tools/nolibc: add namespace functionality

This is used in various selftests and will be handy when integrating
those with nolibc.

Not all configurations support namespaces, so skip the tests where
necessary. Also if the tests are running without privileges.
Enable the namespace configuration for those architectures where it is not
enabled by default.

Signed-off-by: Thomas Weißschuh <[e-mail]>
Acked-by: Willy Tarreau <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Thomas Weißschuh <[e-mail]>

tools/include/nolibc/Makefile

···
 		math.h \
 		nolibc.h \
 		poll.h \
+		sched.h \
 		signal.h \
 		stackprotector.h \
 		std.h \

tools/include/nolibc/nolibc.h

···
 #include "sys/wait.h"
 #include "ctype.h"
 #include "elf.h"
+#include "sched.h"
 #include "signal.h"
 #include "unistd.h"
 #include "stdio.h"

tools/include/nolibc/sched.h

···
+/* SPDX-License-Identifier: LGPL-2.1 OR MIT */
+/*
+ * sched function definitions for NOLIBC
+ * Copyright (C) 2025 Thomas Weißschuh <[e-mail]>
+ */
+
+/* make sure to include all global symbols */
+#include "nolibc.h"
+
+#ifndef _NOLIBC_SCHED_H
+#define _NOLIBC_SCHED_H
+
+#include "sys.h"
+
+#include <linux/sched.h>
+
+/*
+ * int setns(int fd, int nstype);
+ */
+
+static __attribute__((unused))
+int sys_setns(int fd, int nstype)
+{
+	return my_syscall2(__NR_setns, fd, nstype);
+}
+
+static __attribute__((unused))
+int setns(int fd, int nstype)
+{
+	return __sysret(sys_setns(fd, nstype));
+}
+
+
+/*
+ * int unshare(int flags);
+ */
+
+static __attribute__((unused))
+int sys_unshare(int flags)
+{
+	return my_syscall1(__NR_unshare, flags);
+}
+
+static __attribute__((unused))
+int unshare(int flags)
+{
+	return __sysret(sys_unshare(flags));
+}
+
+#endif /* _NOLIBC_SCHED_H */

tools/testing/selftests/nolibc/Makefile

···
 
 EXTRACONFIG_m68k      = -e CONFIG_BLK_DEV_INITRD
 EXTRACONFIG           = $(EXTRACONFIG_$(XARCH))
+EXTRACONFIG_arm       = -e CONFIG_NAMESPACES
+EXTRACONFIG_armthumb  = -e CONFIG_NAMESPACES
 
 # optional tests to run (default = all)
 TEST =

tools/testing/selftests/nolibc/nolibc-test.c

···
 	return 0;
 }
 
+int test_namespace(void)
+{
+	int original_ns, new_ns, ret;
+	ino_t original_ns_ino;
+	struct stat stat_buf;
+
+	original_ns = open("/proc/self/ns/uts", O_RDONLY);
+	if (original_ns == -1)
+		return -1;
+
+	ret = fstat(original_ns, &stat_buf);
+	if (ret)
+		goto out;
+
+	original_ns_ino = stat_buf.st_ino;
+
+	ret = unshare(CLONE_NEWUTS);
+	if (ret)
+		goto out;
+
+	new_ns = open("/proc/self/ns/uts", O_RDONLY);
+	if (new_ns == -1) {
+		ret = new_ns;
+		goto out;
+	}
+
+	ret = fstat(new_ns, &stat_buf);
+	close(new_ns);
+	if (ret)
+		goto out;
+
+	if (stat_buf.st_ino == original_ns_ino) {
+		errno = EINVAL;
+		ret = -1;
+		goto out;
+	}
+
+	ret = setns(original_ns, CLONE_NEWUTS);
+	if (ret)
+		goto out;
+
+	new_ns = open("/proc/self/ns/uts", O_RDONLY);
+	if (new_ns == -1) {
+		ret = new_ns;
+		goto out;
+	}
+
+	ret = fstat(new_ns, &stat_buf);
+	if (ret)
+		goto out;
+
+	close(new_ns);
+
+	if (stat_buf.st_ino != original_ns_ino) {
+		errno = EINVAL;
+		ret = -1;
+		goto out;
+	}
+
+	ret = 0;
+
+out:
+	close(original_ns);
+	return ret;
+}
+
 /* Run syscall tests between IDs <min> and <max>.
  * Return 0 on success, non-zero on failure.
  */
···
 		CASE_TEST(write_zero);        EXPECT_SYSZR(1, write(1, &tmp, 0)); break;
 		CASE_TEST(syscall_noargs);    EXPECT_SYSEQ(1, syscall(__NR_getpid), getpid()); break;
 		CASE_TEST(syscall_args);      EXPECT_SYSER(1, syscall(__NR_statx, 0, NULL, 0, 0, NULL), -1, EFAULT); break;
+		CASE_TEST(namespace);         EXPECT_SYSZR(euid0 && proc, test_namespace()); break;
 		case __LINE__:
 			return ret; /* must be last */
 		/* note: do not set any defaults so as to permit holes above */