78981bb9bd
Reported by David Thompson <dthompson2@worcester.edu> at <https://lists.gnu.org/archive/html/guix-devel/2015-10/msg00284.html>. * gnu/build/file-systems.scm (mount-file-system): When SOURCE matches 'regular-file?', do not create MOUNT-POINT if it already exists. This fixes a bug whereby we would be truncating MOUNT-POINT if it already existed.
365 lines
13 KiB
Scheme
365 lines
13 KiB
Scheme
;;; GNU Guix --- Functional package management for GNU
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;;; Copyright © 2014, 2015 Ludovic Courtès <ludo@gnu.org>
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;;;
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;;; This file is part of GNU Guix.
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;;;
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;;; GNU Guix is free software; you can redistribute it and/or modify it
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;;; under the terms of the GNU General Public License as published by
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;;; the Free Software Foundation; either version 3 of the License, or (at
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;;; your option) any later version.
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;;;
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;;; GNU Guix is distributed in the hope that it will be useful, but
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;;; WITHOUT ANY WARRANTY; without even the implied warranty of
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;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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;;; GNU General Public License for more details.
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;;;
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;;; You should have received a copy of the GNU General Public License
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;;; along with GNU Guix. If not, see <http://www.gnu.org/licenses/>.
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(define-module (gnu build file-systems)
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#:use-module (guix build utils)
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#:use-module (rnrs io ports)
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#:use-module (rnrs bytevectors)
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#:use-module (ice-9 match)
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#:use-module (ice-9 rdelim)
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#:use-module (ice-9 format)
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#:use-module (system foreign)
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#:autoload (system repl repl) (start-repl)
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#:use-module (srfi srfi-1)
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#:use-module (srfi srfi-26)
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#:export (disk-partitions
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partition-label-predicate
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partition-uuid-predicate
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find-partition-by-label
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find-partition-by-uuid
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canonicalize-device-spec
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MS_RDONLY
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MS_NOSUID
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MS_NODEV
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MS_NOEXEC
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MS_BIND
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MS_MOVE
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bind-mount
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mount-flags->bit-mask
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check-file-system
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mount-file-system))
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;;; Commentary:
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;;;
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;;; This modules provides tools to deal with disk partitions, and to mount and
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;;; check file systems.
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;;;
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;;; Code:
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;; 'mount' is already defined in the statically linked Guile used for initial
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;; RAM disks, but in all other cases the (guix build syscalls) module contains
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;; the mount binding.
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(eval-when (expand load eval)
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(unless (defined? 'mount)
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(module-use! (current-module)
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(resolve-interface '(guix build syscalls)))))
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;; Linux mount flags, from libc's <sys/mount.h>.
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(define MS_RDONLY 1)
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(define MS_NOSUID 2)
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(define MS_NODEV 4)
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(define MS_NOEXEC 8)
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(define MS_REMOUNT 32)
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(define MS_BIND 4096)
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(define MS_MOVE 8192)
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(define (bind-mount source target)
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"Bind-mount SOURCE at TARGET."
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(mount source target "" MS_BIND))
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(define-syntax %ext2-endianness
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;; Endianness of ext2 file systems.
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(identifier-syntax (endianness little)))
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;; Offset in bytes of interesting parts of an ext2 superblock. See
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;; <http://www.nongnu.org/ext2-doc/ext2.html#DEF-SUPERBLOCK>.
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;; TODO: Use "packed structs" from Guile-OpenGL or similar.
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(define-syntax %ext2-sblock-magic (identifier-syntax 56))
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(define-syntax %ext2-sblock-creator-os (identifier-syntax 72))
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(define-syntax %ext2-sblock-uuid (identifier-syntax 104))
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(define-syntax %ext2-sblock-volume-name (identifier-syntax 120))
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(define (read-ext2-superblock device)
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"Return the raw contents of DEVICE's ext2 superblock as a bytevector, or #f
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if DEVICE does not contain an ext2 file system."
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(define %ext2-magic
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;; The magic bytes that identify an ext2 file system.
