On Mon, Apr 28, 2025 at 2:45 AM Ming Lei <ming.lei@xxxxxxxxxx> wrote:
>
> Add UBLK_F_AUTO_BUF_REG for supporting to register buffer automatically
> to specified io_uring context and buffer index.
>
> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
> ---
> drivers/block/ublk_drv.c | 56 ++++++++++++++++++++++++++++-------
> include/uapi/linux/ublk_cmd.h | 38 ++++++++++++++++++++++++
> 2 files changed, 84 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
> index 1fd20e481a60..e82618442749 100644
> --- a/drivers/block/ublk_drv.c
> +++ b/drivers/block/ublk_drv.c
> @@ -66,7 +66,8 @@
> | UBLK_F_USER_COPY \
> | UBLK_F_ZONED \
> | UBLK_F_USER_RECOVERY_FAIL_IO \
> - | UBLK_F_UPDATE_SIZE)
> + | UBLK_F_UPDATE_SIZE \
> + | UBLK_F_AUTO_BUF_REG)
>
> #define UBLK_F_ALL_RECOVERY_FLAGS (UBLK_F_USER_RECOVERY \
> | UBLK_F_USER_RECOVERY_REISSUE \
> @@ -146,7 +147,10 @@ struct ublk_uring_cmd_pdu {
>
> struct ublk_io {
> /* userspace buffer address from io cmd */
> - __u64 addr;
> + union {
> + __u64 addr;
> + struct ublk_auto_buf_reg buf;
Maybe add a comment justifying why these fields can overlap? From my
understanding, buf is valid iff UBLK_F_AUTO_BUF_REG is set on the
ublk_queue and addr is valid iff neither UBLK_F_USER_COPY,
UBLK_F_SUPPORT_ZERO_COPY, nor UBLK_F_AUTO_BUF_REG is set.
> + };
> unsigned int flags;
> int res;
>
> @@ -626,7 +630,7 @@ static inline bool ublk_support_zero_copy(const struct ublk_queue *ubq)
>
> static inline bool ublk_support_auto_buf_reg(const struct ublk_queue *ubq)
> {
> - return false;
> + return ubq->flags & UBLK_F_AUTO_BUF_REG;
> }
>
> static inline bool ublk_support_user_copy(const struct ublk_queue *ubq)
> @@ -1177,6 +1181,16 @@ static inline void __ublk_abort_rq(struct ublk_queue *ubq,
> blk_mq_end_request(rq, BLK_STS_IOERR);
> }
>
> +
> +static inline void ublk_init_auto_buf_reg(const struct ublk_io *io,
> + struct io_buf_data *data)
> +{
> + data->index = io->buf.index;
> + data->ring_fd = io->buf.ring_fd;
> + data->has_fd = true;
> + data->registered_fd = io->buf.flags & UBLK_AUTO_BUF_REGISTERED_RING;
> +}
> +
> static bool ublk_auto_buf_reg(struct ublk_queue *ubq, struct request *req,
> struct ublk_io *io, unsigned int issue_flags)
> {
> @@ -1187,6 +1201,9 @@ static bool ublk_auto_buf_reg(struct ublk_queue *ubq, struct request *req,
> };
> int ret;
>
> + if (ublk_support_auto_buf_reg(ubq))
This check seems redundant with the check in the caller? Same comment
about ublk_auto_buf_unreg(). That would allow you to avoid adding the
ubq argument to ublk_auto_buf_unreg().
