Re: [PATCH 12/15] virtio_blk: pass queue_limits to blk_mq_alloc_disk

[Christoph Hellwig <hch@lst.de>]

On Fri, Jun 28, 2024 at 03:25:02PM +0100, John Garry wrote:
> I think that we might need a change like the following change after this:
>
> ----8<----
> [PATCH] virtio_blk: Fix default logical block size
>
> If we fail to read a logical block size in virtblk_read_limits() ->
> virtio_cread_feature(), then we default to what is in
> lim->logical_block_size, but that would be 0.
>
> We can deal with lim->logical_block_size = 0 later in the
> blk_mq_alloc_disk(), but the subsequent code in virtblk_read_limits() 
> cannot, so give a default of SECTOR_SIZE.

I think the right fix would be to initialize it where the virtio code
currently uses the uninitialized lim->logical_block_size.  That assumes
that we really want to handle this case.  If reading the block size
fails, can we really trust reading other less basic attributes?  Or
should we just fail the probe?

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 6c64a67ab9c901..5bde41505818f9 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -1303,7 +1303,7 @@ static int virtblk_read_limits(struct virtio_blk *vblk,
 
 		lim->logical_block_size = blk_size;
 	} else
-		blk_size = lim->logical_block_size;
+		blk_size = SECTOR_SIZE;
 
 	/* Use topology information if available */
 	err = virtio_cread_feature(vdev, VIRTIO_BLK_F_TOPOLOGY,