Opening a pty without a process

Opening a pty without a process

[Nick Roberts]

I would like to associate a buffer with a pty without a process.  How easy
would it be able to adapt start-process to do this when given a nil value
for program name:

(start-process name buffer nil) or (start-process name buffer)

Perhaps a new function would be better because I would like it to return the
name of the pty, e.g,

(open-pty-buffer buffer)
->"/dev/pts/1"

Emacs would need then to monitor the file descriptor using select in
wait_reading_process_output (process.c).

and I would  hook this up with a process using:

M-x gdb
Run gdb (like this): gdb -tty /dev/pts/1 -i=mi myprog

(In practice it's more likely that Emacs will set a Lisp variable to the
value of (open-pty-buffer buffer) and use it behind the users back.)

-- 
Nick                                           http://www.inet.net.nz/~nickrob

Re: Opening a pty without a process

[Nick Roberts]

Previously I wrote:

 > I would like to associate a buffer with a pty without a process.  How easy
 > would it be able to adapt start-process to do this when given a nil value
 > for program name:
 > 
 > (start-process name buffer nil) or (start-process name buffer)
 > 
 > Perhaps a new function would be better because I would like it to return the
 > name of the pty, e.g,
 > 
 > (open-pty-buffer buffer)
 > ->"/dev/pts/1"
 > 
 > Emacs would need then to monitor the file descriptor using select in
 > wait_reading_process_output (process.c).
 > 
 > and I would  hook this up with a process using:
 > 
 > M-x gdb
 > Run gdb (like this): gdb -tty /dev/pts/1 -i=mi myprog
 > 
 > (In practice it's more likely that Emacs will set a Lisp variable to the
 > value of (open-pty-buffer buffer) and use it behind the users back.)

Here's a patch to sketch the ideas that I have.  I would like it to be
considered for eventual inclusion on the trunk.  With it if you evaluate

(start-process "mypty" "*mypty*" nil)
=> #<process mypty>


Then M-x list-processes gives something like:

Proc  Status   Buffer  Tty	  Command
----  ------   ------  ---	  -------
mypty run      *mypty* /dev/pts/1 
shell run      *shell* /dev/pts/3 /bin/bash --noediting -i


In buffer *mypty* do

  M-x comint-mode


Start GDB as follows ("-annotate=3" won't work)

  M-x gdb
  Run gdb (like this): gdb --fullname myprog

where myprog is a program that does IO.

  ...
  (gdb) tty /dev/pts/1
  (gdb) run

Then your program output should appear in *mypty* and GDB should accept
input from there too.


It's still rough: ptys aren't closed when the buffer is killed, input gets
echoed in *mypty*, assumes ptys etc., but I would like feedback before
polishing it any further.

For GDB it means that a dummy process like:

  (make-comint-in-buffer
   "gdb-inferior" (current-buffer) "sleep" nil "1000000000"))

isn't needed.  There must be other situations where this could be useful too.

-- 
Nick                                           http://www.inet.net.nz/~nickrob


2007-11-26  Nick Roberts  <nickrob@snap.net.nz>

	* process.c (create_pty): New function.  Set pid == -2.
	(list_processes_1): Check for no program.
	(Fstart_process): Create a pty if PROGRAM is nil.
	Condition for no program.  Update doc string.
	(start_process_unwind): Remove process if pid == -1.


*** process.c.~1.525~	2007-11-27 09:15:17.000000000 +1300
--- process.c	2007-11-27 09:18:35.000000000 +1300
*************** static int keyboard_bit_set P_ ((SELECT_
*** 309,314 ****
--- 309,315 ----
  static void deactivate_process P_ ((Lisp_Object));
  static void status_notify P_ ((struct Lisp_Process *));
  static int read_process_output P_ ((Lisp_Object, int));
+ static void create_pty P_ ((Lisp_Object));
  
  /* If we support a window system, turn on the code to poll periodically
     to detect C-g.  It isn't actually used when doing interrupt input.  */
*************** list_processes_1 (query_only)
*** 1522,1527 ****
--- 1523,1530 ----
  	  while (1)
  	    {
  	      tem1 = Fcar (tem);
+ 	      if (NILP (tem1))
+ 		break;
  	      Finsert (1, &tem1);
  	      tem = Fcdr (tem);
  	      if (NILP (tem))
*************** at end of BUFFER, unless you specify an 
*** 1571,1578 ****
  function to handle the output.  BUFFER may also be nil, meaning that
  this process is not associated with any buffer.
  
