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@kragniz.eu>
Link: https://lore.kernel.org/r/20250306184147.208723-1-louis@kragniz.eu
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>

1 files changed, 25 insertions, 0 deletions

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]);