Re: [PATCH 3/3] virtio-blk: add support for zoned block devices

[Dmitry Fomichev <Dmitry.Fomichev@wdc.com>]

Hi Pankaj, Damien,

On Tue, 2022-09-20 at 08:59 +0900, Damien Le Moal wrote:
> On 9/19/22 22:41, Pankaj Raghav wrote:
> > Hi Dmitry,
> > 
> > On Sun, Sep 18, 2022 at 10:29:21PM -0400, Dmitry Fomichev wrote:
> > > The zone-specific code in the patch is heavily influenced by NVMe ZNS
> > > code in drivers/nvme/host/zns.c, but it is simpler because the proposed
> > > virtio ZBD draft only covers the zoned device features that are
> > > relevant to the zoned functionality provided by Linux block layer.
> > > 
> > There is a parallel work going on to support non-po2 zone sizes in Linux
> > block layer and drivers[1]. I don't see any reason why we shouldn't make
> > the calculations generic here instead of putting the constraint on zone
> > sectors to be po2 as the virtio spec also supports it.
> 
> That series is not upstream, so implementing against would not be the
> correct approach, especially given that this would also impact qemu code.
> 

I am aware about the effort to support non-^2 zone sizes in the kernel and this
activity actually made me drop the ^2 zone size requirement from the virtio-zbd
specification. I think that the best way to add non-^2 zone size support to this
driver could be a follow up patch to this series. This way, we won't rely on the
code that is not yet merged upstream.

