diff mbox series

tools/nolibc: add support for openat(2)

Message ID 20250302202528.4169024-1-louis@kragniz.eu (mailing list archive)
State New
Headers show
Series tools/nolibc: add support for openat(2) | expand

Commit Message

Louis Taylor March 2, 2025, 8:25 p.m. UTC 
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>
---
 tools/include/nolibc/sys.h                   | 29 ++++++++++++++++++++
 tools/testing/selftests/nolibc/nolibc-test.c | 22 +++++++++++++++
 2 files changed, 51 insertions(+)

Comments

Thomas Weißschuh March 2, 2025, 10:24 p.m. UTC | #1 
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 :-)

> 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.

> +}
> +
> +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?

> +		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.

> +{
> +	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?

> +		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
>
Louis Taylor March 3, 2025, 8:49 a.m. UTC | #2 
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
> >
Louis Taylor March 3, 2025, 9:20 a.m. UTC | #3 
On Mon Mar 3, 2025 at 8:49 AM GMT, Louis Taylor wrote:
> > > +}
> > > +
> > > +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.

Actually, maybe this openat function could just entirely drop the
varargs since compatibility is less of an issue, effectively going back
to the interface before a7604ba149e7 (tools/nolibc/sys: make open() take
a vararg on the 3rd argument, 2022-02-07) rather than copying the
current state.
diff mbox series

Patch

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;