linux-kernel - Re: Block layer - meaning of REQ

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Message-ID: <x49fuv5uxe6.fsf@segfault.boston.devel.redhat.com>
Date:	Fri, 01 Apr 2016 12:06:09 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Alex Bligh <alex@...x.org.uk>
Cc:	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	nbd-general@...ts.sourceforge.net, Eric Blake <eblake@...hat.com>
Subject: Re: Block layer - meaning of REQ_FUA on not write requests

Alex Bligh <alex@...x.org.uk> writes:

> I am trying to clean up the documentation of the NBD protocol. NBD's
> support for Force Unit Access (FUA) was modelled on the linux kernel
> block layer. When I added support a few years ago, I omitted to find
> out exactly what types of request it applies to. Obviously it applies
> to write requests, but how about others (e.g. read)?

Any request with REQ_FUA set will be treated as a flush by the block
layer.  As such, we do not expect reads to have this bit set.

Cheers,
Jeff