! PROGRAM is the program file name.  It is searched for in PATH.
! Remaining arguments are strings to give program as arguments.
  
  If you want to separate standard output from standard error, invoke
  the command through a shell and redirect one of them using the shell
--- 1574,1582 ----
  function to handle the output.  BUFFER may also be nil, meaning that
  this process is not associated with any buffer.
  
! PROGRAM is the program file name.  It is searched for in PATH. If nil,
! just associate a pty with the buffer.  Remaining arguments are strings
! to give program as arguments.
  
  If you want to separate standard output from standard error, invoke
  the command through a shell and redirect one of them using the shell
*************** usage: (start-process NAME BUFFER PROGRA
*** 1628,1634 ****
  
    program = args[2];
  
!   CHECK_STRING (program);
  
    proc = make_process (name);
    /* If an error occurs and we can't start the process, we want to
--- 1632,1639 ----
  
    program = args[2];
  
!   if (!NILP (program))
!     CHECK_STRING (program);
  
    proc = make_process (name);
    /* If an error occurs and we can't start the process, we want to
*************** usage: (start-process NAME BUFFER PROGRA
*** 1675,1681 ****
  	args2[0] = Qstart_process;
  	for (i = 0; i < nargs; i++) args2[i + 1] = args[i];
  	GCPRO2 (proc, current_dir);
! 	coding_systems = Ffind_operation_coding_system (nargs + 1, args2);
  	UNGCPRO;
  	if (CONSP (coding_systems))
  	  val = XCAR (coding_systems);
--- 1680,1687 ----
  	args2[0] = Qstart_process;
  	for (i = 0; i < nargs; i++) args2[i + 1] = args[i];
  	GCPRO2 (proc, current_dir);
! 	if (!NILP (program))
! 	  coding_systems = Ffind_operation_coding_system (nargs + 1, args2);
  	UNGCPRO;
  	if (CONSP (coding_systems))
  	  val = XCAR (coding_systems);
*************** usage: (start-process NAME BUFFER PROGRA
*** 1693,1699 ****
  	    args2[0] = Qstart_process;
  	    for (i = 0; i < nargs; i++) args2[i + 1] = args[i];
  	    GCPRO2 (proc, current_dir);
! 	    coding_systems = Ffind_operation_coding_system (nargs + 1, args2);
  	    UNGCPRO;
  	  }
  	if (CONSP (coding_systems))
--- 1699,1706 ----
  	    args2[0] = Qstart_process;
  	    for (i = 0; i < nargs; i++) args2[i + 1] = args[i];
  	    GCPRO2 (proc, current_dir);
! 	    if (!NILP (program))
! 	      coding_systems = Ffind_operation_coding_system (nargs + 1, args2);
  	    UNGCPRO;
  	  }
  	if (CONSP (coding_systems))
*************** usage: (start-process NAME BUFFER PROGRA
*** 1704,1784 ****
      XPROCESS (proc)->encode_coding_system = val;
    }
  
