[PATCH v3] virtio_blk: add DISCARD and WRIET ZEROES command support

[Changpeng Liu <changpeng.liu@intel.com>]

Existing virtio-blk protocol doesn't have DISCARD/WRITE ZEROES
command support, this will impact the performance when using SSD
backend over file systems.

The idea here is using 16 Bytes payload as one descriptor for
DISCARD/WRITE ZEROES command, users can put several ranges into
one command, for the purpose to support such feature, two feature
flags VIRTIO_BLK_F_DISCARD/VIRTIO_BLK_F_WRITE_ZEROES and two
commands VIRTIO_BLK_T_DISCARD/VIRTIO_BLK_T_WRITE_ZEROES are
introduced, and some parameters are added to the configuration
space to tell the OS the granularity of DISCARD/WRITE ZEROES
commands.

The specification change list here:
https://github.com/oasis-tcs/virtio-spec

CHANGELOG:
v3: finalized the specification change.

Signed-off-by: Changpeng Liu <changpeng.liu@intel.com>
---
 drivers/block/virtio_blk.c      | 96 +++++++++++++++++++++++++++++++++++++++--
 include/uapi/linux/virtio_blk.h | 39 +++++++++++++++++
 2 files changed, 132 insertions(+), 3 deletions(-)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 4a07593c..1943adb 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -172,10 +172,53 @@ static int virtblk_add_req(struct virtqueue *vq, struct virtblk_req *vbr,
 	return virtqueue_add_sgs(vq, sgs, num_out, num_in, vbr, GFP_ATOMIC);
 }
 
+static inline int virtblk_setup_discard_write_zeroes(struct request *req, bool unmap)
+{
+	unsigned short segments = blk_rq_nr_discard_segments(req), n = 0;
+	u32 block_size = queue_logical_block_size(req->q);
+	struct virtio_blk_discard_write_zeroes *range;
+	struct bio *bio;
+
+	if (block_size < 512 || !block_size)
+		return -1;
+
+	range = kmalloc_array(segments, sizeof(*range), GFP_ATOMIC);
+	if (!range)
+		return -1;
+
+	__rq_for_each_bio(bio, req) {
+		u64 sector = bio->bi_iter.bi_sector;
+		u32 num_sectors = bio->bi_iter.bi_size >> 9;
+
+		range[n].flags.unmap = cpu_to_le32(unmap);
+		range[n].flags.reserved = cpu_to_le32(0);
+		range[n].num_sectors = cpu_to_le32(num_sectors);
+		range[n].sector = cpu_to_le64(sector);
+		n++;
+	}
+
+	if (WARN_ON_ONCE(n != segments)) {
+		kfree(range);
+		return -1;
+	}
+
+	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 inline void virtblk_request_done(struct request *req)
 {
 	struct virtblk_req *vbr = blk_mq_rq_to_pdu(req);
 
+	if (req->rq_flags & RQF_SPECIAL_PAYLOAD) {
+		kfree(page_address(req->special_vec.bv_page) +
+		      req->special_vec.bv_offset);
+	}
+
 	switch (req_op(req)) {
 	case REQ_OP_SCSI_IN:
 	case REQ_OP_SCSI_OUT:
@@ -225,6 +268,7 @@ static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx,
 	int qid = hctx->queue_num;
 	int err;
 	bool notify = false;
+	bool unmap = false;
 	u32 type;
 
 	BUG_ON(req->nr_phys_segments + 2 > vblk->sg_elems);
@@ -237,6 +281,13 @@ static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx,
 	case REQ_OP_FLUSH:
 		type = VIRTIO_BLK_T_FLUSH;
 		break;
+	case REQ_OP_DISCARD:
+		type = VIRTIO_BLK_T_DISCARD;
+		break;
+	case REQ_OP_WRITE_ZEROES:
+		type = VIRTIO_BLK_T_WRITE_ZEROES;
+		unmap = !(req->cmd_flags & REQ_NOUNMAP);
+		break;
 	case REQ_OP_SCSI_IN:
 	case REQ_OP_SCSI_OUT:
 		type = VIRTIO_BLK_T_SCSI_CMD;
@@ -256,9 +307,16 @@ static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx,
 
 	blk_mq_start_request(req);
 
+	if (type == VIRTIO_BLK_T_DISCARD || type == VIRTIO_BLK_T_WRITE_ZEROES) {
+		err = virtblk_setup_discard_write_zeroes(req, unmap);
+		if (err)
+			return BLK_STS_IOERR;
+	}
+
 	num = blk_rq_map_sg(hctx->queue, req, vbr->sg);
 	if (num) {
-		if (rq_data_dir(req) == WRITE)
+		if (rq_data_dir(req) == WRITE || type == VIRTIO_BLK_T_DISCARD ||
+		    type == VIRTIO_BLK_T_WRITE_ZEROES)
 			vbr->out_hdr.type |= cpu_to_virtio32(vblk->vdev, VIRTIO_BLK_T_OUT);
 		else
 			vbr->out_hdr.type |= cpu_to_virtio32(vblk->vdev, VIRTIO_BLK_T_IN);
@@ -777,6 +835,38 @@ static int virtblk_probe(struct virtio_device *vdev)
 	if (!err && opt_io_size)
 		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);
+		if (v)
+			q->limits.discard_alignment = v << 9;
+		else
+			q->limits.discard_alignment = 0;
+
+		virtio_cread(vdev, struct virtio_blk_config, max_discard_sectors, &v);
+		if (v)
+			blk_queue_max_discard_sectors(q, v);
+		else
+			blk_queue_max_discard_sectors(q, UINT_MAX);
+
+		virtio_cread(vdev, struct virtio_blk_config, max_discard_seg, &v);
+		if (v)
+			blk_queue_max_discard_segments(q, v);
+		else
+			blk_queue_max_discard_segments(q, USHRT_MAX);
+
+		queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, q);
+	}
+
+	if (virtio_has_feature(vdev, VIRTIO_BLK_F_WRITE_ZEROES)) {
+		virtio_cread(vdev, struct virtio_blk_config, max_write_zeroes_sectors, &v);
+		if (v)
+			blk_queue_max_write_zeroes_sectors(q, v);
+		else
+			blk_queue_max_write_zeroes_sectors(q, UINT_MAX);
+	}
+
 	virtblk_update_capacity(vblk, false);
 	virtio_device_ready(vdev);
 
