guix/gnu/system/file-systems.scm

;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2013, 2014, 2015, 2016, 2017 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 system file-systems)
  #:use-module (ice-9 match)
  #:use-module (srfi srfi-1)
  #:use-module (guix records)
  #:use-module (gnu system uuid)
  #:re-export (uuid                               ;backward compatibility
               string->uuid
               uuid->string)
  #:export (<file-system>
            file-system
            file-system?
            file-system-device
            file-system-title
            file-system-mount-point
            file-system-type
            file-system-needed-for-boot?
            file-system-flags
            file-system-options
            file-system-mount?
            file-system-check?
            file-system-create-mount-point?
            file-system-dependencies

            file-system-type-predicate

            file-system->spec
            spec->file-system
            specification->file-system-mapping

            %fuse-control-file-system
            %binary-format-file-system
            %shared-memory-file-system
            %pseudo-terminal-file-system
            %tty-gid
            %immutable-store
            %control-groups
            %elogind-file-systems

            %base-file-systems
            %container-file-systems

            <file-system-mapping>
            file-system-mapping
            file-system-mapping?
            file-system-mapping-source
            file-system-mapping-target
            file-system-mapping-writable?

            file-system-mapping->bind-mount

            %store-mapping
            %network-configuration-files
            %network-file-mappings))

;;; Commentary:
;;;
;;; Declaring file systems to be mounted.
;;;
;;; Note: this file system is used both in the Shepherd and on the "host
;;; side", so it must not include (gnu packages …) modules.
;;;
;;; Code:

;; File system declaration.
(define-record-type* <file-system> file-system
  make-file-system
  file-system?
  (device           file-system-device)           ; string
  (title            file-system-title             ; 'device | 'label | 'uuid
                    (default 'device))
  (mount-point      file-system-mount-point)      ; string
  (type             file-system-type)             ; string
  (flags            file-system-flags             ; list of symbols
                    (default '()))
  (options          file-system-options           ; string or #f
                    (default #f))
  (mount?           file-system-mount?            ; Boolean
                    (default #t))
  (needed-for-boot? %file-system-needed-for-boot? ; Boolean
                    (default #f))
  (check?           file-system-check?            ; Boolean
                    (default #t))
  (create-mount-point? file-system-create-mount-point? ; Boolean
                       (default #f))
  (dependencies     file-system-dependencies      ; list of <file-system>
                    (default '())))               ; or <mapped-device>

;; Note: This module is used both on the build side and on the host side.
;; Arrange not to pull (guix store) and (guix config) because the latter
;; differs from user to user.
(define (%store-prefix)
  "Return the store prefix."
  (cond ((resolve-module '(guix store) #:ensure #f)
         =>
         (lambda (store)
           ((module-ref store '%store-prefix))))
        ((getenv "NIX_STORE")
         => identity)
        (else
         "/gnu/store")))

(define %not-slash
  (char-set-complement (char-set #\/)))

(define (file-prefix? file1 file2)
  "Return #t if FILE1 denotes the name of a file that is a parent of FILE2,
where both FILE1 and FILE2 are absolute file name.  For example:

  (file-prefix? \"/gnu\" \"/gnu/store\")
  => #t

  (file-prefix? \"/gn\" \"/gnu/store\")
  => #f
"
  (and (string-prefix? "/" file1)
       (string-prefix? "/" file2)
       (let loop ((file1 (string-tokenize file1 %not-slash))
                  (file2 (string-tokenize file2 %not-slash)))
         (match file1
           (()
            #t)
           ((head1 tail1 ...)
            (match file2
              ((head2 tail2 ...)
               (and (string=? head1 head2) (loop tail1 tail2)))
              (()
               #f)))))))

(define (file-system-needed-for-boot? fs)
  "Return true if FS has the 'needed-for-boot?' flag set, or if it holds the
store--e.g., if FS is the root file system."
  (or (%file-system-needed-for-boot? fs)
      (and (file-prefix? (file-system-mount-point fs) (%store-prefix))
           (not (memq 'bind-mount (file-system-flags fs))))))

(define (file-system->spec fs)
  "Return a list corresponding to file-system FS that can be passed to the
initrd code."
  (match fs
    (($ <file-system> device title mount-point type flags options _ _ check?)
     (list (if (uuid? device)
               (uuid-bytevector device)
               device)
           title mount-point type flags options check?))))

