On Sun Mar 2, 2025 at 10:24 PM GMT, Thomas Weißschuh wrote:

Hi Louis,

On 2025-03-02 20:25:23+0000, Louis Taylor wrote:

...

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

Can you say what you are using nolibc for? I'm curious :-)

An incredibly dumb side project which involves creating a very small static binary. So far I've also needed a few other functions (for example clock_gettime) which I've just added local wrappers for, since I'm not sure if they're in scope for nolibc. If they are, I can also send patches for those as well.

...

Signed-off-by: Louis Taylor louis@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

All architectures support openat(), so the #else could be dropped.

I agree, but I followed the existing implementation for sys_open which only uses openat if it is defined. If openat can be assumed to always exist, that other #ifdef should be dropped (which I can do in another patch).

...

+}

+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);
  

mode_t instead of int?

This implementation is yoinked directly from open() below. I have no opinions, but if it should be changed it should be changed in both functions.

...

• 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)

static.

I'll change this. Should the other test_ functions in this file also be static?

...

+{

• 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;
  

AT_FDCWD is already used in test_openat(). What additional value does the test above add?

None, I just wrote that one first before thinking about how I'd test opening something relative to an fd. I'll drop it.

...

• 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