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guix/gnu/build/linux-boot.scm
Ludovic Courtès 01ed3c4fe5 linux-boot: Don't fail if /root/etc/mtab is a dangling symlink. 
Reported Joshua Grant.
Patch suggested by Mark H Weaver.

* gnu/build/linux-boot.scm (mount-root-file-system): Use
  'false-if-exception' instead of 'when (file-exists? ...)' to account
  for dangling symlinks.
2015-01-28 21:32:58 +01:00

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;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2013, 2014, 2015 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 (gnu build linux-boot)
#:use-module (rnrs io ports)
#:use-module (system repl error-handling)
#: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)
#:use-module (gnu build linux-modules)
#:use-module (gnu build file-systems)
#:export (mount-essential-file-systems
linux-command-line
find-long-option
make-essential-device-nodes
configure-qemu-networking
bind-mount
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 (move-essential-file-systems root)
"Move currently mounted essential file systems to ROOT."
(for-each (lambda (dir)
(let ((target (string-append root dir)))
(unless (file-exists? target)
(mkdir target))
(mount dir target "" MS_MOVE)))
'("/proc" "/sys")))
(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 (find-long-option option arguments)
"Find OPTION among ARGUMENTS, where OPTION is something like \"--load\".
Return the value associated with OPTION, or #f on failure."
(let ((opt (string-append option "=")))
(and=> (find (cut string-prefix? opt <>)
arguments)
(lambda (arg)
(substring arg (+ 1 (string-index arg #\=)))))))
(define* (make-disk-device-nodes base major #:optional (minor 0))
"Make the block device nodes around BASE (something like \"/root/dev/sda\")
with the given MAJOR number, starting with MINOR."
(mknod base 'block-special #o644 (device-number major minor))
(let loop ((i 1))
(when (< i 16)
(mknod (string-append base (number->string i))
'block-special #o644 (device-number major (+ minor i)))
(loop (+ i 1)))))
(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.
(make-disk-device-nodes (scope "dev/sda") 8)
(make-disk-device-nodes (scope "dev/sdb") 8 16)
(make-disk-device-nodes (scope "dev/sdc") 8 32)
(make-disk-device-nodes (scope "dev/sdd") 8 48)
;; SCSI CD-ROM devices (aka. "/dev/sr0" etc.).
(mknod (scope "dev/scd0") 'block-special #o644 (device-number 11 0))
(mknod (scope "dev/scd1") 'block-special #o644 (device-number 11 1))
;; The virtio (para-virtualized) block devices, as supported by QEMU/KVM.
(make-disk-device-nodes (scope "dev/vda") 252)
;; 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))
;; Inputs (used by Xorg.)
(unless (file-exists? (scope "dev/input"))
(mkdir (scope "dev/input")))
(mknod (scope "dev/input/mice") 'char-special #o640 (device-number 13 63))
(mknod (scope "dev/input/mouse0") 'char-special #o640 (device-number 13 32))
(mknod (scope "dev/input/event0") 'char-special #o640 (device-number 13 64))
;; System console. This node is magically created by the kernel on the
;; initrd's root, so don't try to create it in that case.
(unless (string=? root "/")
(mknod (scope "dev/console") 'char-special #o600
(device-number 5 1)))
;; TTYs.
(mknod (scope "dev/tty") 'char-special #o600
(device-number 5 0))
(chmod (scope "dev/tty") #o666)
(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)))))
;; Serial line.
(mknod (scope "dev/ttyS0") 'char-special #o660
(device-number 4 64))
;; Pseudo ttys.
(mknod (scope "dev/ptmx") 'char-special #o666
(device-number 5 2))
(chmod (scope "dev/ptmx") #o666)
;; Create /dev/pts; it will be mounted later, at boot time.
(unless (file-exists? (scope "dev/pts"))
(mkdir (scope "dev/pts")))
;; 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, notably relied on by guix-daemon.
(for-each (match-lambda
((file major minor)
(mknod (scope file) 'char-special #o666
(device-number major minor))
(chmod (scope file) #o666)))
'(("dev/null" 1 3)
("dev/zero" 1 5)
("dev/full" 1 7)
("dev/random" 1 8)
("dev/urandom" 1 9)))
(symlink "/proc/self/fd" (scope "dev/fd"))
(symlink "/proc/self/fd/0" (scope "dev/stdin"))
(symlink "/proc/self/fd/1" (scope "dev/stdout"))
(symlink "/proc/self/fd/2" (scope "dev/stderr"))
;; Loopback devices.
(let loop ((i 0))
(when (< i 8)
(mknod (scope (string-append "dev/loop" (number->string i)))
'block-special #o660
(device-number 7 i))
(loop (+ 1 i))))
;; File systems in user space (FUSE).
(mknod (scope "dev/fuse") 'char-special #o666 (device-number 10 229)))
(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))
;; Hello! We used to create /etc/resolv.conf here, with "nameserver
;; 10.0.2.3\n". However, with Linux-libre 3.16, we're getting ENOSPC.
;; And since it's actually unnecessary, it's gone.
(logand (network-interface-flags sock interface) IFF_UP)))
(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 (pidof program)
"Return the PID of the first presumed instance of PROGRAM."
(let ((program (basename program)))
(find (lambda (pid)
(let ((exe (format #f "/proc/~a/exe" pid)))
(and=> (false-if-exception (readlink exe))
(compose (cut string=? program <>) basename))))
(filter-map string->number (scandir "/proc")))))
(define* (mount-root-file-system root type
#:key volatile-root? (unionfs "unionfs"))
"Mount the root file system of type TYPE at device ROOT. If VOLATILE-ROOT?
is true, mount ROOT read-only and make it a union with a writable tmpfs using
UNIONFS."
