[PATCH v1 5/5] io_uring/rsrc: add io_uring_registered_mem_region_get()

[Joanne Koong <joannelkoong@gmail.com>]

Add io_uring_registered_mem_region_get() helper to allow io_uring
command handlers to retrieve the vmapped pointer to the ring's
registered memory region's pages as well as the size of the region. This
provides a way for uring cmd implementations to directly access
pre-registered memory for passing data.

This will be used by fuse for reading/writing header data between the
kernel and the server.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
---
 include/linux/io_uring/cmd.h |  9 +++++++++
 io_uring/rsrc.c              | 18 ++++++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/include/linux/io_uring/cmd.h b/include/linux/io_uring/cmd.h
index f054ec1c8912..82ec6883eda4 100644
--- a/include/linux/io_uring/cmd.h
+++ b/include/linux/io_uring/cmd.h
@@ -51,6 +51,9 @@ int io_uring_cmd_import_fixed_vec(struct io_uring_cmd *ioucmd,
 				  size_t uvec_segs,
 				  int ddir, struct iov_iter *iter,
 				  unsigned issue_flags);
+void *io_uring_registered_mem_region_get(struct io_uring_cmd *cmd,
+					 unsigned *nr_pages,
+					 unsigned issue_flags);
 
 /*
  * Completes the request, i.e. posts an io_uring CQE and deallocates @ioucmd
@@ -131,6 +134,12 @@ static inline int io_uring_cmd_import_fixed_vec(struct io_uring_cmd *ioucmd,
 {
 	return -EOPNOTSUPP;
 }
+static inline void *io_uring_registered_mem_region_get(struct io_uring_cmd *cmd,
+						       unsigned *nr_pages,
+						       unsigned issue_flags)
+{
+	return NULL;
+}
 static inline void __io_uring_cmd_done(struct io_uring_cmd *cmd, s32 ret,
 		u64 ret2, unsigned issue_flags, bool is_cqe32)
 {
diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
index 3fd15bb8f6a7..aea8556cfe64 100644
--- a/io_uring/rsrc.c
+++ b/io_uring/rsrc.c
@@ -1180,6 +1180,24 @@ int io_import_reg_buf(struct io_kiocb *req, struct iov_iter *iter,
 	return io_import_fixed(ddir, iter, node->buf, buf_addr, len);
 }
 
+void *io_uring_registered_mem_region_get(struct io_uring_cmd *cmd,
+					 unsigned *nr_pages,
+					 unsigned issue_flags)
+{
+	struct io_ring_ctx *ctx = cmd_to_io_kiocb(cmd)->ctx;
+	void *ptr;
+
+	io_ring_submit_lock(ctx, issue_flags);
+
+	ptr = ctx->param_region.ptr;
+	*nr_pages = ctx->param_region.nr_pages;
+
+	io_ring_submit_unlock(ctx, issue_flags);
+
+	return ptr;
+}
+EXPORT_SYMBOL_GPL(io_uring_registered_mem_region_get);
+
 /* Lock two rings at once. The rings must be different! */
 static void lock_two_rings(struct io_ring_ctx *ctx1, struct io_ring_ctx *ctx2)
 {
-- 
2.52.0