[RFC PATCH V2 0/9] io_uring: support sqe group and provide group kbuf

[RFC PATCH V2 0/9] io_uring: support sqe group and provide group kbuf

[Ming Lei]

Hello,

The 1st 4 patches are cleanup, and prepare for adding sqe group.

The 5th patch supports generic sqe group which is like link chain, but
allows each sqe in group to be issued in parallel, so N:M dependency can be
supported with sqe group & io link together.

The 6th patch supports one variant of sqe group: allow members to depend
on group leader, so that kernel resource lifetime can be aligned with
group leader or group, then any kernel resource can be shared in this
sqe group, and can be used in generic device zero copy.

The 7th & 8th patches supports providing sqe group buffer via the sqe
group variant.

The 9th patch supports ublk zero copy based on io_uring providing sqe
group buffer.

Tests:

1) pass liburing test
- make runtests

2) write/pass two sqe group test cases:

https://github.com/axboe/liburing/compare/master...ming1:liburing:sqe_group_v2

covers related sqe flags combination and linking groups, both nop and
one multi-destination file copy.

3) ublksrv zero copy:

ublksrv userspace implements zero copy by sqe group & provide group
kbuf:

	git clone https://github.com/ublk-org/ublksrv.git -b group-provide-buf_v2
	make test T=loop/009:nbd/061:nbd/062	#ublk zc tests

When running 64KB block size test on ublk-loop('ublk add -t loop --buffered_io -f $backing'),
it is observed that perf can be doubled.

Any comments are welcome!

V2:
	- add generic sqe group, suggested by Kevin Wolf
	- add REQ_F_SQE_GROUP_DEP which is based on IOSQE_SQE_GROUP, for sharing
	  kernel resource in group wide, suggested by Kevin Wolf
	- remove sqe ext flag, and use the last bit for IOSQE_SQE_GROUP(Pavel),
	in future we still can extend sqe flags with one uring context flag
	- initialize group requests via submit state pattern, suggested by Pavel
	- all kinds of cleanup & bug fixes

Ming Lei (9):
  io_uring: add io_link_req() helper
  io_uring: add io_submit_fail_link() helper
  io_uring: add helper of io_req_commit_cqe()
  io_uring: move marking REQ_F_CQE_SKIP out of io_free_req()
  io_uring: support SQE group
  io_uring: support sqe group with members depending on leader
  io_uring: support providing sqe group buffer
  io_uring/uring_cmd: support provide group kernel buffer
  ublk: support provide io buffer

 drivers/block/ublk_drv.c       | 158 ++++++++++++++-
 include/linux/io_uring/cmd.h   |   7 +
 include/linux/io_uring_types.h |  48 +++++
 include/uapi/linux/io_uring.h  |  10 +-
 include/uapi/linux/ublk_cmd.h  |   7 +-
 io_uring/io_uring.c            | 356 +++++++++++++++++++++++++++++----
 io_uring/io_uring.h            |  29 ++-
 io_uring/kbuf.c                |  60 ++++++
 io_uring/kbuf.h                |  13 ++
 io_uring/net.c                 |  31 ++-
 io_uring/opdef.c               |   5 +
 io_uring/opdef.h               |   2 +
 io_uring/rw.c                  |  20 +-
 io_uring/timeout.c             |   3 +
 io_uring/uring_cmd.c           |  28 +++
 15 files changed, 724 insertions(+), 53 deletions(-)

-- 
2.42.0

[RFC PATCH V2 1/9] io_uring: add io_link_req() helper

[Ming Lei]

Add io_link_req() helper, so that io_submit_sqe() becomes more readable.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 io_uring/io_uring.c | 41 +++++++++++++++++++++++++++--------------
 1 file changed, 27 insertions(+), 14 deletions(-)

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 2675cffbd9a4..c02c9291a2df 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -2172,19 +2172,11 @@ static __cold int io_submit_fail_init(const struct io_uring_sqe *sqe,
 	return 0;
 }
 
-static inline int io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
-			 const struct io_uring_sqe *sqe)
-	__must_hold(&ctx->uring_lock)
+/*
+ * Return NULL if nothing to be queued, otherwise return request for queueing */
+static struct io_kiocb *io_link_sqe(struct io_submit_link *link,
+				    struct io_kiocb *req)
 {
-	struct io_submit_link *link = &ctx->submit_state.link;
-	int ret;
-
-	ret = io_init_req(ctx, req, sqe);
-	if (unlikely(ret))
-		return io_submit_fail_init(sqe, req, ret);
-
-	trace_io_uring_submit_req(req);
-
 	/*
 	 * If we already have a head request, queue this one for async
 	 * submittal once the head completes. If we don't have a head but
@@ -2198,7 +2190,7 @@ static inline int io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
 		link->last = req;
 
 		if (req->flags & IO_REQ_LINK_FLAGS)
-			return 0;
+			return NULL;
 		/* last request of the link, flush it */
 		req = link->head;
 		link->head = NULL;
@@ -2214,9 +2206,30 @@ static inline int io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
 fallback:
 			io_queue_sqe_fallback(req);
 		}
-		return 0;
+		return NULL;
 	}
+	return req;
+}
+
+static inline int io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
+			 const struct io_uring_sqe *sqe)
+	__must_hold(&ctx->uring_lock)
+{
+	struct io_submit_link *link = &ctx->submit_state.link;
+	int ret;
 
+	ret = io_init_req(ctx, req, sqe);
+	if (unlikely(ret))
+		return io_submit_fail_init(sqe, req, ret);
+
+	trace_io_uring_submit_req(req);
+
+	if (unlikely(link->head || (req->flags & (IO_REQ_LINK_FLAGS |
+				    REQ_F_FORCE_ASYNC | REQ_F_FAIL)))) {
+		req = io_link_sqe(link, req);
+		if (!req)
+			return 0;
+	}
 	io_queue_sqe(req);
 	return 0;
 }
-- 
2.42.0

[RFC PATCH V2 2/9] io_uring: add io_submit_fail_link() helper

[Ming Lei]

Add io_submit_fail_link() helper and put linking fail logic into this
helper.

This way simplifies io_submit_fail_init(), and becomes easier to add
sqe group failing logic.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 io_uring/io_uring.c | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index c02c9291a2df..d3b9988cdae4 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -2135,22 +2135,17 @@ static int io_init_req(struct io_ring_ctx *ctx, struct io_kiocb *req,
 	return def->prep(req, sqe);
 }
 
-static __cold int io_submit_fail_init(const struct io_uring_sqe *sqe,
+static __cold int io_submit_fail_link(struct io_submit_link *link,
 				      struct io_kiocb *req, int ret)
 {
-	struct io_ring_ctx *ctx = req->ctx;
-	struct io_submit_link *link = &ctx->submit_state.link;
 	struct io_kiocb *head = link->head;
 
-	trace_io_uring_req_failed(sqe, req, ret);
-
 	/*
 	 * Avoid breaking links in the middle as it renders links with SQPOLL
 	 * unusable. Instead of failing eagerly, continue assembling the link if
 	 * applicable and mark the head with REQ_F_FAIL. The link flushing code
 	 * should find the flag and handle the rest.
 	 */
-	req_fail_link_node(req, ret);
 	if (head && !(head->flags & REQ_F_FAIL))
 		req_fail_link_node(head, -ECANCELED);
 
@@ -2169,9 +2164,24 @@ static __cold int io_submit_fail_init(const struct io_uring_sqe *sqe,
 	else
 		link->head = req;
 	link->last = req;
+
 	return 0;
 }
 
+static __cold int io_submit_fail_init(const struct io_uring_sqe *sqe,
+				      struct io_kiocb *req, int ret)
+{
+	struct io_ring_ctx *ctx = req->ctx;
+	struct io_submit_link *link = &ctx->submit_state.link;
+
+	trace_io_uring_req_failed(sqe, req, ret);
+
+	req_fail_link_node(req, ret);
+
+	/* cover both linked and non-linked request */
+	return io_submit_fail_link(link, req, ret);
+}
+
 /*
  * Return NULL if nothing to be queued, otherwise return request for queueing */
 static struct io_kiocb *io_link_sqe(struct io_submit_link *link,
-- 
2.42.0

[RFC PATCH V2 3/9] io_uring: add helper of io_req_commit_cqe()

[Ming Lei]

Add helper of io_req_commit_cqe() which can be used in posting CQE
from both __io_submit_flush_completions() and io_req_complete_post().

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 io_uring/io_uring.c | 34 ++++++++++++++++++++--------------
 1 file changed, 20 insertions(+), 14 deletions(-)

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index d3b9988cdae4..e4be930e0f1e 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -910,6 +910,22 @@ bool io_req_post_cqe(struct io_kiocb *req, s32 res, u32 cflags)
 	return posted;
 }
 
+static __always_inline void io_req_commit_cqe(struct io_kiocb *req,
+		bool lockless_cq)
+{
+	struct io_ring_ctx *ctx = req->ctx;
+
+	if (unlikely(!io_fill_cqe_req(ctx, req))) {
+		if (lockless_cq) {
+			spin_lock(&ctx->completion_lock);
+			io_req_cqe_overflow(req);
+			spin_unlock(&ctx->completion_lock);
+		} else {
+			io_req_cqe_overflow(req);
+		}
+	}
+}
+
 static void io_req_complete_post(struct io_kiocb *req, unsigned issue_flags)
 {
 	struct io_ring_ctx *ctx = req->ctx;
@@ -932,10 +948,8 @@ static void io_req_complete_post(struct io_kiocb *req, unsigned issue_flags)
 	}
 
 	io_cq_lock(ctx);
-	if (!(req->flags & REQ_F_CQE_SKIP)) {
-		if (!io_fill_cqe_req(ctx, req))
-			io_req_cqe_overflow(req);
-	}
+	if (!(req->flags & REQ_F_CQE_SKIP))
+		io_req_commit_cqe(req, false);
 	io_cq_unlock_post(ctx);
 
 	/*
@@ -1454,16 +1468,8 @@ void __io_submit_flush_completions(struct io_ring_ctx *ctx)
 		struct io_kiocb *req = container_of(node, struct io_kiocb,
 					    comp_list);
 
-		if (!(req->flags & REQ_F_CQE_SKIP) &&
-		    unlikely(!io_fill_cqe_req(ctx, req))) {
-			if (ctx->lockless_cq) {
-				spin_lock(&ctx->completion_lock);
-				io_req_cqe_overflow(req);
-				spin_unlock(&ctx->completion_lock);
-			} else {
-				io_req_cqe_overflow(req);
-			}
-		}
+		if (!(req->flags & REQ_F_CQE_SKIP))
+			io_req_commit_cqe(req, ctx->lockless_cq);
 	}
 	__io_cq_unlock_post(ctx);
 
-- 
2.42.0

[RFC PATCH V2 4/9] io_uring: move marking REQ_F_CQE_SKIP out of io_free_req()

[Ming Lei]

Prepare for supporting sqe group, which requires to post group leader's
CQE after all members' CQEs are posted. For group leader request, we can't
do that in io_req_complete_post, and REQ_F_CQE_SKIP can't be set in
io_free_req().

