html
> I don't know. Honestly I feel nobody except Paolo knows, because we
> don't know his patches yet.

This is true.  On the other hand, the AioContext lock is only used in
some special cases around block jobs and blk_set_aio_context, and in
general the block devices already should not have any dependencies
(unless they crept in without me noticing).

In particular...

> But raw doesn't have an s->lock yet, so I
> think removing the AioContext lock involves some work on it anyway and
> adding this doesn't really change the amount of work.

... BDRVRawState doesn't have any data that changes after open, does it?
 This is why it doesn't have an s->lock.


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