[PATCH net-next 0/2] net/smc: convert getsockopt to getsockopt_iter

[PATCH net-next 0/2] net/smc: convert getsockopt to getsockopt_iter

[Breno Leitao]

SMC is the last protocol to be converted to getsockopt_iter(). As soon
as this series lands, and all the other outstanding conversion patches
land, getsockopt_iter() will be renamed back to getsockopt() and the
first part of the conversion will be complete.

This series converts SMC's getsockopt() to the new getsockopt_iter()
callback, which hands protocols a sockopt_t that abstracts the optval
buffer as an iov_iter and the option length as a plain int instead of
raw (char __user *optval, int __user *optlen) pointers. This is part of
the broader effort to move getsockopt() off __user pointers so that
kernel-backed callers (e.g. io_uring) can issue socket options.

SMC is a proxy socket: only the SOL_SMC level is handled locally, while
every other level is forwarded to the underlying CLC (TCP) socket. That
sub-socket's getsockopt() still operates on __user buffers, so the
pass-through cannot simply forward the sockopt_t. Instead it reconstructs
optval from a user-backed iter_out, forwards the preserved user optlen
pointer (kept in sockopt_t by the base patch), and mirrors the length
reported by the clcsock back into opt->optlen.

Because of that, the SOL_SMC level is fully converted and works with any
iov_iter type, but the CLC pass-through is intentionally limited to
user-backed iters (ubuf) and returns -EOPNOTSUPP otherwise. This is a
deliberate, temporary restriction: SMC will continue to operate on ubuf
only until the underlying protocols (TCP/IP) grow their own
getsockopt_iter() callbacks. Once that generic callback path is enabled,
the pass-through can forward the sockopt_t directly and drop the ubuf
restriction, supporting all iov_iter types.

The series contains:

  1) smc: convert getsockopt to getsockopt_iter / sockopt_t.

  2) selftests: net: I've vibe coded a kselftest exercising both the
     SOL_SMC path and the CLC pass-through, including the
     oversized-buffer writeback.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
Breno Leitao (2):
      smc: convert to getsockopt_iter
      selftests: net: add SMC getsockopt_iter conversion test

 net/smc/af_smc.c                             |  41 +++++--
 net/smc/smc.h                                |   2 +-
 net/smc/smc_inet.c                           |   4 +-
 tools/testing/selftests/net/Makefile         |   1 +
 tools/testing/selftests/net/getsockopt_smc.c | 175 +++++++++++++++++++++++++++
 5 files changed, 208 insertions(+), 15 deletions(-)
---
base-commit: 0a8b288e2248cb62a62f748bc095c2136acf22b2
change-id: 20260604-getsockopt_smc-e2ad719486eb

Best regards,
-- 
Breno Leitao <leitao@debian.org>

[PATCH net-next 1/2] smc: convert to getsockopt_iter

[Breno Leitao]

Convert SMC 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()
- Add linux/uio.h for copy_to_iter()

SMC is a proxy socket: only the SOL_SMC level is handled locally, while
all other levels are forwarded to the underlying CLC (TCP) socket. That
socket's getsockopt() still operates on __user buffers, so the
pass-through is limited to user-backed iters: optval is reconstructed
from iter_out, the original optlen pointer (preserved in sockopt_t) is
forwarded, and the length reported by the clcsock is mirrored back into
opt->optlen so the core writes the correct value to userspace.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
 net/smc/af_smc.c   | 41 +++++++++++++++++++++++++++++------------
 net/smc/smc.h      |  2 +-
 net/smc/smc_inet.c |  4 ++--
 3 files changed, 32 insertions(+), 15 deletions(-)

diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
index b5db69073e20..064d752388d2 100644
--- a/net/smc/af_smc.c
+++ b/net/smc/af_smc.c
@@ -27,6 +27,7 @@
 #include <linux/rcupdate_wait.h>
 #include <linux/ctype.h>
 #include <linux/splice.h>
+#include <linux/uio.h>
 
 #include <net/sock.h>
 #include <net/inet_common.h>
@@ -3017,17 +3018,14 @@ int smc_shutdown(struct socket *sock, int how)
 }
 
 static int __smc_getsockopt(struct socket *sock, int level, int optname,
-			    char __user *optval, int __user *optlen)
+			    sockopt_t *opt)
 {
 	struct smc_sock *smc;
 	int val, len;
 
 	smc = smc_sk(sock->sk);
 
-	if (get_user(len, optlen))
-		return -EFAULT;
-
-	len = min_t(int, len, sizeof(int));
+	len = min_t(int, opt->optlen, sizeof(int));
 
 	if (len < 0)
 		return -EINVAL;
@@ -3040,9 +3038,8 @@ static int __smc_getsockopt(struct socket *sock, int level, int optname,
 		return -EOPNOTSUPP;
 	}
 
