Add an interface for buffers to be recycled back into a kernel-managed
buffer ring.

This is a preparatory patch for fuse over io-uring.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
---
 include/linux/io_uring/cmd.h | 13 +++++++++++
 io_uring/kbuf.c              | 42 ++++++++++++++++++++++++++++++++++++
 io_uring/kbuf.h              |  3 +++
 io_uring/uring_cmd.c         | 11 ++++++++++
 4 files changed, 69 insertions(+)

diff --git a/include/linux/io_uring/cmd.h b/include/linux/io_uring/cmd.h
index 424f071f42e5..7169a2a9a744 100644
--- a/include/linux/io_uring/cmd.h
+++ b/include/linux/io_uring/cmd.h
@@ -88,6 +88,11 @@ int io_uring_cmd_buf_ring_pin(struct io_uring_cmd *ioucmd, unsigned buf_group,
 			      unsigned issue_flags, struct io_buffer_list **bl);
 int io_uring_cmd_buf_ring_unpin(struct io_uring_cmd *ioucmd, unsigned buf_group,
 				unsigned issue_flags);
+
+int io_uring_cmd_kmbuffer_recycle(struct io_uring_cmd *cmd,
+				  unsigned int buf_group, u64 addr,
+				  unsigned int len, unsigned int bid,
+				  unsigned int issue_flags);
 #else
 static inline int
 io_uring_cmd_import_fixed(u64 ubuf, unsigned long len, int rw,
@@ -143,6 +148,14 @@ static inline int io_uring_cmd_buf_ring_unpin(struct io_uring_cmd *ioucmd,
 {
 	return -EOPNOTSUPP;
 }
+static inline int io_uring_cmd_kmbuffer_recycle(struct io_uring_cmd *cmd,
+						unsigned int buf_group,
+						u64 addr, unsigned int len,
+						unsigned int bid,
+						unsigned int issue_flags)
+{
+	return -EOPNOTSUPP;
+}
 #endif
 
 static inline struct io_uring_cmd *io_uring_cmd_from_tw(struct io_tw_req tw_req)
diff --git a/io_uring/kbuf.c b/io_uring/kbuf.c
index 49dc75f24432..f494d896c17e 100644
--- a/io_uring/kbuf.c
+++ b/io_uring/kbuf.c
@@ -101,6 +101,48 @@ void io_kbuf_drop_legacy(struct io_kiocb *req)
 	req->kbuf = NULL;
 }
 
+int io_kmbuf_recycle(struct io_kiocb *req, unsigned int bgid, u64 addr,
+		     unsigned int len, unsigned int bid,
+		     unsigned int issue_flags)
+{
+	struct io_ring_ctx *ctx = req->ctx;
+	struct io_uring_buf_ring *br;
+	struct io_uring_buf *buf;
+	struct io_buffer_list *bl;
+	int ret = -EINVAL;
+
+	if (WARN_ON_ONCE(req->flags & REQ_F_BUFFERS_COMMIT))
+		return ret;
+
+	io_ring_submit_lock(ctx, issue_flags);
+
+	bl = io_buffer_get_list(ctx, bgid);
+
+	if (WARN_ON_ONCE(!(bl->flags & IOBL_BUF_RING)) ||
+	    WARN_ON_ONCE(!(bl->flags & IOBL_KERNEL_MANAGED)))
+		goto done;
+
+	br = bl->buf_ring;
+
+	if (WARN_ON_ONCE((br->tail - bl->head) >= bl->nr_entries))
+		goto done;
+
+	buf = &br->bufs[(br->tail) & bl->mask];
+
+	buf->addr = addr;
+	buf->len = len;
+	buf->bid = bid;
+
+	req->flags &= ~REQ_F_BUFFER_RING;
+
+	br->tail++;
+	ret = 0;
+
+done:
+	io_ring_submit_unlock(ctx, issue_flags);
+	return ret;
+}
+
 bool io_kbuf_recycle_legacy(struct io_kiocb *req, unsigned issue_flags)
 {
 	struct io_ring_ctx *ctx = req->ctx;
diff --git a/io_uring/kbuf.h b/io_uring/kbuf.h
index c4368f35cf11..4d8b7491628e 100644
--- a/io_uring/kbuf.h
+++ b/io_uring/kbuf.h
@@ -146,4 +146,7 @@ int io_kbuf_ring_pin(struct io_kiocb *req, unsigned buf_group,
 		     unsigned issue_flags, struct io_buffer_list **bl);
 int io_kbuf_ring_unpin(struct io_kiocb *req, unsigned buf_group,
 		       unsigned issue_flags);
+int io_kmbuf_recycle(struct io_kiocb *req, unsigned int bgid, u64 addr,
+		     unsigned int len, unsigned int bid,
+		     unsigned int issue_flags);
 #endif
diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
index 8ac79ead4158..b6b675010bfd 100644
--- a/io_uring/uring_cmd.c
+++ b/io_uring/uring_cmd.c
@@ -416,3 +416,14 @@ int io_uring_cmd_buf_ring_unpin(struct io_uring_cmd *ioucmd, unsigned buf_group,
 	return io_kbuf_ring_unpin(req, buf_group, issue_flags);
 }
 EXPORT_SYMBOL_GPL(io_uring_cmd_buf_ring_unpin);
+
+int io_uring_cmd_kmbuffer_recycle(struct io_uring_cmd *ioucmd,
+				  unsigned int buf_group, u64 addr,
+				  unsigned int len, unsigned int bid,
+				  unsigned int issue_flags)
+{
+	struct io_kiocb *req = cmd_to_io_kiocb(ioucmd);
+
+	return io_kmbuf_recycle(req, buf_group, addr, len, bid, issue_flags);
+}
+EXPORT_SYMBOL_GPL(io_uring_cmd_kmbuffer_recycle);
-- 
2.47.3