summaryrefslogtreecommitdiff
path: root/gnu/build/file-systems.scm
blob: c58d23cfbde8272f57dd386f16696118a8ac8ccd (about) (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 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 file-systems)
  #:use-module (guix build utils)
  #:use-module (rnrs io ports)
  #:use-module (rnrs bytevectors)
  #:use-module (ice-9 match)
  #:use-module (ice-9 rdelim)
  #:use-module (ice-9 format)
  #:use-module (system foreign)
  #:autoload   (system repl repl) (start-repl)
  #:use-module (srfi srfi-1)
  #:use-module (srfi srfi-26)
  #:export (disk-partitions
            partition-label-predicate
            partition-uuid-predicate
            find-partition-by-label
            find-partition-by-uuid
            canonicalize-device-spec

            MS_RDONLY
            MS_NOSUID
            MS_NODEV
            MS_NOEXEC
            MS_BIND
            MS_MOVE
            bind-mount

            mount-flags->bit-mask
            check-file-system
            mount-file-system))

;;; Commentary:
;;;
;;; This modules provides tools to deal with disk partitions, and to mount and
;;; check file systems.
;;;
;;; Code:

;; 'mount' is already defined in the statically linked Guile used for initial
;; RAM disks, but in all other cases the (guix build syscalls) module contains
;; the mount binding.
(eval-when (expand load eval)
  (unless (defined? 'mount)
    (module-use! (current-module)
                 (resolve-interface '(guix build syscalls)))))

;; Linux mount flags, from libc's <sys/mount.h>.
(define MS_RDONLY 1)
(define MS_NOSUID 2)
(define MS_NODEV  4)
(define MS_NOEXEC 8)
(define MS_REMOUNT 32)
(define MS_BIND 4096)
(define MS_MOVE 8192)

(define (bind-mount source target)
  "Bind-mount SOURCE at TARGET."
  (mount source target "" MS_BIND))

(define-syntax %ext2-endianness
  ;; Endianness of ext2 file systems.
  (identifier-syntax (endianness little)))

;; Offset in bytes of interesting parts of an ext2 superblock.  See
;; <http://www.nongnu.org/ext2-doc/ext2.html#DEF-SUPERBLOCK>.
;; TODO: Use "packed structs" from Guile-OpenGL or similar.
(define-syntax %ext2-sblock-magic       (identifier-syntax 56))
(define-syntax %ext2-sblock-creator-os  (identifier-syntax 72))
(define-syntax %ext2-sblock-uuid        (identifier-syntax 104))
(define-syntax %ext2-sblock-volume-name (identifier-syntax 120))

(define (read-ext2-superblock device)
  "Return the raw contents of DEVICE's ext2 superblock as a bytevector, or #f
if DEVICE does not contain an ext2 file system."
  (define %ext2-magic
    ;; The magic bytes that identify an ext2 file system.
    #xef53)

  (define superblock-size
    ;; Size of the interesting part of an ext2 superblock.
    264)

  (define block
    ;; The superblock contents.
    (make-bytevector superblock-size))

  (call-with-input-file device
    (lambda (port)
      (seek port 1024 SEEK_SET)

      ;; Note: work around <http://bugs.gnu.org/17466>.
      (and (eqv? superblock-size (get-bytevector-n! port block 0
                                                    superblock-size))
           (let ((magic (bytevector-u16-ref block %ext2-sblock-magic
                                            %ext2-endianness)))
             (and (= magic %ext2-magic)
                  block))))))

(define (ext2-superblock-uuid sblock)
  "Return the UUID of ext2 superblock SBLOCK as a 16-byte bytevector."
  (let ((uuid (make-bytevector 16)))
    (bytevector-copy! sblock %ext2-sblock-uuid uuid 0 16)
    uuid))

(define (ext2-superblock-volume-name sblock)
  "Return the volume name of SBLOCK as a string of at most 16 characters, or
#f if SBLOCK has no volume name."
  (let ((bv (make-bytevector 16)))
    (bytevector-copy! sblock %ext2-sblock-volume-name bv 0 16)

