LKML: Caleb Sander Mateos: Re: [PATCH V4 14/27] ublk: add UBLK_U_IO_FETCH_IO

On Thu, Nov 20, 2025 at 6:00 PM Ming Lei <ming.lei@redhat.com> wrote:
>
> Add UBLK_U_IO_FETCH_IO_CMDS command to enable efficient batch processing
> of I/O requests. This multishot uring_cmd allows the ublk server to fetch
> multiple I/O commands in a single operation, significantly reducing
> submission overhead compared to individual FETCH_REQ* commands.
>
> Key Design Features:
>
> 1. Multishot Operation: One UBLK_U_IO_FETCH_IO_CMDS can fetch many I/O
> commands, with the batch size limited by the provided buffer length.
>
> 2. Dynamic Load Balancing: Multiple fetch commands can be submitted
> simultaneously, but only one is active at any time. This enables
> efficient load distribution across multiple server task contexts.
>
> 3. Implicit State Management: The implementation uses three key variables
> to track state:
> - evts_fifo: Queue of request tags awaiting processing
> - fcmd_head: List of available fetch commands
> - active_fcmd: Currently active fetch command (NULL = none active)
>
> States are derived implicitly:
> - IDLE: No fetch commands available
> - READY: Fetch commands available, none active
> - ACTIVE: One fetch command processing events
>
> 4. Lockless Reader Optimization: The active fetch command can read from
> evts_fifo without locking (single reader guarantee), while writers
> (ublk_queue_rq/ublk_queue_rqs) use evts_lock protection. The memory
> barrier pairing plays key role for the single lockless reader
> optimization.
>
> Implementation Details:
>
> - ublk_queue_rq() and ublk_queue_rqs() save request tags to evts_fifo
> - __ublk_pick_active_fcmd() selects an available fetch command when
> events arrive and no command is currently active

What is __ublk_pick_active_fcmd()? I don't see a function with that name.

> - ublk_batch_dispatch() moves tags from evts_fifo to the fetch command's
> buffer and posts completion via io_uring_mshot_cmd_post_cqe()
> - State transitions are coordinated via evts_lock to maintain consistency
>
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
> drivers/block/ublk_drv.c | 412 +++++++++++++++++++++++++++++++---
> include/uapi/linux/ublk_cmd.h | 7 +
> 2 files changed, 388 insertions(+), 31 deletions(-)
>
> diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
> index cc9c92d97349..2e5e392c939e 100644
> --- a/drivers/block/ublk_drv.c
> +++ b/drivers/block/ublk_drv.c
> @@ -93,6 +93,7 @@
>
> /* ublk batch fetch uring_cmd */
> struct ublk_batch_fcmd {
> + struct list_head node;
> struct io_uring_cmd *cmd;
> unsigned short buf_group;
> };
> @@ -117,7 +118,10 @@ struct ublk_uring_cmd_pdu {
> */
> struct ublk_queue *ubq;
>
> - u16 tag;
> + union {
> + u16 tag;
> + struct ublk_batch_fcmd *fcmd; /* batch io only */
> + };
> };
>
> struct ublk_batch_io_data {
> @@ -229,18 +233,36 @@ struct ublk_queue {
> struct ublk_device *dev;
>
> /*
> - * Inflight ublk request tag is saved in this fifo
> + * Batch I/O State Management:
> + *
> + * The batch I/O system uses implicit state management based on the
> + * combination of three key variables below.
> + *
> + * - IDLE: list_empty(&fcmd_head) && !active_fcmd
> + * No fetch commands available, events queue in evts_fifo
> + *
> + * - READY: !list_empty(&fcmd_head) && !active_fcmd
> + * Fetch commands available but none processing events
> *
> - * There are multiple writer from ublk_queue_rq() or ublk_queue_rqs(),
> - * so lock is required for storing request tag to fifo
> + * - ACTIVE: active_fcmd
> + * One fetch command actively processing events from evts_fifo
> *
> - * Make sure just one reader for fetching request from task work
> - * function to ublk server, so no need to grab the lock in reader
> - * side.
> + * Key Invariants:
> + * - At most one active_fcmd at any time (single reader)
> + * - active_fcmd is always from fcmd_head list when non-NULL
> + * - evts_fifo can be read locklessly by the single active reader
> + * - All state transitions require evts_lock protection
> + * - Multiple writers to evts_fifo require lock protection
> */
> struct {
> DECLARE_KFIFO_PTR(evts_fifo, unsigned short);
> spinlock_t evts_lock;
> +
> + /* List of fetch commands available to process events */
> + struct list_head fcmd_head;
> +
> + /* Currently active fetch command (NULL = none active) */
> + struct ublk_batch_fcmd *active_fcmd;
> }____cacheline_aligned_in_smp;
>
> struct ublk_io ios[] __counted_by(q_depth);
> @@ -292,12 +314,20 @@ static void ublk_abort_queue(struct ublk_device *ub, struct ublk_queue *ubq);
> static inline struct request *__ublk_check_and_get_req(struct ublk_device *ub,
> u16 q_id, u16 tag, struct ublk_io *io, size_t offset);
> static inline unsigned int ublk_req_build_flags(struct request *req);
> +static void ublk_batch_dispatch(struct ublk_queue *ubq,
> + struct ublk_batch_io_data *data,
> + struct ublk_batch_fcmd *fcmd);
>
> static inline bool ublk_dev_support_batch_io(const struct ublk_device *ub)
> {
> return false;
> }
>
> +static inline bool ublk_support_batch_io(const struct ublk_queue *ubq)
> +{
> + return false;
> +}
> +
> static inline void ublk_io_lock(struct ublk_io *io)
> {
> spin_lock(&io->lock);
> @@ -624,13 +654,45 @@ static wait_queue_head_t ublk_idr_wq; /* wait until one idr is freed */
>
> static DEFINE_MUTEX(ublk_ctl_mutex);
>
> +static struct ublk_batch_fcmd *
> +ublk_batch_alloc_fcmd(struct io_uring_cmd *cmd)
> +{
> + struct ublk_batch_fcmd *fcmd = kzalloc(sizeof(*fcmd), GFP_NOIO);