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#xef53)
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(define superblock-size
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;; Size of the interesting part of an ext2 superblock.
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264)
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(define block
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;; The superblock contents.
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(make-bytevector superblock-size))
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(call-with-input-file device
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(lambda (port)
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(seek port 1024 SEEK_SET)
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;; Note: work around <http://bugs.gnu.org/17466>.
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(and (eqv? superblock-size (get-bytevector-n! port block 0
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superblock-size))
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(let ((magic (bytevector-u16-ref block %ext2-sblock-magic
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%ext2-endianness)))
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(and (= magic %ext2-magic)
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block))))))
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(define (ext2-superblock-uuid sblock)
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"Return the UUID of ext2 superblock SBLOCK as a 16-byte bytevector."
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(let ((uuid (make-bytevector 16)))
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(bytevector-copy! sblock %ext2-sblock-uuid uuid 0 16)
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uuid))
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(define (ext2-superblock-volume-name sblock)
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"Return the volume name of SBLOCK as a string of at most 16 characters, or
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#f if SBLOCK has no volume name."
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(let ((bv (make-bytevector 16)))
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(bytevector-copy! sblock %ext2-sblock-volume-name bv 0 16)
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;; This is a Latin-1, nul-terminated string.
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(let ((bytes (take-while (negate zero?) (bytevector->u8-list bv))))
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(if (null? bytes)
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#f
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(list->string (map integer->char bytes))))))
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(define (disk-partitions)
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"Return the list of device names corresponding to valid disk partitions."
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(define (partition? major minor)
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(let ((marker (format #f "/sys/dev/block/~a:~a/partition" major minor)))
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(catch 'system-error
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(lambda ()
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(not (zero? (call-with-input-file marker read))))
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(lambda args
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(if (= ENOENT (system-error-errno args))
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#f
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(apply throw args))))))
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(call-with-input-file "/proc/partitions"
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(lambda (port)
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;; Skip the two header lines.
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(read-line port)
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(read-line port)
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;; Read each subsequent line, and extract the last space-separated
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;; field.
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(let loop ((parts '()))
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(let ((line (read-line port)))
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(if (eof-object? line)
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(reverse parts)
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(match (string-tokenize line)
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(((= string->number major) (= string->number minor)
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blocks name)
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(if (partition? major minor)
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(loop (cons name parts))
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(loop parts))))))))))
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(define (read-ext2-superblock* device)
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"Like 'read-ext2-superblock', but return #f when DEVICE does not exist
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instead of throwing an exception."
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(catch 'system-error
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(lambda ()
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(read-ext2-superblock device))
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(lambda args
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;; When running on the hand-made /dev,
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;; 'disk-partitions' could return partitions for which
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;; we have no /dev node. Handle that gracefully.
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(if (= ENOENT (system-error-errno args))
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(begin
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(format (current-error-port)
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"warning: device '~a' not found~%" device)
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#f)
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(apply throw args)))))
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(define (partition-predicate field =)
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"Return a predicate that returns true if the FIELD of an ext2 superblock is
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= to the given value."
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(lambda (expected)
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"Return a procedure that, when applied to a partition name such as \"sda1\",
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returns #t if that partition's volume name is LABEL."
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(lambda (part)
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(let* ((device (string-append "/dev/" part))
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(sblock (read-ext2-superblock* device)))
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(and sblock
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(let ((actual (field sblock)))
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(and actual
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(= actual expected))))))))
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(define partition-label-predicate
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(partition-predicate ext2-superblock-volume-name string=?))
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(define partition-uuid-predicate
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(partition-predicate ext2-superblock-uuid bytevector=?))
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(define (find-partition-by-label label)
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"Return the first partition found whose volume name is LABEL, or #f if none
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were found."
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(and=> (find (partition-label-predicate label)
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(disk-partitions))
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(cut string-append "/dev/" <>)))
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(define (find-partition-by-uuid uuid)
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"Return the first partition whose unique identifier is UUID (a bytevector),
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or #f if none was found."
