On Tue, Mar 01, 2022 at 02:43:55PM +0900, Akihiko Odaki wrote: > On 2022/02/28 19:51, Stefan Hajnoczi wrote: > > On Thu, Feb 24, 2022 at 06:38:02PM +0900, Akihiko Odaki wrote: > > > Virtual I/O Device (VIRTIO) Version 1.1 > > > https://docs.oasis-open.org/virtio/virtio/v1.1/csprd01/virtio-v1.1-csprd01.html > > > > discard_sector_alignment can be used by OS when splitting a request > > > > based on alignment. > > > > > > According to Documentation/ABI/stable/sysfs-block, the corresponding > > > field in the kernel is, confusingly, discard_granularity, not > > > discard_alignment. > > > > Good catch, struct virtio_blk_config->discard_sector_alignment is Linux > > q->limits.discard_granularity. > > > > > > > > Signed-off-by: Akihiko Odaki <akihiko.odaki@xxxxxxxxx> > > > --- > > > drivers/block/virtio_blk.c | 4 +--- > > > 1 file changed, 1 insertion(+), 3 deletions(-) > > > > > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c > > > index c443cd64fc9b..1fb3c89900e3 100644 > > > --- a/drivers/block/virtio_blk.c > > > +++ b/drivers/block/virtio_blk.c > > > @@ -913,11 +913,9 @@ static int virtblk_probe(struct virtio_device *vdev) > > > blk_queue_io_opt(q, blk_size * opt_io_size); > > > if (virtio_has_feature(vdev, VIRTIO_BLK_F_DISCARD)) { > > > - q->limits.discard_granularity = blk_size; > > > - > > > virtio_cread(vdev, struct virtio_blk_config, > > > discard_sector_alignment, &v); > > > - q->limits.discard_alignment = v ? v << SECTOR_SHIFT : 0; > > > > Should we use struct virtio_blk_config->topology.alignment_offset > > ("offset of first aligned logical block" and used for Linux > > blk_queue_alignment_offset()) for q->limits.discard_alignment? > > Maybe but I'm not sure. I had looked at the code of QEMU > (commit 5c1ee569660d4a205dced9cb4d0306b907fb7599) but it apparently always > sets 0 for virtio_blk_config->topology.alignment_offset. > I don't have a hardware which requires discard_alignment either so I cannot > test it. > > I'd like to leave this patch as is since I cannot deny the possibility that > the host has a different alignment offset for discarding and other > operations. Fair enough. To do it properly we'd need to add a new configuration space field to virtio-blk. Reviewed-by: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
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