[PATCH 8/9] ublk: support provide io buffer

Ming Lei
2024-04-08T01:05:17Z

Implement uring command's IORING_PROVIDE_GROUP_KBUF, and provide
io buffer for userpace to run io_uring operations(FS, network IO),
then ublk zero copy can be supported.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
drivers/block/ublk_drv.c | 156 ++++++++++++++++++++++++++++++++--
include/uapi/linux/ublk_cmd.h | 7 +-
2 files changed, 152 insertions(+), 11 deletions(-)

diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index bea3d5cf8a83..76e3e9e421f3 100644
--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c
@@ -71,6 +71,8 @@ struct ublk_rq_data {
__u64 sector;
__u32 operation;
__u32 nr_zones;
+ bool allocated_bvec;
+ struct io_uring_kernel_buf buf[0];
};

struct ublk_uring_cmd_pdu {
@@ -189,6 +191,8 @@ struct ublk_params_header {
__u32 types;
};

+static inline struct request *__ublk_check_and_get_req(struct ublk_device *ub,
+ struct ublk_queue *ubq, int tag, size_t offset);
static bool ublk_abort_requests(struct ublk_device *ub, struct ublk_queue *ubq);

static inline unsigned int ublk_req_build_flags(struct request *req);
@@ -566,6 +570,11 @@ static inline bool ublk_need_req_ref(const struct ublk_queue *ubq)
return ublk_support_user_copy(ubq);
}

+static inline bool ublk_support_zc(const struct ublk_queue *ubq)
+{
+ return ubq->flags & UBLK_F_SUPPORT_ZERO_COPY;
+}
+
static inline void ublk_init_req_ref(const struct ublk_queue *ubq,
struct request *req)
{
@@ -829,6 +838,70 @@ static size_t ublk_copy_user_pages(const struct request *req,
return done;
}

+/*
+ * The built command buffer is immutable, so it is fine to feed it to
+ * concurrent io_uring provide buf commands
+ */
+static int ublk_init_zero_copy_buffer(struct request *req)
+{
+ struct ublk_rq_data *data = blk_mq_rq_to_pdu(req);
+ struct io_uring_kernel_buf *imu = data->buf;
+ struct req_iterator rq_iter;
+ unsigned int nr_bvecs = 0;
+ struct bio_vec *bvec;
+ unsigned int offset;
+ struct bio_vec bv;
+
+ if (!ublk_rq_has_data(req))
+ goto exit;
+
+ rq_for_each_bvec(bv, req, rq_iter)
+ nr_bvecs++;
+
+ if (!nr_bvecs)
+ goto exit;
+
+ if (req->bio != req->biotail) {
+ int idx = 0;
+
+ bvec = kvmalloc_array(nr_bvecs, sizeof(struct bio_vec),
+ GFP_NOIO);
+ if (!bvec)
+ return -ENOMEM;
+
+ offset = 0;
+ rq_for_each_bvec(bv, req, rq_iter)
+ bvec[idx++] = bv;
+ data->allocated_bvec = true;
+ } else {
+ struct bio *bio = req->bio;
+
+ offset = bio->bi_iter.bi_bvec_done;
+ bvec = __bvec_iter_bvec(bio->bi_io_vec, bio->bi_iter);
+ }
+ imu->bvec = bvec;
+ imu->nr_bvecs = nr_bvecs;
+ imu->offset = offset;
+ imu->len = blk_rq_bytes(req);
+ imu->dir = req_op(req) == REQ_OP_READ ? ITER_DEST : ITER_SOURCE;
+
+ return 0;
+exit:
+ imu->bvec = NULL;
+ return 0;
+}
+
+static void ublk_deinit_zero_copy_buffer(struct request *req)
+{
+ struct ublk_rq_data *data = blk_mq_rq_to_pdu(req);
+ struct io_uring_kernel_buf *imu = data->buf;
+
+ if (data->allocated_bvec) {
+ kvfree(imu->bvec);
+ data->allocated_bvec = false;
+ }
+}
+
static inline bool ublk_need_map_req(const struct request *req)
{
return ublk_rq_has_data(req) && req_op(req) == REQ_OP_WRITE;
@@ -840,13 +913,25 @@ static inline bool ublk_need_unmap_req(const struct request *req)
(req_op(req) == REQ_OP_READ || req_op(req) == REQ_OP_DRV_IN);
}