So move marking REQ_F_CQE_SKIP out of io_free_req().

No functional change.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 io_uring/io_uring.c | 5 +++--
 io_uring/timeout.c  | 3 +++
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index e4be930e0f1e..c184c9a312df 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -1027,8 +1027,6 @@ __cold void io_free_req(struct io_kiocb *req)
 {
 	/* refs were already put, restore them for io_req_task_complete() */
 	req->flags &= ~REQ_F_REFCOUNT;
-	/* we only want to free it, don't post CQEs */
-	req->flags |= REQ_F_CQE_SKIP;
 	req->io_task_work.func = io_req_task_complete;
 	io_req_task_work_add(req);
 }
@@ -1797,6 +1795,9 @@ struct io_wq_work *io_wq_free_work(struct io_wq_work *work)
 	if (req_ref_put_and_test(req)) {
 		if (req->flags & IO_REQ_LINK_FLAGS)
 			nxt = io_req_find_next(req);
+
+		/* we have posted CQEs in io_req_complete_post() */
+		req->flags |= REQ_F_CQE_SKIP;
 		io_free_req(req);
 	}
 	return nxt ? &nxt->work : NULL;
diff --git a/io_uring/timeout.c b/io_uring/timeout.c
index 1c9bf07499b1..202f540aa314 100644
--- a/io_uring/timeout.c
+++ b/io_uring/timeout.c
@@ -47,6 +47,9 @@ static inline void io_put_req(struct io_kiocb *req)
 {
 	if (req_ref_put_and_test(req)) {
 		io_queue_next(req);
+
+		/* we only want to free it, don't post CQEs */
+		req->flags |= REQ_F_CQE_SKIP;
 		io_free_req(req);
 	}
 }
-- 
2.42.0

[RFC PATCH V2 5/9] io_uring: support SQE group

[Ming Lei]

SQE group is defined as one chain of SQEs starting with the first SQE that
has IOSQE_SQE_GROUP set, and ending with the first subsequent SQE that
doesn't have it set, and it is similar with chain of linked SQEs.

Not like linked SQEs, each sqe is issued after the previous one is completed.
All SQEs in one group are submitted in parallel, so there isn't any dependency
among SQEs in one group.

The 1st SQE is group leader, and the other SQEs are group member. The whole
group share single IOSQE_IO_LINK and IOSQE_IO_DRAIN from group leader, and
the two flags are ignored for group members.

When the group is in one link chain, this group isn't submitted until the
previous SQE or group is completed. And the following SQE or group can't
be started if this group isn't completed. Failure from any group member will
fail the group leader, then the link chain can be terminated.

When IOSQE_IO_DRAIN is set for group leader, all requests in this group and
previous requests submitted are drained. Given IOSQE_IO_DRAIN can be set for
group leader only, we respect IO_DRAIN by always completing group leader as
the last one in the group.

Working together with IOSQE_IO_LINK, SQE group provides flexible way to
support N:M dependency, such as:

- group A is chained with group B together
- group A has N SQEs
- group B has M SQEs

then M SQEs in group B depend on N SQEs in group A.

N:M dependency can support some interesting use cases in efficient way:

1) read from multiple files, then write the read data into single file

2) read from single file, and write the read data into multiple files

3) write same data into multiple files, and read data from multiple files and
compare if correct data is written

Also IOSQE_SQE_GROUP takes the last bit in sqe->flags, but we still can
extend sqe->flags with one uring context flag, such as use __pad3 for
non-uring_cmd OPs and part of uring_cmd_flags for uring_cmd OP.

Suggested-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 include/linux/io_uring_types.h |  12 ++
 include/uapi/linux/io_uring.h  |   3 +
 io_uring/io_uring.c            | 246 +++++++++++++++++++++++++++++++--
 io_uring/io_uring.h            |  21 ++-
 4 files changed, 270 insertions(+), 12 deletions(-)

diff --git a/include/linux/io_uring_types.h b/include/linux/io_uring_types.h
index 7a6b190c7da7..62311b0f0e0b 100644
--- a/include/linux/io_uring_types.h
+++ b/include/linux/io_uring_types.h
@@ -202,6 +202,8 @@ struct io_submit_state {
 	/* batch completion logic */
 	struct io_wq_work_list	compl_reqs;
 	struct io_submit_link	link;
+	/* points to current group */
+	struct io_submit_link	group;
 
 	bool			plug_started;
 	bool			need_plug;
@@ -442,6 +444,7 @@ enum {
 	REQ_F_FORCE_ASYNC_BIT	= IOSQE_ASYNC_BIT,
 	REQ_F_BUFFER_SELECT_BIT	= IOSQE_BUFFER_SELECT_BIT,
 	REQ_F_CQE_SKIP_BIT	= IOSQE_CQE_SKIP_SUCCESS_BIT,
+	REQ_F_SQE_GROUP_BIT	= IOSQE_SQE_GROUP_BIT,
 
 	/* first byte is taken by user flags, shift it to not overlap */
 	REQ_F_FAIL_BIT		= 8,
@@ -473,6 +476,7 @@ enum {
 	REQ_F_BL_EMPTY_BIT,
 	REQ_F_BL_NO_RECYCLE_BIT,
 	REQ_F_BUFFERS_COMMIT_BIT,
+	REQ_F_SQE_GROUP_LEADER_BIT,
 
 	/* not a real bit, just to check we're not overflowing the space */
 	__REQ_F_LAST_BIT,
@@ -496,6 +500,8 @@ enum {
 	REQ_F_BUFFER_SELECT	= IO_REQ_FLAG(REQ_F_BUFFER_SELECT_BIT),
 	/* IOSQE_CQE_SKIP_SUCCESS */
 	REQ_F_CQE_SKIP		= IO_REQ_FLAG(REQ_F_CQE_SKIP_BIT),
+	/* IOSQE_SQE_GROUP */
+	REQ_F_SQE_GROUP		= IO_REQ_FLAG(REQ_F_SQE_GROUP_BIT),
 
 	/* fail rest of links */
 	REQ_F_FAIL		= IO_REQ_FLAG(REQ_F_FAIL_BIT),
@@ -553,6 +559,8 @@ enum {
 	REQ_F_BL_NO_RECYCLE	= IO_REQ_FLAG(REQ_F_BL_NO_RECYCLE_BIT),
 	/* buffer ring head needs incrementing on put */
 	REQ_F_BUFFERS_COMMIT	= IO_REQ_FLAG(REQ_F_BUFFERS_COMMIT_BIT),
+	/* sqe group lead */
+	REQ_F_SQE_GROUP_LEADER	= IO_REQ_FLAG(REQ_F_SQE_GROUP_LEADER_BIT),
 };
 
 typedef void (*io_req_tw_func_t)(struct io_kiocb *req, struct io_tw_state *ts);
@@ -666,6 +674,10 @@ struct io_kiocb {
 		u64			extra1;
 		u64			extra2;
 	} big_cqe;
+
+	/* all SQE group members linked here for group lead */
+	struct io_kiocb			*grp_link;
+	int				grp_refs;
 };
 
 struct io_overflow_cqe {
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index f093cb2300d9..f3d74a920dfe 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -123,6 +123,7 @@ enum io_uring_sqe_flags_bit {
 	IOSQE_ASYNC_BIT,
 	IOSQE_BUFFER_SELECT_BIT,
 	IOSQE_CQE_SKIP_SUCCESS_BIT,
+	IOSQE_SQE_GROUP_BIT,
 };
 
 /*
@@ -142,6 +143,8 @@ enum io_uring_sqe_flags_bit {
 #define IOSQE_BUFFER_SELECT	(1U << IOSQE_BUFFER_SELECT_BIT)
 /* don't post CQE if request succeeded */
 #define IOSQE_CQE_SKIP_SUCCESS	(1U << IOSQE_CQE_SKIP_SUCCESS_BIT)
+/* defines sqe group */
+#define IOSQE_SQE_GROUP		(1U << IOSQE_SQE_GROUP_BIT)
 
 /*
  * io_uring_setup() flags
diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index c184c9a312df..465f4244fa0b 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -109,7 +109,8 @@
 			  IOSQE_IO_HARDLINK | IOSQE_ASYNC)
 
 #define SQE_VALID_FLAGS	(SQE_COMMON_FLAGS | IOSQE_BUFFER_SELECT | \
-			IOSQE_IO_DRAIN | IOSQE_CQE_SKIP_SUCCESS)
+			IOSQE_IO_DRAIN | IOSQE_CQE_SKIP_SUCCESS | \
+			IOSQE_SQE_GROUP)
 
 #define IO_REQ_CLEAN_FLAGS (REQ_F_BUFFER_SELECTED | REQ_F_NEED_CLEANUP | \
 				REQ_F_POLLED | REQ_F_INFLIGHT | REQ_F_CREDS | \
@@ -915,6 +916,13 @@ static __always_inline void io_req_commit_cqe(struct io_kiocb *req,
 {
 	struct io_ring_ctx *ctx = req->ctx;
 
