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Date:   Tue, 27 Sep 2022 17:37:50 -0400
From:   "Michael S. Tsirkin" <mst@redhat.com>
To:     Sarthak Kukreti <sarthakkukreti@chromium.org>
Cc:     dm-devel@redhat.com, linux-block@vger.kernel.org,
        linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org,
        virtualization@lists.linux-foundation.org,
        Jens Axboe <axboe@kernel.dk>, Jason Wang <jasowang@redhat.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Stefan Hajnoczi <stefanha@redhat.com>,
        Alasdair Kergon <agk@redhat.com>,
        Mike Snitzer <snitzer@kernel.org>,
        Theodore Ts'o <tytso@mit.edu>,
        Andreas Dilger <adilger.kernel@dilger.ca>,
        Bart Van Assche <bvanassche@google.com>,
        Daniil Lunev <dlunev@google.com>,
        Evan Green <evgreen@google.com>,
        Gwendal Grignou <gwendal@google.com>
Subject: Re: [PATCH RFC 3/8] virtio_blk: Add support for provision requests
Message-ID: <20220927173658-mutt-send-email-mst@kernel.org>
References: <20220915164826.1396245-1-sarthakkukreti@google.com>
 <20220915164826.1396245-4-sarthakkukreti@google.com>
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On Thu, Sep 15, 2022 at 09:48:21AM -0700, Sarthak Kukreti wrote:
> From: Sarthak Kukreti <sarthakkukreti@chromium.org>
> 
> Adds support for provision requests. Provision requests act like
> the inverse of discards.
> 
> Signed-off-by: Sarthak Kukreti <sarthakkukreti@chromium.org>
> ---
>  drivers/block/virtio_blk.c      | 48 +++++++++++++++++++++++++++++++++
>  include/uapi/linux/virtio_blk.h |  9 +++++++
>  2 files changed, 57 insertions(+)
> 
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 30255fcaf181..eacc2bffe1d1 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -178,6 +178,39 @@ static int virtblk_setup_discard_write_zeroes(struct request *req, bool unmap)
>  	return 0;
>  }
>  
> +static int virtblk_setup_provision(struct request *req)
> +{
> +	unsigned short segments = blk_rq_nr_discard_segments(req);
> +	unsigned short n = 0;
> +
> +	struct virtio_blk_discard_write_zeroes *range;
> +	struct bio *bio;
> +	u32 flags = 0;
> +
> +	range = kmalloc_array(segments, sizeof(*range), GFP_ATOMIC);
> +	if (!range)
> +		return -ENOMEM;
> +
> +	__rq_for_each_bio(bio, req) {
> +		u64 sector = bio->bi_iter.bi_sector;
> +		u32 num_sectors = bio->bi_iter.bi_size >> SECTOR_SHIFT;
> +
> +		range[n].flags = cpu_to_le32(flags);
> +		range[n].num_sectors = cpu_to_le32(num_sectors);
> +		range[n].sector = cpu_to_le64(sector);
> +		n++;
> +	}
> +
> +	WARN_ON_ONCE(n != segments);
> +
> +	req->special_vec.bv_page = virt_to_page(range);
> +	req->special_vec.bv_offset = offset_in_page(range);
> +	req->special_vec.bv_len = sizeof(*range) * segments;
> +	req->rq_flags |= RQF_SPECIAL_PAYLOAD;
> +
> +	return 0;
> +}
> +
>  static void virtblk_unmap_data(struct request *req, struct virtblk_req *vbr)
>  {
>  	if (blk_rq_nr_phys_segments(req))
> @@ -243,6 +276,9 @@ static blk_status_t virtblk_setup_cmd(struct virtio_device *vdev,
>  	case REQ_OP_DRV_IN:
>  		type = VIRTIO_BLK_T_GET_ID;
>  		break;
> +	case REQ_OP_PROVISION:
> +		type = VIRTIO_BLK_T_PROVISION;
> +		break;
>  	default:
>  		WARN_ON_ONCE(1);
>  		return BLK_STS_IOERR;
> @@ -256,6 +292,11 @@ static blk_status_t virtblk_setup_cmd(struct virtio_device *vdev,
>  			return BLK_STS_RESOURCE;
>  	}
>  
> +	if (type == VIRTIO_BLK_T_PROVISION) {
> +		if (virtblk_setup_provision(req))
> +			return BLK_STS_RESOURCE;
> +	}
> +
>  	return 0;
>  }
>  
> @@ -1075,6 +1116,12 @@ static int virtblk_probe(struct virtio_device *vdev)
>  		blk_queue_max_write_zeroes_sectors(q, v ? v : UINT_MAX);
>  	}
>  
> +	if (virtio_has_feature(vdev, VIRTIO_BLK_F_PROVISION)) {
> +		virtio_cread(vdev, struct virtio_blk_config,
> +			     max_provision_sectors, &v);
> +		q->limits.max_provision_sectors = v ? v : UINT_MAX;
> +	}
> +
>  	virtblk_update_capacity(vblk, false);
>  	virtio_device_ready(vdev);
>  
> @@ -1177,6 +1224,7 @@ static unsigned int features[] = {
>  	VIRTIO_BLK_F_RO, VIRTIO_BLK_F_BLK_SIZE,
>  	VIRTIO_BLK_F_FLUSH, VIRTIO_BLK_F_TOPOLOGY, VIRTIO_BLK_F_CONFIG_WCE,
>  	VIRTIO_BLK_F_MQ, VIRTIO_BLK_F_DISCARD, VIRTIO_BLK_F_WRITE_ZEROES,
> +	VIRTIO_BLK_F_PROVISION,
>  };
>  
>  static struct virtio_driver virtio_blk = {
> diff --git a/include/uapi/linux/virtio_blk.h b/include/uapi/linux/virtio_blk.h
> index d888f013d9ff..184f8cf6d185 100644
> --- a/include/uapi/linux/virtio_blk.h
> +++ b/include/uapi/linux/virtio_blk.h
> @@ -40,6 +40,7 @@
>  #define VIRTIO_BLK_F_MQ		12	/* support more than one vq */
>  #define VIRTIO_BLK_F_DISCARD	13	/* DISCARD is supported */
>  #define VIRTIO_BLK_F_WRITE_ZEROES	14	/* WRITE ZEROES is supported */
> +#define VIRTIO_BLK_F_PROVISION	15	/* provision is supported */
>  
>  /* Legacy feature bits */
>  #ifndef VIRTIO_BLK_NO_LEGACY
> @@ -120,6 +121,11 @@ struct virtio_blk_config {
>  	 */
>  	__u8 write_zeroes_may_unmap;
>  
> +	/*
> +	 * The maximum number of sectors in a provision request.
> +	 */
> +	__virtio32 max_provision_sectors;
> +
>  	__u8 unused1[3];
>  } __attribute__((packed));
>  
> @@ -155,6 +161,9 @@ struct virtio_blk_config {
>  /* Write zeroes command */
>  #define VIRTIO_BLK_T_WRITE_ZEROES	13
>  
> +/* Provision command */
> +#define VIRTIO_BLK_T_PROVISION	14
> +
>  #ifndef VIRTIO_BLK_NO_LEGACY
>  /* Barrier before this op. */
>  #define VIRTIO_BLK_T_BARRIER	0x80000000


Feature bit has to be reserved in the virtio spec.
Pls do this through the virtio TC mailing list.

> -- 
> 2.31.0