> + ublk_init_auto_buf_reg(io, &data);
> +
> /* one extra reference is dropped by ublk_io_release */
> ublk_init_req_ref(ubq, req, 2);
> ret = io_buffer_register_bvec(io->cmd, &data, issue_flags);
> @@ -2045,7 +2062,7 @@ static int ublk_fetch(struct io_uring_cmd *cmd, struct ublk_queue *ubq,
> */
> if (!buf_addr && !ublk_need_get_data(ubq))
> goto out;
> - } else if (buf_addr) {
> + } else if (buf_addr && !ublk_support_auto_buf_reg(ubq)) {
> /* User copy requires addr to be unset */
> ret = -EINVAL;
> goto out;
> @@ -2058,13 +2075,17 @@ static int ublk_fetch(struct io_uring_cmd *cmd, struct ublk_queue *ubq,
> return ret;
> }
>
> -static void ublk_auto_buf_unreg(struct ublk_io *io, struct io_uring_cmd *cmd,
> +static void ublk_auto_buf_unreg(const struct ublk_queue *ubq,
> + struct ublk_io *io, struct io_uring_cmd *cmd,
> struct request *req, unsigned int issue_flags)
> {
> struct io_buf_data data = {
> .index = req->tag,
> };
>
> + if (ublk_support_auto_buf_reg(ubq))
> + ublk_init_auto_buf_reg(io, &data);
> +
> WARN_ON_ONCE(io_buffer_unregister_bvec(cmd, &data, issue_flags));
> io->flags &= ~UBLK_IO_FLAG_AUTO_BUF_REG;
> }
> @@ -2088,7 +2109,8 @@ static int ublk_commit_and_fetch(const struct ublk_queue *ubq,
> if (!ub_cmd->addr && (!ublk_need_get_data(ubq) ||
> req_op(req) == REQ_OP_READ))
> return -EINVAL;
> - } else if (req_op(req) != REQ_OP_ZONE_APPEND && ub_cmd->addr) {
> + } else if ((req_op(req) != REQ_OP_ZONE_APPEND &&
> + !ublk_support_auto_buf_reg(ubq)) && ub_cmd->addr) {
> /*
> * User copy requires addr to be unset when command is
> * not zone append
> @@ -2097,7 +2119,7 @@ static int ublk_commit_and_fetch(const struct ublk_queue *ubq,
> }
>
> if (io->flags & UBLK_IO_FLAG_AUTO_BUF_REG)
> - ublk_auto_buf_unreg(io, cmd, req, issue_flags);
> + ublk_auto_buf_unreg(ubq, io, cmd, req, issue_flags);
>
> ublk_fill_io_cmd(io, cmd, ub_cmd->addr);
>
> @@ -2788,6 +2810,11 @@ static int ublk_ctrl_add_dev(const struct ublksrv_ctrl_cmd *header)
> else if (!(info.flags & UBLK_F_UNPRIVILEGED_DEV))
> return -EPERM;
>
> + /* F_AUTO_BUF_REG and F_SUPPORT_ZERO_COPY can't co-exist */
> + if ((info.flags & UBLK_F_AUTO_BUF_REG) &&
> + (info.flags & UBLK_F_SUPPORT_ZERO_COPY))
> + return -EINVAL;
> +
> /* forbid nonsense combinations of recovery flags */
> switch (info.flags & UBLK_F_ALL_RECOVERY_FLAGS) {
> case 0:
> @@ -2817,8 +2844,11 @@ static int ublk_ctrl_add_dev(const struct ublksrv_ctrl_cmd *header)
> * For USER_COPY, we depends on userspace to fill request
> * buffer by pwrite() to ublk char device, which can't be
> * used for unprivileged device
> + *
> + * Same with zero copy or auto buffer register.
> */
> - if (info.flags & (UBLK_F_USER_COPY | UBLK_F_SUPPORT_ZERO_COPY))
> + if (info.flags & (UBLK_F_USER_COPY | UBLK_F_SUPPORT_ZERO_COPY |
> + UBLK_F_AUTO_BUF_REG))
> return -EINVAL;
> }
>
> @@ -2876,17 +2906,22 @@ static int ublk_ctrl_add_dev(const struct ublksrv_ctrl_cmd *header)
> UBLK_F_URING_CMD_COMP_IN_TASK;
>
> /* GET_DATA isn't needed any more with USER_COPY or ZERO COPY */
> - if (ub->dev_info.flags & (UBLK_F_USER_COPY | UBLK_F_SUPPORT_ZERO_COPY))
> + if (ub->dev_info.flags & (UBLK_F_USER_COPY | UBLK_F_SUPPORT_ZERO_COPY |
> + UBLK_F_AUTO_BUF_REG))
> ub->dev_info.flags &= ~UBLK_F_NEED_GET_DATA;
>
> /*
> * Zoned storage support requires reuse `ublksrv_io_cmd->addr` for
> * returning write_append_lba, which is only allowed in case of
> * user copy or zero copy
> + *
> + * UBLK_F_AUTO_BUF_REG can't be enabled for zoned because it need
> + * the space for getting ring_fd and buffer index.
