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

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On 13/02/2024 09:36, Nilay Shroff wrote:
+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.

It's relied that atomic_write_unit_max is <= atomic_write_boundary and both are a power-of-2. Please see the NVMe patch, which this is checked. Indeed, it would not make sense if atomic_write_unit_max > atomic_write_boundary (when non-zero).

So if the write is naturally aligned and its size is <= atomic_write_unit_max, then it cannot be straddling a boundary.

Thanks,
John




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