rxrpc: convert to getsockopt_iter

Convert RxRPC socket's getsockopt implementation to use the new
getsockopt_iter callback with sockopt_t.

Key changes:
- Replace (char __user *optval, int __user *optlen) with sockopt_t *opt
- Use opt->optlen for buffer length (input) and returned size (output)
- Use copy_to_iter() instead of put_user()/copy_to_user()

Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Signed-off-by: Breno Leitao <leitao@debian.org>
Link: https://patch.msgid.link/20260520-getsock_four-v3-5-b8c0b16b7780@debian.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/rxrpc/af_rxrpc.c

@@ -16,6 +16,7 @@
 #include <linux/poll.h>
 #include <linux/proc_fs.h>
 #include <linux/key-type.h>
+#include <linux/uio.h>
 #include <net/net_namespace.h>
 #include <net/sock.h>
 #include <net/af_rxrpc.h>
@@ -743,23 +744,24 @@ error:
  * Get socket options.
  */
 static int rxrpc_getsockopt(struct socket *sock, int level, int optname,
-			    char __user *optval, int __user *_optlen)
+			    sockopt_t *opt)
 {
-	int optlen;
+	int optlen, val;
 
 	if (level != SOL_RXRPC)
 		return -EOPNOTSUPP;
 
-	if (get_user(optlen, _optlen))
-		return -EFAULT;
+	optlen = opt->optlen;
 
 	switch (optname) {
 	case RXRPC_SUPPORTED_CMSG:
 		if (optlen < sizeof(int))
 			return -ETOOSMALL;
-		if (put_user(RXRPC__SUPPORTED - 1, (int __user *)optval) ||
-		    put_user(sizeof(int), _optlen))
+		val = RXRPC__SUPPORTED - 1;
+		if (copy_to_iter(&val, sizeof(val), &opt->iter_out) !=
+		    sizeof(val))
 			return -EFAULT;
+		opt->optlen = sizeof(val);
 		return 0;
 
 	default:
@@ -1009,7 +1011,7 @@ static const struct proto_ops rxrpc_rpc_ops = {
 	.listen		= rxrpc_listen,
 	.shutdown	= rxrpc_shutdown,
 	.setsockopt	= rxrpc_setsockopt,
-	.getsockopt	= rxrpc_getsockopt,
+	.getsockopt_iter = rxrpc_getsockopt,
 	.sendmsg	= rxrpc_sendmsg,
 	.recvmsg	= rxrpc_recvmsg,
 	.mmap		= sock_no_mmap,