    ;; This is a Latin-1, nul-terminated string.
    (let ((bytes (take-while (negate zero?) (bytevector->u8-list bv))))
      (if (null? bytes)
          #f
          (list->string (map integer->char bytes))))))

(define (disk-partitions)
  "Return the list of device names corresponding to valid disk partitions."
  (define (partition? major minor)
    (let ((marker (format #f "/sys/dev/block/~a:~a/partition" major minor)))
      (catch 'system-error
        (lambda ()
          (not (zero? (call-with-input-file marker read))))
        (lambda args
          (if (= ENOENT (system-error-errno args))
              #f
              (apply throw args))))))

  (call-with-input-file "/proc/partitions"
    (lambda (port)
      ;; Skip the two header lines.
      (read-line port)
      (read-line port)

      ;; Read each subsequent line, and extract the last space-separated
      ;; field.
      (let loop ((parts '()))
        (let ((line  (read-line port)))
          (if (eof-object? line)
              (reverse parts)
              (match (string-tokenize line)
                (((= string->number major) (= string->number minor)
                  blocks name)
                 (if (partition? major minor)
                     (loop (cons name parts))
                     (loop parts))))))))))

(define (read-ext2-superblock* device)
  "Like 'read-ext2-superblock', but return #f when DEVICE does not exist
instead of throwing an exception."
  (catch 'system-error
    (lambda ()
      (read-ext2-superblock device))
    (lambda args
      ;; When running on the hand-made /dev,
      ;; 'disk-partitions' could return partitions for which
      ;; we have no /dev node.  Handle that gracefully.
      (if (= ENOENT (system-error-errno args))
          (begin
            (format (current-error-port)
                    "warning: device '~a' not found~%" device)
            #f)
          (apply throw args)))))

(define (partition-predicate field =)
  "Return a predicate that returns true if the FIELD of an ext2 superblock is
= to the given value."
  (lambda (expected)
    "Return a procedure that, when applied to a partition name such as \"sda1\",
returns #t if that partition's volume name is LABEL."
    (lambda (part)
      (let* ((device (string-append "/dev/" part))
             (sblock (read-ext2-superblock* device)))
        (and sblock
             (let ((actual (field sblock)))
               (and actual
                    (= actual expected))))))))

(define partition-label-predicate
  (partition-predicate ext2-superblock-volume-name string=?))

(define partition-uuid-predicate
  (partition-predicate ext2-superblock-uuid bytevector=?))

(define (find-partition-by-label label)
  "Return the first partition found whose volume name is LABEL, or #f if none
were found."
  (and=> (find (partition-label-predicate label)
               (disk-partitions))
         (cut string-append "/dev/" <>)))

(define (find-partition-by-uuid uuid)
  "Return the first partition whose unique identifier is UUID (a bytevector),
or #f if none was found."
  (and=> (find (partition-uuid-predicate uuid)
               (disk-partitions))
         (cut string-append "/dev/" <>)))

(define-syntax %network-byte-order
  (identifier-syntax (endianness big)))

(define (uuid->string uuid)
  "Convert UUID, a 16-byte bytevector, to its string representation, something
like \"6b700d61-5550-48a1-874c-a3d86998990e\"."
  ;; See <https://tools.ietf.org/html/rfc4122>.
  (let ((time-low  (bytevector-uint-ref uuid 0 %network-byte-order 4))
        (time-mid  (bytevector-uint-ref uuid 4 %network-byte-order 2))
        (time-hi   (bytevector-uint-ref uuid 6 %network-byte-order 2))
        (clock-seq (bytevector-uint-ref uuid 8 %network-byte-order 2))
        (node      (bytevector-uint-ref uuid 10 %network-byte-order 6)))
    (format #f "~8,'0x-~4,'0x-~4,'0x-~4,'0x-~12,'0x"
            time-low time-mid time-hi clock-seq node)))

(define* (canonicalize-device-spec spec #:optional (title 'any))
  "Return the device name corresponding to SPEC.  TITLE is a symbol, one of
the following:

  • 'device', in which case SPEC is known to designate a device node--e.g.,
     \"/dev/sda1\";
  • 'label', in which case SPEC is known to designate a partition label--e.g.,
     \"my-root-part\";
  • 'uuid', in which case SPEC must be a UUID (a 16-byte bytevector)
     designating a partition;
  • 'any', in which case SPEC can be anything.
"
  (define max-trials
    ;; Number of times we retry partition label resolution, 1 second per
    ;; trial.  Note: somebody reported a delay of 16 seconds (!) before their
    ;; USB key would be detected by the kernel, so we must wait for at least
    ;; this long.
    20)

  (define canonical-title
    ;; The realm of canonicalization.
    (if (eq? title 'any)
        (if (string? spec)
            (if (string-prefix? "/" spec)
                'device
                'label)
            'uuid)
        title))

  (define (resolve find-partition spec fmt)
    (let loop ((count 0))
      (let ((device (find-partition spec)))
        (or device
            ;; Some devices take a bit of time to appear, most notably USB
            ;; storage devices.  Thus, wait for the device to appear.
            (if (> count max-trials)
                (error "failed to resolve partition" (fmt spec))
                (begin
                  (format #t "waiting for partition '~a' to appear...~%"
                          (fmt spec))
                  (sleep 1)
                  (loop (+ 1 count))))))))

  (case canonical-title
    ((device)
     ;; Nothing to do.
     spec)
    ((label)
     ;; Resolve the label.
     (resolve find-partition-by-label spec identity))
    ((uuid)
     (resolve find-partition-by-uuid spec uuid->string))
    (else
     (error "unknown device title" title))))

(define (check-file-system device type)
  "Run a file system check of TYPE on DEVICE."
  (define fsck
    (string-append "fsck." type))

  (let ((status (system* fsck "-v" "-p" "-C" "0" device)))
    (match (status:exit-val status)
      (0
       #t)
      (1
       (format (current-error-port) "'~a' corrected errors on ~a; continuing~%"
               fsck device))
      (2
       (format (current-error-port) "'~a' corrected errors on ~a; rebooting~%"
               fsck device)
       (sleep 3)
       (reboot))
      (code
       (format (current-error-port) "'~a' exited with code ~a on ~a; spawning REPL~%"
               fsck code device)
       (start-repl)))))

(define (mount-flags->bit-mask flags)
  "Return the number suitable for the 'flags' argument of 'mount' that
corresponds to the symbols listed in FLAGS."
  (let loop ((flags flags))
    (match flags
      (('read-only rest ...)
       (logior MS_RDONLY (loop rest)))
      (('bind-mount rest ...)
       (logior MS_BIND (loop rest)))
      (('no-suid rest ...)
       (logior MS_NOSUID (loop rest)))
      (('no-dev rest ...)
       (logior MS_NODEV (loop rest)))
      (('no-exec rest ...)
       (logior MS_NOEXEC (loop rest)))
      (()
       0))))

(define* (mount-file-system spec #:key (root "/root"))
  "Mount the file system described by SPEC under ROOT.  SPEC must have the
form:

  (DEVICE TITLE MOUNT-POINT TYPE (FLAGS ...) OPTIONS CHECK?)

DEVICE, MOUNT-POINT, and TYPE must be strings; OPTIONS can be a string or #f;
FLAGS must be a list of symbols.  CHECK? is a Boolean indicating whether to
run a file system check."
  (match spec
    ((source title mount-point type (flags ...) options check?)
     (let ((source      (canonicalize-device-spec source title))
           (mount-point (string-append root "/" mount-point))
           (flags       (mount-flags->bit-mask flags)))
       (when check?
         (check-file-system source type))
       (mkdir-p mount-point)
       (mount source mount-point type flags options)

       ;; For read-only bind mounts, an extra remount is needed, as per
       ;; <http://lwn.net/Articles/281157/>, which still applies to Linux 4.0.
       (when (and (= MS_BIND (logand flags MS_BIND))
                  (= MS_RDONLY (logand flags MS_RDONLY)))
         (let ((flags (logior MS_BIND MS_REMOUNT MS_RDONLY)))
           (mount source mount-point type flags #f)))))))

;;; file-systems.scm ends here