io_uring/zcrx: return ifq id to the user

IORING_OP_RECV_ZC requests take a zcrx object id via sqe::zcrx_ifq_idx,
which binds it to the corresponding if / queue. However, we don't return
that id back to the user. It's fine as currently there can be only one
zcrx and the user assumes that its id should be 0, but as we'll need
multiple zcrx objects in the future let's explicitly pass it back on
registration.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/8714667d370651962f7d1a169032e5f02682a73e.1744722517.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: isilence

include/uapi/linux/io_uring.h

@@ -1010,7 +1010,9 @@ struct io_uring_zcrx_ifq_reg {
 	__u64	region_ptr; /* struct io_uring_region_desc * */
 
 	struct io_uring_zcrx_offsets offsets;
-	__u64	__resv[4];
+	__u32	zcrx_id;
+	__u32	__resv2;
+	__u64	__resv[3];
 };
 
 #ifdef __cplusplus

io_uring/zcrx.c

@@ -354,7 +354,8 @@ int io_register_zcrx_ifq(struct io_ring_ctx *ctx,
 		return -EFAULT;
 	if (copy_from_user(&rd, u64_to_user_ptr(reg.region_ptr), sizeof(rd)))
 		return -EFAULT;
-	if (memchr_inv(&reg.__resv, 0, sizeof(reg.__resv)))
+	if (memchr_inv(&reg.__resv, 0, sizeof(reg.__resv)) ||
+	    reg.__resv2 || reg.zcrx_id)
 		return -EINVAL;
 	if (reg.if_rxq == -1 || !reg.rq_entries || reg.flags)
 		return -EINVAL;