-static int ublk_map_io(const struct ublk_queue *ubq, const struct request *req,
+static int ublk_map_io(const struct ublk_queue *ubq, struct request *req,
struct ublk_io *io)
{
const unsigned int rq_bytes = blk_rq_bytes(req);

- if (ublk_support_user_copy(ubq))
+ if (ublk_support_user_copy(ubq)) {
+ if (ublk_support_zc(ubq)) {
+ int ret = ublk_init_zero_copy_buffer(req);
+
+ /*
+ * The only failure is -ENOMEM for allocating providing
+ * buffer command, return zero so that we can requeue
+ * this req.
+ */
+ if (unlikely(ret))
+ return 0;
+ }
return rq_bytes;
+ }

/*
* no zero copy, we delay copy WRITE request data into ublksrv
@@ -864,13 +949,16 @@ static int ublk_map_io(const struct ublk_queue *ubq, const struct request *req,
}

static int ublk_unmap_io(const struct ublk_queue *ubq,
- const struct request *req,
+ struct request *req,
struct ublk_io *io)
{
const unsigned int rq_bytes = blk_rq_bytes(req);

- if (ublk_support_user_copy(ubq))
+ if (ublk_support_user_copy(ubq)) {
+ if (ublk_support_zc(ubq))
+ ublk_deinit_zero_copy_buffer(req);
return rq_bytes;
+ }

if (ublk_need_unmap_req(req)) {
struct iov_iter iter;
@@ -1016,6 +1104,7 @@ static inline void __ublk_complete_rq(struct request *req)

return;
exit:
+ ublk_deinit_zero_copy_buffer(req);
blk_mq_end_request(req, res);
}

@@ -1658,6 +1747,46 @@ static inline void ublk_prep_cancel(struct io_uring_cmd *cmd,
io_uring_cmd_mark_cancelable(cmd, issue_flags);
}

+static void ublk_io_buf_giveback_cb(const struct io_uring_kernel_buf *buf)
+{
+ struct ublk_rq_data *data = container_of(buf, struct ublk_rq_data, buf[0]);
+ struct request *req = blk_mq_rq_from_pdu(data);
+ struct ublk_queue *ubq = req->mq_hctx->driver_data;
+
+ ublk_put_req_ref(ubq, req);
+}
+
+static int ublk_provide_io_buf(struct io_uring_cmd *cmd,
+ struct ublk_queue *ubq, int tag)
+{
+ struct ublk_device *ub = cmd->file->private_data;
+ struct ublk_rq_data *data;
+ struct request *req;
+
+ if (!ub)
+ return -EPERM;
+
+ req = __ublk_check_and_get_req(ub, ubq, tag, 0);
+ if (!req)
+ return -EINVAL;
+
+ pr_devel("%s: qid %d tag %u request bytes %u\n",
+ __func__, tag, ubq->q_id, blk_rq_bytes(req));
+
+ data = blk_mq_rq_to_pdu(req);
+
+ /*
+ * io_uring guarantees that the callback will be called after
+ * the provided buffer is consumed, and it is automatic removal
+ * before this uring command is freed.
+ *
+ * This request won't be completed unless the callback is called,
+ * so ublk module won't be unloaded too.
+ */
+ return io_uring_cmd_provide_kbuf(cmd, data->buf,
+ ublk_io_buf_giveback_cb);
+}
+
static int __ublk_ch_uring_cmd(struct io_uring_cmd *cmd,
unsigned int issue_flags,
const struct ublksrv_io_cmd *ub_cmd)
@@ -1674,6 +1803,10 @@ static int __ublk_ch_uring_cmd(struct io_uring_cmd *cmd,
__func__, cmd->cmd_op, ub_cmd->q_id, tag,
ub_cmd->result);

