guix/gnu/build/file-systems.scm
David Craven 974e02da76
file-systems: Refactor file system detection logic.
* gnu/build/file-systems.scm (read-superblock,
  null-terminated-latin1->string): New variables.
  (sub-bytevector): Move to general section.
  (ext2-superblock?, read-ext2-superblock): New variables.
  (ext2-superblock-uuid, ext2-superblock-volume-name): Use
  sub-bytevector and null-terminated-latin1->string.
  (%ext2-sblock-magic, %ext2-sblock-creator-os, %ext2-sblock-uuid,
  %ext2-sblock-volume-name): Inline constants.
  (luks-superblock?, read-luks-header): New variables.
  (%luks-header-size, %luks-magic): Inline.
  (partition-label-predicate, partition-uuid-predicate,
  luks-partition-uuid-predicate): Use new functions.
2017-01-06 15:06:42 +01:00

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;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2014, 2015, 2016 Ludovic Courtès <ludo@gnu.org>
;;; Copyright © 2016 David Craven <david@craven.ch>
;;;
;;; 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 (guix build bournish)
#:use-module (guix build syscalls)
#: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 (ice-9 regex)
#: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
partition-luks-uuid-predicate
find-partition-by-label
find-partition-by-uuid
find-partition-by-luks-uuid
canonicalize-device-spec
uuid->string
string->uuid
bind-mount
mount-flags->bit-mask
check-file-system
mount-file-system)
#:re-export (mount
umount
MS_BIND
MS_MOVE
MS_RDONLY))
;;; 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, in which case the bindings in (guix build syscalls) do not work
;; (the FFI bindings do not work there). Override them in that case.
(when (module-defined? the-scm-module 'mount)
(set! mount (@ (guile) mount))
(set! umount (@ (guile) umount)))
(define (bind-mount source target)
"Bind-mount SOURCE at TARGET."
(mount source target "" MS_BIND))
(define (read-superblock device offset size magic?)
"Read a superblock of SIZE from OFFSET and DEVICE. Return the raw
superblock on success, and #f if no valid superblock was found. MAGIC?
takes a bytevector and returns #t when it's a valid superblock."
(call-with-input-file device
(lambda (port)
(seek port offset SEEK_SET)
(let ((block (make-bytevector size)))
(match (get-bytevector-n! port block 0 (bytevector-length block))
((? eof-object?)
#f)
((? number? len)
(and (= len (bytevector-length block))
(and (magic? block)
block))))))))
(define (sub-bytevector bv start size)
"Return a copy of the SIZE bytes of BV starting from offset START."
(let ((result (make-bytevector size)))
(bytevector-copy! bv start result 0 size)
result))
(define (null-terminated-latin1->string bv)
"Return the volume name of SBLOCK as a string of at most 256 characters, or
#f if SBLOCK has no volume name."
;; 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)))))
;;;
;;; Ext2 file systems.
;;;
;; <http://www.nongnu.org/ext2-doc/ext2.html#DEF-SUPERBLOCK>.
;; TODO: Use "packed structs" from Guile-OpenGL or similar.
(define-syntax %ext2-endianness
;; Endianness of ext2 file systems.
(identifier-syntax (endianness little)))
(define (ext2-superblock? sblock)
"Return #t when SBLOCK is an ext2 superblock."
(let ((magic (bytevector-u16-ref sblock 56 %ext2-endianness)))
(= magic #xef53)))
(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."
(read-superblock device 1024 264 ext2-superblock?))
(define (ext2-superblock-uuid sblock)
"Return the UUID of ext2 superblock SBLOCK as a 16-byte bytevector."
(sub-bytevector sblock 104 16))
(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."
(null-terminated-latin1->string (sub-bytevector sblock 120 16)))
;;;
;;; LUKS encrypted devices.
;;;
;; The LUKS header format is described in "LUKS On-Disk Format Specification":
;; <https://gitlab.com/cryptsetup/cryptsetup/wikis/Specification>. We follow
;; version 1.2.1 of this document.
(define-syntax %luks-endianness
;; Endianness of LUKS headers.
(identifier-syntax (endianness big)))
(define (luks-superblock? sblock)
"Return #t when SBLOCK is a luks superblock."
(define %luks-magic
;; The 'LUKS_MAGIC' constant.
(u8-list->bytevector (append (map char->integer (string->list "LUKS"))
(list #xba #xbe))))
(let ((magic (sub-bytevector sblock 0 6))
(version (bytevector-u16-ref sblock 6 %luks-endianness)))
(and (bytevector=? magic %luks-magic)
(= version 1))))
(define (read-luks-header file)
"Read a LUKS header from FILE. Return the raw header on success, and #f if
not valid header was found."
;; Size in bytes of the LUKS header, including key slots.
(read-superblock file 0 592 luks-superblock?))
(define (luks-header-uuid header)
"Return the LUKS UUID from HEADER, as a 16-byte bytevector."
;; 40 bytes are reserved for the UUID, but in practice, it contains the 36
;; bytes of its ASCII representation.
