[PATCH V9 6/7] io_uring/uring_cmd: support leasing device kernel buffer to io_uring

[Ming Lei <ming.lei@redhat.com>]

Add API of io_uring_cmd_lease_kbuf() for driver to lease its kernel
buffer to io_uring.

The leased buffer can only be consumed by io_uring OPs in group wide,
and the uring_cmd has to be one group leader.

This way can support generic device zero copy over device buffer in
userspace:

- create one sqe group
- lease one device buffer to io_uring by the group leader of uring_cmd
- io_uring member OPs consume this kernel buffer by passing IOSQE_IO_DRAIN
  which isn't used for group member, and mapped to GROUP_BUF.
- the kernel buffer is returned back after all member OPs are completed

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 include/linux/io_uring/cmd.h |  7 +++++++
 io_uring/uring_cmd.c         | 10 ++++++++++
 2 files changed, 17 insertions(+)

diff --git a/include/linux/io_uring/cmd.h b/include/linux/io_uring/cmd.h
index 578a3fdf5c71..8a6f1db1ca84 100644
--- a/include/linux/io_uring/cmd.h
+++ b/include/linux/io_uring/cmd.h
@@ -60,6 +60,8 @@ void io_uring_cmd_mark_cancelable(struct io_uring_cmd *cmd,
 /* Execute the request from a blocking context */
 void io_uring_cmd_issue_blocking(struct io_uring_cmd *ioucmd);
 
+int io_uring_cmd_lease_kbuf(struct io_uring_cmd *ioucmd,
+		const struct io_mapped_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)
@@ -82,6 +84,11 @@ static inline void io_uring_cmd_mark_cancelable(struct io_uring_cmd *cmd,
 static inline void io_uring_cmd_issue_blocking(struct io_uring_cmd *ioucmd)
 {
 }
+static inline int io_uring_cmd_lease_kbuf(struct io_uring_cmd *ioucmd,
+		const struct io_mapped_buf *grp_kbuf)
+{
+	return -EOPNOTSUPP;
+}
 #endif
 
 /*
diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
index 40b8b777ba12..5d59183212f6 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 +176,15 @@ void io_uring_cmd_done(struct io_uring_cmd *ioucmd, ssize_t ret, ssize_t res2,
 }
 EXPORT_SYMBOL_GPL(io_uring_cmd_done);
 
+int io_uring_cmd_lease_kbuf(struct io_uring_cmd *ioucmd,
+			    const struct io_mapped_buf *grp_kbuf)
+{
+	struct io_kiocb *req = cmd_to_io_kiocb(ioucmd);
+
+	return io_lease_group_kbuf(req, grp_kbuf);
+}
+EXPORT_SYMBOL_GPL(io_uring_cmd_lease_kbuf);
+
 static int io_uring_cmd_prep_setup(struct io_kiocb *req,
 				   const struct io_uring_sqe *sqe)
 {
-- 
2.47.0