glob vs '*/' vs GLOB_ONLYDIR vs xfs

[DJ Delorie via Libc-alpha <libc-alpha@sourceware.org>]

in posix/glob.c we have this comment:

  /* POSIX requires all slashes to be matched.  This means that with
     a trailing slash we must match only directories.  */
  if (pattern[0] && pattern[strlen (pattern) - 1] == '/')
    flags |= GLOB_ONLYDIR;

In "man glob" we see:

       GLOB_ONLYDIR
              This is a _hint_ to glob() that the caller is interested
              only in directories that match the pattern.

So, for starters, we're relying on "a hint" to implement a "must".

If you're running glob on an XFS filesystem, readdir() doesn't
reliably fill in d_type, and the "hint" fails:

#include <stdlib.h>
#include <glob.h>

main(int argc, char **argv) {
  glob_t g;
  int i;

  glob (argv[1], 0, NULL, &g);
  for (i=0; i<g.gl_pathc; i++)
    printf("glob[%d] = `%s'\n", i, g.gl_pathv[i]);

  return 0;
}

$ ls -l
total 4
-rw-r--r-- 1 dj games 56 Aug  4 22:45 Makefile
drwxr-xr-x 2 dj games 10 Aug  4 22:44 hellod/
-rw-r--r-- 1 dj games  0 Aug  4 22:44 hellof

$ pwd
/greed/dj/gnu/make-4.3/dj

$ ~/src/globtest 'hello*/'
glob[0] = `hellod/'
glob[1] = `hellof'

$ ~/src/globtest 'hello*'
glob[0] = `hellod'
glob[1] = `hellof'


If we instead run this on a different filesystem type (tmpfs in this
case), it works as I expect:

$ ls -l
total 4
-rw-r--r-- 1 dj games 56 Aug  4 22:45 Makefile
drwxr-xr-x 2 dj games  6 Aug  4 22:44 hellod/
-rw-r--r-- 1 dj games  0 Aug  4 22:44 hellof

$ pwd
/tmp/make-4.3/dj

$ ~/src/globtest 'hello*/'
glob[0] = `hellod/'

$ ~/src/globtest 'hello*'
glob[0] = `hellod'
glob[1] = `hellof'


Is this a bug in glob(), or a misunderstanding of its documentation?