[PATCH v3] fstat: add test and documentation for an edge case.

[Matteo Croce]

Il giorno lun 23 giu 2025 alle ore 15:16 Adhemerval Zanella Netto
<adhemerval.zanella@linaro.org> ha scritto:
>
>
>
> On 14/06/25 08:25, Matteo Croce wrote:
> > From: Matteo Croce <teknoraver@meta.com>
> >
> > The fstatat behaviour when the target is a dangling symlink is different
> > if flags contains AT_SYMLINK_NOFOLLOW or not.
> > Add a test for this and document it.
> > ---
> >  io/tst-stat.c       | 16 +++++++++++++++-
> >  manual/filesys.texi |  5 +++--
> >  2 files changed, 18 insertions(+), 3 deletions(-)
> >
> > diff --git a/io/tst-stat.c b/io/tst-stat.c
> > index 61bdbfb638..56c7bbb186 100644
> > --- a/io/tst-stat.c
> > +++ b/io/tst-stat.c
> > @@ -62,12 +62,22 @@ fstatat_check (int fd, const char *path, struct stat *st)
> >    TEST_COMPARE (fstatat (fd, path, st, 0), 0);
> >  }
> >
> > +static void
> > +fstatat_link (const char *path, struct stat *st)
> > +{
> > +  TEST_COMPARE (fstatat (AT_FDCWD, path, st, 0), -1);
> > +  TEST_COMPARE (errno, ENOENT);
> > +
> > +  TEST_COMPARE (fstatat (AT_FDCWD, path, st, AT_SYMLINK_NOFOLLOW), 0);
>
> Maybe also add a check if the result is the one expected?
>

What do you mean by result, the struct stat content?

> The rest look ok to me, thanks for working on this.
>

Regards,

> > +}
> > +
> >  typedef void (*test_t)(int, const char *path, struct stat *);
> >
> >  static int
> >  do_test (void)
> >  {
> >    char *path;
> > +  const char *linkame = "tst-fstat.linkname";
> >    int fd = create_temp_file ("tst-fstat.", &path);
> >    TEST_VERIFY_EXIT (fd >= 0);
> >    support_write_file_string (path, "abc");
> > @@ -81,13 +91,13 @@ do_test (void)
> >      printf ("warning: timestamp with nanoseconds not supported\n");
> >
> >    struct statx stx;
> > +  struct stat st;
> >    TEST_COMPARE (statx (fd, path, 0, STATX_BASIC_STATS, &stx), 0);
> >
> >    test_t tests[] = { stat_check, lstat_check, fstat_check, fstatat_check };
> >
> >    for (int i = 0; i < array_length (tests); i++)
> >      {
> > -      struct stat st;
> >        tests[i](fd, path, &st);
> >
> >        TEST_COMPARE (stx.stx_dev_major, major (st.st_dev));
> > @@ -111,6 +121,10 @@ do_test (void)
> >       }
> >      }
> >
> > +  symlink ("tst-fstat.target", linkame);
> > +  add_temp_file (linkame);
> > +  fstatat_link (linkame, &st);
> > +
> >    return 0;
> >  }
> >
> > diff --git a/manual/filesys.texi b/manual/filesys.texi
> > index d0ced84bf6..4406201dab 100644
> > --- a/manual/filesys.texi
> > +++ b/manual/filesys.texi
> > @@ -2397,8 +2397,9 @@ The descriptor @var{filedes} is not associated with a directory, and
> >  @var{filename} is a relative file name.
> >
> >  @item ENOENT
> > -The file named by @var{filename} does not exist, or @var{filename} is an
> > -empty string and @var{flags} does not contain @code{AT_EMPTY_PATH}.
> > +The file named by @var{filename} does not exist, it's a dangling symbolic link
> > +and @var{flags} does not contain @code{AT_SYMLINK_NOFOLLOW}, or @var{filename}
> > +is an empty string and @var{flags} does not contain @code{AT_EMPTY_PATH}.
> >  @end table
> >
> >  When the sources are compiled with @code{_FILE_OFFSET_BITS == 64} this
>


-- 
Matteo Croce

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