- #ifdef VMS
-   /* Make a one member argv with all args concatenated
-      together separated by a blank.  */
-   len = SBYTES (program) + 2;
-   for (i = 3; i < nargs; i++)
-     {
-       tem = args[i];
-       CHECK_STRING (tem);
-       len += SBYTES (tem) + 1;	/* count the blank */
-     }
-   new_argv = (unsigned char *) alloca (len);
-   strcpy (new_argv, SDATA (program));
-   for (i = 3; i < nargs; i++)
-     {
-       tem = args[i];
-       CHECK_STRING (tem);
-       strcat (new_argv, " ");
-       strcat (new_argv, SDATA (tem));
-     }
-   /* Need to add code here to check for program existence on VMS */
- 
- #else /* not VMS */
-   new_argv = (unsigned char **) alloca ((nargs - 1) * sizeof (char *));
- 
-   /* If program file name is not absolute, search our path for it.
-      Put the name we will really use in TEM.  */
-   if (!IS_DIRECTORY_SEP (SREF (program, 0))
-       && !(SCHARS (program) > 1
- 	   && IS_DEVICE_SEP (SREF (program, 1))))
-     {
-       struct gcpro gcpro1, gcpro2, gcpro3, gcpro4;
- 
-       tem = Qnil;
-       GCPRO4 (name, program, buffer, current_dir);
-       openp (Vexec_path, program, Vexec_suffixes, &tem, make_number (X_OK));
-       UNGCPRO;
-       if (NILP (tem))
- 	report_file_error ("Searching for program", Fcons (program, Qnil));
-       tem = Fexpand_file_name (tem, Qnil);
-     }
-   else
-     {
-       if (!NILP (Ffile_directory_p (program)))
- 	error ("Specified program for new process is a directory");
-       tem = program;
-     }
- 
-   /* If program file name starts with /: for quoting a magic name,
-      discard that.  */
-   if (SBYTES (tem) > 2 && SREF (tem, 0) == '/'
-       && SREF (tem, 1) == ':')
-     tem = Fsubstring (tem, make_number (2), Qnil);
- 
-   /* Encode the file name and put it in NEW_ARGV.
-      That's where the child will use it to execute the program.  */
-   tem = ENCODE_FILE (tem);
-   new_argv[0] = SDATA (tem);
- 
-   /* Here we encode arguments by the coding system used for sending
-      data to the process.  We don't support using different coding
-      systems for encoding arguments and for encoding data sent to the
-      process.  */
- 
-   for (i = 3; i < nargs; i++)
-     {
-       tem = args[i];
-       CHECK_STRING (tem);
-       if (STRING_MULTIBYTE (tem))
- 	tem = (code_convert_string_norecord
- 	       (tem, XPROCESS (proc)->encode_coding_system, 1));
-       new_argv[i - 2] = SDATA (tem);
-     }
-   new_argv[i - 2] = 0;
- #endif /* not VMS */
- 
    XPROCESS (proc)->decoding_buf = make_uninit_string (0);
    XPROCESS (proc)->decoding_carryover = 0;
    XPROCESS (proc)->encoding_buf = make_uninit_string (0);
--- 1711,1716 ----
*************** usage: (start-process NAME BUFFER PROGRA
*** 1786,1792 ****
    XPROCESS (proc)->inherit_coding_system_flag
      = !(NILP (buffer) || !inherit_process_coding_system);
  
!   create_process (proc, (char **) new_argv, current_dir);
  
    return unbind_to (count, proc);
  }
--- 1718,1804 ----
    XPROCESS (proc)->inherit_coding_system_flag
      = !(NILP (buffer) || !inherit_process_coding_system);
  
!   if (!NILP (program))
!     {
! #ifdef VMS
!       /* Make a one member argv with all args concatenated
! 	 together separated by a blank.  */
!       len = SBYTES (program) + 2;
!       for (i = 3; i < nargs; i++)
! 	{
! 	  tem = args[i];
! 	  CHECK_STRING (tem);
! 	  len += SBYTES (tem) + 1;	/* count the blank */
! 	}
!       new_argv = (unsigned char *) alloca (len);
!       strcpy (new_argv, SDATA (program));
!       for (i = 3; i < nargs; i++)
! 	{
! 	  tem = args[i];
! 	  CHECK_STRING (tem);
! 	  strcat (new_argv, " ");
! 	  strcat (new_argv, SDATA (tem));
! 	}
!       /* Need to add code here to check for program existence on VMS */
! 
! #else /* not VMS */
!       new_argv = (unsigned char **) alloca ((nargs - 1) * sizeof (char *));
! 
!       /* If program file name is not absolute, search our path for it.
! 	 Put the name we will really use in TEM.  */
!       if (!IS_DIRECTORY_SEP (SREF (program, 0))
! 	  && !(SCHARS (program) > 1
! 	       && IS_DEVICE_SEP (SREF (program, 1))))
! 	{
! 	  struct gcpro gcpro1, gcpro2, gcpro3, gcpro4;
! 
! 	  tem = Qnil;
! 	  GCPRO4 (name, program, buffer, current_dir);
! 	  openp (Vexec_path, program, Vexec_suffixes, &tem, make_number (X_OK));
! 	  UNGCPRO;
! 	  if (NILP (tem))
! 	    report_file_error ("Searching for program", Fcons (program, Qnil));
! 	  tem = Fexpand_file_name (tem, Qnil);
! 	}
!       else
! 	{
! 	  if (!NILP (Ffile_directory_p (program)))
! 	    error ("Specified program for new process is a directory");
! 	  tem = program;
! 	}
! 
!       /* If program file name starts with /: for quoting a magic name,
! 	 discard that.  */
!       if (SBYTES (tem) > 2 && SREF (tem, 0) == '/'
! 	  && SREF (tem, 1) == ':')
! 	tem = Fsubstring (tem, make_number (2), Qnil);
! 
!       /* Encode the file name and put it in NEW_ARGV.
! 	 That's where the child will use it to execute the program.  */
!       tem = ENCODE_FILE (tem);
!       new_argv[0] = SDATA (tem);
! 
!       /* Here we encode arguments by the coding system used for sending
! 	 data to the process.  We don't support using different coding
! 	 systems for encoding arguments and for encoding data sent to the
! 	 process.  */
! 
!       for (i = 3; i < nargs; i++)
! 	{
! 	  tem = args[i];
! 	  CHECK_STRING (tem);
! 	  if (STRING_MULTIBYTE (tem))
! 	    tem = (code_convert_string_norecord
! 		   (tem, XPROCESS (proc)->encode_coding_system, 1));
! 	  new_argv[i - 2] = SDATA (tem);
! 	}
!       new_argv[i - 2] = 0;
! #endif /* not VMS */
! 
!       create_process (proc, (char **) new_argv, current_dir);
!     }
!   else
!     create_pty (proc);
  