(define (spec->file-system sexp)
  "Deserialize SEXP, a list, to the corresponding <file-system> object."
  (match sexp
    ((device title mount-point type flags options check?)
     (file-system
       (device device) (title title)
       (mount-point mount-point) (type type)
       (flags flags) (options options)
       (check? check?)))))

(define (specification->file-system-mapping spec writable?)
  "Read the SPEC and return the corresponding <file-system-mapping>.  SPEC is
a string of the form \"SOURCE\" or \"SOURCE=TARGET\".  The former specifies
that SOURCE from the host should be mounted at SOURCE in the other system.
The latter format specifies that SOURCE from the host should be mounted at
TARGET in the other system."
  (let ((index (string-index spec #\=)))
    (if index
        (file-system-mapping
         (source (substring spec 0 index))
         (target (substring spec (+ 1 index)))
         (writable? writable?))
        (file-system-mapping
         (source spec)
         (target spec)
         (writable? writable?)))))


;;;
;;; Common file systems.
;;;

(define %fuse-control-file-system
  ;; Control file system for Linux' file systems in user-space (FUSE).
  (file-system
    (device "fusectl")
    (mount-point "/sys/fs/fuse/connections")
    (type "fusectl")
    (check? #f)))

(define %binary-format-file-system
  ;; Support for arbitrary executable binary format.
  (file-system
    (device "binfmt_misc")
    (mount-point "/proc/sys/fs/binfmt_misc")
    (type "binfmt_misc")
    (check? #f)))

(define %tty-gid
  ;; ID of the 'tty' group.  Allocate it statically to make it easy to refer
  ;; to it from here and from the 'tty' group definitions.
  996)

(define %pseudo-terminal-file-system
  ;; The pseudo-terminal file system.  It needs to be mounted so that
  ;; statfs(2) returns DEVPTS_SUPER_MAGIC like libc's getpt(3) expects (and
  ;; thus openpty(3) and its users, such as xterm.)
  (file-system
    (device "none")
    (mount-point "/dev/pts")
    (type "devpts")
    (check? #f)
    (needed-for-boot? #f)
    (create-mount-point? #t)
    (options (string-append "gid=" (number->string %tty-gid) ",mode=620"))))

(define %shared-memory-file-system
  ;; Shared memory.
  (file-system
    (device "tmpfs")
    (mount-point "/dev/shm")
    (type "tmpfs")
    (check? #f)
    (flags '(no-suid no-dev))
    (options "size=50%")                         ;TODO: make size configurable
    (create-mount-point? #t)))

(define %immutable-store
  ;; Read-only store to avoid users or daemons accidentally modifying it.
  ;; 'guix-daemon' has provisions to remount it read-write in its own name
  ;; space.
  (file-system
    (device (%store-prefix))
    (mount-point (%store-prefix))
    (type "none")
    (check? #f)
    (flags '(read-only bind-mount))))

(define %control-groups
  (let ((parent (file-system
                  (device "cgroup")
                  (mount-point "/sys/fs/cgroup")
                  (type "tmpfs")
                  (check? #f))))
    (cons parent
          (map (lambda (subsystem)
                 (file-system
                   (device "cgroup")
                   (mount-point (string-append "/sys/fs/cgroup/" subsystem))
                   (type "cgroup")
                   (check? #f)
                   (options subsystem)
                   (create-mount-point? #t)

                   ;; This must be mounted after, and unmounted before the
                   ;; parent directory.
                   (dependencies (list parent))))
               '("cpuset" "cpu" "cpuacct" "memory" "devices" "freezer"
                 "blkio" "perf_event" "hugetlb")))))

