[v2,4/5] API: Add tst_clone

diff --git a/doc/test-writing-guidelines.txt b/doc/test-writing-guidelines.txt
index f3a55cf26..dd1911ceb 100644
--- a/doc/test-writing-guidelines.txt
+++ b/doc/test-writing-guidelines.txt
@@ -547,9 +547,9 @@  void tst_flush(void);
 Flush output streams, handling errors appropriately.
 
 This function is rarely needed when you have to flush the output streams
-before calling 'fork()' or 'clone()'. Note that the 'SAFE_FORK()' calls this
-function automatically. See 3.4 FILE buffers and fork() for explanation why is
-this needed.
+before calling 'fork()' or 'clone()'. Note that the 'SAFE_FORK()' and 'SAFE_CLONE()'
+calls this function automatically. See 3.4 FILE buffers and fork() for explanation
+why is this needed.
 
 2.2.3 Test temporary directory
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -732,10 +732,10 @@  This happens when 'stdout' gets redirected to a file. In this case, the
 'stdout' is not line buffered, but block buffered. Hence after a fork content
 of the buffers will be printed by the parent and each of the children.
 
-To avoid that you should use 'SAFE_FORK()'.
+To avoid that you should use 'SAFE_FORK()', 'SAFE_CLONE()' or 'tst_clone()'.
 
 IMPORTANT: You have to set the '.forks_child' flag in the test structure
-           if your testcase forks.
+           if your testcase forks or calls 'SAFE_CLONE()'.
 
 2.2.8 Doing the test in the child process
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -769,6 +769,23 @@  The 'tst_reap_children()' function makes the process wait for all of its
 children and exits with 'tst_brk(TBROK, ...)' if any of them returned
 a non zero exit code.
 
+When using 'SAFE_CLONE' or 'tst_clone', this may not work depending on
+the parameters passed to clone. The following call to 'SAFE_CLONE' is
+identical to 'fork()', so will work as expected.
+
+[source,c]
+--------------------------------------------------------------------------------
+const struct tst_clone_args args = {
+	.exit_signal = SIGCHLD,
+};
+
+SAFE_CLONE(&args);
+--------------------------------------------------------------------------------
+
+If 'exit_signal' is set to something else, then this will break
+'tst_reap_children'. It's not expected that all parameters to clone will
+work with the LTP library unless specific action is taken by the test code.
+
 .Using 'tst_res()' from binaries started by 'exec()'
 [source,c]
 -------------------------------------------------------------------------------
diff --git a/include/tst_clone.h b/include/tst_clone.h
index 88188525d..9ffdc68d1 100644
--- a/include/tst_clone.h
+++ b/include/tst_clone.h
@@ -5,6 +5,34 @@ 
 #ifndef TST_CLONE_H__
 #define TST_CLONE_H__
 
+#ifdef TST_TEST_H__
+
+/* The parts of clone3's clone_args we support */
+struct tst_clone_args {
+	uint64_t flags;
+	uint64_t exit_signal;
+};
+
+/* clone3 with fallbacks to clone when possible. Be aware that it
+ * returns -1 if clone3 fails (except ENOSYS), but -2 if clone fails.
+ *
+ * Without CLONE_VM this acts like fork so you may want to set
+ * tst_test.forks_child (safe_clone requires this).
+ *
+ * You should set exit_signal to SIGCHLD for
+ * tst_reap_children. Otherwise you must call wait with the
+ * appropriate parameters.
+ */
+pid_t tst_clone(const struct tst_clone_args *args);
+
+pid_t safe_clone(const char *file, const int lineno,
+		 const struct tst_clone_args *args);
+
+/* "Safe" version of tst_clone */
+#define SAFE_CLONE(args) safe_clone(__FILE__, __LINE__, args)
+
+#endif	/* TST_TEST_H__ */
+
 /* Functions from lib/cloner.c */
 int ltp_clone(unsigned long flags, int (*fn)(void *arg), void *arg,
 		size_t stack_size, void *stack);
diff --git a/include/tst_test.h b/include/tst_test.h
index c87251870..7dab5f761 100644
--- a/include/tst_test.h
+++ b/include/tst_test.h
@@ -29,7 +29,6 @@ 
 #include "tst_process_state.h"
 #include "tst_atomic.h"
 #include "tst_kvercmp.h"
-#include "tst_clone.h"
 #include "tst_kernel.h"
 #include "tst_minmax.h"
 #include "tst_get_bad_addr.h"
@@ -94,6 +93,7 @@  pid_t safe_fork(const char *filename, unsigned int lineno);
 #include "tst_safe_macros.h"
 #include "tst_safe_file_ops.h"
 #include "tst_safe_net.h"
+#include "tst_clone.h"
 
 /*
  * Wait for all children and exit with TBROK if
diff --git a/lib/tst_clone.c b/lib/tst_clone.c
new file mode 100644
index 000000000..07e7f0767
--- /dev/null
+++ b/lib/tst_clone.c
@@ -0,0 +1,46 @@ 
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* Copyright (c) 2021 SUSE LLC
+ * Richard Palethorpe <rpalethorpe@suse.com>
+ */
+
+#define TST_NO_DEFAULT_MAIN
+
+#include <stddef.h>
+
+#include "tst_test.h"
+#include "lapi/clone.h"
+
+pid_t tst_clone(const struct tst_clone_args *tst_args)
+{
+	struct clone_args args = {
+		.flags = tst_args->flags,
+		.exit_signal = tst_args->exit_signal,
+	};
+	int flags;
+	pid_t pid = -1;
+
+	tst_flush();
+
+	errno = ENOSYS;
+	if (__NR_clone3 != __LTP__NR_INVALID_SYSCALL)
+		pid = syscall(__NR_clone3, &args, sizeof(args));
+
+	if (pid == -1 && errno != ENOSYS)
+		return -1;
+
+	if (pid != -1)
+		return pid;
+
+	flags = args.exit_signal | args.flags;
+
+#ifdef __s390x__
+	pid = syscall(__NR_clone, NULL, flags);
+#else
+	pid = syscall(__NR_clone, flags, NULL);
+#endif
+
+	if (pid == -1)
+		return -2;
+
+	return pid;
+}
diff --git a/lib/tst_test.c b/lib/tst_test.c
index 0714f0a0e..6bbee030b 100644
--- a/lib/tst_test.c
+++ b/lib/tst_test.c
@@ -424,6 +424,31 @@  pid_t safe_fork(const char *filename, unsigned int lineno)
 	return pid;
 }
 
+pid_t safe_clone(const char *file, const int lineno,
+		 const struct tst_clone_args *args)
+{
+	pid_t pid;
+
+	if (!tst_test->forks_child)
+		tst_brk(TBROK, "test.forks_child must be set!");
+
+	pid = tst_clone(args);
+
+	switch (pid) {
+	case -1:
+		tst_brk_(file, lineno, TBROK | TERRNO, "clone3 failed");
+		break;
+	case -2:
+		tst_brk_(file, lineno, TBROK | TERRNO, "clone failed");
+		return -1;
+	}
+
+	if (!pid)
+		atexit(tst_free_all);
+
+	return pid;
+}
+
 static struct option {
 	char *optstr;
 	char *help;