    return unbind_to (count, proc);
  }
*************** start_process_unwind (proc)
*** 1803,1809 ****
      abort ();
  
    /* Was PROC started successfully?  */
!   if (XPROCESS (proc)->pid <= 0)
      remove_process (proc);
  
    return Qnil;
--- 1815,1821 ----
      abort ();
  
    /* Was PROC started successfully?  */
!   if (XPROCESS (proc)->pid == -1)
      remove_process (proc);
  
    return Qnil;
*************** create_process_sigchld ()
*** 1836,1841 ****
--- 1848,1939 ----
  #endif
  #endif
  
+ void
+ create_pty (process)
+ {
+   int inchannel, outchannel;
+ 
+   /* Use volatile to protect variables from being clobbered by longjmp.  */
+   volatile int forkin, forkout;
+   volatile int pty_flag = 0;
+ 
+   inchannel = outchannel = -1;
+ 
+ #ifdef HAVE_PTYS
+   if (!NILP (Vprocess_connection_type))
+     outchannel = inchannel = allocate_pty ();
+ 
+   if (inchannel >= 0)
+     {
+ #if ! defined (USG) || defined (USG_SUBTTY_WORKS)
+       /* On most USG systems it does not work to open the pty's tty here,
+ 	 then close it and reopen it in the child.  */
+ #ifdef O_NOCTTY
+       /* Don't let this terminal become our controlling terminal
+ 	 (in case we don't have one).  */
+       forkout = forkin = emacs_open (pty_name, O_RDWR | O_NOCTTY, 0);
+ #else
+       forkout = forkin = emacs_open (pty_name, O_RDWR, 0);
+ #endif
+       if (forkin < 0)
+ 	report_file_error ("Opening pty", Qnil);
+ #if defined (RTU) || defined (UNIPLUS) || defined (DONT_REOPEN_PTY)
+       /* In the case that vfork is defined as fork, the parent process
+ 	 (Emacs) may send some data before the child process completes
+ 	 tty options setup.  So we setup tty before forking.  */
+       child_setup_tty (forkout);
+ #endif /* RTU or UNIPLUS or DONT_REOPEN_PTY */
+ #else
+       forkin = forkout = -1;
+ #endif /* not USG, or USG_SUBTTY_WORKS */
+       pty_flag = 1;
+     }
+   else
+ #endif /* HAVE_PTYS */
+ 
+ /* Stride people say it's a mystery why this is needed
+    as well as the O_NDELAY, but that it fails without this.  */
+ #if defined (STRIDE) || (defined (pfa) && defined (HAVE_PTYS))
+   {
+     int one = 1;
+     ioctl (inchannel, FIONBIO, &one);
+   }
+ #endif
+ 
+ #ifdef O_NONBLOCK
+   fcntl (inchannel, F_SETFL, O_NONBLOCK);
+   fcntl (outchannel, F_SETFL, O_NONBLOCK);
+ #else
+ #ifdef O_NDELAY
+   fcntl (inchannel, F_SETFL, O_NDELAY);
+   fcntl (outchannel, F_SETFL, O_NDELAY);
+ #endif
+ #endif
+ 
+   /* Record this as an active process, with its channels.
+      As a result, child_setup will close Emacs's side of the pipes.  */
+   chan_process[inchannel] = process;
+   XPROCESS (process)->infd = inchannel;
+   XPROCESS (process)->outfd = outchannel;
+ 
+   /* Previously we recorded the tty descriptor used in the subprocess.
+      It was only used for getting the foreground tty process, so now
+      we just reopen the device (see emacs_get_tty_pgrp) as this is
+      more portable (see USG_SUBTTY_WORKS above).  */
+ 
+   XPROCESS (process)->pty_flag = pty_flag;
+   XPROCESS (process)->status = Qrun;
+   setup_process_coding_systems (process);
+ 
+   FD_SET (inchannel, &input_wait_mask);
+   FD_SET (inchannel, &non_keyboard_wait_mask);
+   if (inchannel > max_process_desc)
+     max_process_desc = inchannel;
+ 
+   XPROCESS (process)->pid = -2;
+   XPROCESS (process)->tty_name = build_string (pty_name);
+ }
+ 
  #ifndef VMS /* VMS version of this function is in vmsproc.c.  */
  void
  create_process (process, new_argv, current_dir)

