# Re: \[PATCH 08/10\] selftests/net: SO\_PEERPIDFD\_THREAD

- From: Alexander Mikhalitsyn \<hidden\>
- Date: 2026-09-07 10:51:54 
- List: netdev
- Page: https://ratatoskr.run/netdev/2026/09/17524503
- Thread: https://ratatoskr.run/netdev/2026/08/17483571/t.md

```text
Am Mo., 31. Aug. 2026 um 13:21 Uhr schrieb Christian Brauner
[ref]:
>
> Add tests for SO_PEERPIDFD_THREAD.
>
> Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

LGTM

Reviewed-by: Alexander Mikhalitsyn <redacted>

> ---
>  tools/testing/selftests/net/af_unix/scm_pidfd.c | 97 +++++++++++++++++++++++++
>  1 file changed, 97 insertions(+)
>
> diff --git a/tools/testing/selftests/net/af_unix/scm_pidfd.c b/tools/testing/selftests/net/af_unix/scm_pidfd.c
> index 019c48e1cdcd..bbbd5e7b4fa7 100644
> --- a/tools/testing/selftests/net/af_unix/scm_pidfd.c
> +++ b/tools/testing/selftests/net/af_unix/scm_pidfd.c
> @@ -32,6 +32,10 @@
>  #define SO_PASSPIDFD_THREAD 86
>  #endif
>
> +#ifndef SO_PEERPIDFD_THREAD
> +#define SO_PEERPIDFD_THREAD 87
> +#endif
> +
>  #define CHILD_EXIT_CODE_OK 123
>
>  static void child_die()
> @@ -822,4 +826,97 @@ TEST(scm_pidfd_thread_creds)
>         EXPECT_EQ(ids.pid, info.tgid);
>  }
>
> +static void *peer_connect_thread(void *arg)
> +{
> +       struct sock_addr *sa = arg;
> +       struct thread_ids ids = {
> +               .pid = getpid(),
> +               .tid = gettid(),
> +       };
> +       int fd;
> +       char sync;
> +
> +       fd = socket(AF_UNIX, SOCK_STREAM, 0);
> +       if (fd < 0)
> +               return (void *)1;
> +
> +       if (connect(fd, (struct sockaddr *)&sa->listen_addr, sa->addrlen))
> +               return (void *)1;
> +
> +       if (send(fd, &ids, sizeof(ids), 0) != sizeof(ids))
> +               return (void *)1;
> +
> +       /* stay alive until the server has looked at our pidfd */
> +       if (read(fd, &sync, 1) != 1)
> +               return (void *)1;
> +
> +       close(fd);
> +       return NULL;
> +}
> +
> +static int peer_pidfd_info(int fd, int optname, struct pidfd_info *info)
> +{
> +       int pidfd;
> +       socklen_t len = sizeof(pidfd);
> +
> +       if (getsockopt(fd, SOL_SOCKET, optname, &pidfd, &len)) {
> +               log_err("getsockopt(SO_PEERPIDFD*)");
> +               return -1;
> +       }
> +
> +       info->mask = PIDFD_INFO_PID;
> +       if (ioctl(pidfd, PIDFD_GET_INFO, info)) {
> +               log_err("ioctl(PIDFD_GET_INFO)");
> +               close(pidfd);
> +               return -1;
> +       }
> +
> +       close(pidfd);
> +       return 0;
> +}
> +
> +/* SO_PEERPIDFD_THREAD returns a pidfd for the peer's connecting thread. */
> +TEST(so_peerpidfd_thread)
> +{
> +       struct sock_addr sa;
> +       struct thread_ids ids;
> +       struct pidfd_info info;
> +       pthread_t thread;
> +       void *tret;
> +       int server, cfd;
> +
> +       server = socket(AF_UNIX, SOCK_STREAM, 0);
> +       ASSERT_LE(0, server);
> +
> +       fill_sockaddr(&sa, true);
> +       ASSERT_EQ(0, bind(server, (struct sockaddr *)&sa.listen_addr, sa.addrlen));
> +       ASSERT_EQ(0, listen(server, 1));
> +
> +       ASSERT_EQ(0, pthread_create(&thread, NULL, peer_connect_thread, &sa));
> +
> +       cfd = accept(server, NULL, NULL);
> +       ASSERT_LE(0, cfd);
> +
> +       ASSERT_EQ(sizeof(ids), recv(cfd, &ids, sizeof(ids), MSG_WAITALL));
> +       ASSERT_NE(ids.pid, ids.tid);
> +
> +       /* SO_PEERPIDFD refers to the peer's thread-group. */
> +       ASSERT_EQ(0, peer_pidfd_info(cfd, SO_PEERPIDFD, &info));
> +       EXPECT_EQ(ids.pid, info.pid);
> +       EXPECT_EQ(ids.pid, info.tgid);
> +
> +       /* SO_PEERPIDFD_THREAD refers to the connecting thread. */
> +       ASSERT_EQ(0, peer_pidfd_info(cfd, SO_PEERPIDFD_THREAD, &info));
> +       EXPECT_EQ(ids.tid, info.pid);
> +       EXPECT_EQ(ids.pid, info.tgid);
> +
> +       /* release the connecting thread */
> +       ASSERT_EQ(1, write(cfd, "x", 1));
> +       ASSERT_EQ(0, pthread_join(thread, &tret));
> +       ASSERT_EQ(NULL, tret);
> +
> +       close(cfd);
> +       close(server);
> +}
> +
>  TEST_HARNESS_MAIN
>
> --
> 2.53.0
>
```