> */
> if (ublk_dev_is_zoned(ub) &&
> (!IS_ENABLED(CONFIG_BLK_DEV_ZONED) || !(ub->dev_info.flags &
> - (UBLK_F_USER_COPY | UBLK_F_SUPPORT_ZERO_COPY)))) {
> + (UBLK_F_USER_COPY | UBLK_F_SUPPORT_ZERO_COPY)) ||
> + (ub->dev_info.flags & UBLK_F_AUTO_BUF_REG))) {
> ret = -EINVAL;
> goto out_free_dev_number;
> }
> @@ -3403,6 +3438,7 @@ static int __init ublk_init(void)
>
> BUILD_BUG_ON((u64)UBLKSRV_IO_BUF_OFFSET +
> UBLKSRV_IO_BUF_TOTAL_SIZE < UBLKSRV_IO_BUF_OFFSET);
> + BUILD_BUG_ON(sizeof(struct ublk_auto_buf_reg) != sizeof(__u64));
>
> init_waitqueue_head(&ublk_idr_wq);
>
> diff --git a/include/uapi/linux/ublk_cmd.h b/include/uapi/linux/ublk_cmd.h
> index be5c6c6b16e0..3d7c8c69cf06 100644
> --- a/include/uapi/linux/ublk_cmd.h
> +++ b/include/uapi/linux/ublk_cmd.h
> @@ -219,6 +219,30 @@
> */
> #define UBLK_F_UPDATE_SIZE (1ULL << 10)
>
> +/*
> + * request buffer is registered automatically to ublk server specified
> + * io_uring context before delivering this io command to ublk server,
> + * meantime it is un-registered automatically when completing this io
> + * command.
> + *
> + * For using this feature:
> + *
> + * - ublk server has to create sparse buffer table
> + *
> + * - pass io_ring context FD from `ublksrv_io_cmd.buf.ring_fd`, and the FD
> + * can be registered io_ring FD if `UBLK_AUTO_BUF_REGISTERED_RING` is set
> + * in `ublksrv_io_cmd.flags`, or plain FD
> + *
> + * - pass buffer index from `ublksrv_io_cmd.buf.index`
> + *
> + * This way avoids extra cost from two uring_cmd, but also simplifies backend
> + * implementation, such as, the dependency on IO_REGISTER_IO_BUF and
> + * IO_UNREGISTER_IO_BUF becomes not necessary.
> + *
> + * This feature isn't available for UBLK_F_ZONED
> + */
> +#define UBLK_F_AUTO_BUF_REG (1ULL << 11)
> +
> /* device state */
> #define UBLK_S_DEV_DEAD 0
> #define UBLK_S_DEV_LIVE 1
> @@ -339,6 +363,14 @@ static inline __u32 ublksrv_get_flags(const struct ublksrv_io_desc *iod)
> return iod->op_flags >> 8;
> }
>
> +struct ublk_auto_buf_reg {
> + __s32 ring_fd;
> + __u16 index;
> +#define UBLK_AUTO_BUF_REGISTERED_RING (1 << 0)
> + __u8 flags;
The flag could potentially be stored in ublk_io's flags field instead
to avoid taking up this byte.
Best,
Caleb
> + __u8 _pad;
> +};
> +
> /* issued to ublk driver via /dev/ublkcN */
> struct ublksrv_io_cmd {
> __u16 q_id;
> @@ -363,6 +395,12 @@ struct ublksrv_io_cmd {
> */
> __u64 addr;
> __u64 zone_append_lba;
> +
> + /*
> + * for AUTO_BUF_REG feature, F_ZONED can't be supported,
> + * and ->addr isn't used for zero copy
> + */
> + struct ublk_auto_buf_reg auto_buf;
> };
> };
>
> --
> 2.47.0
>
