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io_uring: expose single mmap capability 

After commit 75b28affdd 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>
This commit is contained in:
Jens Axboe 2019-09-06 10:26:21 -06:00
parent 75b28affdd
commit ac90f249e1
2 changed files with 9 additions and 1 deletions
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2
fs/io_uring.c
View File

@ -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);

8
include/uapi/linux/io_uring.h
View File

@ -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
*/