@@ -885,14 +975,14 @@ static int virtblk_restore(struct virtio_device *vdev)
 	VIRTIO_BLK_F_SCSI,
 #endif
 	VIRTIO_BLK_F_FLUSH, VIRTIO_BLK_F_TOPOLOGY, VIRTIO_BLK_F_CONFIG_WCE,
-	VIRTIO_BLK_F_MQ,
+	VIRTIO_BLK_F_MQ, VIRTIO_BLK_F_DISCARD, VIRTIO_BLK_F_WRITE_ZEROES,
 }
 ;
 static unsigned int features[] = {
 	VIRTIO_BLK_F_SEG_MAX, VIRTIO_BLK_F_SIZE_MAX, VIRTIO_BLK_F_GEOMETRY,
 	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_MQ, VIRTIO_BLK_F_DISCARD, VIRTIO_BLK_F_WRITE_ZEROES,
 };
 
 static struct virtio_driver virtio_blk = {
diff --git a/include/uapi/linux/virtio_blk.h b/include/uapi/linux/virtio_blk.h
index 9ebe4d9..78a60e6 100644
--- a/include/uapi/linux/virtio_blk.h
+++ b/include/uapi/linux/virtio_blk.h
@@ -38,6 +38,8 @@
 #define VIRTIO_BLK_F_BLK_SIZE	6	/* Block size of disk is available*/
 #define VIRTIO_BLK_F_TOPOLOGY	10	/* Topology information is available */
 #define VIRTIO_BLK_F_MQ		12	/* support more than one vq */
+#define VIRTIO_BLK_F_DISCARD	13	/* DISCARD command is supported */
+#define VIRTIO_BLK_F_WRITE_ZEROES	14	/* WRITE ZEROES command is supported */
 
 /* Legacy feature bits */
 #ifndef VIRTIO_BLK_NO_LEGACY
@@ -86,6 +88,22 @@ struct virtio_blk_config {
 
 	/* number of vqs, only available when VIRTIO_BLK_F_MQ is set */
 	__u16 num_queues;
+	/* The maximum discard segment size (if VIRTIO_BLK_F_DISCARD) */
+	__u32 max_discard_sectors;
+	/* The maximum number of discard segments (if VIRTIO_BLK_F_DISCARD) */
+	__u32 max_discard_seg;
+	/* The sector alignment for discard (if VIRTIO_BLK_F_DISCARD) */
+	__u32 discard_sector_alignment;
+	/* The maximum number of write zeroes sectors (if VIRTIO_BLK_F_WRITE_ZEROES) */
+	__u32 max_write_zeroes_sectors;
+	/* The maximum number of write zeroes segments (if VIRTIO_BLK_F_WRITE_ZEROES) */
+	__u32 max_write_zeroes_seg;
+	/* Device clear this bit when write zeroes command cannot result in
+	 * deallocating one or more sectors
+	 * (if VIRTIO_BLK_F_WRITE_ZEROES with unmap bit)
+	 */
+	__u8 write_zeroes_may_unmap;
+	__u8 unused1[3];
 } __attribute__((packed));
 
 /*
@@ -114,6 +132,12 @@ struct virtio_blk_config {
 /* Get device ID command */
 #define VIRTIO_BLK_T_GET_ID    8
 
+/* Discard command */
+#define VIRTIO_BLK_T_DISCARD	11
+
+/* Write zeroes command */
+#define VIRTIO_BLK_T_WRITE_ZEROES	13
+
 #ifndef VIRTIO_BLK_NO_LEGACY
 /* Barrier before this op. */
 #define VIRTIO_BLK_T_BARRIER	0x80000000
@@ -133,6 +157,21 @@ struct virtio_blk_outhdr {
 	__virtio64 sector;
 };
 
+/*
+ * discard/write zeroes range for each request.
+ */
+struct virtio_blk_discard_write_zeroes {
+	/* discard/write zeroes start sector */
+	__virtio64 sector;
+	/* number of discard/write zeroes sectors */
+	__virtio32 num_sectors;
+	/* valid for write zeroes command */
+	struct {
+		__virtio32 unmap:1;
+		__virtio32 reserved:31;
+	} flags;
+};
+
 #ifndef VIRTIO_BLK_NO_LEGACY
 struct virtio_scsi_inhdr {
 	__virtio32 errors;
-- 
1.9.3