Re: how to handle devpts

[Louis Rilling <Louis.Rilling-aw0BnHfMbSpBDgjK7y7TUQ@public.gmane.org>]

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Hi Serge,

On 30/11/09 14:22 -0600, Serge E. Hallyn wrote:
> We currently checkpoint and restart unix98 ptys in the kernel.
> So what do we want to do about the userspace part?  In particular,
> if I run the following test program and checkpoint it, it
> has `tty` open.  What do we want to do about that?
> 
> Just having user-cr/restart.c take an option to mount a new
> instance of devpts isn't enough - we don't get hooked up to
> restart.c's stdin/out obviously, and restart succeeds but the
> restarted program exists with -EIO.  At the same time, just
> doing a cradvise type of thing to plug fds 0,1,2 suffice for
> this testcase, but not for something more complicated which
> also has other unix98 ptys open.

In Kerrighed we are implementing something à-la-cradvise: we allow the
caller of sys_restart() to give replacement fds for arbitrary files. To achieve
this, each checkpointed file descriptor (struct file) has a unique key, and
sys_restart() takes a substitution table in parameter, where an entry is a
pair (key, fd).

In Kerrighed sys_checkpoint() exports a human-readable table of checkpointed
file descriptors, with types, fd in each checkpointed task, etc.
With Oren's patchset, I presume that some userspace tool could extract such a
table from the checkpoint.

Hope this makes the discussion progress...

Louis

> 
> Do we require that it be run in screen?  Then what about the
> screen session's terminals themselves?
> 
> Anyway, I have this feeling that other have already thought
> through this, so here is the simple program for discussion:
> 
> #include <stdio.h>
> #include <curses.h>
> #include <string.h>
> 
> int main(int argc, char *argv[])
> {
> #define MAXLEN 20
> 	char input[MAXLEN+1];
> 	int i = 0;
> 
> 	initscr();
> 	cbreak();
> 	//noecho();
> 	nonl();
> 	intrflush(stdscr, FALSE);
> 	keypad(stdscr, TRUE);
> 
> 	addstr("Enter some text: ");
> 	memset(input, 0, MAXLEN+1);
> 	while (1) {
> 		input[i] = getch();
> 		if (input[i] == KEY_ENTER || input[i]=='\r')
> 			break;
> 		i++;
> 		if (i == MAXLEN)
> 			break;
> 	}
> 	endwin();
> 	printf("I read the text: %s\n", input);
> 	return 0;
> }
> 
> -serge
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-- 
Dr Louis Rilling			Kerlabs
Skype: louis.rilling			Batiment Germanium
Phone: (+33|0) 6 80 89 08 23		80 avenue des Buttes de Coesmes
http://www.kerlabs.com/			35700 Rennes

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