guix-play/guix/build/linux-initrd.scm

;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2013, 2014 Ludovic Courtès <ludo@gnu.org>
;;;
;;; This file is part of GNU Guix.
;;;
;;; GNU Guix 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 of the License, or (at
;;; your option) any later version.
;;;
;;; GNU Guix 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 GNU Guix.  If not, see <http://www.gnu.org/licenses/>.

(define-module (guix build linux-initrd)
  #:use-module (rnrs io ports)
  #:use-module (system foreign)
  #:autoload   (system repl repl) (start-repl)
  #:autoload   (system base compile) (compile-file)
  #:use-module (srfi srfi-1)
  #:use-module (srfi srfi-26)
  #:use-module (ice-9 match)
  #:use-module (ice-9 ftw)
  #:use-module (guix build utils)
  #:export (mount-essential-file-systems
            linux-command-line
            make-essential-device-nodes
            configure-qemu-networking
            mount-qemu-smb-share
            mount-qemu-9p
            bind-mount
            load-linux-module*
            device-number
            boot-system))

;;; Commentary:
;;;
;;; Utility procedures useful in a Linux initial RAM disk (initrd).  Note that
;;; many of these use procedures not yet available in vanilla Guile (`mount',
;;; `load-linux-module', etc.); these are provided by a Guile patch used in
;;; the GNU distribution.
;;;
;;; Code:

(define* (mount-essential-file-systems #:key (root "/"))
  "Mount /proc and /sys under ROOT."
  (define (scope dir)
    (string-append root
                   (if (string-suffix? "/" root)
                       ""
                       "/")
                   dir))

  (unless (file-exists? (scope "proc"))
    (mkdir (scope "proc")))
  (mount "none" (scope "proc") "proc")

  (unless (file-exists? (scope "sys"))
    (mkdir (scope "sys")))
  (mount "none" (scope "sys") "sysfs"))

(define (linux-command-line)
  "Return the Linux kernel command line as a list of strings."
  (string-tokenize
   (call-with-input-file "/proc/cmdline"
     get-string-all)))

(define* (make-essential-device-nodes #:key (root "/"))
  "Make essential device nodes under ROOT/dev."
  ;; The hand-made udev!

  (define (scope dir)
    (string-append root
                   (if (string-suffix? "/" root)
                       ""
                       "/")
                   dir))

  (unless (file-exists? (scope "dev"))
    (mkdir (scope "dev")))

  ;; Make the device nodes for SCSI disks.
  (mknod (scope "dev/sda") 'block-special #o644 (device-number 8 0))
  (mknod (scope "dev/sda1") 'block-special #o644 (device-number 8 1))
  (mknod (scope "dev/sda2") 'block-special #o644 (device-number 8 2))

  ;; The virtio (para-virtualized) block devices, as supported by QEMU/KVM.
  (mknod (scope "dev/vda") 'block-special #o644 (device-number 252 0))
  (mknod (scope "dev/vda1") 'block-special #o644 (device-number 252 1))
  (mknod (scope "dev/vda2") 'block-special #o644 (device-number 252 2))

  ;; Memory (used by Xorg's VESA driver.)
  (mknod (scope "dev/mem") 'char-special #o640 (device-number 1 1))
  (mknod (scope "dev/kmem") 'char-special #o640 (device-number 1 2))

  ;; TTYs.
  (mknod (scope "dev/tty") 'char-special #o600
         (device-number 5 0))
  (let loop ((n 0))
    (and (< n 50)
         (let ((name (format #f "dev/tty~a" n)))
           (mknod (scope name) 'char-special #o600
                  (device-number 4 n))
           (loop (+ 1 n)))))

  ;; Rendez-vous point for syslogd.
  (mknod (scope "dev/log") 'socket #o666 0)
  (mknod (scope "dev/kmsg") 'char-special #o600 (device-number 1 11))

