[RFC PATCH v4 06/16] io_uring: add mmap support for shared ifq ringbuffers

[David Wei <dw@davidwei.uk>]

From: David Wei <davidhwei@meta.com>

This patch adds mmap support for ifq refill 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_RQ_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              | 15 ++++++++++++++-
 3 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 7b643fe420c5..a085ed60478f 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -438,6 +438,8 @@ enum {
 #define IORING_OFF_PBUF_RING		0x80000000ULL
 #define IORING_OFF_PBUF_SHIFT		16
 #define IORING_OFF_MMAP_MASK		0xf8000000ULL
+#define IORING_OFF_RQ_RING		0x20000000ULL
+#define IORING_OFF_RQ_SHIFT		16
 
 /*
  * Filled with the offset for mmap(2)
diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 5614c47cecd9..280f2a2fd1fe 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -3434,6 +3434,11 @@ static void *io_uring_validate_mmap_request(struct file *file,
 			return ERR_PTR(-EINVAL);
 		break;
 		}
+	case IORING_OFF_RQ_RING:
+		if (!ctx->ifq)
+			return ERR_PTR(-EINVAL);
+		ptr = ctx->ifq->rq_ring;
+		break;
 	default:
 		return ERR_PTR(-EINVAL);
 	}
diff --git a/io_uring/zc_rx.c b/io_uring/zc_rx.c
index e6c33f94c086..6987bb991418 100644
--- a/io_uring/zc_rx.c
+++ b/io_uring/zc_rx.c
@@ -58,6 +58,7 @@ 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;
 	int ret;
 
 	if (!(ctx->flags & IORING_SETUP_DEFER_TASKRUN &&
@@ -80,8 +81,20 @@ int io_register_zc_rx_ifq(struct io_ring_ctx *ctx,
 
 	ifq->rq_entries = reg.rq_entries;
 	ifq->if_rxq_id = reg.if_rxq_id;
-	ctx->ifq = ifq;
 
+	ring_sz = sizeof(struct io_uring);
+	rqes_sz = sizeof(struct io_uring_rbuf_rqe) * ifq->rq_entries;
+	reg.mmap_sz = ring_sz + rqes_sz;
+	reg.rq_off.rqes = ring_sz;
+	reg.rq_off.head = offsetof(struct io_uring, head);
+	reg.rq_off.tail = offsetof(struct io_uring, 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);
-- 
2.43.0