+	/*
+	 * For group leader, cqe has to be committed after all members are
+	 * committed, when the request becomes normal one.
+	 */
+	if (unlikely(req_is_group_leader(req)))
+		return;
+
 	if (unlikely(!io_fill_cqe_req(ctx, req))) {
 		if (lockless_cq) {
 			spin_lock(&ctx->completion_lock);
@@ -926,6 +934,116 @@ static __always_inline void io_req_commit_cqe(struct io_kiocb *req,
 	}
 }
 
+static inline bool need_queue_group_members(struct io_kiocb *req)
+{
+	return req_is_group_leader(req) && !!req->grp_link;
+}
+
+/* Can only be called after this request is issued */
+static inline struct io_kiocb *get_group_leader(struct io_kiocb *req)
+{
+	if (req->flags & REQ_F_SQE_GROUP) {
+		if (req_is_group_leader(req))
+			return req;
+		return req->grp_link;
+	}
+	return NULL;
+}
+
+/* called from io_req_defer_failed() only */
+static void io_fail_group_members(struct io_kiocb *req)
+	__must_hold(&req->ctx->uring_lock)
+{
+	struct io_kiocb *member = req->grp_link;
+
+	if (!member)
+		return;
+
+	while (member) {
+		struct io_kiocb *next = member->grp_link;
+
+		member->grp_link = req;
+		io_req_defer_failed(member, -ECANCELED);
+		member = next;
+	}
+	req->grp_link = NULL;
+}
+
+static void io_queue_group_members(struct io_kiocb *req, bool async)
+{
+	struct io_kiocb *member = req->grp_link;
+
+	if (!member)
+		return;
+
+	while (member) {
+		struct io_kiocb *next = member->grp_link;
+
+		member->grp_link = req;
+		trace_io_uring_submit_req(member);
+		if (async)
+			member->flags |= REQ_F_FORCE_ASYNC;
+		if (member->flags & REQ_F_FORCE_ASYNC)
+			io_req_task_queue(member);
+		else
+			io_queue_sqe(member);
+		member = next;
+	}
+	req->grp_link = NULL;
+}
+
+static void io_commit_group_cqe(struct io_kiocb *lead)
+{
+	lead->flags &= ~REQ_F_SQE_GROUP_LEADER;
+	if (!(lead->flags & REQ_F_CQE_SKIP))
+		io_req_commit_cqe(lead, lead->ctx->lockless_cq);
+}
+
+bool __io_complete_group_req(struct io_kiocb *req,
+			     struct io_kiocb *lead)
+{
+	WARN_ON_ONCE(!(req->flags & REQ_F_SQE_GROUP));
+
+	if (WARN_ON_ONCE(lead->grp_refs <= 0))
+		return false;
+	if (req != lead) {
+		req->flags &= ~REQ_F_SQE_GROUP;
+		/*
+		 * Set linked leader as failed if any member is failed, so
+		 * the remained link chain can be terminated
+		 */
+		if (unlikely((req->flags & REQ_F_FAIL) &&
+			     (lead->flags & IO_REQ_LINK_FLAGS)))
+			req_set_fail(lead);
+	}
+	return !--lead->grp_refs;
+}
+
+/* Complete group request and collect completed leader for freeing */
+static inline void io_complete_group_req(struct io_kiocb *req,
+		struct io_wq_work_list *grp_list)
+{
+	/*
+	 * If the leader is in completion list, its refcount has been
+	 * dropped before adding to list, since we need to avoid to deal
+	 * with two same leaders when iterating completion list
+	 */
+	if (req->flags & REQ_F_SQE_GROUP_LEADER) {
+		io_commit_group_cqe(req);
+	} else {
+		struct io_kiocb *lead = get_group_leader(req);
+
+		/*
+		 * Now this group is done, post its CQE out, and collect
+		 * it just for release
+		 */
+		if (__io_complete_group_req(req, lead)) {
+			io_commit_group_cqe(lead);
+			wq_list_add_head(&lead->comp_list, grp_list);
+		}
+	}
+}
+
 static void io_req_complete_post(struct io_kiocb *req, unsigned issue_flags)
 {
 	struct io_ring_ctx *ctx = req->ctx;
@@ -970,6 +1088,10 @@ void io_req_defer_failed(struct io_kiocb *req, s32 res)
 	io_req_set_res(req, res, io_put_kbuf(req, IO_URING_F_UNLOCKED));
 	if (def->fail)
 		def->fail(req);
+
+	if (req_is_group_leader(req))
+		io_fail_group_members(req);
+
 	io_req_complete_defer(req);
 }
 
@@ -1459,6 +1581,7 @@ void __io_submit_flush_completions(struct io_ring_ctx *ctx)
 	__must_hold(&ctx->uring_lock)
 {
 	struct io_submit_state *state = &ctx->submit_state;
+	struct io_wq_work_list grp_list = {NULL};
 	struct io_wq_work_node *node;
 
 	__io_cq_lock(ctx);
@@ -1468,9 +1591,15 @@ void __io_submit_flush_completions(struct io_ring_ctx *ctx)
 
 		if (!(req->flags & REQ_F_CQE_SKIP))
 			io_req_commit_cqe(req, ctx->lockless_cq);
+
+		if (req->flags & REQ_F_SQE_GROUP)
+			io_complete_group_req(req, &grp_list);
 	}
 	__io_cq_unlock_post(ctx);
 
+	if (!wq_list_empty(&grp_list))
+		__wq_list_splice(&grp_list, state->compl_reqs.first);
+
 	if (!wq_list_empty(&ctx->submit_state.compl_reqs)) {
 		io_free_batch_list(ctx, state->compl_reqs.first);
 		INIT_WQ_LIST(&state->compl_reqs);
@@ -1677,8 +1806,12 @@ static u32 io_get_sequence(struct io_kiocb *req)
 	struct io_kiocb *cur;
 
 	/* need original cached_sq_head, but it was increased for each req */
-	io_for_each_link(cur, req)
-		seq--;
+	io_for_each_link(cur, req) {
+		if (req_is_group_leader(cur))
+			seq -= cur->grp_refs;
+		else
+			seq--;
+	}
 	return seq;
 }
 
@@ -1793,11 +1926,20 @@ struct io_wq_work *io_wq_free_work(struct io_wq_work *work)
 	struct io_kiocb *nxt = NULL;
 
 	if (req_ref_put_and_test(req)) {
-		if (req->flags & IO_REQ_LINK_FLAGS)
-			nxt = io_req_find_next(req);
+		/*
+		 * CQEs have been posted in io_req_complete_post() except
+		 * for group leader, and we can't advance the link for
+		 * group leader until its CQE is posted.
+		 *
+		 * TODO: try to avoid defer and complete leader in io_wq
+		 * context directly
+		 */
+		if (!req_is_group_leader(req)) {
+			req->flags |= REQ_F_CQE_SKIP;
+			if (req->flags & IO_REQ_LINK_FLAGS)
+				nxt = io_req_find_next(req);
+		}
 
-		/* we have posted CQEs in io_req_complete_post() */
-		req->flags |= REQ_F_CQE_SKIP;
 		io_free_req(req);
 	}
 	return nxt ? &nxt->work : NULL;
@@ -1863,6 +2005,8 @@ void io_wq_submit_work(struct io_wq_work *work)
 		}
 	}
 
+	if (need_queue_group_members(req))
+		io_queue_group_members(req, true);
 	do {
 		ret = io_issue_sqe(req, issue_flags);
 		if (ret != -EAGAIN)
@@ -1977,6 +2121,9 @@ static inline void io_queue_sqe(struct io_kiocb *req)
 	 */
 	if (unlikely(ret))
 		io_queue_async(req, ret);
+
+	if (need_queue_group_members(req))
+		io_queue_group_members(req, false);
 }
 
 static void io_queue_sqe_fallback(struct io_kiocb *req)
@@ -2142,6 +2289,56 @@ static int io_init_req(struct io_ring_ctx *ctx, struct io_kiocb *req,
 	return def->prep(req, sqe);
 }
 
+static struct io_kiocb *io_group_sqe(struct io_submit_link *group,
+				     struct io_kiocb *req)
+{
+	/*
+	 * Group chain is similar with link chain: starts with 1st sqe with
+	 * REQ_F_SQE_GROUP, and ends with the 1st sqe without REQ_F_SQE_GROUP
+	 */
+	if (group->head) {
+		struct io_kiocb *lead = group->head;
+
+		/* members can't be in link chain, can't be drained */
+		req->flags &= ~(IO_REQ_LINK_FLAGS | REQ_F_IO_DRAIN);
+		lead->grp_refs += 1;
+		group->last->grp_link = req;
+		group->last = req;
+
+		if (req->flags & REQ_F_SQE_GROUP)
+			return NULL;
+
+		req->grp_link = NULL;
+		req->flags |= REQ_F_SQE_GROUP;
+		group->head = NULL;
+		return lead;
+	} else if (req->flags & REQ_F_SQE_GROUP) {
+		group->head = req;
+		group->last = req;
+		req->grp_refs = 1;
+		req->flags |= REQ_F_SQE_GROUP_LEADER;
+		return NULL;
+	} else {
+		return req;
+	}
+}
+
+static __cold struct io_kiocb *io_submit_fail_group(
+		struct io_submit_link *link, struct io_kiocb *req)
+{
+	struct io_kiocb *lead = link->head;
+
+	/*
+	 * Instead of failing eagerly, continue assembling the group link
+	 * if applicable and mark the leader with REQ_F_FAIL. The group
+	 * flushing code should find the flag and handle the rest
+	 */
+	if (lead && !(lead->flags & REQ_F_FAIL))
+		req_fail_link_node(lead, -ECANCELED);
+
+	return io_group_sqe(link, req);
+}
+
 static __cold int io_submit_fail_link(struct io_submit_link *link,
 				      struct io_kiocb *req, int ret)
 {
@@ -2180,11 +2377,18 @@ static __cold int io_submit_fail_init(const struct io_uring_sqe *sqe,
 {
 	struct io_ring_ctx *ctx = req->ctx;
 	struct io_submit_link *link = &ctx->submit_state.link;
+	struct io_submit_link *group = &ctx->submit_state.group;
 
 	trace_io_uring_req_failed(sqe, req, ret);
 
 	req_fail_link_node(req, ret);
 
