linux-kernel - Re: [PATCH] nvme: Fix nvme_setup_command metadata trace event for cdw10

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Message-ID: <20220706161825.GA1962@lst.de>
Date:   Wed, 6 Jul 2022 18:18:25 +0200
From:   Christoph Hellwig <hch@....de>
To:     Keith Busch <kbusch@...nel.org>
Cc:     John Garry <john.garry@...wei.com>, axboe@...com, hch@....de,
        sagi@...mberg.me, linux-nvme@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] nvme: Fix nvme_setup_command metadata trace event for
 cdw10

On Wed, Jul 06, 2022 at 10:13:22AM -0600, Keith Busch wrote:
> Did you test what the trace looks like afte this? We're losing valuable trace
> data here. The field is supposed to get CDW's 10 - 15, so that's 24 bytes. I
> don't know why it cares that the address of the field being read is only 4
> bytes; we want everything that comes after it too.

Because accesses should not spawn boundaries of members in structs unless
copying the entire struct.  If we want to trace the various fields we
need to individually assign them.

Anyway, I'm dropping this patch from nvme-5.19 for now to let the
discussion conclude.