An allocation in the I/O path seems unfortunate. Is there not room to
store the struct ublk_batch_fcmd in the io_uring_cmd pdu?
> +
> + if (fcmd) {
> + fcmd->cmd = cmd;
> + fcmd->buf_group = READ_ONCE(cmd->sqe->buf_index);

Is it necessary to store sample this here just to pass it back to the
io_uring layer? Wouldn't the io_uring layer already have access to it
in struct io_kiocb's buf_index field?

> + }
> + return fcmd;
> +}
> +
> +static void ublk_batch_free_fcmd(struct ublk_batch_fcmd *fcmd)
> +{
> + kfree(fcmd);
> +}
> +
> +static void __ublk_release_fcmd(struct ublk_queue *ubq)
> +{
> + WRITE_ONCE(ubq->active_fcmd, NULL);
> +}
>
> -static void ublk_batch_deinit_fetch_buf(const struct ublk_batch_io_data *data,
> +/*
> + * Nothing can move on, so clear ->active_fcmd, and the caller should stop
> + * dispatching
> + */
> +static void ublk_batch_deinit_fetch_buf(struct ublk_queue *ubq,
> + const struct ublk_batch_io_data *data,
> struct ublk_batch_fcmd *fcmd,
> int res)
> {
> + spin_lock(&ubq->evts_lock);
> + list_del(&fcmd->node);
> + WARN_ON_ONCE(fcmd != ubq->active_fcmd);
> + __ublk_release_fcmd(ubq);
> + spin_unlock(&ubq->evts_lock);
> +
> io_uring_cmd_done(fcmd->cmd, res, data->issue_flags);
> - fcmd->cmd = NULL;
> + ublk_batch_free_fcmd(fcmd);
> }
>
> static int ublk_batch_fetch_post_cqe(struct ublk_batch_fcmd *fcmd,
> @@ -1491,6 +1553,8 @@ static int __ublk_batch_dispatch(struct ublk_queue *ubq,
> bool needs_filter;
> int ret;
>
> + WARN_ON_ONCE(data->cmd != fcmd->cmd);
> +
> sel = io_uring_cmd_buffer_select(fcmd->cmd, fcmd->buf_group, &len,
> data->issue_flags);
> if (sel.val < 0)
> @@ -1548,23 +1612,94 @@ static int __ublk_batch_dispatch(struct ublk_queue *ubq,
> return ret;
> }
>
> -static __maybe_unused int
> -ublk_batch_dispatch(struct ublk_queue *ubq,
> - const struct ublk_batch_io_data *data,
> - struct ublk_batch_fcmd *fcmd)
> +static struct ublk_batch_fcmd *__ublk_acquire_fcmd(
> + struct ublk_queue *ubq)
> +{
> + struct ublk_batch_fcmd *fcmd;
> +
> + lockdep_assert_held(&ubq->evts_lock);
> +
> + /*
> + * Ordering updating ubq->evts_fifo and checking ubq->active_fcmd.
> + *
> + * The pair is the smp_mb() in ublk_batch_dispatch().
> + *
> + * If ubq->active_fcmd is observed as non-NULL, the new added tags
