Add a way to share an ifq from a src ring that is real (i.e. bound to a
HW RX queue) with other rings. This is done by passing a new flag
IORING_ZCRX_IFQ_REG_SHARE in the registration struct
io_uring_zcrx_ifq_reg, alongside the fd of the src ring and its ifq id
to be shared.

Signed-off-by: David Wei <dw@davidwei.uk>
---
 include/uapi/linux/io_uring.h |  4 +++
 io_uring/zcrx.c               | 65 ++++++++++++++++++++++++++++++++++-
 2 files changed, 68 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 04797a9b76bc..4da4552a4215 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -1063,6 +1063,10 @@ struct io_uring_zcrx_area_reg {
 	__u64	__resv2[2];
 };
 
+enum io_uring_zcrx_ifq_reg_flags {
+	IORING_ZCRX_IFQ_REG_SHARE	= 1,
+};
+
 /*
  * Argument for IORING_REGISTER_ZCRX_IFQ
  */
diff --git a/io_uring/zcrx.c b/io_uring/zcrx.c
index 6324dfa61ce0..094bd595d517 100644
--- a/io_uring/zcrx.c
+++ b/io_uring/zcrx.c
@@ -22,10 +22,10 @@
 #include <uapi/linux/io_uring.h>
 
 #include "io_uring.h"
-#include "kbuf.h"
 #include "memmap.h"
 #include "zcrx.h"
 #include "rsrc.h"
+#include "register.h"
 
 #define IO_ZCRX_AREA_SUPPORTED_FLAGS	(IORING_ZCRX_AREA_DMABUF)
 
@@ -546,6 +546,67 @@ struct io_mapped_region *io_zcrx_get_region(struct io_ring_ctx *ctx,
 	return ifq ? &ifq->region : NULL;
 }
 
+static int io_share_zcrx_ifq(struct io_ring_ctx *ctx,
+			     struct io_uring_zcrx_ifq_reg __user *arg,
+			     struct io_uring_zcrx_ifq_reg *reg)
+{
+	struct io_ring_ctx *src_ctx;
+	struct io_zcrx_ifq *src_ifq;
+	struct file *file;
+	int src_fd, ret;
+	u32 src_id, id;
+
+	src_fd = reg->if_idx;
+	src_id = reg->if_rxq;
+
+	file = io_uring_register_get_file(src_fd, false);
+	if (IS_ERR(file))
+		return PTR_ERR(file);
+
+	src_ctx = file->private_data;
+	if (src_ctx == ctx)
+		return -EBADFD;
+
+	mutex_unlock(&ctx->uring_lock);
+	mutex_lock(&src_ctx->uring_lock);
+
+	src_ifq = xa_load(&src_ctx->zcrx_ctxs, src_id);
+	if (!src_ifq) {
+		mutex_unlock(&src_ctx->uring_lock);
+		fput(file);
+		mutex_lock(&ctx->uring_lock);
+		return -EINVAL;
+	}
+
+	refcount_inc(&src_ifq->refs);
+	mutex_unlock(&src_ctx->uring_lock);
+	fput(file);
+	mutex_lock(&ctx->uring_lock);
+
+	scoped_guard(mutex, &ctx->mmap_lock) {
+		ret = xa_alloc(&ctx->zcrx_ctxs, &id, NULL, xa_limit_31b, GFP_KERNEL);
+		if (ret)
+			return ret;
+	}
+
+	reg->zcrx_id = id;
+	if (copy_to_user(arg, reg, sizeof(*reg))) {
+		ret = -EFAULT;
+		goto err;
+	}
+
+	scoped_guard(mutex, &ctx->mmap_lock) {
+		ret = -ENOMEM;
+		if (xa_store(&ctx->zcrx_ctxs, id, src_ifq, GFP_KERNEL))
+			goto err;
+	}
+	return 0;
+err:
+	scoped_guard(mutex, &ctx->mmap_lock)
+		xa_erase(&ctx->zcrx_ctxs, id);
+	return ret;
+}
+
 int io_register_zcrx_ifq(struct io_ring_ctx *ctx,
 			  struct io_uring_zcrx_ifq_reg __user *arg)
 {
@@ -571,6 +632,8 @@ int io_register_zcrx_ifq(struct io_ring_ctx *ctx,
 		return -EINVAL;
 	if (copy_from_user(&reg, arg, sizeof(reg)))
 		return -EFAULT;
+	if (reg.flags & IORING_ZCRX_IFQ_REG_SHARE)
+		return io_share_zcrx_ifq(ctx, arg, &reg);
 	if (copy_from_user(&rd, u64_to_user_ptr(reg.region_ptr), sizeof(rd)))
 		return -EFAULT;
 	if (!mem_is_zero(&reg.__resv, sizeof(reg.__resv)) ||
-- 
2.47.3