Re: Opening a pty without a process

[Richard Stallman]

What's the point of doing this instead of running GDB as a subprocess
of Emacs in the usual way?  (Since that is already implemented.)

Re: Opening a pty without a process

[Nick Roberts]

 > What's the point of doing this instead of running GDB as a subprocess
 > of Emacs in the usual way?  (Since that is already implemented.)

I think there's some confusion.  GDB would still run as a subprocess of Emacs
and have it's own pty associated with the GUD buffer.  I'm talking about
giving the the debuggee it's own pty and buffer instead of sharing the
GUD buffer, i.e., one for GDB IO and another for program IO.  Since the
debuggee is *not* a child of Emacs it cannot be set up with a pty in the
usual way.  Currently this is done with a buffer using a dummy process
to fake a separate pty.

The advantage of using a separate pty is that Emacs doesn't have to guess
whether user input is meant to be sent to the debuggee (immediately) or GDB
(queued for later).

-- 
Nick                                           http://www.inet.net.nz/~nickrob

Re: Opening a pty without a process

[Richard Stallman]

      I'm talking about
    giving the the debuggee it's own pty and buffer instead of sharing the
    GUD buffer, i.e., one for GDB IO and another for program IO.

I see.  Yes, that is useful.

It is useful enough that I think it is well worth having special
features in the C code of Emacs to make this clean for Lisp programs.

Re: Opening a pty without a process

[Nick Roberts]

 >       I'm talking about
 >     giving the the debuggee it's own pty and buffer instead of sharing the
 >     GUD buffer, i.e., one for GDB IO and another for program IO.
 > 
 > I see.  Yes, that is useful.
 > 
 > It is useful enough that I think it is well worth having special
 > features in the C code of Emacs to make this clean for Lisp programs.

Good.  I'll spend sometime doing that and post again.

-- 
Nick                                           http://www.inet.net.nz/~nickrob

Re: Opening a pty without a process

[Stefan Monnier]

>> (open-pty-buffer buffer)
-> "/dev/pts/1"

How 'bout:

   (defun open-pty-buffer (buffer)
     (let* ((process-connection-type 'pty)
            (proc (start-process "foo" buffer "sh" "-c"
                                 "while sleep 3600; do :; done")))
       (process-tty-name proc)))

I guess it would be convenient indeed to be able to use nil for the
program rather than a contraption like the one above.  OTOH we could
just use `hexl' by adding a flag to it (it's already abused in a similar
way by `ielm').

BTW in your patch I do not understand where the create_pty code comes
from.  It seems to come from Emacs code, in which case it is code
duplication and should be avoided.