> + * can be visisible in ublk_batch_dispatch() with the barrier pairing.
> + */
> + smp_mb();
> + if (READ_ONCE(ubq->active_fcmd)) {
> + fcmd = NULL;
> + } else {
> + fcmd = list_first_entry_or_null(&ubq->fcmd_head,
> + struct ublk_batch_fcmd, node);
> + WRITE_ONCE(ubq->active_fcmd, fcmd);
> + }
> + return fcmd;
> +}
> +
> +static void ublk_batch_tw_cb(struct io_uring_cmd *cmd,
> + unsigned int issue_flags)
> +{
> + struct ublk_uring_cmd_pdu *pdu = ublk_get_uring_cmd_pdu(cmd);
> + struct ublk_batch_fcmd *fcmd = pdu->fcmd;
> + struct ublk_batch_io_data data = {
> + .ub = pdu->ubq->dev,
> + .cmd = fcmd->cmd,
> + .issue_flags = issue_flags,
> + };
> +
> + WARN_ON_ONCE(pdu->ubq->active_fcmd != fcmd);
> +
> + ublk_batch_dispatch(pdu->ubq, &data, fcmd);
> +}
> +
> +static void ublk_batch_dispatch(struct ublk_queue *ubq,
> + struct ublk_batch_io_data *data,
> + struct ublk_batch_fcmd *fcmd)
> {
> + struct ublk_batch_fcmd *new_fcmd;

Is the new_fcmd variable necessary? Can fcmd be reused instead?

> + void *handle;
> + bool empty;
> int ret = 0;
>
> +again:
> while (!ublk_io_evts_empty(ubq)) {
> ret = __ublk_batch_dispatch(ubq, data, fcmd);
> if (ret <= 0)
> break;
> }
>
> - if (ret < 0)
> - ublk_batch_deinit_fetch_buf(data, fcmd, ret);
> + if (ret < 0) {
> + ublk_batch_deinit_fetch_buf(ubq, data, fcmd, ret);
> + return;
> + }
>
> - return ret;
> + handle = io_uring_cmd_ctx_handle(fcmd->cmd);
> + __ublk_release_fcmd(ubq);
> + /*
> + * Order clearing ubq->active_fcmd from __ublk_release_fcmd() and
> + * checking ubq->evts_fifo.
> + *
> + * The pair is the smp_mb() in __ublk_acquire_fcmd().
> + */
> + smp_mb();
> + empty = ublk_io_evts_empty(ubq);
> + if (likely(empty))

nit: empty variable seems unnecessary

> + return;
> +
> + spin_lock(&ubq->evts_lock);
> + new_fcmd = __ublk_acquire_fcmd(ubq);
> + spin_unlock(&ubq->evts_lock);
> +
> + if (!new_fcmd)
> + return;
> + if (handle == io_uring_cmd_ctx_handle(new_fcmd->cmd)) {

This check seems to be meant to decide whether the new and old
UBLK_U_IO_FETCH_IO_CMDS commands can execute in the same task work?
But belonging to the same io_uring context doesn't necessarily mean
that the same task issued them. It seems like it would be safer to
always dispatch new_fcmd->cmd to task work.

