[PATCH v1 10/30] io_uring/kbuf: add io_uring_is_kmbuf_ring()

[Joanne Koong <joannelkoong@gmail.com>]

Add a function io_uring_is_kmbuf_ring() that returns true if there is a
kernel-managed buffer ring at the specified buffer group.

This is a preparatory patch for upcoming fuse kernel-managed buffer
support, which needs to ensure the buffer ring registered by the server
is a kernel-managed buffer ring.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
---
 include/linux/io_uring/buf.h |  9 +++++++++
 io_uring/kbuf.c              | 19 +++++++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/include/linux/io_uring/buf.h b/include/linux/io_uring/buf.h
index 839c5a0b3bf3..90ab5cde7d11 100644
--- a/include/linux/io_uring/buf.h
+++ b/include/linux/io_uring/buf.h
@@ -16,6 +16,9 @@ int io_uring_buf_table_unpin(struct io_ring_ctx *ctx, unsigned issue_flags);
 int io_uring_kmbuf_recycle_pinned(struct io_kiocb *req,
 				  struct io_buffer_list *bl, u64 addr,
 				  unsigned int len, unsigned int bid);
+
+bool io_uring_is_kmbuf_ring(struct io_ring_ctx *ctx, unsigned int buf_group,
+			    unsigned int issue_flags);
 #else
 static inline int io_uring_buf_ring_pin(struct io_ring_ctx *ctx,
 					unsigned buf_group,
@@ -46,6 +49,12 @@ int io_uring_kmbuf_recycle_pinned(struct io_kiocb *req,
 {
 	return -EOPNOTSUPP;
 }
+static inline bool io_uring_is_kmbuf_ring(struct io_ring_ctx *ctx,
+					  unsigned int buf_group,
+					  unsigned int issue_flags)
+{
+	return false;
+}
 #endif /* CONFIG_IO_URING */
 
 #endif /* _LINUX_IO_URING_BUF_H */
diff --git a/io_uring/kbuf.c b/io_uring/kbuf.c
index 82a4c550633d..8a94de6e530f 100644
--- a/io_uring/kbuf.c
+++ b/io_uring/kbuf.c
@@ -945,3 +945,22 @@ int io_register_kmbuf_ring(struct io_ring_ctx *ctx, void __user *arg)
 
 	return 0;
 }
+
+bool io_uring_is_kmbuf_ring(struct io_ring_ctx *ctx, unsigned int buf_group,
+			    unsigned int issue_flags)
+{
+	struct io_buffer_list *bl;
+	bool is_kmbuf_ring = false;
+
+	io_ring_submit_lock(ctx, issue_flags);
+
+	bl = io_buffer_get_list(ctx, buf_group);
+	if (likely(bl) && (bl->flags & IOBL_KERNEL_MANAGED)) {
+		WARN_ON_ONCE(!(bl->flags & IOBL_BUF_RING));
+		is_kmbuf_ring = true;
+	}
+
+	io_ring_submit_unlock(ctx, issue_flags);
+	return is_kmbuf_ring;
+}
+EXPORT_SYMBOL_GPL(io_uring_is_kmbuf_ring);
-- 
2.47.3