+	if (group->head || (req->flags & REQ_F_SQE_GROUP)) {
+		req = io_submit_fail_group(group, req);
+		if (!req)
+			return 0;
+	}
+
 	/* cover both linked and non-linked request */
 	return io_submit_fail_link(link, req, ret);
 }
@@ -2232,7 +2436,7 @@ static inline int io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
 			 const struct io_uring_sqe *sqe)
 	__must_hold(&ctx->uring_lock)
 {
-	struct io_submit_link *link = &ctx->submit_state.link;
+	struct io_submit_state *state = &ctx->submit_state;
 	int ret;
 
 	ret = io_init_req(ctx, req, sqe);
@@ -2241,9 +2445,17 @@ static inline int io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
 
 	trace_io_uring_submit_req(req);
 
-	if (unlikely(link->head || (req->flags & (IO_REQ_LINK_FLAGS |
-				    REQ_F_FORCE_ASYNC | REQ_F_FAIL)))) {
-		req = io_link_sqe(link, req);
+	if (unlikely(state->group.head ||
+		     (req->flags & REQ_F_SQE_GROUP))) {
+		req = io_group_sqe(&state->group, req);
+		if (!req)
+			return 0;
+	}
+
+	if (unlikely(state->link.head ||
+		     (req->flags & (IO_REQ_LINK_FLAGS | REQ_F_FORCE_ASYNC |
+				    REQ_F_FAIL)))) {
+		req = io_link_sqe(&state->link, req);
 		if (!req)
 			return 0;
 	}
@@ -2258,6 +2470,17 @@ static void io_submit_state_end(struct io_ring_ctx *ctx)
 {
 	struct io_submit_state *state = &ctx->submit_state;
 
+	/* the last member must set REQ_F_SQE_GROUP */
+	if (unlikely(state->group.head)) {
+		struct io_kiocb *lead = state->group.head;
+
+		state->group.last->grp_link = NULL;
+		if (lead->flags & IO_REQ_LINK_FLAGS)
+			io_link_sqe(&state->link, lead);
+		else
+			io_queue_sqe_fallback(lead);
+	}
+
 	if (unlikely(state->link.head))
 		io_queue_sqe_fallback(state->link.head);
 	/* flush only after queuing links as they can generate completions */
@@ -2277,6 +2500,7 @@ static void io_submit_state_start(struct io_submit_state *state,
 	state->submit_nr = max_ios;
 	/* set only head, no need to init link_last in advance */
 	state->link.head = NULL;
+	state->group.head = NULL;
 }
 
 static void io_commit_sqring(struct io_ring_ctx *ctx)
diff --git a/io_uring/io_uring.h b/io_uring/io_uring.h
index 624ca9076a50..416c14c6f050 100644
--- a/io_uring/io_uring.h
+++ b/io_uring/io_uring.h
@@ -67,6 +67,8 @@ void io_req_defer_failed(struct io_kiocb *req, s32 res);
 bool io_post_aux_cqe(struct io_ring_ctx *ctx, u64 user_data, s32 res, u32 cflags);
 bool io_req_post_cqe(struct io_kiocb *req, s32 res, u32 cflags);
 void __io_commit_cqring_flush(struct io_ring_ctx *ctx);
+bool __io_complete_group_req(struct io_kiocb *req,
+			     struct io_kiocb *lead);
 
 struct file *io_file_get_normal(struct io_kiocb *req, int fd);
 struct file *io_file_get_fixed(struct io_kiocb *req, int fd,
@@ -342,6 +344,16 @@ static inline void io_tw_lock(struct io_ring_ctx *ctx, struct io_tw_state *ts)
 	lockdep_assert_held(&ctx->uring_lock);
 }
 
+static inline bool req_is_group_leader(struct io_kiocb *req)
+{
+	return req->flags & REQ_F_SQE_GROUP_LEADER;
+}
+
+static inline bool req_is_group_member(struct io_kiocb *req)
+{
+	return !req_is_group_leader(req) && (req->flags & REQ_F_SQE_GROUP);
+}
+
 /*
  * Don't complete immediately but use deferred completion infrastructure.
  * Protected by ->uring_lock and can only be used either with
@@ -354,7 +366,14 @@ static inline void io_req_complete_defer(struct io_kiocb *req)
 
 	lockdep_assert_held(&req->ctx->uring_lock);
 
-	wq_list_add_tail(&req->comp_list, &state->compl_reqs);
+	/*
+	 * Group leader won't be added to ->compl_reqs until the whole
+	 * group is completed. Either it is added here or inserted after
+	 * the last member is completed.
+	 */
+	if (likely(!req_is_group_leader(req)) ||
+	    __io_complete_group_req(req, req))
+		wq_list_add_tail(&req->comp_list, &state->compl_reqs);
 }
 
 static inline void io_commit_cqring_flush(struct io_ring_ctx *ctx)
-- 
2.42.0

[RFC PATCH V2 6/9] io_uring: support sqe group with members depending on leader

[Ming Lei]

Generic sqe group provides flexible way for supporting N:M dependency
between groups.

However, some resource can't cross OPs, such as kernel buffer, otherwise
the buffer may be leaked easily in case that any OP failure or application
panic.

Add flag REQ_F_SQE_GROUP_DEP for allowing members to depend on group leader,
so that group members won't be queued until the leader request is completed,
and we still commit leader's CQE after all members CQE are posted. With this
way, the kernel resource lifetime can be aligned with group leader or group,
one typical use case is to support zero copy for device internal buffer.

This use case may not be generic enough, so set it only for specific OP which
can serve as group leader, meantime we have run out of sqe flags.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 include/linux/io_uring_types.h |  3 +++
 io_uring/io_uring.c            | 36 +++++++++++++++++++++++++---------
 io_uring/io_uring.h            |  3 +++
 3 files changed, 33 insertions(+), 9 deletions(-)

diff --git a/include/linux/io_uring_types.h b/include/linux/io_uring_types.h
index 62311b0f0e0b..5cbc9d3346a7 100644
--- a/include/linux/io_uring_types.h
+++ b/include/linux/io_uring_types.h
@@ -477,6 +477,7 @@ enum {
 	REQ_F_BL_NO_RECYCLE_BIT,
 	REQ_F_BUFFERS_COMMIT_BIT,
 	REQ_F_SQE_GROUP_LEADER_BIT,
+	REQ_F_SQE_GROUP_DEP_BIT,
 
 	/* not a real bit, just to check we're not overflowing the space */
 	__REQ_F_LAST_BIT,
@@ -561,6 +562,8 @@ enum {
 	REQ_F_BUFFERS_COMMIT	= IO_REQ_FLAG(REQ_F_BUFFERS_COMMIT_BIT),
 	/* sqe group lead */
 	REQ_F_SQE_GROUP_LEADER	= IO_REQ_FLAG(REQ_F_SQE_GROUP_LEADER_BIT),
+	/* sqe group with members depending on leader */
+	REQ_F_SQE_GROUP_DEP	= IO_REQ_FLAG(REQ_F_SQE_GROUP_DEP_BIT),
 };
 
 typedef void (*io_req_tw_func_t)(struct io_kiocb *req, struct io_tw_state *ts);
diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 465f4244fa0b..236765bc786c 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -936,7 +936,14 @@ static __always_inline void io_req_commit_cqe(struct io_kiocb *req,
 
 static inline bool need_queue_group_members(struct io_kiocb *req)
 {
-	return req_is_group_leader(req) && !!req->grp_link;
+	if (likely(!(req->flags & REQ_F_SQE_GROUP)))
+		return false;
+
+	if (!(req->flags & REQ_F_SQE_GROUP_LEADER) ||
+			(req->flags & REQ_F_SQE_GROUP_DEP))
+		return false;
+
+	return !!req->grp_link;
 }
 
 /* Can only be called after this request is issued */
@@ -969,7 +976,7 @@ static void io_fail_group_members(struct io_kiocb *req)
 	req->grp_link = NULL;
 }
 
-static void io_queue_group_members(struct io_kiocb *req, bool async)
+void io_queue_group_members(struct io_kiocb *req, bool async)
 {
 	struct io_kiocb *member = req->grp_link;
 
@@ -980,13 +987,20 @@ static void io_queue_group_members(struct io_kiocb *req, bool async)
 		struct io_kiocb *next = member->grp_link;
 
 		member->grp_link = req;
-		trace_io_uring_submit_req(member);
-		if (async)
-			member->flags |= REQ_F_FORCE_ASYNC;
-		if (member->flags & REQ_F_FORCE_ASYNC)
-			io_req_task_queue(member);
-		else
-			io_queue_sqe(member);
+
+		/* members have to be failed if they depends on leader */
+		if (unlikely((req->flags & REQ_F_FAIL) &&
+			     (req->flags & REQ_F_SQE_GROUP_DEP))) {
+			io_req_task_queue_fail(member, -ECANCELED);
+		} else {
+			trace_io_uring_submit_req(member);
+			if (async)
+				member->flags |= REQ_F_FORCE_ASYNC;
+			if (member->flags & REQ_F_FORCE_ASYNC)
+				io_req_task_queue(member);
+			else
+				io_queue_sqe(member);
+		}
 		member = next;
 	}
 	req->grp_link = NULL;
@@ -1065,6 +1079,10 @@ static void io_req_complete_post(struct io_kiocb *req, unsigned issue_flags)
 		return;
 	}
 
+	/* now queue members if they depends on this leader */
+	if (req_is_group_leader(req) && (req->flags & REQ_F_SQE_GROUP_DEP))
+		io_queue_group_members(req, true);
+
 	io_cq_lock(ctx);
 	if (!(req->flags & REQ_F_CQE_SKIP))
 		io_req_commit_cqe(req, false);
diff --git a/io_uring/io_uring.h b/io_uring/io_uring.h
index 416c14c6f050..6cf27204503a 100644
--- a/io_uring/io_uring.h
+++ b/io_uring/io_uring.h
@@ -69,6 +69,7 @@ bool io_req_post_cqe(struct io_kiocb *req, s32 res, u32 cflags);
 void __io_commit_cqring_flush(struct io_ring_ctx *ctx);
 bool __io_complete_group_req(struct io_kiocb *req,
 			     struct io_kiocb *lead);
+void io_queue_group_members(struct io_kiocb *req, bool async);
 
 struct file *io_file_get_normal(struct io_kiocb *req, int fd);
 struct file *io_file_get_fixed(struct io_kiocb *req, int fd,
@@ -374,6 +375,8 @@ static inline void io_req_complete_defer(struct io_kiocb *req)
 	if (likely(!req_is_group_leader(req)) ||
 	    __io_complete_group_req(req, req))
 		wq_list_add_tail(&req->comp_list, &state->compl_reqs);
+	else if (req_is_group_leader(req) && (req->flags & REQ_F_SQE_GROUP_DEP))
+		io_queue_group_members(req, false);
 }
 
 static inline void io_commit_cqring_flush(struct io_ring_ctx *ctx)
-- 
2.42.0

[RFC PATCH V2 7/9] io_uring: support providing sqe group buffer

[Ming Lei]

SQE group with REQ_F_SQE_GROUP_DEP introduces one new mechanism to share
resource among one group of requests, and all member requests can consume
the resource provided by group lead efficiently in parallel.