> + data->cmd = new_fcmd->cmd;
> + fcmd = new_fcmd;
> + goto again;
> + }
> + io_uring_cmd_complete_in_task(new_fcmd->cmd, ublk_batch_tw_cb);
> }
>
> static void ublk_cmd_tw_cb(struct io_uring_cmd *cmd,
> @@ -1576,13 +1711,27 @@ static void ublk_cmd_tw_cb(struct io_uring_cmd *cmd,
> ublk_dispatch_req(ubq, pdu->req, issue_flags);
> }
>
> -static void ublk_queue_cmd(struct ublk_queue *ubq, struct request *rq)
> +static void ublk_queue_cmd(struct ublk_queue *ubq, struct request *rq, bool last)
> {
> - struct io_uring_cmd *cmd = ubq->ios[rq->tag].cmd;
> - struct ublk_uring_cmd_pdu *pdu = ublk_get_uring_cmd_pdu(cmd);
> + if (ublk_support_batch_io(ubq)) {
> + unsigned short tag = rq->tag;
> + struct ublk_batch_fcmd *fcmd = NULL;
>
> - pdu->req = rq;
> - io_uring_cmd_complete_in_task(cmd, ublk_cmd_tw_cb);
> + spin_lock(&ubq->evts_lock);
> + kfifo_put(&ubq->evts_fifo, tag);
> + if (last)
> + fcmd = __ublk_acquire_fcmd(ubq);
> + spin_unlock(&ubq->evts_lock);
> +
> + if (fcmd)
> + io_uring_cmd_complete_in_task(fcmd->cmd, ublk_batch_tw_cb);
> + } else {
> + struct io_uring_cmd *cmd = ubq->ios[rq->tag].cmd;
> + struct ublk_uring_cmd_pdu *pdu = ublk_get_uring_cmd_pdu(cmd);
> +
> + pdu->req = rq;
> + io_uring_cmd_complete_in_task(cmd, ublk_cmd_tw_cb);
> + }
> }
>
> static void ublk_cmd_list_tw_cb(struct io_uring_cmd *cmd,
> @@ -1600,14 +1749,44 @@ static void ublk_cmd_list_tw_cb(struct io_uring_cmd *cmd,
> } while (rq);
> }
>
> -static void ublk_queue_cmd_list(struct ublk_io *io, struct rq_list *l)
> +static void ublk_batch_queue_cmd_list(struct ublk_queue *ubq, struct rq_list *l)
> {
> - struct io_uring_cmd *cmd = io->cmd;
> - struct ublk_uring_cmd_pdu *pdu = ublk_get_uring_cmd_pdu(cmd);
> + unsigned short tags[MAX_NR_TAG];
> + struct ublk_batch_fcmd *fcmd;
> + struct request *rq;
> + unsigned cnt = 0;
> +
> + spin_lock(&ubq->evts_lock);
> + rq_list_for_each(l, rq) {
> + tags[cnt++] = (unsigned short)rq->tag;
> + if (cnt >= MAX_NR_TAG) {
> + kfifo_in(&ubq->evts_fifo, tags, cnt);
> + cnt = 0;
> + }
> + }
> + if (cnt)
> + kfifo_in(&ubq->evts_fifo, tags, cnt);
> + fcmd = __ublk_acquire_fcmd(ubq);
> + spin_unlock(&ubq->evts_lock);
>
> - pdu->req_list = rq_list_peek(l);
> rq_list_init(l);
> - io_uring_cmd_complete_in_task(cmd, ublk_cmd_list_tw_cb);
> + if (fcmd)
> + io_uring_cmd_complete_in_task(fcmd->cmd, ublk_batch_tw_cb);
> +}
> +
> +static void ublk_queue_cmd_list(struct ublk_queue *ubq, struct ublk_io *io,
> + struct rq_list *l, bool batch)
> +{
> + if (batch) {
> + ublk_batch_queue_cmd_list(ubq, l);
> + } else {
> + struct io_uring_cmd *cmd = io->cmd;
> + struct ublk_uring_cmd_pdu *pdu = ublk_get_uring_cmd_pdu(cmd);
> +
> + pdu->req_list = rq_list_peek(l);
> + rq_list_init(l);
> + io_uring_cmd_complete_in_task(cmd, ublk_cmd_list_tw_cb);
> + }
> }
>
> static enum blk_eh_timer_return ublk_timeout(struct request *rq)
> @@ -1686,7 +1865,7 @@ static blk_status_t ublk_queue_rq(struct blk_mq_hw_ctx *hctx,
> return BLK_STS_OK;
> }
>
> - ublk_queue_cmd(ubq, rq);
> + ublk_queue_cmd(ubq, rq, bd->last);
> return BLK_STS_OK;
> }
>
> @@ -1698,11 +1877,25 @@ static inline bool ublk_belong_to_same_batch(const struct ublk_io *io,
> (io->task == io2->task);
> }
>
> -static void ublk_queue_rqs(struct rq_list *rqlist)
> +static void ublk_commit_rqs(struct blk_mq_hw_ctx *hctx)
> +{
> + struct ublk_queue *ubq = hctx->driver_data;
> + struct ublk_batch_fcmd *fcmd;
> +
> + spin_lock(&ubq->evts_lock);
> + fcmd = __ublk_acquire_fcmd(ubq);
> + spin_unlock(&ubq->evts_lock);
> +
> + if (fcmd)
> + io_uring_cmd_complete_in_task(fcmd->cmd, ublk_batch_tw_cb);
> +}
> +
> +static void __ublk_queue_rqs(struct rq_list *rqlist, bool batch)
> {
> struct rq_list requeue_list = { };
> struct rq_list submit_list = { };
> struct ublk_io *io = NULL;
> + struct ublk_queue *ubq = NULL;
> struct request *req;
>
> while ((req = rq_list_pop(rqlist))) {
> @@ -1716,16 +1909,27 @@ static void ublk_queue_rqs(struct rq_list *rqlist)
>
> if (io && !ublk_belong_to_same_batch(io, this_io) &&
> !rq_list_empty(&submit_list))
> - ublk_queue_cmd_list(io, &submit_list);
> + ublk_queue_cmd_list(ubq, io, &submit_list, batch);

