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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)
;; 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 wifexited (status)
#+sbcl (sb-posix:wifexited status))
(defun wexitstatus (status)
#+sbcl (sb-posix:wexitstatus status))
(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)))))
(defclass fork-connection (local-connection) ())
(defgeneric post-fork (connection)
(:documentation
"Code to execute after forking but before calling CONTINUE-DEPLOY*."))
(defmethod continue-connection ((connection fork-connection) remaining)
(unless (lisp-connection-p)
(error "Forking requires a Lisp-type connection."))
#-(or sbcl) (error "Don't know how to safely fork() in this Lisp")
(upload-all-prerequisite-data
:connection connection :upload-string-data nil)
(with-remote-temporary-file (output)
(with-remote-temporary-file (error)
(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
(with-backtrace-and-exit-code
;; Capture child stdout in case *STANDARD-OUTPUT* has been
;; rebound to somewhere else in the parent, e.g. by
;; APPLY-AND-PRINT. The parent can then send the contents of the
;; file named by OUTPUT to the correct stream. Capture child
;; stderr so that we can include it in FAILED-CHANGE condition;
;; otherwise if we are within SEQPROPS, for example, stderr won't
;; be made visible to the user. We don't use pipe(2) because
;; then we'd need implementation-specific code to bind streams to
;; the FDs.
(with-open-file (*standard-output*
output :direction :output :if-exists :append)
(with-open-file (*error-output*
error :direction :output :if-exists :append)
(mapc #'clear-input
(list *standard-input* *debug-io* *terminal-io*))
(cancel-unwind-protect-in-parent-cleanup)
;; While some kinds of data source will still work given
;; certain subtypes of FORK-CONNECTION (e.g. if they've
;; already cached the data in memory, or if it's also
;; accessible to whomever we will SETUID to), others won't,
;; so drop all registrations and rely on the call to
;; UPLOAD-ALL-PREREQUISITE-DATA above.
(reset-data-sources)
(post-fork connection)
;; 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* connection remaining)))))
(t
(multiple-value-bind (pid status) (waitpid child 0)
(declare (ignore pid))
(fresh-line)
(princ (readfile output))
(if (wifexited status)
(return-exit
(wexitstatus status)
:on-failure (failed-change
"~&Fork connection child failed; stderr was~%~%~A"
(readfile error)))
(failed-change
"~&Fork connection child did not exit normally, status #x~(~4,'0X~)"
status)))))))))
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