This patch uses the added sqe group feature REQ_F_SQE_GROUP_DEP to share
kernel buffer in sqe group:

- the group lead provides kernel buffer to member requests

- member requests use the provided buffer to do FS or network IO, or more
operations in future

- this kernel buffer is returned back after member requests use it up

This way looks a bit similar with kernel's pipe/splice, but there are some
important differences:

- splice is for transferring data between two FDs via pipe, and fd_out can
only read data from pipe; this feature can borrow buffer from group lead to
members, so member request can write data to this buffer if the provided
buffer is allowed to write to.

- splice implements data transfer by moving pages between subsystem and
pipe, that means page ownership is transferred, and this way is one of the
most complicated thing of splice; this patch supports scenarios in which
the buffer can't be transferred, and buffer is only borrowed to member
requests, and is returned back after member requests consume the provided
buffer, so buffer lifetime is simplified a lot. Especially the buffer is
guaranteed to be returned back.

- splice can't run in async way basically

It can help to implement generic zero copy between device and related
operations, such as ublk, fuse, vdpa, even network receive or whatever.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 include/linux/io_uring_types.h | 33 +++++++++++++++++++
 io_uring/io_uring.c            | 10 +++++-
 io_uring/io_uring.h            |  5 +++
 io_uring/kbuf.c                | 60 ++++++++++++++++++++++++++++++++++
 io_uring/kbuf.h                | 13 ++++++++
 io_uring/net.c                 | 31 +++++++++++++++++-
 io_uring/opdef.c               |  5 +++
 io_uring/opdef.h               |  2 ++
 io_uring/rw.c                  | 20 +++++++++++-
 9 files changed, 176 insertions(+), 3 deletions(-)

diff --git a/include/linux/io_uring_types.h b/include/linux/io_uring_types.h
index 5cbc9d3346a7..e414c3544f72 100644
--- a/include/linux/io_uring_types.h
+++ b/include/linux/io_uring_types.h
@@ -6,6 +6,7 @@
 #include <linux/task_work.h>
 #include <linux/bitmap.h>
 #include <linux/llist.h>
+#include <linux/bvec.h>
 #include <uapi/linux/io_uring.h>
 
 enum {
@@ -39,6 +40,26 @@ enum io_uring_cmd_flags {
 	IO_URING_F_COMPAT		= (1 << 12),
 };
 
+struct io_uring_kernel_buf;
+typedef void (io_uring_buf_giveback_t) (const struct io_uring_kernel_buf *);
+
+/* buffer provided from kernel */
+struct io_uring_kernel_buf {
+	unsigned long		len;
+	unsigned short		nr_bvecs;
+	unsigned char		dir;	/* ITER_SOURCE or ITER_DEST */
+
+	/* offset in the 1st bvec */
+	unsigned int		offset;
+	const struct bio_vec	*bvec;
+
+	/* called when we are done with this buffer */
+	io_uring_buf_giveback_t	*grp_kbuf_ack;
+
+	/* private field, user don't touch it */
+	struct bio_vec		__bvec[];
+};
+
 struct io_wq_work_node {
 	struct io_wq_work_node *next;
 };
@@ -478,6 +499,7 @@ enum {
 	REQ_F_BUFFERS_COMMIT_BIT,
 	REQ_F_SQE_GROUP_LEADER_BIT,
 	REQ_F_SQE_GROUP_DEP_BIT,
+	REQ_F_GROUP_KBUF_BIT,
 
 	/* not a real bit, just to check we're not overflowing the space */
 	__REQ_F_LAST_BIT,
@@ -564,6 +586,8 @@ enum {
 	REQ_F_SQE_GROUP_LEADER	= IO_REQ_FLAG(REQ_F_SQE_GROUP_LEADER_BIT),
 	/* sqe group with members depending on leader */
 	REQ_F_SQE_GROUP_DEP	= IO_REQ_FLAG(REQ_F_SQE_GROUP_DEP_BIT),
+	/* group lead provides kbuf for members, set for both lead and member */
+	REQ_F_GROUP_KBUF	= IO_REQ_FLAG(REQ_F_GROUP_KBUF_BIT),
 };
 
 typedef void (*io_req_tw_func_t)(struct io_kiocb *req, struct io_tw_state *ts);
@@ -647,6 +671,15 @@ struct io_kiocb {
 		 * REQ_F_BUFFER_RING is set.
 		 */
 		struct io_buffer_list	*buf_list;
+
+		/*
+		 * store kernel buffer provided by sqe group lead, valid
+		 * IFF REQ_F_GROUP_KBUF
+		 *
+		 * The buffer meta is immutable since it is shared by
+		 * all member requests
+		 */
+		const struct io_uring_kernel_buf *grp_kbuf;
 	};
 
 	union {
diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 236765bc786c..48108c6f9a7f 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -114,7 +114,7 @@
 
 #define IO_REQ_CLEAN_FLAGS (REQ_F_BUFFER_SELECTED | REQ_F_NEED_CLEANUP | \
 				REQ_F_POLLED | REQ_F_INFLIGHT | REQ_F_CREDS | \
-				REQ_F_ASYNC_DATA)
+				REQ_F_ASYNC_DATA | REQ_F_GROUP_KBUF)
 
 #define IO_REQ_CLEAN_SLOW_FLAGS (REQ_F_REFCOUNT | REQ_F_LINK | REQ_F_HARDLINK |\
 				 IO_REQ_CLEAN_FLAGS)
@@ -380,6 +380,11 @@ static bool req_need_defer(struct io_kiocb *req, u32 seq)
 
 static void io_clean_op(struct io_kiocb *req)
 {
+	/* GROUP_KBUF is only available for REQ_F_SQE_GROUP_DEP */
+	if ((req->flags & (REQ_F_GROUP_KBUF | REQ_F_SQE_GROUP_DEP)) ==
+			(REQ_F_GROUP_KBUF | REQ_F_SQE_GROUP_DEP))
+		io_group_kbuf_drop(req);
+
 	if (req->flags & REQ_F_BUFFER_SELECTED) {
 		spin_lock(&req->ctx->completion_lock);
 		io_kbuf_drop(req);
@@ -984,9 +989,12 @@ void io_queue_group_members(struct io_kiocb *req, bool async)
 		return;
 
 	while (member) {
+		const struct io_issue_def *def = &io_issue_defs[member->opcode];
 		struct io_kiocb *next = member->grp_link;
 
 		member->grp_link = req;
+		if ((req->flags & REQ_F_GROUP_KBUF) && def->accept_group_kbuf)
+			member->flags |= REQ_F_GROUP_KBUF;
 
 		/* members have to be failed if they depends on leader */
 		if (unlikely((req->flags & REQ_F_FAIL) &&
diff --git a/io_uring/io_uring.h b/io_uring/io_uring.h
index 6cf27204503a..be6755b5cec1 100644
--- a/io_uring/io_uring.h
+++ b/io_uring/io_uring.h
@@ -355,6 +355,11 @@ static inline bool req_is_group_member(struct io_kiocb *req)
 	return !req_is_group_leader(req) && (req->flags & REQ_F_SQE_GROUP);
 }
 
+static inline bool req_support_group_dep(struct io_kiocb *req)
+{
+	return req_is_group_leader(req) && (req->flags & REQ_F_SQE_GROUP_DEP);
+}
+
 /*
  * Don't complete immediately but use deferred completion infrastructure.
  * Protected by ->uring_lock and can only be used either with
diff --git a/io_uring/kbuf.c b/io_uring/kbuf.c
index d2945c9c812b..4293bed374b7 100644
--- a/io_uring/kbuf.c
+++ b/io_uring/kbuf.c
@@ -823,3 +823,63 @@ int io_pbuf_mmap(struct file *file, struct vm_area_struct *vma)
 	io_put_bl(ctx, bl);
 	return ret;
 }
+
+int io_provide_group_kbuf(struct io_kiocb *req,
+		const struct io_uring_kernel_buf *grp_kbuf)
+{
+	if (unlikely(!req_support_group_dep(req)))
+		return -EINVAL;
+
+	/*
+	 * Borrow this buffer from one kernel subsystem, and return them
+	 * by calling `grp_kbuf_ack` when the group lead is freed.
+	 *
+	 * Not like pipe/splice, this kernel buffer is always owned by the
+	 * provider, and has to be returned back.
+	 */
+	req->grp_kbuf = grp_kbuf;
+	req->flags |= REQ_F_GROUP_KBUF;
+
+	return 0;
+}
+
+int io_import_group_kbuf(struct io_kiocb *req, unsigned long buf_off,
+		unsigned int len, int dir, struct iov_iter *iter)
+{
+	struct io_kiocb *lead = req->grp_link;
+	const struct io_uring_kernel_buf *kbuf;
+	unsigned long offset;
+
+	WARN_ON_ONCE(!(req->flags & REQ_F_GROUP_KBUF));
+
+	if (!req_is_group_member(req))
+		return -EINVAL;
+
+	if (!lead || !req_support_group_dep(lead) || !lead->grp_kbuf)
+		return -EINVAL;
+
+	/* req->fused_cmd_kbuf is immutable */
+	kbuf = lead->grp_kbuf;
+	offset = kbuf->offset;
+
+	if (!kbuf->bvec)
+		return -EINVAL;
+
+	if (dir != kbuf->dir)
+		return -EINVAL;
+
+	if (unlikely(buf_off > kbuf->len))
+		return -EFAULT;
+
+	if (unlikely(len > kbuf->len - buf_off))
+		return -EFAULT;
+
+	/* don't use io_import_fixed which doesn't support multipage bvec */
+	offset += buf_off;
+	iov_iter_bvec(iter, dir, kbuf->bvec, kbuf->nr_bvecs, offset + len);
+
+	if (offset)
+		iov_iter_advance(iter, offset);
+
+	return 0;
+}
diff --git a/io_uring/kbuf.h b/io_uring/kbuf.h
index b90aca3a57fa..2e1b7f91efb6 100644
--- a/io_uring/kbuf.h
+++ b/io_uring/kbuf.h
@@ -82,6 +82,11 @@ struct io_buffer_list *io_pbuf_get_bl(struct io_ring_ctx *ctx,
 				      unsigned long bgid);
 int io_pbuf_mmap(struct file *file, struct vm_area_struct *vma);
 
