From: Jens Axboe <axboe@kernel.dk>
Date: Fri, 6 Sep 2019 16:26:21 +0000 (-0600)
Subject: io_uring: expose single mmap capability
X-Git-Tag: v5.4-rc1~150^2~8
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=ac90f249e15cd2a850daa9e36e15f81ce1ff6550;p=thirdparty%2Fkernel%2Flinux.git

io_uring: expose single mmap capability

After commit 75b28affdd6a we can get by with just a single mmap to
map both the sq and cq ring. However, userspace doesn't know that.

Add a features variable to io_uring_params, and notify userspace
that the kernel has this ability. This can then be used in liburing
(or in applications directly) to avoid the second mmap.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 17dfe57c57f8c..be24596e90d75 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -3391,6 +3391,8 @@ static int io_uring_create(unsigned entries, struct io_uring_params *p)
 	p->cq_off.ring_entries = offsetof(struct io_rings, cq_ring_entries);
 	p->cq_off.overflow = offsetof(struct io_rings, cq_overflow);
 	p->cq_off.cqes = offsetof(struct io_rings, cqes);
+
+	p->features = IORING_FEAT_SINGLE_MMAP;
 	return ret;
 err:
 	io_ring_ctx_wait_and_kill(ctx);
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 1e1652f25cc19..96ee9d94b73e2 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -128,11 +128,17 @@ struct io_uring_params {
 	__u32 flags;
 	__u32 sq_thread_cpu;
 	__u32 sq_thread_idle;
-	__u32 resv[5];
+	__u32 features;
+	__u32 resv[4];
 	struct io_sqring_offsets sq_off;
 	struct io_cqring_offsets cq_off;
 };
 
+/*
+ * io_uring_params->features flags
+ */
+#define IORING_FEAT_SINGLE_MMAP		(1U << 0)
+
 /*
  * io_uring_register(2) opcodes and arguments
  */