        Stefan

Re: Opening a pty without a process

[Nick Roberts]

 > >> (open-pty-buffer buffer)
 > -> "/dev/pts/1"
 > 
 > How 'bout:
 > 
 >    (defun open-pty-buffer (buffer)
 >      (let* ((process-connection-type 'pty)
 >             (proc (start-process "foo" buffer "sh" "-c"
 >                                  "while sleep 3600; do :; done")))
 >        (process-tty-name proc)))

In gdb-mi.el (in ELPA) I do:

 (define-derived-mode gdb-inferior-io-mode comint-mode "Inferior I/O"
   "Major mode for gdb inferior-io."
   :syntax-table nil :abbrev-table nil
   ;; We want to use comint because it has various nifty and familiar
   ;; features.  We don't need a process, but comint wants one, so create
   ;; a dummy one.
   (make-comint-in-buffer
    "gdb-inferior" (current-buffer) "sleep" nil "1000000000"))

and then set the terminal for program IO in GDB:

  (gdb-input
  ;; Needs GDB 6.4 onwards
  (list
    (concat "-inferior-tty-set "
	    (process-tty-name (get-process "gdb-inferior")) "\n")
	    'ignore))

but it seems a bit of a hack

 > I guess it would be convenient indeed to be able to use nil for the
 > program rather than a contraption like the one above.  OTOH we could
 > just use `hexl' by adding a flag to it (it's already abused in a similar
 > way by `ielm').

Could ielm use a buffer like the one I'm proposing?

 > BTW in your patch I do not understand where the create_pty code comes
 > from.  It seems to come from Emacs code, in which case it is code
 > duplication and should be avoided.

It's almost the first half of create_process.  Sure it would make sense to
reuse code once it has been agreed that the function is useful.

-- 
Nick                                           http://www.inet.net.nz/~nickrob

Re: Opening a pty without a process

[Stefan Monnier]

>> >> (open-pty-buffer buffer)
-> "/dev/pts/1"
>> 
>> How 'bout:
>> 
>> (defun open-pty-buffer (buffer)
>> (let* ((process-connection-type 'pty)
>> (proc (start-process "foo" buffer "sh" "-c"
>> "while sleep 3600; do :; done")))
>> (process-tty-name proc)))

> In gdb-mi.el (in ELPA) I do:

>  (define-derived-mode gdb-inferior-io-mode comint-mode "Inferior I/O"
>    "Major mode for gdb inferior-io."
>    :syntax-table nil :abbrev-table nil
>    ;; We want to use comint because it has various nifty and familiar
>    ;; features.  We don't need a process, but comint wants one, so create
>    ;; a dummy one.
>    (make-comint-in-buffer
>     "gdb-inferior" (current-buffer) "sleep" nil "1000000000"))

> and then set the terminal for program IO in GDB:

>   (gdb-input
>   ;; Needs GDB 6.4 onwards
>   (list
>     (concat "-inferior-tty-set "
> 	    (process-tty-name (get-process "gdb-inferior")) "\n")
> 	    'ignore))

> but it seems a bit of a hack

Yes, I guess `sleep' works as well.

>> I guess it would be convenient indeed to be able to use nil for the
>> program rather than a contraption like the one above.  OTOH we could
>> just use `hexl' by adding a flag to it (it's already abused in a similar
>> way by `ielm').

> Could ielm use a buffer like the one I'm proposing?

No.  It needs "cat" (and used to use "cat").

>> BTW in your patch I do not understand where the create_pty code comes
>> from.  It seems to come from Emacs code, in which case it is code
>> duplication and should be avoided.

> It's almost the first half of create_process.  Sure it would make sense to
> reuse code once it has been agreed that the function is useful.

Please do that,


        Stefan

Re: Opening a pty without a process

[Richard Stallman]

       (defun open-pty-buffer (buffer)
	 (let* ((process-connection-type 'pty)
		(proc (start-process "foo" buffer "sh" "-c"
				     "while sleep 3600; do :; done")))
	   (process-tty-name proc)))

    I guess it would be convenient indeed to be able to use nil for the
    program rather than a contraption like the one above.  OTOH we could
    just use `hexl' by adding a flag to it (it's already abused in a similar
    way by `ielm').

I think it would be much cleaner to do this at C level
and dispense with the need to run any program in this pty.