linux-kernel - Re: [PATCH 21/21] nvme: Support atomic writes

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Message-ID: <20231109153603.GA2188@lst.de>
Date:   Thu, 9 Nov 2023 16:36:03 +0100
From:   Christoph Hellwig <hch@....de>
To:     John Garry <john.g.garry@...cle.com>
Cc:     axboe@...nel.dk, kbusch@...nel.org, hch@....de, sagi@...mberg.me,
        jejb@...ux.ibm.com, martin.petersen@...cle.com, djwong@...nel.org,
        viro@...iv.linux.org.uk, brauner@...nel.org,
        chandan.babu@...cle.com, dchinner@...hat.com,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nvme@...ts.infradead.org, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, tytso@....edu, jbongio@...gle.com,
        linux-api@...r.kernel.org, Alan Adamson <alan.adamson@...cle.com>
Subject: Re: [PATCH 21/21] nvme: Support atomic writes

> +			if (le16_to_cpu(id->nabspf))
> +				boundary = (le16_to_cpu(id->nabspf) + 1) * bs;
> +
> +			if (is_power_of_2(boundary) || !boundary) {
> +				blk_queue_atomic_write_max_bytes(disk->queue, atomic_bs);
> +				blk_queue_atomic_write_unit_min_sectors(disk->queue, 1);
> +				blk_queue_atomic_write_unit_max_sectors(disk->queue,
> +									atomic_bs / bs);
> +				blk_queue_atomic_write_boundary_bytes(disk->queue, boundary);
> +			} else {
> +				dev_err(ns->ctrl->device, "Unsupported atomic boundary=0x%x\n",
> +					boundary);
> +			}

Please figure out a way to split the atomic configuration into a
helper and avoid all those crazy long lines,  preferable also avoid
the double calls to the block helpers as well while you're at it.

Also I really want a check in the NVMe I/O path that any request
with the atomic flag set actually adhers to the limits to at least
partially paper over the annoying lack of a separate write atomic
command in nvme.