(define (mark-as-not-killable pid)
;; Tell the 'user-processes' dmd service that PID must be kept alive when
;; shutting down.
(mkdir-p "/root/etc/dmd")
(let ((port (open-file "/root/etc/dmd/do-not-kill" "a")))
(chmod port #o600)
(write pid port)
(newline port)
(close-port port)))
(if volatile-root?
(begin
(mkdir-p "/real-root")
(mount root "/real-root" type MS_RDONLY)
(mkdir-p "/rw-root")
(mount "none" "/rw-root" "tmpfs")
;; We want read-write /dev nodes.
(make-essential-device-nodes #:root "/rw-root")
;; Make /root a union of the tmpfs and the actual root. Use
;; 'max_files' to set a high RLIMIT_NOFILE for the unionfs process
;; itself. Failing to do that, we quickly run out of file
;; descriptors; see <http://bugs.gnu.org/17827>.
(unless (zero? (system* unionfs "-o"
"cow,allow_other,use_ino,suid,dev,max_files=65536"
"/rw-root=RW:/real-root=RO"
"/root"))
(error "unionfs failed"))
;; Make sure unionfs remains alive till the end. Because
;; 'fuse_daemonize' doesn't tell the PID of the forked daemon, we
;; have to resort to 'pidof' here.
(mark-as-not-killable (pidof unionfs)))
(begin
(check-file-system root type)
(mount root "/root" type)))
;; Make sure /root/etc/mtab is a symlink to /proc/self/mounts.
(false-if-exception
(delete-file "/root/etc/mtab"))
(symlink "/proc/self/mounts" "/root/etc/mtab"))
(define (switch-root root)
"Switch to ROOT as the root file system, in a way similar to what
util-linux' switch_root(8) does."
(move-essential-file-systems root)
(chdir root)
;; Since we're about to 'rm -rf /', try to make sure we're on an initrd.
;; TODO: Use 'statfs' to check the fs type, like klibc does.
(when (or (not (file-exists? "/init")) (directory-exists? "/home"))
(format (current-error-port)
"The root file system is probably not an initrd; \
bailing out.~%root contents: ~s~%" (scandir "/"))
(force-output (current-error-port))
(exit 1))
;; Delete files from the old root, without crossing mount points (assuming
;; there are no mount points in sub-directories.) That means we're leaving
;; the empty ROOT directory behind us, but that's OK.
(let ((root-device (stat:dev (stat "/"))))
(for-each (lambda (file)
(unless (member file '("." ".."))
(let* ((file (string-append "/" file))
(device (stat:dev (lstat file))))
(when (= device root-device)
(delete-file-recursively file)))))
(scandir "/")))
;; Make ROOT the new root.
(mount root "/" "" MS_MOVE)
(chroot ".")
(chdir "/")
(when (file-exists? "/dev/console")
;; Close the standard file descriptors since they refer to the old
;; /dev/console, and reopen them.
(let ((console (open-file "/dev/console" "r+b0")))
(for-each close-fdes '(0 1 2))
(dup2 (fileno console) 0)
(dup2 (fileno console) 1)
(dup2 (fileno console) 2)
(close-port console))))
(define* (boot-system #:key
(linux-modules '())
linux-module-directory
qemu-guest-networking?
volatile-root?
pre-mount
(mounts '()))
"This procedure is meant to be called from an initrd. Boot a system by
first loading LINUX-MODULES (a list of module names) from
LINUX-MODULE-DIRECTORY, then setting up QEMU guest networking if
QEMU-GUEST-NETWORKING? is true, calling PRE-MOUNT, 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'.
Mount the root file system, specified by the '--root' command-line argument,
if any.
MOUNTS must be a list suitable for 'mount-file-system'.
When VOLATILE-ROOT? is true, the root file system is writable but any changes
to it are lost."
(define root-mount-point?
(match-lambda
((device _ "/" _ ...) #t)
(_ #f)))
(define root-fs-type
(or (any (match-lambda
((device _ "/" type _ ...) type)
(_ #f))
mounts)
"ext4"))
(define (lookup-module name)
(string-append linux-module-directory "/"
(ensure-dot-ko name)))
(display "Welcome, this is GNU's early boot Guile.\n")
(display "Use '--repl' for an initrd REPL.\n\n")
(call-with-error-handling
(lambda ()
(mount-essential-file-systems)
(let* ((args (linux-command-line))
(to-load (find-long-option "--load" args))
(root (find-long-option "--root" args)))
(when (member "--repl" args)
(start-repl))
(display "loading kernel modules...\n")
(current-module-debugging-port (current-output-port))
(for-each (cut load-linux-module* <>
#:lookup-module lookup-module)
(map lookup-module 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"))
(when (procedure? pre-mount)
;; Do whatever actions are needed before mounting the root file
;; system--e.g., installing device mappings. Error out when the
;; return value is false.
(unless (pre-mount)
(error "pre-mount actions failed")))
(if root
(mount-root-file-system (canonicalize-device-spec root)
root-fs-type
#:volatile-root? volatile-root?)
(mount "none" "/root" "tmpfs"))
(unless (file-exists? "/root/dev")
(mkdir "/root/dev")
(make-essential-device-nodes #:root "/root"))
;; Mount the specified file systems.
(for-each mount-file-system
(remove root-mount-point? mounts))
(if to-load
(begin
(switch-root "/root")
(format #t "loading '~a'...\n" to-load)
;; TODO: Remove /lib, /share, and /loader.go.
(primitive-load to-load)
(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
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