-	if (put_user(len, optlen))
-		return -EFAULT;
-	if (copy_to_user(optval, &val, len))
+	opt->optlen = len;
+	if (copy_to_iter(&val, len, &opt->iter_out) != len)
 		return -EFAULT;
 
 	return 0;
@@ -3168,13 +3165,26 @@ int smc_setsockopt(struct socket *sock, int level, int optname,
 }
 
 int smc_getsockopt(struct socket *sock, int level, int optname,
-		   char __user *optval, int __user *optlen)
+		   sockopt_t *opt)
 {
 	struct smc_sock *smc;
 	int rc;
 
 	if (level == SOL_SMC)
-		return __smc_getsockopt(sock, level, optname, optval, optlen);
+		return __smc_getsockopt(sock, level, optname, opt);
+
+	/* Other levels apply to the CLC socket, whose getsockopt() still
+	 * operates on __user buffers. Reconstruct the userspace pointers and
+	 * forward the call; kernel-backed callers (e.g. io_uring) are not
+	 * supported for this pass-through.
+	 *
+	 * TODO: this pass-through is limited to user-backed iters because the
+	 * underlying protocols (TCP/IP) have not been converted to
+	 * getsockopt_iter() yet. Once they are, forward the sockopt_t directly
+	 * and drop this restriction so all iov_iter types are supported.
+	 */
+	if (!iter_is_ubuf(&opt->iter_out) || !opt->optlen_user)
+		return -EOPNOTSUPP;
 
 	smc = smc_sk(sock->sk);
 	mutex_lock(&smc->clcsock_release_lock);
@@ -3188,8 +3198,15 @@ int smc_getsockopt(struct socket *sock, int level, int optname,
 		return -EOPNOTSUPP;
 	}
 	rc = smc->clcsock->ops->getsockopt(smc->clcsock, level, optname,
-					   optval, optlen);
+					   opt->iter_out.ubuf, opt->optlen_user);
 	mutex_unlock(&smc->clcsock_release_lock);
+
+	/* The clcsock wrote the resulting length to the user optlen pointer;
+	 * mirror it into opt->optlen so the core writes the same value back.
+	 */
+	if (get_user(opt->optlen, opt->optlen_user))
+		return -EFAULT;
+
 	return rc;
 }
 
@@ -3341,7 +3358,7 @@ static const struct proto_ops smc_sock_ops = {
 	.listen		= smc_listen,
 	.shutdown	= smc_shutdown,
 	.setsockopt	= smc_setsockopt,
-	.getsockopt	= smc_getsockopt,
+	.getsockopt_iter = smc_getsockopt,
 	.sendmsg	= smc_sendmsg,
 	.recvmsg	= smc_recvmsg,
 	.mmap		= sock_no_mmap,
diff --git a/net/smc/smc.h b/net/smc/smc.h
index 52145df83f6e..e62549067b67 100644
--- a/net/smc/smc.h
+++ b/net/smc/smc.h
@@ -59,7 +59,7 @@ int smc_shutdown(struct socket *sock, int how);
 int smc_setsockopt(struct socket *sock, int level, int optname,
 		   sockptr_t optval, unsigned int optlen);
 int smc_getsockopt(struct socket *sock, int level, int optname,
-		   char __user *optval, int __user *optlen);
+		   sockopt_t *opt);
 int smc_sendmsg(struct socket *sock, struct msghdr *msg, size_t len);
 int smc_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
 		int flags);
diff --git a/net/smc/smc_inet.c b/net/smc/smc_inet.c
index a94084b4a498..419240fedbc3 100644
--- a/net/smc/smc_inet.c
+++ b/net/smc/smc_inet.c
@@ -44,7 +44,7 @@ static const struct proto_ops smc_inet_stream_ops = {
 	.listen		= smc_listen,
 	.shutdown	= smc_shutdown,
 	.setsockopt	= smc_setsockopt,
-	.getsockopt	= smc_getsockopt,
+	.getsockopt_iter = smc_getsockopt,
 	.sendmsg	= smc_sendmsg,
 	.recvmsg	= smc_recvmsg,
 	.mmap		= sock_no_mmap,
@@ -91,7 +91,7 @@ static const struct proto_ops smc_inet6_stream_ops = {
 	.listen		= smc_listen,
 	.shutdown	= smc_shutdown,
 	.setsockopt	= smc_setsockopt,
-	.getsockopt	= smc_getsockopt,
+	.getsockopt_iter = smc_getsockopt,
 	.sendmsg	= smc_sendmsg,
 	.recvmsg	= smc_recvmsg,
 	.mmap		= sock_no_mmap,

-- 
2.53.0-Meta

Re: [PATCH net-next 1/2] smc: convert to getsockopt_iter

[Breno Leitao]

