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>

diff --git a/tools/include/nolibc/sys.h b/tools/include/nolibc/sys.h
index 8f44c33b121300e80b41c971019484007d050b17..3cd938f9abdabd64dbd9535902db84c13e14eb7b 100644 (file)
--- 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 79c3e6a845f31443c768de4c1f106e5ae014358b..e8faddcecf9d7b544f8699d317d3d765dccf3db3 100644 (file)
--- a/tools/testing/selftests/nolibc/nolibc-test.c
+++ b/tools/testing/selftests/nolibc/nolibc-test.c
@@ -1028,6 +1028,22 @@ int test_rlimit(void)
        return 0;
 }
 
+int test_openat(void)
+{
+       int dev, null;
+
+       dev = openat(AT_FDCWD, "/dev", O_DIRECTORY);
+       if (dev < 0)
+               return -1;
+
+       null = openat(dev, "null", O_RDONLY);
+       close(dev);
+       if (null < 0)
+               return -1;
+
+       close(null);
+       return 0;
+}
 
 /* Run syscall tests between IDs <min> and <max>.
  * Return 0 on success, non-zero on failure.
@@ -1116,6 +1132,7 @@ 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_SYSZR(1, test_openat()); 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;