selftests/nolibc: condition some tests on /proc existence

If /proc is not available (program run inside a chroot or without
sufficient permissions), it's better to disable the associated tests.
Some will be preserved like the ones which check for a failure to
create some entries there since they're still supposed to fail.
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

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

@@ -413,11 +413,15 @@ int test_getdents64(const char *dir)
 int run_syscall(int min, int max)
 {
 	struct stat stat_buf;
+	int proc;
 	int test;
 	int tmp;
 	int ret = 0;
 	void *p1, *p2;
 
+	/* <proc> indicates whether or not /proc is mounted */
+	proc = stat("/proc", &stat_buf) == 0;
+
 	for (test = min; test >= 0 && test <= max; test++) {
 		int llen = 0; // line length
 
@@ -438,12 +442,12 @@ int run_syscall(int min, int max)
 		CASE_TEST(chdir_root);        EXPECT_SYSZR(1, chdir("/")); break;
 		CASE_TEST(chdir_dot);         EXPECT_SYSZR(1, chdir(".")); break;
 		CASE_TEST(chdir_blah);        EXPECT_SYSER(1, chdir("/blah"), -1, ENOENT); break;
-		CASE_TEST(chmod_net);         EXPECT_SYSZR(1, chmod("/proc/self/net", 0555)); break;
-		CASE_TEST(chmod_self);        EXPECT_SYSER(1, chmod("/proc/self", 0555), -1, EPERM); break;
-		CASE_TEST(chown_self);        EXPECT_SYSER(1, chown("/proc/self", 0, 0), -1, EPERM); break;
+		CASE_TEST(chmod_net);         EXPECT_SYSZR(proc, chmod("/proc/self/net", 0555)); break;
+		CASE_TEST(chmod_self);        EXPECT_SYSER(proc, chmod("/proc/self", 0555), -1, EPERM); break;
+		CASE_TEST(chown_self);        EXPECT_SYSER(proc, chown("/proc/self", 0, 0), -1, EPERM); break;
 		CASE_TEST(chroot_root);       EXPECT_SYSZR(1, chroot("/")); break;
 		CASE_TEST(chroot_blah);       EXPECT_SYSER(1, chroot("/proc/self/blah"), -1, ENOENT); break;
-		CASE_TEST(chroot_exe);        EXPECT_SYSER(1, chroot("/proc/self/exe"), -1, ENOTDIR); break;
+		CASE_TEST(chroot_exe);        EXPECT_SYSER(proc, chroot("/proc/self/exe"), -1, ENOTDIR); break;
 		CASE_TEST(close_m1);          EXPECT_SYSER(1, close(-1), -1, EBADF); break;
 		CASE_TEST(close_dup);         EXPECT_SYSZR(1, close(dup(0))); break;
 		CASE_TEST(dup_0);             tmp = dup(0);  EXPECT_SYSNE(1, tmp, -1); close(tmp); break;
@@ -464,7 +468,7 @@ int run_syscall(int min, int max)
 		CASE_TEST(link_root1);        EXPECT_SYSER(1, link("/", "/"), -1, EEXIST); break;
 		CASE_TEST(link_blah);         EXPECT_SYSER(1, link("/proc/self/blah", "/blah"), -1, ENOENT); break;
 		CASE_TEST(link_dir);          EXPECT_SYSER(1, link("/", "/blah"), -1, EPERM); break;
-		CASE_TEST(link_cross);        EXPECT_SYSER(1, link("/proc/self/net", "/blah"), -1, EXDEV); break;
+		CASE_TEST(link_cross);        EXPECT_SYSER(proc, link("/proc/self/net", "/blah"), -1, EXDEV); break;
 		CASE_TEST(lseek_m1);          EXPECT_SYSER(1, lseek(-1, 0, SEEK_SET), -1, EBADF); break;
 		CASE_TEST(lseek_0);           EXPECT_SYSER(1, lseek(0, 0, SEEK_SET), -1, ESPIPE); break;
 		CASE_TEST(mkdir_root);        EXPECT_SYSER(1, mkdir("/", 0755), -1, EEXIST); break;