On Fri, Jun 05, 2026 at 05:13:25AM -0700, Breno Leitao wrote:
> Convert SMC 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()
> - Add linux/uio.h for copy_to_iter()
> 
> SMC is a proxy socket: only the SOL_SMC level is handled locally, while
> all other levels are forwarded to the underlying CLC (TCP) socket. That
> socket's getsockopt() still operates on __user buffers, so the
> pass-through is limited to user-backed iters: optval is reconstructed
> from iter_out, the original optlen pointer (preserved in sockopt_t) is
> forwarded, and the length reported by the clcsock is mirrored back into
> opt->optlen so the core writes the correct value to userspace.
> 
> Signed-off-by: Breno Leitao <leitao@debian.org>

Damn, this is not building. let me send a fixed version (v2).

--
pw-bot: cr

[PATCH net-next 2/2] selftests: net: add SMC getsockopt_iter conversion test

[Breno Leitao]

Add a kselftest that exercises the SMC getsockopt() paths converted to
the getsockopt_iter() / sockopt_t callback:

- SOL_SMC options (SMC_LIMIT_HS), handled directly by smc_getsockopt(),
  which returns the int value through copy_to_iter() and reports the
  written length in opt->optlen.

- The CLC pass-through (e.g. SOL_TCP), where smc_getsockopt() forwards to
  the underlying TCP socket: optval is reconstructed from iter_out, the
  optlen pointer is forwarded, and the clamped length is mirrored back
  through opt->optlen. The oversized-buffer case (input optlen differs
  from output) specifically guards against a missing writeback sync.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
 tools/testing/selftests/net/Makefile         |   1 +
 tools/testing/selftests/net/getsockopt_smc.c | 175 +++++++++++++++++++++++++++
 2 files changed, 176 insertions(+)