(define %elogind-file-systems
  ;; We don't use systemd, but these file systems are needed for elogind,
  ;; which was extracted from systemd.
  (list (file-system
          (device "none")
          (mount-point "/run/systemd")
          (type "tmpfs")
          (check? #f)
          (flags '(no-suid no-dev no-exec))
          (options "mode=0755")
          (create-mount-point? #t))
        (file-system
          (device "none")
          (mount-point "/run/user")
          (type "tmpfs")
          (check? #f)
          (flags '(no-suid no-dev no-exec))
          (options "mode=0755")
          (create-mount-point? #t))
        ;; Elogind uses cgroups to organize processes, allowing it to map PIDs
        ;; to sessions.  Elogind's cgroup hierarchy isn't associated with any
        ;; resource controller ("subsystem").
        (file-system
          (device "cgroup")
          (mount-point "/sys/fs/cgroup/elogind")
          (type "cgroup")
          (check? #f)
          (options "none,name=elogind")
          (create-mount-point? #t)
          (dependencies (list (car %control-groups))))))

(define %base-file-systems
  ;; List of basic file systems to be mounted.  Note that /proc and /sys are
  ;; currently mounted by the initrd.
  (append (list %pseudo-terminal-file-system
                %shared-memory-file-system
                %immutable-store)
          %control-groups))

;; File systems for Linux containers differ from %base-file-systems in that
;; they impose additional restrictions such as no-exec or need different
;; options to function properly.
;;
;; The file system flags and options conform to the libcontainer
;; specification:
;; https://github.com/docker/libcontainer/blob/master/SPEC.md#filesystem
(define %container-file-systems
  (list
   ;; Pseudo-terminal file system.
   (file-system
     (device "none")
     (mount-point "/dev/pts")
     (type "devpts")
     (flags '(no-exec no-suid))
     (needed-for-boot? #t)
     (create-mount-point? #t)
     (check? #f)
     (options "newinstance,ptmxmode=0666,mode=620"))
   ;; Shared memory file system.
   (file-system
     (device "tmpfs")
     (mount-point "/dev/shm")
     (type "tmpfs")
     (flags '(no-exec no-suid no-dev))
     (options "mode=1777,size=65536k")
     (needed-for-boot? #t)
     (create-mount-point? #t)
     (check? #f))
   ;; Message queue file system.
   (file-system
     (device "mqueue")
     (mount-point "/dev/mqueue")
     (type "mqueue")
     (flags '(no-exec no-suid no-dev))
     (needed-for-boot? #t)
     (create-mount-point? #t)
     (check? #f))))


;;;
;;; Shared file systems, for VMs/containers.
;;;

;; Mapping of host file system SOURCE to mount point TARGET in the guest.
(define-record-type* <file-system-mapping> file-system-mapping
  make-file-system-mapping
  file-system-mapping?
  (source    file-system-mapping-source)          ;string
  (target    file-system-mapping-target)          ;string
  (writable? file-system-mapping-writable?        ;Boolean
             (default #f)))

(define (file-system-mapping->bind-mount mapping)
  "Return a file system that realizes MAPPING, a <file-system-mapping>, using
a bind mount."
  (match mapping
    (($ <file-system-mapping> source target writable?)
     (file-system
       (mount-point target)
       (device source)
       (type "none")
       (flags (if writable?
                  '(bind-mount)
                  '(bind-mount read-only)))
       (check? #f)
       (create-mount-point? #t)))))

(define %store-mapping
  ;; Mapping of the host's store into the guest.
  (file-system-mapping
   (source (%store-prefix))
   (target (%store-prefix))
   (writable? #f)))

(define %network-configuration-files
  ;; List of essential network configuration files.
  '("/etc/resolv.conf"
    "/etc/nsswitch.conf"
    "/etc/services"
    "/etc/hosts"))

(define %network-file-mappings
  ;; List of file mappings for essential network files.
  (filter-map (lambda (file)
                (file-system-mapping
                 (source file)
                 (target file)
                 ;; XXX: On some GNU/Linux systems, /etc/resolv.conf is a
                 ;; symlink to a file in a tmpfs which, for an unknown reason,
                 ;; cannot be bind mounted read-only within the container.
                 (writable? (string=? file "/etc/resolv.conf"))))
              %network-configuration-files))

(define (file-system-type-predicate type)
  "Return a predicate that, when passed a file system, returns #t if that file
system has the given TYPE."
  (lambda (fs)
    (string=? (file-system-type fs) type)))

;;; file-systems.scm ends here