[SCM] GNU Autoconf source repository branch, master, updated. v2.68-70-g64a4d17

[Eric Blake]

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- Log -----------------------------------------------------------------
commit 64a4d1799faf2ab8d1359c85c0ca84a036d44b28
Author: Eric Blake <address@hidden>
Date:   Mon Jun 13 17:33:07 2011 -0600

    doc: mention more about ksh cloexec behavior
    
    * doc/autoconf.texi (File Descriptors): Clarify that only the exec
    builtin suffers from cloexec issues.
    
    Signed-off-by: Eric Blake <address@hidden>

-----------------------------------------------------------------------

Summary of changes:
 ChangeLog         |    4 +++
 doc/autoconf.texi |   56 +++++++++++++++++++++++-----------------------------
 2 files changed, 29 insertions(+), 31 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 03541e0..885e545 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,9 @@
 2011-06-14  Eric Blake  <address@hidden>
 
+       doc: mention more about ksh cloexec behavior
+       * doc/autoconf.texi (File Descriptors): Clarify that only the exec
+       builtin suffers from cloexec issues.
+
        doc: update quoting example
        * doc/autoconf.texi (Autoconf Language): Add AC_LANG_SOURCE use.
        * THANKS: Update.
diff --git a/doc/autoconf.texi b/doc/autoconf.texi
index 99b1fd1..6ec0dc4 100644
--- a/doc/autoconf.texi
+++ b/doc/autoconf.texi
@@ -15442,45 +15442,39 @@ As a workaround, @command{echo} or @command{eval} can 
be used.
 Don't rely on file descriptors 0, 1, and 2 remaining closed in a
 subsidiary program.  If any of these descriptors is closed, the
 operating system may open an unspecified file for the descriptor in the
-new process image.  Posix says this may be done only if the subsidiary
-program is set-user-ID or set-group-ID, but HP-UX 11.23 does
-it even for ordinary programs.
-
-Don't rely on open file descriptors being open in child processes.  In
address@hidden, file descriptors above 2 which are opened using
+new process image.  Posix 2008 says this may be done only if the
+subsidiary program is set-user-ID or set-group-ID, but HP-UX 11.23 does
+it even for ordinary programs, and the next version of Posix will allow
+HP-UX behavior.
+
+If you want a file descriptor above 2 to be inherited into a child
+process, then you must use redirections specific to that command or a
+containing subshell or command group, rather than relying on
address@hidden in the shell. In @command{ksh} as well as HP-UX
address@hidden, file descriptors above 2 which are opened using
 @samp{exec @var{n}>file} are closed by a subsequent @samp{exec} (such as
-that involved in the fork-and-exec which runs a program or script).
-Thus, using @command{sh}, we have:
+that involved in the fork-and-exec which runs a program or script):
 
 @example
-$ @kbd{cat ./descrips}
-#!/bin/sh -
-echo hello >&5
-$ @kbd{exec 5>t}
-$ @kbd{./descrips}
-$ @kbd{cat t}
+$ @kbd{echo 'echo hello >&5' >k
+$ @kbd{/bin/sh -c 'exec 5>t; ksh ./k; exec 5>&-; cat t}
 hello
-$
address@hidden example
-
address@hidden
-But using ksh:
-
address@hidden
-$ @kbd{exec 5>t}
-$ @kbd{./descrips}
+$ @kbd{bash -c 'exec 5>t; ksh ./k; exec 5>&-; cat t}
+hello
+$ @kbd{ksh -c 'exec 5>t; ksh ./k; exec 5>&-; cat t}
+./k[1]: 5: cannot open [Bad file number]
+$ @kbd{ksh -c '(ksh ./k) 5>t; cat t'}
+hello
+$ @kbd{ksh -c '@{ ksh ./k; @} 5>t; cat t'}
+hello
+$ @kbd{ksh -c '5>t ksh ./k; cat t}
 hello
-$ @kbd{cat t}
-$
 @end example
 
address@hidden
-Within the process which runs the @samp{descrips} script, file
-descriptor 5 is closed.
-
 Don't rely on duplicating a closed file descriptor to cause an
-error.  With Solaris @command{/bin/sh}, when the redirection fails, the
-output goes to the original file descriptor.
+error.  With Solaris @command{/bin/sh}, failed duplication is silently
+ignored, which can cause unintended leaks to the original file
+descriptor.  In this example, observe the leak to standard output:
 
 @example
 $ @kbd{bash -c 'echo hi >&3' 3>&-; echo $?}


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