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ublk: zc register/unregister bvec
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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>
Link: https://lore.kernel.org/r/20250227223916.143006-6-kbusch@meta.com
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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Keith Busch authored and Jens Axboe committed Feb 28, 2025
1 parent 27cb27b commit 1f6540e
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Showing 2 changed files with 56 additions and 7 deletions.
59 changes: 52 additions & 7 deletions drivers/block/ublk_drv.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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 \
Expand Down Expand Up @@ -196,12 +199,14 @@ 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)
Expand Down Expand Up @@ -581,7 +586,7 @@ 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)
Expand Down Expand Up @@ -1747,6 +1752,45 @@ 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)
Expand Down Expand Up @@ -1798,6 +1842,10 @@ 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)) {
Expand Down Expand Up @@ -2459,7 +2507,7 @@ 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;
}

Expand Down Expand Up @@ -2527,9 +2575,6 @@ 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);
Expand Down Expand Up @@ -2860,7 +2905,7 @@ 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;
Expand Down
4 changes: 4 additions & 0 deletions include/uapi/linux/ublk_cmd.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand Down

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