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Date:   Thu, 3 Nov 2022 00:49:41 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Jens Axboe <axboe@kernel.dk>
Cc:     Christoph Hellwig <hch@infradead.org>,
        Damien Le Moal <damien.lemoal@opensource.wdc.com>,
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        "Maciej S . Szmigiero" <mail@maciej.szmigiero.name>,
        Hannes Reinecke <hare@suse.de>
Subject: Re: [PATCH v4 1/7] block: Prevent the use of REQ_FUA with read
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On Wed, Nov 02, 2022 at 09:17:54AM -0600, Jens Axboe wrote:
> 
> This looks fine, but if we're never expecting this to happen, I do think
> it should just go into libata instead as that's the only user that
> cares about it. Yes, that'll lose the backtrace for who submitted it
> potentially, but you can debug it pretty easily at that point if you
> run into it.

FUA and PREFLUSH are bits only defined for writes.  libata might be the
first thing blowing up, but it really is a block layer constraint.
So validity checking what is being sent to the block layer at the
highest possible lyer is a good thing to ensure we don't get us in
trouble by someone accidentally sending one down or even expecting it
to work.  Especially as at least SCSI actually defines semantics for FUA
on reads, but they are completely bogus and useless.