This seems to assume that all the requests belong to the same
ublk_queue, which isn't required

> io = this_io;
> + ubq = this_q;
> rq_list_add_tail(&submit_list, req);
> }
>
> if (!rq_list_empty(&submit_list))
> - ublk_queue_cmd_list(io, &submit_list);
> + ublk_queue_cmd_list(ubq, io, &submit_list, batch);

Same here

> *rqlist = requeue_list;
> }
>
> +static void ublk_queue_rqs(struct rq_list *rqlist)
> +{
> + __ublk_queue_rqs(rqlist, false);
> +}
> +
> +static void ublk_batch_queue_rqs(struct rq_list *rqlist)
> +{
> + __ublk_queue_rqs(rqlist, true);
> +}
> +
> static int ublk_init_hctx(struct blk_mq_hw_ctx *hctx, void *driver_data,
> unsigned int hctx_idx)
> {
> @@ -1743,6 +1947,14 @@ static const struct blk_mq_ops ublk_mq_ops = {
> .timeout = ublk_timeout,
> };
>
> +static const struct blk_mq_ops ublk_batch_mq_ops = {
> + .commit_rqs = ublk_commit_rqs,
> + .queue_rq = ublk_queue_rq,
> + .queue_rqs = ublk_batch_queue_rqs,
> + .init_hctx = ublk_init_hctx,
> + .timeout = ublk_timeout,
> +};
> +
> static void ublk_queue_reinit(struct ublk_device *ub, struct ublk_queue *ubq)
> {
> int i;
> @@ -2120,6 +2332,56 @@ static void ublk_cancel_cmd(struct ublk_queue *ubq, unsigned tag,
> io_uring_cmd_done(io->cmd, UBLK_IO_RES_ABORT, issue_flags);
> }
>
> +static void ublk_batch_cancel_cmd(struct ublk_queue *ubq,
> + struct ublk_batch_fcmd *fcmd,
> + unsigned int issue_flags)
> +{
> + bool done;
> +
> + spin_lock(&ubq->evts_lock);
> + done = (ubq->active_fcmd != fcmd);

Needs to use READ_ONCE() since __ublk_release_fcmd() can be called
without holding evts_lock?

