linux-kernel - [PATCH v2 1/5] tools/nolibc: add support for openat(2)

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Message-ID: <20250304075846.66563-1-louis@kragniz.eu>
Date: Tue,  4 Mar 2025 07:58:15 +0000
From: Louis Taylor <louis@...gniz.eu>
To: Willy Tarreau <w@....eu>,
	Thomas Weißschuh <linux@...ssschuh.net>,
	Shuah Khan <shuah@...nel.org>
Cc: Louis Taylor <louis@...gniz.eu>,
	linux-kernel@...r.kernel.org,
	linux-kselftest@...r.kernel.org
Subject: [PATCH v2 1/5] tools/nolibc: add support for openat(2)

openat is useful to avoid needing to construct relative paths, so expose
a wrapper for using it directly.

Signed-off-by: Louis Taylor <louis@...gniz.eu>
---
 tools/include/nolibc/sys.h                   | 25 ++++++++++++++++++++
 tools/testing/selftests/nolibc/nolibc-test.c | 21 ++++++++++++++++
 2 files changed, 46 insertions(+)

diff --git a/tools/include/nolibc/sys.h b/tools/include/nolibc/sys.h
index 8f44c33b1213..3cd938f9abda 100644
--- a/tools/include/nolibc/sys.h
+++ b/tools/include/nolibc/sys.h
@@ -765,6 +765,31 @@ int mount(const char *src, const char *tgt,
 	return __sysret(sys_mount(src, tgt, fst, flags, data));
 }
 
+/*
+ * int openat(int dirfd, const char *path, int flags[, mode_t mode]);
+ */
+
+static __attribute__((unused))
+int sys_openat(int dirfd, const char *path, int flags, mode_t mode)
+{
+	return my_syscall4(__NR_openat, dirfd, path, flags, mode);
+}
+
+static __attribute__((unused))
+int openat(int dirfd, const char *path, int flags, ...)
+{
+	mode_t mode = 0;
+
+	if (flags & O_CREAT) {
+		va_list args;
+
+		va_start(args, flags);
+		mode = va_arg(args, mode_t);
+		va_end(args);
+	}
+
+	return __sysret(sys_openat(dirfd, path, flags, mode));
+}
 
 /*
  * int open(const char *path, int flags[, mode_t mode]);
diff --git a/tools/testing/selftests/nolibc/nolibc-test.c b/tools/testing/selftests/nolibc/nolibc-test.c
index 79c3e6a845f3..2a1629938dd6 100644
--- a/tools/testing/selftests/nolibc/nolibc-test.c
+++ b/tools/testing/selftests/nolibc/nolibc-test.c
@@ -1028,6 +1028,26 @@ int test_rlimit(void)
 	return 0;
 }
 
+static int test_openat(void)
+{
+	int dev;
+	int null;
+
+	dev = openat(AT_FDCWD, "/dev", O_DIRECTORY);
+	if (dev < 0)
+		return -1;
+
+	null = openat(dev, "null", 0);
+	if (null < 0) {
+		close(dev);
+		return -1;
+	}
+
+	close(dev);
+	close(null);
+
+	return 0;
+}
 
 /* Run syscall tests between IDs <min> and <max>.
  * Return 0 on success, non-zero on failure.
@@ -1116,6 +1136,7 @@ int run_syscall(int min, int max)
 		CASE_TEST(mmap_munmap_good);  EXPECT_SYSZR(1, test_mmap_munmap()); break;
 		CASE_TEST(open_tty);          EXPECT_SYSNE(1, tmp = open("/dev/null", 0), -1); if (tmp != -1) close(tmp); break;
 		CASE_TEST(open_blah);         EXPECT_SYSER(1, tmp = open("/proc/self/blah", 0), -1, ENOENT); if (tmp != -1) close(tmp); break;
+		CASE_TEST(openat_dir);        EXPECT_SYSNE(1, test_openat(), -1); break;
 		CASE_TEST(pipe);              EXPECT_SYSZR(1, test_pipe()); break;
 		CASE_TEST(poll_null);         EXPECT_SYSZR(1, poll(NULL, 0, 0)); break;
 		CASE_TEST(poll_stdout);       EXPECT_SYSNE(1, ({ struct pollfd fds = { 1, POLLOUT, 0}; poll(&fds, 1, 0); }), -1); break;
-- 
2.45.2