FreeBSD process substitution bug

FreeBSD process substitution bug

[Steve Atwell]

It seems that zsh process substitution doesn't work properly on recent 
versions of FreeBSD.  Here's what happens:

% cat <(date)
cat: /dev/fd/11: No such file or directory

This happens to me on FreeBSD 5.4 with zsh 4.2.5 built with default 
configure options.

I'm not on the list, so please Cc responses to me.

-- 
Steve Atwell <satwell@disjoint.net>

Re: FreeBSD process substitution bug

[Peter Stephenson]

Steve Atwell wrote:
> It seems that zsh process substitution doesn't work properly on recent 
> versions of FreeBSD.  Here's what happens:
> 
> % cat <(date)
> cat: /dev/fd/11: No such file or directory
> 
> This happens to me on FreeBSD 5.4 with zsh 4.2.5 built with default 
> configure options.

That suggests there's something wrong with the following configure test:
any idea what?  You should find it works if you #undef PATH_DEV_FD in
config.h.

dnl ----------------------------
dnl CHECK FOR /dev/fd FILESYSTEM
dnl ----------------------------
AH_TEMPLATE([PATH_DEV_FD],
[Define to the path of the /dev/fd filesystem.])
AC_CACHE_CHECK(for /dev/fd filesystem, zsh_cv_sys_path_dev_fd,
[for zsh_cv_sys_path_dev_fd in /proc/self/fd /dev/fd no; do
   test x`echo ok|cat $zsh_cv_sys_path_dev_fd/0 2>/dev/null` = xok && break
 done])
if test $zsh_cv_sys_path_dev_fd != no; then
  AC_DEFINE_UNQUOTED(PATH_DEV_FD, "$zsh_cv_sys_path_dev_fd")
fi

-- 
Peter Stephenson <p.w.stephenson@ntlworld.com>
Web page still at http://www.pwstephenson.fsnet.co.uk/

Re: FreeBSD process substitution bug

[Steve Atwell]

On Sat, Oct 29, 2005 at 11:02:26AM +0100, Peter Stephenson wrote:
>Steve Atwell wrote:
>> % cat <(date)
>> cat: /dev/fd/11: No such file or directory
>> 
>> This happens to me on FreeBSD 5.4 with zsh 4.2.5 built with default 
>> configure options.
>
>That suggests there's something wrong with the following configure test:
>any idea what?  You should find it works if you #undef PATH_DEV_FD in
>config.h.

I did a little more investigation and found the problem.  FreeBSD 5.x by 
default only provides file descriptors 0, 1, and 2 for the current 
process in /dev/fd.  If you want to be able to access other file 
descriptors, you have to mount the special fdescfs filesystem on 
/dev/fd.  The configure test to see if zsh can use /dev/fd succeeds 
because it only tests /dev/fd/0.

-- 
Steve Atwell <satwell@disjoint.net>

Re: FreeBSD process substitution bug

[Peter Stephenson]

> I did a little more investigation and found the problem.  FreeBSD 5.x by 
> default only provides file descriptors 0, 1, and 2 for the current 
> process in /dev/fd.  If you want to be able to access other file 
> descriptors, you have to mount the special fdescfs filesystem on 
> /dev/fd.  The configure test to see if zsh can use /dev/fd succeeds 
> because it only tests /dev/fd/0.

Thanks for the research.  Can you see if the following gives you a
working command substitution in this case?

Index: configure.ac
===================================================================
RCS file: /cvsroot/zsh/zsh/configure.ac,v
retrieving revision 1.41
diff -u -r1.41 configure.ac
--- configure.ac	28 Oct 2005 17:34:33 -0000	1.41
+++ configure.ac	30 Oct 2005 16:31:06 -0000
@@ -1603,7 +1603,7 @@
 [Define to the path of the /dev/fd filesystem.])
 AC_CACHE_CHECK(for /dev/fd filesystem, zsh_cv_sys_path_dev_fd,
 [for zsh_cv_sys_path_dev_fd in /proc/self/fd /dev/fd no; do
-   test x`echo ok|cat $zsh_cv_sys_path_dev_fd/0 2>/dev/null` = xok && break
+   test x`echo ok|(exec 3<&0; cat $zsh_cv_sys_path_dev_fd/3 2>/dev/null;)` = xok && break
  done])
 if test $zsh_cv_sys_path_dev_fd != no; then
   AC_DEFINE_UNQUOTED(PATH_DEV_FD, "$zsh_cv_sys_path_dev_fd")


-- 
Peter Stephenson <p.w.stephenson@ntlworld.com>
Web page still at http://www.pwstephenson.fsnet.co.uk/

Re: FreeBSD process substitution bug

[Bart Schaefer]

On Oct 30,  4:33pm, Peter Stephenson wrote:
} Subject: Re: FreeBSD process substitution bug
}
} +   test x`echo ok|(exec 3<&0; cat $zsh_cv_sys_path_dev_fd/3 2>/dev/null;)` = xok && break

I was going to suggest something like that, but I wonder if we should
deliberately choose a higher-numbered descriptor than 3.

Re: FreeBSD process substitution bug

[Peter Stephenson]

Bart Schaefer wrote:
> On Oct 30,  4:33pm, Peter Stephenson wrote:
> } Subject: Re: FreeBSD process substitution bug
> }
> } +   test x`echo ok|(exec 3<&0; cat $zsh_cv_sys_path_dev_fd/3 2>/dev/null;)`
>  = xok && break
> 
> I was going to suggest something like that, but I wonder if we should
> deliberately choose a higher-numbered descriptor than 3.

I thought about that.  We can't use 10 or higher as we'd like (that's
where the shell will put the fd's it uses) since the shell syntax
doesn't support it.  I couldn't think of any really good reason to pick
9 rather than 3, but it's an easy change that's at worst harmless if you
want to change it.  I've now committed the patch with an extra comment.

-- 
Peter Stephenson <p.w.stephenson@ntlworld.com>
Web page still at http://www.pwstephenson.fsnet.co.uk/

Re: FreeBSD process substitution bug

[Steve Atwell]

On Sun, Oct 30, 2005 at 04:33:05PM +0000, Peter Stephenson wrote:
>Thanks for the research.  Can you see if the following gives you a
>working command substitution in this case?

Yes, it's detected properly with that patch.  Thanks.

-- 
Steve Atwell <satwell@disjoint.net>