+int io_provide_group_kbuf(struct io_kiocb *req,
+		const struct io_uring_kernel_buf *grp_kbuf);
+int io_import_group_kbuf(struct io_kiocb *req, unsigned long buf_off,
+		unsigned int len, int dir, struct iov_iter *iter);
+
 static inline bool io_kbuf_recycle_ring(struct io_kiocb *req)
 {
 	/*
@@ -180,4 +185,12 @@ static inline unsigned int io_put_kbufs(struct io_kiocb *req, int nbufs,
 {
 	return __io_put_kbufs(req, nbufs, issue_flags);
 }
+
+static inline void io_group_kbuf_drop(struct io_kiocb *req)
+{
+	const struct io_uring_kernel_buf *gbuf = req->grp_kbuf;
+
+	if (gbuf && gbuf->grp_kbuf_ack)
+		gbuf->grp_kbuf_ack(gbuf);
+}
 #endif
diff --git a/io_uring/net.c b/io_uring/net.c
index b0bf8471ecb7..34da6b5a31fb 100644
--- a/io_uring/net.c
+++ b/io_uring/net.c
@@ -78,6 +78,13 @@ struct io_sr_msg {
  */
 #define MULTISHOT_MAX_RETRY	32
 
+#define user_ptr_to_u64(x) (		\
+{					\
+	typecheck(void __user *, (x));	\
+	(u64)(unsigned long)(x);	\
+}					\
+)
+
 int io_shutdown_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 {
 	struct io_shutdown *shutdown = io_kiocb_to_cmd(req, struct io_shutdown);
@@ -364,7 +371,7 @@ static int io_send_setup(struct io_kiocb *req)
 		kmsg->msg.msg_name = &kmsg->addr;
 		kmsg->msg.msg_namelen = sr->addr_len;
 	}
-	if (!io_do_buffer_select(req)) {
+	if (!io_do_buffer_select(req) && !(req->flags & REQ_F_GROUP_KBUF)) {
 		ret = import_ubuf(ITER_SOURCE, sr->buf, sr->len,
 				  &kmsg->msg.msg_iter);
 		if (unlikely(ret < 0))
@@ -584,6 +591,15 @@ int io_send(struct io_kiocb *req, unsigned int issue_flags)
 	if (issue_flags & IO_URING_F_NONBLOCK)
 		flags |= MSG_DONTWAIT;
 
+	if (req->flags & REQ_F_GROUP_KBUF) {
+		ret = io_import_group_kbuf(req,
+					user_ptr_to_u64(sr->buf),
+					sr->len, ITER_SOURCE,
+					&kmsg->msg.msg_iter);
+		if (unlikely(ret))
+			return ret;
+	}
+
 retry_bundle:
 	if (io_do_buffer_select(req)) {
 		struct buf_sel_arg arg = {
@@ -1131,6 +1147,11 @@ int io_recv(struct io_kiocb *req, unsigned int issue_flags)
 		if (unlikely(ret))
 			goto out_free;
 		sr->buf = NULL;
+	} else if (req->flags & REQ_F_GROUP_KBUF) {
+		ret = io_import_group_kbuf(req, user_ptr_to_u64(sr->buf),
+				sr->len, ITER_DEST, &kmsg->msg.msg_iter);
+		if (unlikely(ret))
+			goto out_free;
 	}
 
 	kmsg->msg.msg_inq = -1;
@@ -1333,6 +1354,14 @@ static int io_send_zc_import(struct io_kiocb *req, struct io_async_msghdr *kmsg)
 		if (unlikely(ret))
 			return ret;
 		kmsg->msg.sg_from_iter = io_sg_from_iter;
+	} else if (req->flags & REQ_F_GROUP_KBUF) {
+		struct io_sr_msg *sr = io_kiocb_to_cmd(req, struct io_sr_msg);
+
+		ret = io_import_group_kbuf(req, user_ptr_to_u64(sr->buf),
+				sr->len, ITER_SOURCE, &kmsg->msg.msg_iter);
+		if (unlikely(ret))
+			return ret;
+		kmsg->msg.sg_from_iter = io_sg_from_iter;
 	} else {
 		ret = import_ubuf(ITER_SOURCE, sr->buf, sr->len, &kmsg->msg.msg_iter);
 		if (unlikely(ret))
diff --git a/io_uring/opdef.c b/io_uring/opdef.c
index 2de5cca9504e..92b657a063a0 100644
--- a/io_uring/opdef.c
+++ b/io_uring/opdef.c
@@ -246,6 +246,7 @@ const struct io_issue_def io_issue_defs[] = {
 		.ioprio			= 1,
 		.iopoll			= 1,
 		.iopoll_queue		= 1,
+		.accept_group_kbuf	= 1,
 		.async_size		= sizeof(struct io_async_rw),
 		.prep			= io_prep_read,
 		.issue			= io_read,
@@ -260,6 +261,7 @@ const struct io_issue_def io_issue_defs[] = {
 		.ioprio			= 1,
 		.iopoll			= 1,
 		.iopoll_queue		= 1,
+		.accept_group_kbuf	= 1,
 		.async_size		= sizeof(struct io_async_rw),
 		.prep			= io_prep_write,
 		.issue			= io_write,
@@ -282,6 +284,7 @@ const struct io_issue_def io_issue_defs[] = {
 		.audit_skip		= 1,
 		.ioprio			= 1,
 		.buffer_select		= 1,
+		.accept_group_kbuf	= 1,
 #if defined(CONFIG_NET)
 		.async_size		= sizeof(struct io_async_msghdr),
 		.prep			= io_sendmsg_prep,
@@ -297,6 +300,7 @@ const struct io_issue_def io_issue_defs[] = {
 		.buffer_select		= 1,
 		.audit_skip		= 1,
 		.ioprio			= 1,
+		.accept_group_kbuf	= 1,
 #if defined(CONFIG_NET)
 		.async_size		= sizeof(struct io_async_msghdr),
 		.prep			= io_recvmsg_prep,
@@ -424,6 +428,7 @@ const struct io_issue_def io_issue_defs[] = {
 		.pollout		= 1,
 		.audit_skip		= 1,
 		.ioprio			= 1,
+		.accept_group_kbuf	= 1,
 #if defined(CONFIG_NET)
 		.async_size		= sizeof(struct io_async_msghdr),
 		.prep			= io_send_zc_prep,
diff --git a/io_uring/opdef.h b/io_uring/opdef.h
index 7ee6f5aa90aa..a53970655c82 100644
--- a/io_uring/opdef.h
+++ b/io_uring/opdef.h
@@ -29,6 +29,8 @@ struct io_issue_def {
 	unsigned		iopoll_queue : 1;
 	/* vectored opcode, set if 1) vectored, and 2) handler needs to know */
 	unsigned		vectored : 1;
+	/* opcodes which accept provided group kbuf */
+	unsigned		accept_group_kbuf : 1;
 
 	/* size of async data needed, if any */
 	unsigned short		async_size;
diff --git a/io_uring/rw.c b/io_uring/rw.c
index a6bf2ea8db91..4ae3ab9f2160 100644
--- a/io_uring/rw.c
+++ b/io_uring/rw.c
@@ -235,7 +235,8 @@ static int io_prep_rw_setup(struct io_kiocb *req, int ddir, bool do_import)
 	if (io_rw_alloc_async(req))
 		return -ENOMEM;
 
-	if (!do_import || io_do_buffer_select(req))
+	if (!do_import || io_do_buffer_select(req) ||
+	    (req->flags & REQ_F_GROUP_KBUF))
 		return 0;
 
 	rw = req->async_data;
@@ -620,11 +621,16 @@ static inline loff_t *io_kiocb_ppos(struct kiocb *kiocb)
  */
 static ssize_t loop_rw_iter(int ddir, struct io_rw *rw, struct iov_iter *iter)
 {
+	struct io_kiocb *req = cmd_to_io_kiocb(rw);
 	struct kiocb *kiocb = &rw->kiocb;
 	struct file *file = kiocb->ki_filp;
 	ssize_t ret = 0;
 	loff_t *ppos;
 
+	/* group buffer is kernel buffer and doesn't have userspace addr */
+	if (req->flags & REQ_F_GROUP_KBUF)
+		return -EOPNOTSUPP;
+
 	/*
 	 * Don't support polled IO through this interface, and we can't
 	 * support non-blocking either. For the latter, this just causes
@@ -830,6 +836,11 @@ static int __io_read(struct io_kiocb *req, unsigned int issue_flags)
 		ret = io_import_iovec(ITER_DEST, req, io, issue_flags);
 		if (unlikely(ret < 0))
 			return ret;
+	} else if (req->flags & REQ_F_GROUP_KBUF) {
+		ret = io_import_group_kbuf(req, rw->addr, rw->len, ITER_DEST,
+				&io->iter);
+		if (unlikely(ret))
+			return ret;
 	}
 
 	ret = io_rw_init_file(req, FMODE_READ);
@@ -1012,6 +1023,13 @@ int io_write(struct io_kiocb *req, unsigned int issue_flags)
 	ssize_t ret, ret2;
 	loff_t *ppos;
 
+	if (req->flags & REQ_F_GROUP_KBUF) {
+		ret = io_import_group_kbuf(req, rw->addr, rw->len, ITER_SOURCE,
+				&io->iter);
+		if (unlikely(ret))
+			return ret;
+	}
+
 	ret = io_rw_init_file(req, FMODE_WRITE);
 	if (unlikely(ret))
 		return ret;
-- 
2.42.0

[RFC PATCH V2 8/9] io_uring/uring_cmd: support provide group kernel buffer

[Ming Lei]

Allow uring command to be group leader for providing kernel buffer,
and this way can support generic device zero copy over device buffer.

