[PATCH 4/6] ublk: zc register/unregister bvec

Keith Busch
2025-02-03T15:45:35Z

From: Keith Busch <kbusch@kernel.org>

Provide new operations for the user to request mapping an active request
to an io uring instance's buf_table. The user has to provide the index
it wants to install the buffer.

A reference count is taken on the request to ensure it can't be
completed while it is active in a ring's buf_table.

Signed-off-by: Keith Busch <kbusch@kernel.org>
---
drivers/block/ublk_drv.c | 139 +++++++++++++++++++++++++---------
include/uapi/linux/ublk_cmd.h | 4 +
2 files changed, 107 insertions(+), 36 deletions(-)

diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index 529085181f355..58f224b5687b9 100644
--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c
@@ -51,6 +51,9 @@
/* private ioctl command mirror */
#define UBLK_CMD_DEL_DEV_ASYNC _IOC_NR(UBLK_U_CMD_DEL_DEV_ASYNC)

+#define UBLK_IO_REGISTER_IO_BUF _IOC_NR(UBLK_U_IO_REGISTER_IO_BUF)
+#define UBLK_IO_UNREGISTER_IO_BUF _IOC_NR(UBLK_U_IO_UNREGISTER_IO_BUF)
+
/* All UBLK_F_* have to be included into UBLK_F_ALL */
#define UBLK_F_ALL (UBLK_F_SUPPORT_ZERO_COPY \
| UBLK_F_URING_CMD_COMP_IN_TASK \
@@ -76,6 +79,9 @@ struct ublk_rq_data {
struct llist_node node;

struct kref ref;
+
+#define UBLK_ZC_REGISTERED 0
+ unsigned long flags;
};

struct ublk_uring_cmd_pdu {
@@ -201,7 +207,7 @@ static inline struct ublksrv_io_desc *ublk_get_iod(struct ublk_queue *ubq,
int tag);
static inline bool ublk_dev_is_user_copy(const struct ublk_device *ub)
{
- return ub->dev_info.flags & UBLK_F_USER_COPY;
+ return ub->dev_info.flags & (UBLK_F_USER_COPY | UBLK_F_SUPPORT_ZERO_COPY);
}

static inline bool ublk_dev_is_zoned(const struct ublk_device *ub)
@@ -581,7 +587,7 @@ static void ublk_apply_params(struct ublk_device *ub)

static inline bool ublk_support_user_copy(const struct ublk_queue *ubq)
{
- return ubq->flags & UBLK_F_USER_COPY;
+ return ubq->flags & (UBLK_F_USER_COPY | UBLK_F_SUPPORT_ZERO_COPY);
}

static inline bool ublk_need_req_ref(const struct ublk_queue *ubq)
@@ -1747,6 +1753,96 @@ static inline void ublk_prep_cancel(struct io_uring_cmd *cmd,
io_uring_cmd_mark_cancelable(cmd, issue_flags);
}

+
+static inline struct request *__ublk_check_and_get_req(struct ublk_device *ub,
+ struct ublk_queue *ubq, int tag, size_t offset)
+{
+ struct request *req;
+
+ if (!ublk_need_req_ref(ubq))
+ return NULL;
+
+ req = blk_mq_tag_to_rq(ub->tag_set.tags[ubq->q_id], tag);
+ if (!req)
+ return NULL;
+
+ if (!ublk_get_req_ref(ubq, req))
+ return NULL;
+
+ if (unlikely(!blk_mq_request_started(req) || req->tag != tag))
+ goto fail_put;
+
+ if (!ublk_rq_has_data(req))
+ goto fail_put;
+
+ if (offset > blk_rq_bytes(req))
+ goto fail_put;
+
+ return req;
+fail_put:
+ ublk_put_req_ref(ubq, req);
+ return NULL;
+}
+
+static int ublk_register_io_buf(struct io_uring_cmd *cmd,
+ struct ublk_queue *ubq, int tag,
+ const struct ublksrv_io_cmd *ub_cmd)
+{
+ struct io_ring_ctx *ctx = cmd_to_io_kiocb(cmd)->ctx;
+ struct ublk_device *ub = cmd->file->private_data;
+ int index = (int)ub_cmd->addr, ret;
+ 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;
+
+ data = blk_mq_rq_to_pdu(req);
+ if (test_and_set_bit(UBLK_ZC_REGISTERED, &data->flags)) {
+ ublk_put_req_ref(ubq, req);
+ return -EBUSY;
+ }
+
+ ret = io_buffer_register_bvec(ctx, req, index);
+ if (ret) {
+ clear_bit(UBLK_ZC_REGISTERED, &data->flags);
+ ublk_put_req_ref(ubq, req);
+ return ret;
+ }
+
+ return 0;
+}
+
+static int ublk_unregister_io_buf(struct io_uring_cmd *cmd,
+ struct ublk_queue *ubq, int tag,
+ const struct ublksrv_io_cmd *ub_cmd)
+{
+ struct io_ring_ctx *ctx = cmd_to_io_kiocb(cmd)->ctx;
+ struct ublk_device *ub = cmd->file->private_data;
+ int index = (int)ub_cmd->addr;
+ struct ublk_rq_data *data;
+ struct request *req;
+
+ if (!ub)
+ return -EPERM;
+
+ req = blk_mq_tag_to_rq(ub->tag_set.tags[ubq->q_id], tag);
+ if (!req)
+ return -EINVAL;
+
+ data = blk_mq_rq_to_pdu(req);
+ if (!test_and_clear_bit(UBLK_ZC_REGISTERED, &data->flags))
+ return -EINVAL;
+
+ ublk_put_req_ref(ubq, req);
+ io_buffer_unregister_bvec(ctx, index);
+ return 0;
+}
+
static int __ublk_ch_uring_cmd(struct io_uring_cmd *cmd,
unsigned int issue_flags,
const struct ublksrv_io_cmd *ub_cmd)
@@ -1798,6 +1894,10 @@ static int __ublk_ch_uring_cmd(struct io_uring_cmd *cmd,