<there is one more comment about your proposed changes below>

> > 
> > I took a quick look, and changing the calculations from po2 specific to
> > generic will not be in the hot path and can be trivially changed. I have
> > suggested the changes inline to make the virtio blk driver zone size 
> > agnostic. I haven't tested the changes but it is very
> > similar to the changes I did in the drivers/nvme/host/zns.c in my patch
> > series[2].
> > 
> > [1]
> > https://lore.kernel.org/linux-block/20220912082204.51189-1-p.raghav@samsung.com/
> > [2]
> > https://lore.kernel.org/linux-block/20220912082204.51189-6-p.raghav@samsung.com/
> > 
> > > Co-developed-by: Stefan Hajnoczi <stefanha@gmail.com>
> > > Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>
> > > Signed-off-by: Dmitry Fomichev <dmitry.fomichev@wdc.com>
> > > ---
> > >  drivers/block/virtio_blk.c      | 381 ++++++++++++++++++++++++++++++--
> > >  include/uapi/linux/virtio_blk.h | 106 +++++++++
> > >  2 files changed, 469 insertions(+), 18 deletions(-)
> > > 
> > <snip>
> > > +#ifdef CONFIG_BLK_DEV_ZONED
> > > +static void *virtblk_alloc_report_buffer(struct virtio_blk *vblk,
> > > +                                         unsigned int nr_zones,
> > > +                                         unsigned int zone_sectors,
> > > +                                         size_t *buflen)
> > > +{
> > > +       struct request_queue *q = vblk->disk->queue;
> > > +       size_t bufsize;
> > > +       void *buf;
> > > +
> > -       nr_zones = min_t(unsigned int, nr_zones,
> > -                        get_capacity(vblk->disk) >> ilog2(zone_sectors));
> > 
> > +       nr_zones = min_t(unsigned int, nr_zones,
> > +                        div64_u64(get_capacity(vblk->disk), zone_sectors));
> > 
> > > +
> > > +       bufsize = sizeof(struct virtio_blk_zone_report) +
> > > +               nr_zones * sizeof(struct virtio_blk_zone_descriptor);
> > > +       bufsize = min_t(size_t, bufsize,
> > > +                       queue_max_hw_sectors(q) << SECTOR_SHIFT);
> > > +       bufsize = min_t(size_t, bufsize, queue_max_segments(q) <<
> > > PAGE_SHIFT);
> > > +
> > > +       while (bufsize >= sizeof(struct virtio_blk_zone_report)) {
> > > +               buf = __vmalloc(bufsize, GFP_KERNEL | __GFP_NORETRY);
> > > +               if (buf) {
> > > +                       *buflen = bufsize;
> > > +                       return buf;
> > > +               }
> > > +               bufsize >>= 1;
> > > +       }
> > > +
> > > +       return NULL;
> > > +}
> > > +
> > > +static int virtblk_submit_zone_report(struct virtio_blk *vblk,
> > > +                                      char *report_buf, size_t report_len,
> > > +                                      sector_t sector)
> > > +{
> > > +       struct request_queue *q = vblk->disk->queue;
> > > +       struct request *req;
> > > +       struct virtblk_req *vbr;
> > > +       int err;
> > > +
> > > +       req = blk_mq_alloc_request(q, REQ_OP_DRV_IN, 0);
> > > +       if (IS_ERR(req))
> > > +               return PTR_ERR(req);
> > > +
> > > +       vbr = blk_mq_rq_to_pdu(req);
> > > +       vbr->in_hdr_len = sizeof(vbr->status);
> > > +       vbr->out_hdr.type = cpu_to_virtio32(vblk->vdev,
> > > VIRTIO_BLK_T_ZONE_REPORT);
> > > +       vbr->out_hdr.sector = cpu_to_virtio64(vblk->vdev, sector);
> > > +
> > > +       err = blk_rq_map_kern(q, req, report_buf, report_len, GFP_KERNEL);
> > > +       if (err)
> > > +               goto out;
> > > +
> > > +       blk_execute_rq(req, false);
> > > +       err = blk_status_to_errno(virtblk_result(vbr->status));
> > > +out:return -ENODEV;
> > > +       blk_mq_free_request(req);
> > > +       return err;
> > > +}
> > > +
> > > +static int virtblk_parse_zone(struct virtio_blk *vblk,
> > > +                              struct virtio_blk_zone_descriptor *entry,
> > > +                              unsigned int idx, unsigned int zone_sectors,
> > > +                              report_zones_cb cb, void *data)
> > > +{
> > > +       struct blk_zone zone = { };
> > > +
> > > +       if (entry->z_type != VIRTIO_BLK_ZT_SWR &&
> > > +           entry->z_type != VIRTIO_BLK_ZT_SWP &&
> > > +           entry->z_type != VIRTIO_BLK_ZT_CONV) {
> > > +               dev_err(&vblk->vdev->dev, "invalid zone type %#x\n",
> > > +                       entry->z_type);
> > > +               return -EINVAL;
> > > +       }
> > > +
> > > +       zone.type = entry->z_type;
> > > +       zone.cond = entry->z_state;
> > > +       zone.len = zone_sectors;
> > > +       zone.capacity = le64_to_cpu(entry->z_cap);
> > > +       zone.start = le64_to_cpu(entry->z_start);
> > > +       if (zone.cond == BLK_ZONE_COND_FULL)
> > > +               zone.wp = zone.start + zone.len;
> > > +       else
> > > +               zone.wp = le64_to_cpu(entry->z_wp);
> > > +
> > > +       return cb(&zone, idx, data);
> > > +}
> > > +
> > > +static int virtblk_report_zones(struct gendisk *disk, sector_t sector,
> > > +                                unsigned int nr_zones, report_zones_cb cb,
> > > +                                void *data)
> > > +{
> > > +       struct virtio_blk *vblk = disk->private_data;
> > > +       struct virtio_blk_zone_report *report;
> > > +       unsigned int zone_sectors = vblk->zone_sectors;
> > > +       unsigned int nz, i;
> > > +       int ret, zone_idx = 0;
> > > +       size_t buflen;
> > +       u64 remainder;
> > > +
> > > +       if (WARN_ON_ONCE(!vblk->zone_sectors))
> > > +               return -EOPNOTSUPP;
> > > +
> > > +       report = virtblk_alloc_report_buffer(vblk, nr_zones,
> > > +                                            zone_sectors, &buflen);
> > > +       if (!report)
> > > +               return -ENOMEM;
> > > +
> > -       sector &= ~(zone_sectors - 1);
> > 
> > +       div64_u64_rem(sector, zone_sectors, &remainder);
> > +       sector -= remainder;
> > > +       while (zone_idx < nr_zones && sector < get_capacity(vblk->disk)) {
> > > +               memset(report, 0, buflen);
> > > +
> > > +               ret = virtblk_submit_zone_report(vblk, (char *)report,
> > > +                                                buflen, sector);
> > > +               if (ret) {
> > > +                       if (ret > 0)
> > > +                               ret = -EIO;
> > > +                       goto out_free;
> > > +               }
> > > +
> > > +               nz = min((unsigned int)le64_to_cpu(report->nr_zones),
> > > nr_zones);
> > > +               if (!nz)
> > > +                       break;
> > > +
> > > +               for (i = 0; i < nz && zone_idx < nr_zones; i++) {
> > > +                       ret = virtblk_parse_zone(vblk, &report->zones[i],
> > > +                                                zone_idx, zone_sectors,
> > > cb, data);
> > > +                       if (ret)
> > > +                               goto out_free;
> > > +                       zone_idx++;
> > > +               }
> > > +
> > > +               sector += zone_sectors * nz;
> > > +       }
> > > +
> > > +       if (zone_idx > 0)
> > > +               ret = zone_idx;
> > > +       else
> > > +               ret = -EINVAL;
> > > +out_free:
> > > +       kvfree(report);
> > > +       return ret;
> > > +}
> > > +
> > <snip>
> > > +static int virtblk_probe_zoned_device(struct virtio_device *vdev,
> > > +                                      struct virtio_blk *vblk,
> > > +                                      struct request_queue *q)
> > > +{
> > <snip>
> > > +       blk_queue_physical_block_size(q, le32_to_cpu(v));
> > > +       blk_queue_io_min(q, le32_to_cpu(v));
> > > +
> > > +       dev_dbg(&vdev->dev, "write granularity = %u\n", le32_to_cpu(v));
> > > +
> > -       /*
> > -        * virtio ZBD specification doesn't require zones to be a power of
> > -        * two sectors in size, but the code in this driver expects that.
> > -        */
> > -       virtio_cread(vdev, struct virtio_blk_config, zoned.zone_sectors, &v);
> > -       if (v == 0 || !is_power_of_2(v)) {
> > -               dev_err(&vdev->dev,
> > -                       "zoned device with non power of two zone size %u\n",
> > v);
> > -               return -ENODEV;
> > -       }