(let ((uuid (sub-bytevector header 168 36)))
(string->uuid (utf8->string uuid))))
;;;
;;; Partition lookup.
;;;
(define (disk-partitions)
"Return the list of device names corresponding to valid disk partitions."
(define (last-character str)
(string-ref str (- (string-length str) 1)))
(define (partition? name major minor)
;; Select device names that end in a digit, like libblkid's 'probe_all'
;; function does. Checking for "/sys/dev/block/MAJOR:MINOR/partition"
;; doesn't work for partitions coming from mapped devices.
(and (char-set-contains? char-set:digit (last-character name))
(> major 2))) ;ignore RAM disks and floppy disks
(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? name major minor)
(loop (cons name parts))
(loop parts))))))))))
(define (ENOENT-safe proc)
"Wrap the one-argument PROC such that ENOENT errors are caught and lead to a
warning and #f as the result."
(lambda (device)
(catch 'system-error
(lambda ()
(proc 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.
(let ((errno (system-error-errno args)))
(cond ((= ENOENT errno)
(format (current-error-port)
"warning: device '~a' not found~%" device)
#f)
((= ENOMEDIUM errno) ;for removable media
#f)
(else
(apply throw args))))))))
(define (partition-predicate read field =)
"Return a predicate that returns true if the FIELD of partition header that
was READ is = to the given value."
(let ((read (ENOENT-safe read)))
(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 device)))
(and sblock
(let ((actual (field sblock)))
(and actual
(= actual expected)))))))))
(define partition-label-predicate
(partition-predicate read-ext2-superblock
ext2-superblock-volume-name
string=?))
(define partition-uuid-predicate
(partition-predicate read-ext2-superblock
ext2-superblock-uuid
bytevector=?))
(define luks-partition-uuid-predicate
(partition-predicate read-luks-header
luks-header-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 (find-partition-by-luks-uuid uuid)
"Return the first LUKS partition whose unique identifier is UUID (a bytevector),
or #f if none was found."
(and=> (find (luks-partition-uuid-predicate uuid)
(disk-partitions))
(cut string-append "/dev/" <>)))
;;;
;;; UUIDs.
;;;
(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 %uuid-rx
;; The regexp of a UUID.
(make-regexp "^([[:xdigit:]]{8})-([[:xdigit:]]{4})-([[:xdigit:]]{4})-([[:xdigit:]]{4})-([[:xdigit:]]{12})$"))
(define (string->uuid str)
"Parse STR as a DCE UUID (see <https://tools.ietf.org/html/rfc4122>) and
return its contents as a 16-byte bytevector. Return #f if STR is not a valid
UUID representation."
(and=> (regexp-exec %uuid-rx str)
(lambda (match)
(letrec-syntax ((hex->number
(syntax-rules ()
((_ index)
(string->number (match:substring match index)
16))))
(put!
(syntax-rules ()
((_ bv index (number len) rest ...)
(begin
(bytevector-uint-set! bv index number
(endianness big) len)
(put! bv (+ index len) rest ...)))
((_ bv index)
bv))))
(let ((time-low (hex->number 1))
(time-mid (hex->number 2))
(time-hi (hex->number 3))
(clock-seq (hex->number 4))
(node (hex->number 5))
(uuid (make-bytevector 16)))
(put! uuid 0
(time-low 4) (time-mid 2) (time-hi 2)
(clock-seq 2) (node 6)))))))
(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)
;; The "--root=SPEC" kernel command-line option always provides a
;; string, but the string can represent a device, a UUID, or a
;; label. So check for all three.
(cond ((string-prefix? "/" spec) 'device)
((string->uuid spec) 'uuid)
(else '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
(if (string? spec)
(string->uuid spec)
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 Bourne-like REPL~%"
fsck code device)
(start-repl %bournish-language)))))
(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 (regular-file? file-name)
"Return #t if FILE-NAME is a regular file."
(eq? (stat:type (stat file-name)) 'regular))
(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."
(define (mount-nfs source mount-point type flags options)
(let* ((idx (string-rindex source #\:))
(host-part (string-take source idx))
;; Strip [] from around host if present
(host (match (string-split host-part (string->char-set "[]"))
(("" h "") h)
((h) h)))
(aa (match (getaddrinfo host "nfs") ((x . _) x)))
(sa (addrinfo:addr aa))
(inet-addr (inet-ntop (sockaddr:fam sa)
(sockaddr:addr sa))))
;; Mounting an NFS file system requires passing the address
;; of the server in the addr= option
(mount source mount-point type flags
(string-append "addr="
inet-addr
(if options
(string-append "," options)
"")))))
(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))
;; Create the mount point. Most of the time this is a directory, but
;; in the case of a bind mount, a regular file may be needed.
(if (and (= MS_BIND (logand flags MS_BIND))
(regular-file? source))
(unless (file-exists? mount-point)
(mkdir-p (dirname mount-point))
(call-with-output-file mount-point (const #t)))
(mkdir-p mount-point))
(cond
((string-prefix? "nfs" type)
(mount-nfs source mount-point type flags options))
(else
(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