[PATCH] tools/nolibc: add support for openat(2)

[Louis Taylor]

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

Signed-off-by: Louis Taylor <lo...@kragniz.eu>
---
 tools/include/nolibc/sys.h                   | 29 ++++++++++++++++++++
 tools/testing/selftests/nolibc/nolibc-test.c | 22 +++++++++++++++
 2 files changed, 51 insertions(+)

diff --git a/tools/include/nolibc/sys.h b/tools/include/nolibc/sys.h
index 8f44c33b1213..e5ff34df4aee 100644
--- a/tools/include/nolibc/sys.h
+++ b/tools/include/nolibc/sys.h
@@ -765,6 +765,35 @@ 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)
+{
+#ifdef __NR_openat
+       return my_syscall4(__NR_openat, dirfd, path, flags, mode);
+#else
+       return __nolibc_enosys(__func__, dirfd, path, flags, mode);
+#endif
+}
+
+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, int);
+               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..97ded6c76f99 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;
 }
 
+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 +1136,8 @@ 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_fdcwd);      EXPECT_SYSNE(1, tmp = 
openat(AT_FDCWD, "/dev/null", 0), -1); 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