The following patch will use the way to support zero copy for ublk.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 include/linux/io_uring/cmd.h  |  7 +++++++
 include/uapi/linux/io_uring.h |  7 ++++++-
 io_uring/uring_cmd.c          | 28 ++++++++++++++++++++++++++++
 3 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/include/linux/io_uring/cmd.h b/include/linux/io_uring/cmd.h
index 447fbfd32215..fde3a2ec7d9a 100644
--- a/include/linux/io_uring/cmd.h
+++ b/include/linux/io_uring/cmd.h
@@ -48,6 +48,8 @@ void __io_uring_cmd_do_in_task(struct io_uring_cmd *ioucmd,
 void io_uring_cmd_mark_cancelable(struct io_uring_cmd *cmd,
 		unsigned int issue_flags);
 
+int io_uring_cmd_provide_kbuf(struct io_uring_cmd *ioucmd,
+		const struct io_uring_kernel_buf *grp_kbuf);
 #else
 static inline int io_uring_cmd_import_fixed(u64 ubuf, unsigned long len, int rw,
 			      struct iov_iter *iter, void *ioucmd)
@@ -67,6 +69,11 @@ static inline void io_uring_cmd_mark_cancelable(struct io_uring_cmd *cmd,
 		unsigned int issue_flags)
 {
 }
+static inline int io_uring_cmd_provide_kbuf(struct io_uring_cmd *ioucmd,
+		const struct io_uring_kernel_buf *grp_kbuf)
+{
+	return -EOPNOTSUPP;
+}
 #endif
 
 /*
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index f3d74a920dfe..922f29b07ccc 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -268,9 +268,14 @@ enum io_uring_op {
  * sqe->uring_cmd_flags		top 8bits aren't available for userspace
  * IORING_URING_CMD_FIXED	use registered buffer; pass this flag
  *				along with setting sqe->buf_index.
+ * IORING_PROVIDE_GROUP_KBUF	this command provides group kernel buffer
+ *				for member requests which can retrieve
+ *				any sub-buffer with offset(sqe->addr) and
+ *				len(sqe->len)
  */
 #define IORING_URING_CMD_FIXED	(1U << 0)
-#define IORING_URING_CMD_MASK	IORING_URING_CMD_FIXED
+#define IORING_PROVIDE_GROUP_KBUF	(1U << 1)
+#define IORING_URING_CMD_MASK	(IORING_URING_CMD_FIXED | IORING_PROVIDE_GROUP_KBUF)
 
 
 /*
diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
index 21ac5fb2d5f0..14744eac9158 100644
--- a/io_uring/uring_cmd.c
+++ b/io_uring/uring_cmd.c
@@ -15,6 +15,7 @@
 #include "alloc_cache.h"
 #include "rsrc.h"
 #include "uring_cmd.h"
+#include "kbuf.h"
 
 static struct uring_cache *io_uring_async_get(struct io_kiocb *req)
 {
@@ -175,6 +176,26 @@ void io_uring_cmd_done(struct io_uring_cmd *ioucmd, ssize_t ret, ssize_t res2,
 }
 EXPORT_SYMBOL_GPL(io_uring_cmd_done);
 
+/*
+ * Provide kernel buffer for sqe group members to consume, and the caller
+ * has to guarantee that the provided buffer and the callback are valid
+ * until the callback is called.
+ */
+int io_uring_cmd_provide_kbuf(struct io_uring_cmd *ioucmd,
+		const struct io_uring_kernel_buf *grp_kbuf)
+{
+	struct io_kiocb *req = cmd_to_io_kiocb(ioucmd);
+
+	if (unlikely(!(ioucmd->flags & IORING_PROVIDE_GROUP_KBUF)))
+		return -EINVAL;
+
+	if (unlikely(!req_support_group_dep(req)))
+		return -EINVAL;
+
+	return io_provide_group_kbuf(req, grp_kbuf);
+}
+EXPORT_SYMBOL_GPL(io_uring_cmd_provide_kbuf);
+
 static int io_uring_cmd_prep_setup(struct io_kiocb *req,
 				   const struct io_uring_sqe *sqe)
 {
@@ -207,6 +228,13 @@ int io_uring_cmd_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	if (ioucmd->flags & ~IORING_URING_CMD_MASK)
 		return -EINVAL;
 
+	if (ioucmd->flags & IORING_PROVIDE_GROUP_KBUF) {
+		/* LEADER flag isn't set yet, so check GROUP only */
+		if (!(req->flags & REQ_F_SQE_GROUP))
+			return -EINVAL;
+		req->flags |= REQ_F_SQE_GROUP_DEP;
+	}
+
 	if (ioucmd->flags & IORING_URING_CMD_FIXED) {
 		struct io_ring_ctx *ctx = req->ctx;
 		u16 index;
-- 
2.42.0

[RFC PATCH V2 9/9] ublk: support provide io buffer

[Ming Lei]

Implement uring command's IORING_PROVIDE_GROUP_KBUF, and provide
io buffer for userpace to run io_uring operations(FS, network IO),
then ublk zero copy can be supported.

userspace code:

	https://github.com/ublk-org/ublksrv/tree/group-provide-buf.v2
	git clone https://github.com/ublk-org/ublksrv.git -b group-provide-buf.v2

And both loop and nbd zero copy(io_uring send and send zc) are covered.

Performance improvement is quite obvious in big block size test, such as
'loop --buffered_io' perf is doubled in 64KB block test("loop/007 vs
loop/009").

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 drivers/block/ublk_drv.c      | 158 ++++++++++++++++++++++++++++++++--
 include/uapi/linux/ublk_cmd.h |   7 +-
 2 files changed, 154 insertions(+), 11 deletions(-)

diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index bea3d5cf8a83..ef07b907437d 100644
--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c
@@ -71,6 +71,8 @@ struct ublk_rq_data {
 	__u64 sector;
 	__u32 operation;
 	__u32 nr_zones;
+	bool allocated_bvec;
+	struct io_uring_kernel_buf buf[0];
 };
 
 struct ublk_uring_cmd_pdu {
@@ -189,11 +191,15 @@ struct ublk_params_header {
 	__u32	types;
 };
 
+static inline struct request *__ublk_check_and_get_req(struct ublk_device *ub,
+		struct ublk_queue *ubq, int tag, size_t offset);
 static bool ublk_abort_requests(struct ublk_device *ub, struct ublk_queue *ubq);
 
 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 void ublk_io_buf_giveback_cb(const struct io_uring_kernel_buf *buf);
+
 static inline bool ublk_dev_is_user_copy(const struct ublk_device *ub)
 {
 	return ub->dev_info.flags & UBLK_F_USER_COPY;
@@ -566,6 +572,11 @@ static inline bool ublk_need_req_ref(const struct ublk_queue *ubq)
 	return ublk_support_user_copy(ubq);
 }
 
+static inline bool ublk_support_zc(const struct ublk_queue *ubq)
+{
+	return ubq->flags & UBLK_F_SUPPORT_ZERO_COPY;
+}
+
 static inline void ublk_init_req_ref(const struct ublk_queue *ubq,
 		struct request *req)
 {
@@ -829,6 +840,71 @@ static size_t ublk_copy_user_pages(const struct request *req,
 	return done;
 }
 
+/*
+ * The built command buffer is immutable, so it is fine to feed it to
+ * concurrent io_uring provide buf commands
+ */
+static int ublk_init_zero_copy_buffer(struct request *req)
+{
+	struct ublk_rq_data *data = blk_mq_rq_to_pdu(req);
+	struct io_uring_kernel_buf *imu = data->buf;
+	struct req_iterator rq_iter;
+	unsigned int nr_bvecs = 0;
+	struct bio_vec *bvec;
+	unsigned int offset;
+	struct bio_vec bv;
+
+	if (!ublk_rq_has_data(req))
+		goto exit;
+
+	rq_for_each_bvec(bv, req, rq_iter)
+		nr_bvecs++;
+
+	if (!nr_bvecs)
+		goto exit;
+
+	if (req->bio != req->biotail) {
+		int idx = 0;
+
+		bvec = kvmalloc_array(nr_bvecs, sizeof(struct bio_vec),
+				GFP_NOIO);
+		if (!bvec)
+			return -ENOMEM;
+
+		offset = 0;
+		rq_for_each_bvec(bv, req, rq_iter)
+			bvec[idx++] = bv;
+		data->allocated_bvec = true;
+	} else {
+		struct bio *bio = req->bio;
+
+		offset = bio->bi_iter.bi_bvec_done;
+		bvec = __bvec_iter_bvec(bio->bi_io_vec, bio->bi_iter);
+	}
+	imu->bvec = bvec;
+	imu->nr_bvecs = nr_bvecs;
+	imu->offset = offset;
+	imu->len = blk_rq_bytes(req);
+	imu->dir = req_op(req) == REQ_OP_READ ? ITER_DEST : ITER_SOURCE;
+	imu->grp_kbuf_ack = ublk_io_buf_giveback_cb;
+
+	return 0;
+exit:
+	imu->bvec = NULL;
+	return 0;
+}
+
+static void ublk_deinit_zero_copy_buffer(struct request *req)
+{
+	struct ublk_rq_data *data = blk_mq_rq_to_pdu(req);
+	struct io_uring_kernel_buf *imu = data->buf;
+
+	if (data->allocated_bvec) {
+		kvfree(imu->bvec);
+		data->allocated_bvec = false;
+	}
+}
+
 static inline bool ublk_need_map_req(const struct request *req)
 {
 	return ublk_rq_has_data(req) && req_op(req) == REQ_OP_WRITE;
@@ -840,13 +916,25 @@ static inline bool ublk_need_unmap_req(const struct request *req)
 	       (req_op(req) == REQ_OP_READ || req_op(req) == REQ_OP_DRV_IN);
 }
 
