linux-kernel - Re: [PATCH v2 1/5] tools/nolibc: add support for openat(2)

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Message-Id: <D89EB2A6K6H8.SDEMLB4O6NMR@kragniz.eu>
Date: Thu, 06 Mar 2025 18:30:19 +0000
From: "Louis Taylor" <louis@...gniz.eu>
To: Thomas Weißschuh <linux@...ssschuh.net>
Cc: "Willy Tarreau" <w@....eu>, "Shuah Khan" <shuah@...nel.org>,
 <linux-kernel@...r.kernel.org>, <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH v2 1/5] tools/nolibc: add support for openat(2)

On Thu Mar 6, 2025 at 5:10 PM GMT, Thomas Weißschuh wrote:
> On 2025-03-04 07:58:15+0000, Louis Taylor wrote:
> > openat is useful to avoid needing to construct relative paths, so expose
> > a wrapper for using it directly.
> > 
> > Signed-off-by: Louis Taylor <louis@...gniz.eu>
>
> Looks good. I have some tiny nitpicks inline,
> but if you prefer I can also pick it up as-is.
>
> Acked-by: Thomas Weißschuh <linux@...ssschuh.net>

No problem, I'll send another version.

> > ---
> >  tools/include/nolibc/sys.h                   | 25 ++++++++++++++++++++
> >  tools/testing/selftests/nolibc/nolibc-test.c | 21 ++++++++++++++++
> >  2 files changed, 46 insertions(+)
> > 
> > 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]);
> > diff --git a/tools/testing/selftests/nolibc/nolibc-test.c b/tools/testing/selftests/nolibc/nolibc-test.c
> > index 79c3e6a845f3..2a1629938dd6 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;
> >  }
> >  
> > +static int test_openat(void)
>
> As mentioned in my other mail, this in fact should not be static.
> Sorry for the back and forth.

Ah that's fine, I'll drop the other patch as well.

> > +{
> > +	int dev;
> > +	int null;
>
> Can be on a single line.
>
> > +
> > +	dev = openat(AT_FDCWD, "/dev", O_DIRECTORY);
> > +	if (dev < 0)
> > +		return -1;
> > +
> > +	null = openat(dev, "null", 0);
>
> As per the standard:
>
> 	The argument flags must include one of the following access modes:
> 	O_RDONLY, O_WRONLY, or O_RDWR.
>
> The other tests don't do it either and on Linux it doesn't matter
> because O_RDONLY == 0. But if we are here anyways.
>
> close(dev) could be moved here for some saved lines.
>
> > +	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 +1136,7 @@ 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_SYSNE(1, test_openat(), -1); break;
>
> EXPECT_SYSZR() should work here.
>
> >  		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
> >