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-rw-r--r--samples/pidfd/Makefile6
-rw-r--r--samples/pidfd/pidfd-metadata.c112
2 files changed, 118 insertions, 0 deletions
diff --git a/samples/pidfd/Makefile b/samples/pidfd/Makefile
new file mode 100644
index 000000000000..0ff97784177a
--- /dev/null
+++ b/samples/pidfd/Makefile
@@ -0,0 +1,6 @@
+# SPDX-License-Identifier: GPL-2.0
+
+hostprogs-y := pidfd-metadata
+always := $(hostprogs-y)
+HOSTCFLAGS_pidfd-metadata.o += -I$(objtree)/usr/include
+all: pidfd-metadata
diff --git a/samples/pidfd/pidfd-metadata.c b/samples/pidfd/pidfd-metadata.c
new file mode 100644
index 000000000000..640f5f757c57
--- /dev/null
+++ b/samples/pidfd/pidfd-metadata.c
@@ -0,0 +1,112 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#define _GNU_SOURCE
+#include <err.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <inttypes.h>
+#include <limits.h>
+#include <sched.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/syscall.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#ifndef CLONE_PIDFD
+#define CLONE_PIDFD 0x00001000
+#endif
+
+static int do_child(void *args)
+{
+ printf("%d\n", getpid());
+ _exit(EXIT_SUCCESS);
+}
+
+static pid_t pidfd_clone(int flags, int *pidfd)
+{
+ size_t stack_size = 1024;
+ char *stack[1024] = { 0 };
+
+#ifdef __ia64__
+ return __clone2(do_child, stack, stack_size, flags | SIGCHLD, NULL, pidfd);
+#else
+ return clone(do_child, stack + stack_size, flags | SIGCHLD, NULL, pidfd);
+#endif
+}
+
+static inline int sys_pidfd_send_signal(int pidfd, int sig, siginfo_t *info,
+ unsigned int flags)
+{
+ return syscall(__NR_pidfd_send_signal, pidfd, sig, info, flags);
+}
+
+static int pidfd_metadata_fd(pid_t pid, int pidfd)
+{
+ int procfd, ret;
+ char path[100];
+
+ snprintf(path, sizeof(path), "/proc/%d", pid);
+ procfd = open(path, O_DIRECTORY | O_RDONLY | O_CLOEXEC);
+ if (procfd < 0) {
+ warn("Failed to open %s\n", path);
+ return -1;
+ }
+
+ /*
+ * Verify that the pid has not been recycled and our /proc/<pid> handle
+ * is still valid.
+ */
+ ret = sys_pidfd_send_signal(pidfd, 0, NULL, 0);
+ if (ret < 0) {
+ switch (errno) {
+ case EPERM:
+ /* Process exists, just not allowed to signal it. */
+ break;
+ default:
+ warn("Failed to signal process\n");
+ close(procfd);
+ procfd = -1;
+ }
+ }
+
+ return procfd;
+}
+
+int main(int argc, char *argv[])
+{
+ int pidfd = 0, ret = EXIT_FAILURE;
+ char buf[4096] = { 0 };
+ pid_t pid;
+ int procfd, statusfd;
+ ssize_t bytes;
+
+ pid = pidfd_clone(CLONE_PIDFD, &pidfd);
+ if (pid < 0)
+ exit(ret);
+
+ procfd = pidfd_metadata_fd(pid, pidfd);
+ close(pidfd);
+ if (procfd < 0)
+ goto out;
+
+ statusfd = openat(procfd, "status", O_RDONLY | O_CLOEXEC);
+ close(procfd);
+ if (statusfd < 0)
+ goto out;
+
+ bytes = read(statusfd, buf, sizeof(buf));
+ if (bytes > 0)
+ bytes = write(STDOUT_FILENO, buf, bytes);
+ close(statusfd);
+ ret = EXIT_SUCCESS;
+
+out:
+ (void)wait(NULL);
+
+ exit(ret);
+}