[PATCHv8 5/6] ublk: zc register/unregister bvec

Keith Busch
2025-02-27T22:39:27Z

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 | 59 ++++++++++++++++++++++++++++++-----
include/uapi/linux/ublk_cmd.h | 4 +++
2 files changed, 56 insertions(+), 7 deletions(-)

diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index e8f52d8341fba..8d7d6862a80f5 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 \
@@ -197,12 +200,14 @@ struct ublk_params_header {

static bool ublk_abort_requests(struct ublk_device *ub, struct ublk_queue *ubq);

+static inline struct request *__ublk_check_and_get_req(struct ublk_device *ub,
+ struct ublk_queue *ubq, int tag, size_t offset);
static inline unsigned int ublk_req_build_flags(struct request *req);
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)
@@ -592,7 +597,7 @@ 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)
@@ -1758,6 +1763,45 @@ static inline void ublk_prep_cancel(struct io_uring_cmd *cmd,
io_uring_cmd_mark_cancelable(cmd, issue_flags);
}

+static void ublk_io_release(void *priv)
+{
+ struct request *rq = priv;
+ struct ublk_queue *ubq = rq->mq_hctx->driver_data;
+
+ ublk_put_req_ref(ubq, rq);
+}
+
+static int ublk_register_io_buf(struct io_uring_cmd *cmd,
+ struct ublk_queue *ubq, unsigned int tag,
+ const struct ublksrv_io_cmd *ub_cmd,
+ unsigned int issue_flags)
+{
+ struct ublk_device *ub = cmd->file->private_data;
+ int index = (int)ub_cmd->addr, ret;
+ struct request *req;
+
+ req = __ublk_check_and_get_req(ub, ubq, tag, 0);
+ if (!req)
+ return -EINVAL;
+
+ ret = io_buffer_register_bvec(cmd, req, ublk_io_release, index,
+ issue_flags);
+ if (ret) {
+ ublk_put_req_ref(ubq, req);
+ return ret;
+ }
+
+ return 0;
+}
+
+static int ublk_unregister_io_buf(struct io_uring_cmd *cmd,
+ const struct ublksrv_io_cmd *ub_cmd,
+ unsigned int issue_flags)
+{
+ io_buffer_unregister_bvec(cmd, ub_cmd->addr, issue_flags);
+ return 0;
+}
+
static int __ublk_ch_uring_cmd(struct io_uring_cmd *cmd,
unsigned int issue_flags,
const struct ublksrv_io_cmd *ub_cmd)
@@ -1809,6 +1853,10 @@ 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, issue_flags);
+ case UBLK_IO_UNREGISTER_IO_BUF:
+ return ublk_unregister_io_buf(cmd, ub_cmd, issue_flags);
case UBLK_IO_FETCH_REQ:
/* UBLK_IO_FETCH_REQ is only allowed before queue is setup */
if (ublk_queue_ready(ubq)) {
@@ -2475,7 +2523,7 @@ static int ublk_ctrl_add_dev(struct io_uring_cmd *cmd)
* buffer by pwrite() to ublk char device, which can't be
* used for unprivileged device
*/
- if (info.flags & UBLK_F_USER_COPY)
+ if (info.flags & (UBLK_F_USER_COPY | UBLK_F_SUPPORT_ZERO_COPY))
return -EINVAL;
}

@@ -2543,9 +2591,6 @@ 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);
@@ -2876,7 +2921,7 @@ 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 8093acdeaa114..7255b36b5cf63 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