ret = -EINVAL;
switch (_IOC_NR(cmd_op)) {
+ case UBLK_IO_REGISTER_IO_BUF:
+ return ublk_register_io_buf(cmd, ubq, tag, ub_cmd);
+ case UBLK_IO_UNREGISTER_IO_BUF:
+ return ublk_unregister_io_buf(cmd, ubq, tag, ub_cmd);
case UBLK_IO_FETCH_REQ:
/* UBLK_IO_FETCH_REQ is only allowed before queue is setup */
if (ublk_queue_ready(ubq)) {
@@ -1872,36 +1972,6 @@ static int __ublk_ch_uring_cmd(struct io_uring_cmd *cmd,
return -EIOCBQUEUED;
}

-static inline struct request *__ublk_check_and_get_req(struct ublk_device *ub,
- struct ublk_queue *ubq, int tag, size_t offset)
-{
- struct request *req;
-
- if (!ublk_need_req_ref(ubq))
- return NULL;
-
- req = blk_mq_tag_to_rq(ub->tag_set.tags[ubq->q_id], tag);
- if (!req)
- return NULL;
-
- if (!ublk_get_req_ref(ubq, req))
- return NULL;
-
- if (unlikely(!blk_mq_request_started(req) || req->tag != tag))
- goto fail_put;
-
- if (!ublk_rq_has_data(req))
- goto fail_put;
-
- if (offset > blk_rq_bytes(req))
- goto fail_put;
-
- return req;
-fail_put:
- ublk_put_req_ref(ubq, req);
- return NULL;
-}
-
static inline int ublk_ch_uring_cmd_local(struct io_uring_cmd *cmd,
unsigned int issue_flags)
{
@@ -2527,9 +2597,6 @@ 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;
-
ub->dev_info.nr_hw_queues = min_t(unsigned int,
ub->dev_info.nr_hw_queues, nr_cpu_ids);
ublk_align_max_io_size(ub);
@@ -2860,7 +2927,7 @@ static int ublk_ctrl_get_features(struct io_uring_cmd *cmd)
{
const struct ublksrv_ctrl_cmd *header = io_uring_sqe_cmd(cmd->sqe);
void __user *argp = (void __user *)(unsigned long)header->addr;
- u64 features = UBLK_F_ALL & ~UBLK_F_SUPPORT_ZERO_COPY;
+ u64 features = UBLK_F_ALL;

if (header->len != UBLK_FEATURES_LEN || !header->addr)
return -EINVAL;
diff --git a/include/uapi/linux/ublk_cmd.h b/include/uapi/linux/ublk_cmd.h
index a8bc98bb69fce..74246c926b55f 100644
--- a/include/uapi/linux/ublk_cmd.h
+++ b/include/uapi/linux/ublk_cmd.h
@@ -94,6 +94,10 @@
_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_REGISTER_IO_BUF \
+ _IOWR('u', 0x23, struct ublksrv_io_cmd)
+#define UBLK_U_IO_UNREGISTER_IO_BUF \
+ _IOWR('u', 0x24, struct ublksrv_io_cmd)

/* only ABORT means that no re-fetch */
#define UBLK_IO_RES_OK 0
--
2.43.5