  ;; Other useful nodes.
  (mknod (scope "dev/null") 'char-special #o666 (device-number 1 3))
  (mknod (scope "dev/zero") 'char-special #o666 (device-number 1 5))
  (chmod (scope "dev/null") #o666)
  (chmod (scope "dev/zero") #o666))

(define %host-qemu-ipv4-address
  (inet-pton AF_INET "10.0.2.10"))

(define* (configure-qemu-networking #:optional (interface "eth0"))
  "Setup the INTERFACE network interface and /etc/resolv.conf according to
QEMU's default networking settings (see net/slirp.c in QEMU for default
networking values.)  Return #t if INTERFACE is up, #f otherwise."
  (display "configuring QEMU networking...\n")
  (let* ((sock    (socket AF_INET SOCK_STREAM 0))
         (address (make-socket-address AF_INET %host-qemu-ipv4-address 0))
         (flags   (network-interface-flags sock interface)))
    (set-network-interface-address sock interface address)
    (set-network-interface-flags sock interface (logior flags IFF_UP))

    (unless (file-exists? "/etc")
      (mkdir "/etc"))
    (call-with-output-file "/etc/resolv.conf"
      (lambda (p)
        (display "nameserver 10.0.2.3\n" p)))

    (logand (network-interface-flags sock interface) IFF_UP)))

(define (mount-qemu-smb-share share mount-point)
  "Mount QEMU's CIFS/SMB SHARE at MOUNT-POINT.

Vanilla QEMU's `-smb' option just exports a /qemu share, whereas our
`qemu-with-multiple-smb-shares' package exports the /xchg and /store shares
 (the latter allows the store to be shared between the host and guest.)"

  (format #t "mounting QEMU's SMB share `~a'...\n" share)
  (let ((server "10.0.2.4"))
    (mount (string-append "//" server share) mount-point "cifs" 0
           (string->pointer "guest,sec=none"))))

(define (mount-qemu-9p source mount-point)
  "Mount QEMU's 9p file system from SOURCE at MOUNT-POINT.

This uses the 'virtio' transport, which requires the various virtio Linux
modules to be loaded."

  (format #t "mounting QEMU's 9p share '~a'...\n" source)
  (let ((server "10.0.2.4"))
    (mount source mount-point "9p" 0
           (string->pointer "trans=virtio"))))

(define (bind-mount source target)
  "Bind-mount SOURCE at TARGET."
  (define MS_BIND 4096)                           ; from libc's <sys/mount.h>

  (mount source target "" MS_BIND))

(define (load-linux-module* file)
  "Load Linux module from FILE, the name of a `.ko' file."
  (define (slurp module)
    (call-with-input-file file get-bytevector-all))

  (load-linux-module (slurp file)))

(define (device-number major minor)
  "Return the device number for the device with MAJOR and MINOR, for use as
the last argument of `mknod'."
  (+ (* major 256) minor))

(define* (boot-system #:key
                      (linux-modules '())
                      qemu-guest-networking?
                      guile-modules-in-chroot?
                      volatile-root?
                      (mounts '()))
  "This procedure is meant to be called from an initrd.  Boot a system by
first loading LINUX-MODULES, then setting up QEMU guest networking if
QEMU-GUEST-NETWORKING? is true, mounting the file systems specified in MOUNTS,
and finally booting into the new root if any.  The initrd supports kernel
command-line options '--load', '--root', and '--repl'.

MOUNTS must be a list of elements of the form:

  (FILE-SYSTEM-TYPE SOURCE TARGET)

When GUILE-MODULES-IN-CHROOT? is true, make core Guile modules available in
the new root.