This part can't be omitted entirely because it contains the call to read
zone_sectors value from virtio-blk configuration space. This code instead could
be changed to something like

	virtio_cread(vdev, struct virtio_blk_config, zoned.zone_sectors, &v);
	if (v == 0) {
		dev_err(&vdev->dev,
			"zoned device with zero zone size %u\n", v);
		return -ENODEV;
	}

DF

> > > +
> > > +       dev_dbg(&vdev->dev, "zone sectors = %u\n", le32_to_cpu(v));
> > > +       vblk->zone_sectors = le32_to_cpu(v);
> > > +
> > > +       if (virtio_has_feature(vdev, VIRTIO_BLK_F_DISCARD)) {
> > > +               dev_warn(&vblk->vdev->dev,
> > > +                        "ignoring negotiated F_DISCARD for zoned
> > > device\n");
> > > +               blk_queue_max_discard_sectors(q, 0);
> > > +       }
> > > +
> > > +       ret = blk_revalidate_disk_zones(vblk->disk, NULL);
> > > +       if (!ret) {
> > > +               virtio_cread(vdev, struct virtio_blk_config,
> > > +                            zoned.max_append_sectors, &v);
> > > +               if (!v) {
> > > +                       dev_warn(&vdev->dev, "zero max_append_sectors
> > > reported\n");
> > > +                       return -ENODEV;
> > > +               }
> > > +               blk_queue_max_zone_append_sectors(q, le32_to_cpu(v));
> > > +               dev_dbg(&vdev->dev, "max append sectors = %u\n",
> > > le32_to_cpu(v));
> > > +
> > > +       }
> > > +
> > > +       return ret;
> > > +}
> > > +
> > 
>