> + if (done)
> + list_del(&fcmd->node);
> + spin_unlock(&ubq->evts_lock);
> +
> + if (done) {
> + io_uring_cmd_done(fcmd->cmd, UBLK_IO_RES_ABORT, issue_flags);
> + ublk_batch_free_fcmd(fcmd);
> + }
> +}
> +
> +static void ublk_batch_cancel_queue(struct ublk_queue *ubq)
> +{
> + LIST_HEAD(fcmd_list);
> +
> + spin_lock(&ubq->evts_lock);
> + ubq->force_abort = true;
> + list_splice_init(&ubq->fcmd_head, &fcmd_list);
> + if (ubq->active_fcmd)
> + list_move(&ubq->active_fcmd->node, &ubq->fcmd_head);

Similarly, needs READ_ONCE()?

> + spin_unlock(&ubq->evts_lock);
> +
> + while (!list_empty(&fcmd_list)) {
> + struct ublk_batch_fcmd *fcmd = list_first_entry(&fcmd_list,
> + struct ublk_batch_fcmd, node);
> +
> + ublk_batch_cancel_cmd(ubq, fcmd, IO_URING_F_UNLOCKED);
> + }
> +}
> +
> +static void ublk_batch_cancel_fn(struct io_uring_cmd *cmd,
> + unsigned int issue_flags)
> +{
> + struct ublk_uring_cmd_pdu *pdu = ublk_get_uring_cmd_pdu(cmd);
> + struct ublk_batch_fcmd *fcmd = pdu->fcmd;
> + struct ublk_queue *ubq = pdu->ubq;
> +
> + if (!ubq->canceling)

Is it not racy to access ubq->canceling without any lock held?

> + ublk_start_cancel(ubq->dev);
> +
> + ublk_batch_cancel_cmd(ubq, fcmd, issue_flags);
> +}
> +
> /*
> * The ublk char device won't be closed when calling cancel fn, so both
> * ublk device and queue are guaranteed to be live
> @@ -2171,6 +2433,11 @@ static void ublk_cancel_queue(struct ublk_queue *ubq)
> {
> int i;
>
> + if (ublk_support_batch_io(ubq)) {
> + ublk_batch_cancel_queue(ubq);
> + return;
> + }
> +
> for (i = 0; i < ubq->q_depth; i++)
> ublk_cancel_cmd(ubq, i, IO_URING_F_UNLOCKED);
> }
> @@ -3091,6 +3358,74 @@ static int ublk_check_batch_cmd(const struct ublk_batch_io_data *data)
> return ublk_check_batch_cmd_flags(uc);
> }
>
> +static int ublk_batch_attach(struct ublk_queue *ubq,
> + struct ublk_batch_io_data *data,
> + struct ublk_batch_fcmd *fcmd)
> +{
> + struct ublk_batch_fcmd *new_fcmd = NULL;
> + bool free = false;
> +
> + spin_lock(&ubq->evts_lock);
> + if (unlikely(ubq->force_abort || ubq->canceling)) {
> + free = true;
> + } else {
> + list_add_tail(&fcmd->node, &ubq->fcmd_head);
> + new_fcmd = __ublk_acquire_fcmd(ubq);
> + }
> + spin_unlock(&ubq->evts_lock);
> +
> + /*
> + * If the two fetch commands are originated from same io_ring_ctx,
> + * run batch dispatch directly. Otherwise, schedule task work for
> + * doing it.
> + */
> + if (new_fcmd && io_uring_cmd_ctx_handle(new_fcmd->cmd) ==
> + io_uring_cmd_ctx_handle(fcmd->cmd)) {
> + data->cmd = new_fcmd->cmd;
> + ublk_batch_dispatch(ubq, data, new_fcmd);
> + } else if (new_fcmd) {
> + io_uring_cmd_complete_in_task(new_fcmd->cmd,
> + ublk_batch_tw_cb);
> + }

Return early if (!new_fcmd) to reduce indentation?

> +
> + if (free) {
> + ublk_batch_free_fcmd(fcmd);
> + return -ENODEV;
> + }

Move the if (free) check directly after spin_unlock(&ubq->evts_lock)?

