selftests/pidfd: add pidfs file handle selftests

Add selftests for pidfs file handles.

Link: https://lore.kernel.org/r/20241202-imstande-einsicht-d78753e1c632@brauner
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: brauner

tools/testing/selftests/pidfd/.gitignore

@@ -6,3 +6,4 @@ pidfd_wait
 pidfd_fdinfo_test
 pidfd_getfd_test
 pidfd_setns_test
+pidfd_file_handle_test

tools/testing/selftests/pidfd/Makefile

@@ -2,7 +2,8 @@
 CFLAGS += -g $(KHDR_INCLUDES) -pthread -Wall
 
 TEST_GEN_PROGS := pidfd_test pidfd_fdinfo_test pidfd_open_test \
-	pidfd_poll_test pidfd_wait pidfd_getfd_test pidfd_setns_test
+	pidfd_poll_test pidfd_wait pidfd_getfd_test pidfd_setns_test \
+	pidfd_file_handle_test
 
 include ../lib.mk
 

tools/testing/selftests/pidfd/pidfd.h

@@ -17,6 +17,7 @@
 #include <sys/wait.h>
 
 #include "../kselftest.h"
+#include "../clone3/clone3_selftests.h"
 
 #ifndef P_PIDFD
 #define P_PIDFD 3
@@ -68,6 +69,11 @@
 #define PIDFD_SKIP 3
 #define PIDFD_XFAIL 4
 
+static inline int sys_waitid(int which, pid_t pid, siginfo_t *info, int options)
+{
+	return syscall(__NR_waitid, which, pid, info, options, NULL);
+}
+
 static inline int wait_for_pid(pid_t pid)
 {
 	int status, ret;
@@ -114,4 +120,37 @@ static inline int sys_memfd_create(const char *name, unsigned int flags)
 	return syscall(__NR_memfd_create, name, flags);
 }
 
+static inline pid_t create_child(int *pidfd, unsigned flags)
+{
+	struct __clone_args args = {
+		.flags		= CLONE_PIDFD | flags,
+		.exit_signal	= SIGCHLD,
+		.pidfd		= ptr_to_u64(pidfd),
+	};
+
+	return sys_clone3(&args, sizeof(struct __clone_args));
+}
+
+static inline ssize_t read_nointr(int fd, void *buf, size_t count)
+{
+	ssize_t ret;
+
+	do {
+		ret = read(fd, buf, count);
+	} while (ret < 0 && errno == EINTR);
+
+	return ret;
+}
+
+static inline ssize_t write_nointr(int fd, const void *buf, size_t count)
+{
+	ssize_t ret;
+
+	do {
+		ret = write(fd, buf, count);
+	} while (ret < 0 && errno == EINTR);
+
+	return ret;
+}
+
 #endif /* __PIDFD_H */