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.

Jens Axboe committed 7 years ago

Commit ac90f241 parent 75b28af2 files · +9 −1Browse files

Showing the changes to include/uapi/linux (1 of 2 files). Show all

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include/uapi/linux/io_uring.h+7−1

@@ -128,11 +128,17 @@ struct io_uring_params { · 127 unmodified lines
128	128	__u32 flags;
129	129	__u32 sq_thread_cpu;
130	130	__u32 sq_thread_idle;
131		− __u32 resv[5];
	131	+ __u32 features;
	132	+ __u32 resv[4];
132	133	struct io_sqring_offsets sq_off;
133	134	struct io_cqring_offsets cq_off;
134	135	};
135	136
	137	+/*
	138	+ * io_uring_params->features flags
	139	+ */
	140	+#define IORING_FEAT_SINGLE_MMAP (1U << 0)
	141	+
136	142	/*
137	143	* io_uring_register(2) opcodes and arguments
138	144	*/