Re: avoid mkdir/selinux failure when mknod is a shell built-in

[Jim Meyering]

Eric Blake <address@hidden> wrote:

> According to Jim Meyering on 4/16/2008 2:33 AM:
> | This test would fail not only because the built-in mknod
> | doesn't support -Z, but because it doesn't know about 'p' pipes.
> |
> |     tests: avoid mkdir/selinux failure when mknod is a shell built-in
> |     * tests/mkdir/selinux: Skip the mknod test if it's a built-in.
>
> Couldn't you try to defeat the shell builtin by using a subshell and exec
> to force the PATH lookup?  For example, on bash:
>
> $ printf --version | head -n1
> bash: printf: --: invalid option
> printf: usage: printf [-v var] format [arguments]
> $ (exec printf --version) | head -n1
> printf (GNU coreutils) 6.10

My first reaction was "great! that looks much better".
Unfortunately, the technique doesn't work with that shell:

  openbsd$ ./mknod --version|head -1
  mknod (GNU coreutils) 6.10.188-7cb24
  openbsd$ PATH=. /bin/sh -c 'mknod --version'|head -1
  /bin/sh: mknod: --: unknown option
  /bin/sh: mknod: usage: mknod [-m mode] name [b | c] major minor
  /bin/sh: mknod: usage: mknod [-m mode] name p

However, if m4/gl_POSIX_SHELL were to test for this, I could
clean up this test as you suggest, and simply skip it whenever
POSIX_SHELL is empty.  Volunteers?

> Doesn't this also mean that you need to patch mknod.c to print
> USAGE_BUILTIN_WARNING?

Yes.  Good catch!
Thanks!

        mknod --help: note that this command may be a shell built-in
        * src/mknod.c (usage): Print USAGE_BUILTIN_WARNING.
        Suggestion from Eric Blake.

diff --git a/src/mknod.c b/src/mknod.c
index 8a1718d..445117c 100644
--- a/src/mknod.c
+++ b/src/mknod.c
@@ -83,6 +83,7 @@ otherwise, as decimal.  TYPE may be:\n\
   c, u   create a character (unbuffered) special file\n\
   p      create a FIFO\n\
 "), stdout);
+      printf (USAGE_BUILTIN_WARNING, PROGRAM_NAME);
       emit_bug_reporting_address ();
     }
   exit (status);
--
1.5.5.56.gbcf7f