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;;; 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.fork)
(named-readtables:in-readtable :consfigurator)
#+sbcl (eval-when (:compile-toplevel :load-toplevel :execute)
(require "sb-posix"))
;; Use only implementation-specific fork and waitpid calls to avoid thread
;; woes. Things like chroot(2) and setuid(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 can-probably-fork ()
"Return nil if we can detect other running threads, and the Lisp
implementation is known not to support forking when there are other threads.
A return value other than nil indicates only that we couldn't detect
circumstances in which it is known that we cannot fork, not that we are sure
we can fork -- a thread might be only partly initialised at the time we check,
for example, such that we don't see it."
(and
#+sbcl (> 2 (length (sb-thread:list-all-threads)))))
;; TODO there is unwanted variable capture going on here
(defmacro with-fork-connection ((remaining) &body forms)
`(progn
(unless (lisp-connection-p)
(error "Forking requires a Lisp-type connection."))
#-(or sbcl) (error "Don't know how to safely fork() in this Lisp")
;; 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-bind ((serious-condition
(lambda (c)
(trivial-backtrace:print-backtrace
c :output *error-output*)
(uiop:quit 2))))
;; 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*))
(reset-remote-home)
,@forms
;; 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)))
(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
"Fork connection child failed, status #x~(~4,'0X~)" status)))
nil)))))
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