[RFC PATCH v3 08/20] io_uring: add mmap support for shared ifq ringbuffers

David Wei
2023-12-19T21:04:13Z

From: David Wei <davidhwei@meta.com>

This patch adds mmap support for ifq rbuf rings. There are two rings and
a struct io_rbuf_ring that contains the head and tail ptrs into each
ring.

Just like the io_uring SQ/CQ rings, userspace issues a single mmap call
using the io_uring fd w/ magic offset IORING_OFF_RBUF_RING. An opaque
ptr is returned to userspace, which is then expected to use the offsets
returned in the registration struct to get access to the head/tail and
rings.

Signed-off-by: David Wei <dw@davidwei.uk>
---
include/uapi/linux/io_uring.h | 2 ++
io_uring/io_uring.c | 5 +++++
io_uring/zc_rx.c | 19 ++++++++++++++++++-
3 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 024a6f79323b..839933e562e6 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -428,6 +428,8 @@ enum {
#define IORING_OFF_PBUF_RING 0x80000000ULL
#define IORING_OFF_PBUF_SHIFT 16
#define IORING_OFF_MMAP_MASK 0xf8000000ULL
+#define IORING_OFF_RBUF_RING 0x20000000ULL
+#define IORING_OFF_RBUF_SHIFT 16

/*
* Filled with the offset for mmap(2)
diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 7fff01d57e9e..02d6d638bd65 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -3516,6 +3516,11 @@ static void *io_uring_validate_mmap_request(struct file *file,
return ERR_PTR(-EINVAL);
break;
}
+ case IORING_OFF_RBUF_RING:
+ if (!ctx->ifq)
+ return ERR_PTR(-EINVAL);
+ ptr = ctx->ifq->ring;
+ break;
default:
return ERR_PTR(-EINVAL);
}
diff --git a/io_uring/zc_rx.c b/io_uring/zc_rx.c
index 5fc94cad5e3a..7e3e6f6d446b 100644
--- a/io_uring/zc_rx.c
+++ b/io_uring/zc_rx.c
@@ -61,6 +61,7 @@ int io_register_zc_rx_ifq(struct io_ring_ctx *ctx,
{
struct io_uring_zc_rx_ifq_reg reg;
struct io_zc_rx_ifq *ifq;
+ size_t ring_sz, rqes_sz, cqes_sz;
int ret;

if (!(ctx->flags & IORING_SETUP_DEFER_TASKRUN))
@@ -87,8 +88,24 @@ int io_register_zc_rx_ifq(struct io_ring_ctx *ctx,
ifq->rq_entries = reg.rq_entries;
ifq->cq_entries = reg.cq_entries;
ifq->if_rxq_id = reg.if_rxq_id;
- ctx->ifq = ifq;

+ ring_sz = sizeof(struct io_rbuf_ring);
+ rqes_sz = sizeof(struct io_uring_rbuf_rqe) * ifq->rq_entries;
+ cqes_sz = sizeof(struct io_uring_rbuf_cqe) * ifq->cq_entries;
+ reg.mmap_sz = ring_sz + rqes_sz + cqes_sz;
+ reg.rq_off.rqes = ring_sz;
+ reg.cq_off.cqes = ring_sz + rqes_sz;
+ reg.rq_off.head = offsetof(struct io_rbuf_ring, rq.head);
+ reg.rq_off.tail = offsetof(struct io_rbuf_ring, rq.tail);
+ reg.cq_off.head = offsetof(struct io_rbuf_ring, cq.head);
+ reg.cq_off.tail = offsetof(struct io_rbuf_ring, cq.tail);
+
+ if (copy_to_user(arg, &reg, sizeof(reg))) {
+ ret = -EFAULT;
+ goto err;
+ }
+
+ ctx->ifq = ifq;
return 0;
err:
io_zc_rx_ifq_free(ifq);
--
2.39.3