linux-kernel - Re:[PATCH v3 10/15] block: Add fops atomic write support

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Date: Tue, 13 Feb 2024 15:06:19 +0530
From: Nilay Shroff <nilay@...ux.ibm.com>
To: john.g.garry@...cle.com
Cc: axboe@...nel.dk, brauner@...nel.org, bvanassche@....org,
        dchinner@...hat.com, djwong@...nel.org, hch@....de, jack@...e.cz,
        jbongio@...gle.com, jejb@...ux.ibm.com, kbusch@...nel.org,
        linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
        linux-scsi@...r.kernel.org, linux-xfs@...r.kernel.org,
        martin.petersen@...cle.com, ming.lei@...hat.com, ojaswin@...ux.ibm.com,
        sagi@...mberg.me, tytso@....edu, viro@...iv.linux.org.uk
Subject: Re:[PATCH v3 10/15] block: Add fops atomic write support

>+static bool blkdev_atomic_write_valid(struct block_device *bdev, loff_t pos,
>+				      struct iov_iter *iter)
>+{
>+	struct request_queue *q = bdev_get_queue(bdev);
>+	unsigned int min_bytes = queue_atomic_write_unit_min_bytes(q);
>+	unsigned int max_bytes = queue_atomic_write_unit_max_bytes(q);
>+
>+	if (!iter_is_ubuf(iter))
>+		return false;
>+	if (iov_iter_count(iter) & (min_bytes - 1))
>+		return false;
>+	if (!is_power_of_2(iov_iter_count(iter)))
>+		return false;
>+	if (pos & (iov_iter_count(iter) - 1))
>+		return false;
>+	if (iov_iter_count(iter) > max_bytes)
>+		return false;
>+	return true;
>+}

Here do we need to also validate whether the IO doesn't straddle 
the atmic bondary limit (if it's non-zero)? We do check that IO 
doesn't straddle the atomic boundary limit but that happens very 
late in the IO code path either during blk-merge or in NVMe driver 
code.

Thanks,
--Nilay