diff --git a/tools/testing/selftests/net/Makefile b/tools/testing/selftests/net/Makefile
index 5ca6c557fc3f..5b50f718dbde 100644
--- a/tools/testing/selftests/net/Makefile
+++ b/tools/testing/selftests/net/Makefile
@@ -177,6 +177,7 @@ TEST_GEN_PROGS := \
 	bind_wildcard \
 	epoll_busy_poll \
 	getsockopt_iter \
+	getsockopt_smc \
 	icmp_rfc4884 \
 	ipv6_fragmentation \
 	proc_net_pktgen \
diff --git a/tools/testing/selftests/net/getsockopt_smc.c b/tools/testing/selftests/net/getsockopt_smc.c
new file mode 100644
index 000000000000..239deefb3187
--- /dev/null
+++ b/tools/testing/selftests/net/getsockopt_smc.c
@@ -0,0 +1,175 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Exercise the SMC getsockopt() paths that were converted to the
+ * getsockopt_iter() / sockopt_t callback.
+ *
+ * Two distinct paths are covered:
+ *
+ *   - SOL_SMC options (SMC_LIMIT_HS) are handled directly by
+ *     smc_getsockopt(), which returns the int value through copy_to_iter()
+ *     and reports the written length in opt->optlen.
+ *
+ *   - Other levels (e.g. SOL_TCP) are forwarded to the underlying CLC (TCP)
+ *     socket, whose getsockopt() still operates on __user buffers. The
+ *     converted smc_getsockopt() reconstructs the userspace optval from
+ *     iter_out, forwards the original optlen pointer, and mirrors the length
+ *     the clcsock reported back into opt->optlen so the core writes the right
+ *     value to userspace.
+ *
+ * The kernel-buffer (kvec) path of the CLC pass-through returns -EOPNOTSUPP
+ * and is not reachable from a userspace getsockopt(), so it is not tested
+ * here.
+ *
+ * Author: Breno Leitao <leitao@debian.org>
+ */
+#include <errno.h>
+#include <stdint.h>
+#include <string.h>
+#include <unistd.h>
+#include <netinet/in.h>
+#include <netinet/tcp.h>
+#include <sys/socket.h>
+
+#include "kselftest_harness.h"
+
+#ifndef AF_SMC
+#define AF_SMC 43
+#endif
+#ifndef SMCPROTO_SMC
+#define SMCPROTO_SMC 0
+#endif
+#ifndef SOL_SMC
+#define SOL_SMC 286
+#endif
+#ifndef SMC_LIMIT_HS
+#define SMC_LIMIT_HS 1
+#endif
+
+FIXTURE(smc) {
+	int fd;
+};
+
+FIXTURE_SETUP(smc)
+{
+	self->fd = socket(AF_SMC, SOCK_STREAM, SMCPROTO_SMC);
+	if (self->fd < 0)
+		SKIP(return, "AF_SMC unavailable (errno %d) - load the smc module",
+		     errno);
+}
+
+FIXTURE_TEARDOWN(smc)
+{
+	if (self->fd >= 0)
+		close(self->fd);
+}
+
+/* ---------- SOL_SMC: handled directly by smc_getsockopt() ---------- */
+
+/* SMC_LIMIT_HS is reported back as a 4-byte int via copy_to_iter(). */
+TEST_F(smc, limit_hs_default)
+{
+	socklen_t optlen = sizeof(int);
+	int val = 0xdeadbeef;
+
+	ASSERT_EQ(0, getsockopt(self->fd, SOL_SMC, SMC_LIMIT_HS, &val, &optlen));
+	EXPECT_EQ(sizeof(int), optlen);
+	EXPECT_TRUE(val == 0 || val == 1);
+}
+
+/* A value set via setsockopt() must be readable back unchanged. */
+TEST_F(smc, limit_hs_set_get)
+{
+	socklen_t optlen = sizeof(int);
+	int val = 1;
+
+	ASSERT_EQ(0, setsockopt(self->fd, SOL_SMC, SMC_LIMIT_HS, &val, optlen));
+
+	val = -1;
+	ASSERT_EQ(0, getsockopt(self->fd, SOL_SMC, SMC_LIMIT_HS, &val, &optlen));
+	EXPECT_EQ(sizeof(int), optlen);
+	EXPECT_EQ(1, val);
+}
+
+/* setsockopt() stores !!val, so a non-1 truthy value reads back as 1. */
+TEST_F(smc, limit_hs_set_get_clear)
+{
+	socklen_t optlen = sizeof(int);
+	int val = 0;
+
+	ASSERT_EQ(0, setsockopt(self->fd, SOL_SMC, SMC_LIMIT_HS, &val, optlen));
+
+	val = -1;
+	ASSERT_EQ(0, getsockopt(self->fd, SOL_SMC, SMC_LIMIT_HS, &val, &optlen));
+	EXPECT_EQ(sizeof(int), optlen);
+	EXPECT_EQ(0, val);
+}
+
+/* An oversized buffer is clamped: optlen is reported back as sizeof(int). */
+TEST_F(smc, limit_hs_oversize_clamped)
+{
+	socklen_t optlen;
+	char buf[16] = {};
+
+	optlen = sizeof(buf);
+	ASSERT_EQ(0, getsockopt(self->fd, SOL_SMC, SMC_LIMIT_HS, buf, &optlen));
+	EXPECT_EQ(sizeof(int), optlen);
+}
+
+/* An unknown SOL_SMC option is rejected with -EOPNOTSUPP. */
+TEST_F(smc, bad_optname)
+{
+	socklen_t optlen = sizeof(int);
+	int val;
+
+	ASSERT_EQ(-1, getsockopt(self->fd, SOL_SMC, 0x7fff, &val, &optlen));
+	EXPECT_EQ(EOPNOTSUPP, errno);
+}
+
+/* ---------- CLC pass-through: forwarded to the underlying TCP socket ------ */
+
+/* A TCP option set on the SMC socket is applied to the CLC socket and must be
+ * readable back through the pass-through, exercising optval reconstruction.
+ */
+TEST_F(smc, clc_tcp_nodelay_set_get)
+{
+	socklen_t optlen = sizeof(int);
+	int val = 1;
+
+	ASSERT_EQ(0, setsockopt(self->fd, IPPROTO_TCP, TCP_NODELAY,
+				&val, optlen));
+
+	val = -1;
+	ASSERT_EQ(0, getsockopt(self->fd, IPPROTO_TCP, TCP_NODELAY,
+				&val, &optlen));
+	EXPECT_EQ(sizeof(int), optlen);
+	EXPECT_EQ(1, val);
+}
+
+/* With an oversized buffer the clcsock clamps the reported length to
+ * sizeof(int). That length is produced by the clcsock writing the user optlen
+ * pointer, and must be mirrored back through opt->optlen; since the input
+ * optlen (16) differs from the output (4), this fails if the writeback sync
+ * in smc_getsockopt() is missing.
+ */
+TEST_F(smc, clc_tcp_nodelay_oversize_clamped)
+{
+	socklen_t optlen;
+	char buf[16] = {};
+
+	optlen = sizeof(buf);
+	ASSERT_EQ(0, getsockopt(self->fd, IPPROTO_TCP, TCP_NODELAY,
+				buf, &optlen));
+	EXPECT_EQ(sizeof(int), optlen);
+}
+
+/* An error from the clcsock (unknown TCP option) is propagated unchanged. */
+TEST_F(smc, clc_bad_optname)
+{
+	socklen_t optlen = sizeof(int);
+	int val;
+
+	ASSERT_EQ(-1, getsockopt(self->fd, IPPROTO_TCP, 0x7fff, &val, &optlen));
+	EXPECT_EQ(ENOPROTOOPT, errno);
+}
+
+TEST_HARNESS_MAIN

-- 
2.53.0-Meta