> + return -EIOCBQUEUED;

> +}
> +
> +static int ublk_handle_batch_fetch_cmd(struct ublk_batch_io_data *data)
> +{
> + struct ublk_queue *ubq = ublk_get_queue(data->ub, data->header.q_id);
> + struct ublk_batch_fcmd *fcmd = ublk_batch_alloc_fcmd(data->cmd);
> + struct ublk_uring_cmd_pdu *pdu = ublk_get_uring_cmd_pdu(data->cmd);
> +
> + if (!fcmd)
> + return -ENOMEM;
> +
> + pdu->ubq = ubq;
> + pdu->fcmd = fcmd;
> + io_uring_cmd_mark_cancelable(data->cmd, data->issue_flags);
> +
> + return ublk_batch_attach(ubq, data, fcmd);
> +}
> +
> +static int ublk_validate_batch_fetch_cmd(struct ublk_batch_io_data *data,
> + const struct ublk_batch_io *uc)
> +{
> + if (!(data->cmd->flags & IORING_URING_CMD_MULTISHOT))
> + return -EINVAL;
> +
> + if (uc->elem_bytes != sizeof(__u16))
> + return -EINVAL;
> +
> + if (uc->flags != 0)
> + return -E2BIG;
> +
> + return 0;
> +}
> +
> static int ublk_ch_batch_io_uring_cmd(struct io_uring_cmd *cmd,
> unsigned int issue_flags)
> {
> @@ -3113,6 +3448,11 @@ static int ublk_ch_batch_io_uring_cmd(struct io_uring_cmd *cmd,
> if (data.header.q_id >= ub->dev_info.nr_hw_queues)
> goto out;
>
> + if (unlikely(issue_flags & IO_URING_F_CANCEL)) {
> + ublk_batch_cancel_fn(cmd, issue_flags);
> + return 0;
> + }

Move this to the top of the function before the other logic that's not
necessary in the cancel case?

Best,
Caleb

> +
> switch (cmd_op) {
> case UBLK_U_IO_PREP_IO_CMDS:
> ret = ublk_check_batch_cmd(&data);
> @@ -3126,6 +3466,12 @@ static int ublk_ch_batch_io_uring_cmd(struct io_uring_cmd *cmd,
> goto out;
> ret = ublk_handle_batch_commit_cmd(&data);
> break;
> + case UBLK_U_IO_FETCH_IO_CMDS:
> + ret = ublk_validate_batch_fetch_cmd(&data, uc);
> + if (ret)
> + goto out;
> + ret = ublk_handle_batch_fetch_cmd(&data);
> + break;
> default:
> ret = -EOPNOTSUPP;
> }
> @@ -3327,6 +3673,7 @@ static int ublk_init_queue(struct ublk_device *ub, int q_id)
> ret = ublk_io_evts_init(ubq, ubq->q_depth, numa_node);
> if (ret)
> goto fail;
> + INIT_LIST_HEAD(&ubq->fcmd_head);
> }
> ub->queues[q_id] = ubq;
> ubq->dev = ub;
> @@ -3451,7 +3798,10 @@ static void ublk_align_max_io_size(struct ublk_device *ub)
>
> static int ublk_add_tag_set(struct ublk_device *ub)
> {
> - ub->tag_set.ops = &ublk_mq_ops;
> + if (ublk_dev_support_batch_io(ub))
> + ub->tag_set.ops = &ublk_batch_mq_ops;
> + else
> + 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;
> diff --git a/include/uapi/linux/ublk_cmd.h b/include/uapi/linux/ublk_cmd.h
> index 295ec8f34173..cd894c1d188e 100644
> --- a/include/uapi/linux/ublk_cmd.h
> +++ b/include/uapi/linux/ublk_cmd.h
> @@ -120,6 +120,13 @@
> #define UBLK_U_IO_COMMIT_IO_CMDS \
> _IOWR('u', 0x26, struct ublk_batch_io)
>
> +/*
> + * Fetch io commands to provided buffer in multishot style,
> + * `IORING_URING_CMD_MULTISHOT` is required for this command.
> + */
> +#define UBLK_U_IO_FETCH_IO_CMDS \
> + _IOWR('u', 0x27, struct ublk_batch_io)
> +
> /* only ABORT means that no re-fetch */
> #define UBLK_IO_RES_OK 0
> #define UBLK_IO_RES_NEED_GET_DATA 1
> --
> 2.47.0
>