+ if ((cmd->flags & IORING_PROVIDE_GROUP_KBUF) &&
+ cmd_op != UBLK_U_IO_PROVIDE_IO_BUF)
+ return -EOPNOTSUPP;
+
if (ub_cmd->q_id >= ub->dev_info.nr_hw_queues)
goto out;

@@ -1709,6 +1842,8 @@ static int __ublk_ch_uring_cmd(struct io_uring_cmd *cmd,

ret = -EINVAL;
switch (_IOC_NR(cmd_op)) {
+ case _IOC_NR(UBLK_U_IO_PROVIDE_IO_BUF):
+ return ublk_provide_io_buf(cmd, ubq, tag);
case UBLK_IO_FETCH_REQ:
/* UBLK_IO_FETCH_REQ is only allowed before queue is setup */
if (ublk_queue_ready(ubq)) {
@@ -2128,11 +2263,14 @@ static void ublk_align_max_io_size(struct ublk_device *ub)

static int ublk_add_tag_set(struct ublk_device *ub)
{
+ int zc = !!(ub->dev_info.flags & UBLK_F_SUPPORT_ZERO_COPY);
+ struct ublk_rq_data *data;
+
ub->tag_set.ops = &ublk_mq_ops;
ub->tag_set.nr_hw_queues = ub->dev_info.nr_hw_queues;
ub->tag_set.queue_depth = ub->dev_info.queue_depth;
ub->tag_set.numa_node = NUMA_NO_NODE;
- ub->tag_set.cmd_size = sizeof(struct ublk_rq_data);
+ ub->tag_set.cmd_size = struct_size(data, buf, zc);
ub->tag_set.flags = BLK_MQ_F_SHOULD_MERGE;
ub->tag_set.driver_data = ub;
return blk_mq_alloc_tag_set(&ub->tag_set);
@@ -2417,8 +2555,12 @@ static int ublk_ctrl_add_dev(struct io_uring_cmd *cmd)
goto out_free_dev_number;
}

- /* We are not ready to support zero copy */
- ub->dev_info.flags &= ~UBLK_F_SUPPORT_ZERO_COPY;
+ /* zero copy depends on user copy */
+ if ((ub->dev_info.flags & UBLK_F_SUPPORT_ZERO_COPY) &&
+ !ublk_dev_is_user_copy(ub)) {
+ ret = -EINVAL;
+ goto out_free_dev_number;
+ }

ub->dev_info.nr_hw_queues = min_t(unsigned int,
ub->dev_info.nr_hw_queues, nr_cpu_ids);
diff --git a/include/uapi/linux/ublk_cmd.h b/include/uapi/linux/ublk_cmd.h
index c8dc5f8ea699..897ace0794c2 100644
--- a/include/uapi/linux/ublk_cmd.h
+++ b/include/uapi/linux/ublk_cmd.h
@@ -94,6 +94,8 @@
_IOWR('u', UBLK_IO_COMMIT_AND_FETCH_REQ, struct ublksrv_io_cmd)
#define UBLK_U_IO_NEED_GET_DATA \
_IOWR('u', UBLK_IO_NEED_GET_DATA, struct ublksrv_io_cmd)
+#define UBLK_U_IO_PROVIDE_IO_BUF \
+ _IOWR('u', 0x23, struct ublksrv_io_cmd)

/* only ABORT means that no re-fetch */
#define UBLK_IO_RES_OK 0
@@ -126,10 +128,7 @@
#define UBLKSRV_IO_BUF_TOTAL_BITS (UBLK_QID_OFF + UBLK_QID_BITS)
#define UBLKSRV_IO_BUF_TOTAL_SIZE (1ULL << UBLKSRV_IO_BUF_TOTAL_BITS)

-/*
- * zero copy requires 4k block size, and can remap ublk driver's io
- * request into ublksrv's vm space
- */
+/* io_uring provide kbuf command based zero copy */
#define UBLK_F_SUPPORT_ZERO_COPY (1ULL << 0)

/*
--
2.42.0