;;; Consfigurator -- Lisp declarative configuration management system

;;; Copyright (C) 2021  Sean Whitton <spwhitton@spwhitton.name>

;;; This file is free software; you can redistribute it and/or modify
;;; it under the terms of the GNU General Public License as published by
;;; the Free Software Foundation; either version 3, or (at your option)
;;; any later version.

;;; This file is distributed in the hope that it will be useful,
;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;;; GNU General Public License for more details.

;;; You should have received a copy of the GNU General Public License
;;; along with this program.  If not, see <http://www.gnu.org/licenses/>.

(in-package :consfigurator.connection.chroot.fork)
#+sbcl (eval-when (:compile-toplevel :load-toplevel :execute)
	 (require "sb-posix"))

;; use only implementation-specific fork and waitpid calls to avoid thread
;; woes.  chroot(2), however, should be okay.

(defun fork ()
  #+sbcl (sb-posix:fork))

(defun waitpid (pid options)
  ;; normalise any other implementations such that we always return
  ;; (values PID EXIT-STATUS), as SB-POSIX:WAITPID does
  #+sbcl (sb-posix:waitpid pid options))

(defun chroot (path)
  #+sbcl      (sb-posix:chroot path)
  #-(or sbcl) (foreign-funcall "chroot" :string path :int))

(defmethod establish-connection ((type (eql :chroot.fork)) remaining &key into)
  (unless (lisp-connection-p)
    (error "Forking into a chroot requires a Lisp-type connection"))
  #-(or sbcl) (error "Don't know how to safely fork() in this Lisp")
  (format t "Forking into chroot at ~A~%" into)
  ;; TODO copy required prerequisite data into the chroot -- propellor uses a
  ;; bind mount but we might be the root Lisp, in which case we don't have a
  ;; cache to bind mount in.  use chroot.shell connection to upload?
  (mapc #'force-output
	(list *standard-output* *error-output* *debug-io* *terminal-io*))
  (let ((child (fork)))
    (case child
      ;; note that SB-POSIX:FORK can only return >=0
      (-1
       (error "fork(2) failed"))
      (0
       (handler-case
	   (progn
	     ;; TODO either (reset-data-sources), or bind a restart to convert
	     ;; data source errors into failed-change (or ignore them?  or
	     ;; what?), as they may or may not be available inside the chroot,
	     ;; depending on whether the data source code needs to read files
	     ;; outside of the chroot or already has the data cached, a socket
	     ;; open etc.
	     (mapc #'clear-input
		   (list *standard-input* *debug-io* *terminal-io*))
	     (unless (zerop (chroot into))
	       (error "chroot(2) failed; are you root?"))
	     ;; chdir, else our current working directory is a pointer to
	     ;; something outside the chroot
	     (uiop:chdir "/")
	     ;; it would be nice to reenter Consfigurator's primary loop by
	     ;; just calling (return-from establish-connection
	     ;; (establish-connection :local)) here, but we need to kill off
	     ;; the child afterwards, rather than returning to the child's
	     ;; REPL or whatever else
	     (continue-deploy* remaining)
	     (uiop:quit 0))
	 (serious-condition (c)
	   (format *error-output* ":CHROOT.FORK child failed: ~A~%" c)
	   (uiop:quit 2))))
      (t
       (multiple-value-bind (_ status) (waitpid child 0)
	 (declare (ignore _))
	 (unless (zerop status)
	   ;; TODO instead of parsing the status ourselves here, maybe we can
	   ;; call the various C macros for parsing the status in wait(2)
	   (error ":CHROOT.FORK child failed, status #x~(~4,'0X~)" status)))
       nil))))