When VOLATILE-ROOT? is true, the root file system is writable but any changes
to it are lost."
  (define (resolve file)
    ;; If FILE is a symlink to an absolute file name, resolve it as if we were
    ;; under /root.
    (let ((st (lstat file)))
      (if (eq? 'symlink (stat:type st))
          (let ((target (readlink file)))
            (resolve (string-append "/root" target)))
          file)))

  (define MS_RDONLY 1)

  (display "Welcome, this is GNU's early boot Guile.\n")
  (display "Use '--repl' for an initrd REPL.\n\n")

  (mount-essential-file-systems)
  (let* ((args    (linux-command-line))
         (option  (lambda (opt)
                    (let ((opt (string-append opt "=")))
                      (and=> (find (cut string-prefix? opt <>)
                                   args)
                             (lambda (arg)
                               (substring arg (+ 1 (string-index arg #\=))))))))
         (to-load (option "--load"))
         (root    (option "--root")))

    (when (member "--repl" args)
      (start-repl))

    (display "loading kernel modules...\n")
    (for-each (compose load-linux-module*
                       (cut string-append "/modules/" <>))
              linux-modules)

    (when qemu-guest-networking?
      (unless (configure-qemu-networking)
        (display "network interface is DOWN\n")))

    ;; Make /dev nodes.
    (make-essential-device-nodes)

    ;; Prepare the real root file system under /root.
    (unless (file-exists? "/root")
      (mkdir "/root"))
    (if root
        (catch #t
          (lambda ()
            (if volatile-root?
                (begin
                  ;; XXX: For lack of a union file system...
                  (mkdir-p "/real-root")
                  (mount root "/real-root" "ext3" MS_RDONLY)
                  (mount "none" "/root" "tmpfs")

                  ;; XXX: 'copy-recursively' cannot deal with device nodes, so
                  ;; explicitly avoid /dev.
                  (for-each (lambda (file)
                              (unless (string=? "dev" file)
                                (copy-recursively (string-append "/real-root/"
                                                                 file)
                                                  (string-append "/root/"
                                                                 file)
                                                  #:log (%make-void-port
                                                         "w"))))
                            (scandir "/real-root"
                                     (lambda (file)
                                       (not (member file '("." ".."))))))

                  ;; TODO: Unmount /real-root.
                  )
                (mount root "/root" "ext3")))
          (lambda args
            (format (current-error-port) "exception while mounting '~a': ~s~%"
                    root args)
            (start-repl)))
        (mount "none" "/root" "tmpfs"))

    (mount-essential-file-systems #:root "/root")

    (unless (file-exists? "/root/dev")
      (mkdir "/root/dev")
      (make-essential-device-nodes #:root "/root"))

    ;; Mount the specified file systems.
    (for-each (match-lambda
               (('cifs source target)
                (let ((target (string-append "/root/" target)))
                  (mkdir-p target)
                  (mount-qemu-smb-share source target)))
               (('9p source target)
                (let ((target (string-append "/root/" target)))
                  (mkdir-p target)
                  (mount-qemu-9p source target))))
              mounts)

    (when guile-modules-in-chroot?
      ;; Copy the directories that contain .scm and .go files so that the
      ;; child process in the chroot can load modules (we would bind-mount
      ;; them but for some reason that fails with EINVAL -- XXX).
      (mkdir-p "/root/share")
      (mkdir-p "/root/lib")
      (mount "none" "/root/share" "tmpfs")
      (mount "none" "/root/lib" "tmpfs")
      (copy-recursively "/share" "/root/share"
                        #:log (%make-void-port "w"))
      (copy-recursively "/lib" "/root/lib"
                        #:log (%make-void-port "w")))

    (if to-load
        (begin
          (format #t "loading '~a'...\n" to-load)
          (chroot "/root")
          ;; TODO: Remove /lib, /share, and /loader.go.
          (catch #t
            (lambda ()
              (primitive-load to-load))
            (lambda args
              (format (current-error-port) "'~a' raised an exception: ~s~%"
                      to-load args)
              (start-repl)))
          (format (current-error-port)
                  "boot program '~a' terminated, rebooting~%"
                  to-load)
          (sleep 2)
          (reboot))
        (begin
          (display "no boot file passed via '--load'\n")
          (display "entering a warm and cozy REPL\n")
          (start-repl)))))

;;; linux-initrd.scm ends here