-static int ublk_map_io(const struct ublk_queue *ubq, const struct request *req,
+static int ublk_map_io(const struct ublk_queue *ubq, struct request *req,
 		struct ublk_io *io)
 {
 	const unsigned int rq_bytes = blk_rq_bytes(req);
 
-	if (ublk_support_user_copy(ubq))
+	if (ublk_support_user_copy(ubq)) {
+		if (ublk_support_zc(ubq)) {
+			int ret = ublk_init_zero_copy_buffer(req);
+
+			/*
+			 * The only failure is -ENOMEM for allocating providing
+			 * buffer command, return zero so that we can requeue
+			 * this req.
+			 */
+			if (unlikely(ret))
+				return 0;
+		}
 		return rq_bytes;
+	}
 
 	/*
 	 * no zero copy, we delay copy WRITE request data into ublksrv
@@ -864,13 +952,16 @@ static int ublk_map_io(const struct ublk_queue *ubq, const struct request *req,
 }
 
 static int ublk_unmap_io(const struct ublk_queue *ubq,
-		const struct request *req,
+		struct request *req,
 		struct ublk_io *io)
 {
 	const unsigned int rq_bytes = blk_rq_bytes(req);
 
-	if (ublk_support_user_copy(ubq))
+	if (ublk_support_user_copy(ubq)) {
+		if (ublk_support_zc(ubq))
+			ublk_deinit_zero_copy_buffer(req);
 		return rq_bytes;
+	}
 
 	if (ublk_need_unmap_req(req)) {
 		struct iov_iter iter;
@@ -1016,6 +1107,7 @@ static inline void __ublk_complete_rq(struct request *req)
 
 	return;
 exit:
+	ublk_deinit_zero_copy_buffer(req);
 	blk_mq_end_request(req, res);
 }
 
@@ -1658,6 +1750,45 @@ static inline void ublk_prep_cancel(struct io_uring_cmd *cmd,
 	io_uring_cmd_mark_cancelable(cmd, issue_flags);
 }
 
+static void ublk_io_buf_giveback_cb(const struct io_uring_kernel_buf *buf)
+{
+	struct ublk_rq_data *data = container_of(buf, struct ublk_rq_data, buf[0]);
+	struct request *req = blk_mq_rq_from_pdu(data);
+	struct ublk_queue *ubq = req->mq_hctx->driver_data;
+
+	ublk_put_req_ref(ubq, req);
+}
+
+static int ublk_provide_io_buf(struct io_uring_cmd *cmd,
+		struct ublk_queue *ubq, int tag)
+{
+	struct ublk_device *ub = cmd->file->private_data;
+	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;
+
+	pr_devel("%s: qid %d tag %u request bytes %u\n",
+			__func__, tag, ubq->q_id, blk_rq_bytes(req));
+
+	data = blk_mq_rq_to_pdu(req);
+
+	/*
+	 * io_uring guarantees that the callback will be called after
+	 * the provided buffer is consumed, and it is automatic removal
+	 * before this uring command is freed.
+	 *
+	 * This request won't be completed unless the callback is called,
+	 * so ublk module won't be unloaded too.
+	 */
+	return io_uring_cmd_provide_kbuf(cmd, data->buf);
+}
+
 static int __ublk_ch_uring_cmd(struct io_uring_cmd *cmd,
 			       unsigned int issue_flags,
 			       const struct ublksrv_io_cmd *ub_cmd)
@@ -1674,6 +1805,10 @@ static int __ublk_ch_uring_cmd(struct io_uring_cmd *cmd,
 			__func__, cmd->cmd_op, ub_cmd->q_id, tag,
 			ub_cmd->result);
 
+	if ((cmd->flags & IORING_PROVIDE_GROUP_KBUF) &&
+			cmd_op != UBLK_U_IO_PROVIDE_IO_BUF)
+		return -EOPNOTSUPP;
+
 	if (ub_cmd->q_id >= ub->dev_info.nr_hw_queues)
 		goto out;
 
@@ -1709,6 +1844,8 @@ static int __ublk_ch_uring_cmd(struct io_uring_cmd *cmd,
 
 	ret = -EINVAL;
 	switch (_IOC_NR(cmd_op)) {
+	case _IOC_NR(UBLK_U_IO_PROVIDE_IO_BUF):
+		return ublk_provide_io_buf(cmd, ubq, tag);
 	case UBLK_IO_FETCH_REQ:
 		/* UBLK_IO_FETCH_REQ is only allowed before queue is setup */
 		if (ublk_queue_ready(ubq)) {
@@ -2128,11 +2265,14 @@ static void ublk_align_max_io_size(struct ublk_device *ub)
 
 static int ublk_add_tag_set(struct ublk_device *ub)
 {
+	int zc = !!(ub->dev_info.flags & UBLK_F_SUPPORT_ZERO_COPY);
+	struct ublk_rq_data *data;
+
 	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;
-	ub->tag_set.cmd_size = sizeof(struct ublk_rq_data);
+	ub->tag_set.cmd_size = struct_size(data, buf, zc);
 	ub->tag_set.flags = BLK_MQ_F_SHOULD_MERGE;
 	ub->tag_set.driver_data = ub;
 	return blk_mq_alloc_tag_set(&ub->tag_set);
@@ -2417,8 +2557,12 @@ 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;
+	/* zero copy depends on user copy */
+	if ((ub->dev_info.flags & UBLK_F_SUPPORT_ZERO_COPY) &&
+			!ublk_dev_is_user_copy(ub)) {
+		ret = -EINVAL;
+		goto out_free_dev_number;
+	}
 
 	ub->dev_info.nr_hw_queues = min_t(unsigned int,
 			ub->dev_info.nr_hw_queues, nr_cpu_ids);
diff --git a/include/uapi/linux/ublk_cmd.h b/include/uapi/linux/ublk_cmd.h
index c8dc5f8ea699..897ace0794c2 100644
--- a/include/uapi/linux/ublk_cmd.h
+++ b/include/uapi/linux/ublk_cmd.h
@@ -94,6 +94,8 @@
 	_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_PROVIDE_IO_BUF	\
+	_IOWR('u', 0x23, struct ublksrv_io_cmd)
 
 /* only ABORT means that no re-fetch */
 #define UBLK_IO_RES_OK			0
@@ -126,10 +128,7 @@
 #define UBLKSRV_IO_BUF_TOTAL_BITS	(UBLK_QID_OFF + UBLK_QID_BITS)
 #define UBLKSRV_IO_BUF_TOTAL_SIZE	(1ULL << UBLKSRV_IO_BUF_TOTAL_BITS)
 
-/*
- * zero copy requires 4k block size, and can remap ublk driver's io
- * request into ublksrv's vm space
- */
+/* io_uring provide kbuf command based zero copy */
 #define UBLK_F_SUPPORT_ZERO_COPY	(1ULL << 0)
 
 /*
-- 
2.42.0

Re: [RFC PATCH V2 0/9] io_uring: support sqe group and provide group kbuf

[Ming Lei]

On Tue, May 07, 2024 at 12:22:36AM +0800, Ming Lei wrote:
> Hello,
> 
> The 1st 4 patches are cleanup, and prepare for adding sqe group.
> 
> The 5th patch supports generic sqe group which is like link chain, but
> allows each sqe in group to be issued in parallel, so N:M dependency can be
> supported with sqe group & io link together.
> 
> The 6th patch supports one variant of sqe group: allow members to depend
> on group leader, so that kernel resource lifetime can be aligned with
> group leader or group, then any kernel resource can be shared in this
> sqe group, and can be used in generic device zero copy.
> 
> The 7th & 8th patches supports providing sqe group buffer via the sqe
> group variant.
> 
> The 9th patch supports ublk zero copy based on io_uring providing sqe
> group buffer.
> 
> Tests:
> 
> 1) pass liburing test
> - make runtests
> 
> 2) write/pass two sqe group test cases:
> 
> https://github.com/axboe/liburing/compare/master...ming1:liburing:sqe_group_v2
> 
> covers related sqe flags combination and linking groups, both nop and
> one multi-destination file copy.
> 
> 3) ublksrv zero copy:
> 
> ublksrv userspace implements zero copy by sqe group & provide group
> kbuf:
> 
> 	git clone https://github.com/ublk-org/ublksrv.git -b group-provide-buf_v2
> 	make test T=loop/009:nbd/061:nbd/062	#ublk zc tests
> 
> When running 64KB block size test on ublk-loop('ublk add -t loop --buffered_io -f $backing'),
> it is observed that perf can be doubled.
> 
> Any comments are welcome!
> 
> V2:
> 	- add generic sqe group, suggested by Kevin Wolf
> 	- add REQ_F_SQE_GROUP_DEP which is based on IOSQE_SQE_GROUP, for sharing
> 	  kernel resource in group wide, suggested by Kevin Wolf
> 	- remove sqe ext flag, and use the last bit for IOSQE_SQE_GROUP(Pavel),
> 	in future we still can extend sqe flags with one uring context flag
> 	- initialize group requests via submit state pattern, suggested by Pavel
> 	- all kinds of cleanup & bug fixes

Please ignore V2, and will send V3 with simplification & cleanup, and
many fixes on error handling code path.


Thanks,
Ming