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(and=> (find (partition-uuid-predicate uuid)
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(disk-partitions))
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(cut string-append "/dev/" <>)))
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(define-syntax %network-byte-order
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(identifier-syntax (endianness big)))
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(define (uuid->string uuid)
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"Convert UUID, a 16-byte bytevector, to its string representation, something
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like \"6b700d61-5550-48a1-874c-a3d86998990e\"."
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;; See <https://tools.ietf.org/html/rfc4122>.
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(let ((time-low (bytevector-uint-ref uuid 0 %network-byte-order 4))
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(time-mid (bytevector-uint-ref uuid 4 %network-byte-order 2))
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(time-hi (bytevector-uint-ref uuid 6 %network-byte-order 2))
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(clock-seq (bytevector-uint-ref uuid 8 %network-byte-order 2))
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(node (bytevector-uint-ref uuid 10 %network-byte-order 6)))
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(format #f "~8,'0x-~4,'0x-~4,'0x-~4,'0x-~12,'0x"
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time-low time-mid time-hi clock-seq node)))
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(define* (canonicalize-device-spec spec #:optional (title 'any))
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"Return the device name corresponding to SPEC. TITLE is a symbol, one of
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the following:
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• 'device', in which case SPEC is known to designate a device node--e.g.,
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\"/dev/sda1\";
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• 'label', in which case SPEC is known to designate a partition label--e.g.,
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\"my-root-part\";
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• 'uuid', in which case SPEC must be a UUID (a 16-byte bytevector)
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designating a partition;
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• 'any', in which case SPEC can be anything.
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"
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(define max-trials
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;; Number of times we retry partition label resolution, 1 second per
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;; trial. Note: somebody reported a delay of 16 seconds (!) before their
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;; USB key would be detected by the kernel, so we must wait for at least
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;; this long.
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20)
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(define canonical-title
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;; The realm of canonicalization.
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(if (eq? title 'any)
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(if (string? spec)
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(if (string-prefix? "/" spec)
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'device
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'label)
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'uuid)
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title))
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(define (resolve find-partition spec fmt)
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(let loop ((count 0))
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(let ((device (find-partition spec)))
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(or device
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;; Some devices take a bit of time to appear, most notably USB
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;; storage devices. Thus, wait for the device to appear.
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(if (> count max-trials)
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(error "failed to resolve partition" (fmt spec))
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(begin
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(format #t "waiting for partition '~a' to appear...~%"
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(fmt spec))
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(sleep 1)
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(loop (+ 1 count))))))))
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(case canonical-title
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((device)
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;; Nothing to do.
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spec)
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((label)
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;; Resolve the label.
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(resolve find-partition-by-label spec identity))
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((uuid)
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(resolve find-partition-by-uuid spec uuid->string))
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(else
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(error "unknown device title" title))))
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(define (check-file-system device type)
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"Run a file system check of TYPE on DEVICE."
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(define fsck
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(string-append "fsck." type))
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(let ((status (system* fsck "-v" "-p" "-C" "0" device)))
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(match (status:exit-val status)
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(0
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#t)
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(1
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(format (current-error-port) "'~a' corrected errors on ~a; continuing~%"
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fsck device))
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(2
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(format (current-error-port) "'~a' corrected errors on ~a; rebooting~%"
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fsck device)
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(sleep 3)
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(reboot))
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(code
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(format (current-error-port) "'~a' exited with code ~a on ~a; spawning REPL~%"
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fsck code device)
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(start-repl)))))
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(define (mount-flags->bit-mask flags)
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"Return the number suitable for the 'flags' argument of 'mount' that
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corresponds to the symbols listed in FLAGS."
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(let loop ((flags flags))
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(match flags
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(('read-only rest ...)
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(logior MS_RDONLY (loop rest)))
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(('bind-mount rest ...)
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(logior MS_BIND (loop rest)))
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(('no-suid rest ...)
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(logior MS_NOSUID (loop rest)))
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(('no-dev rest ...)
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(logior MS_NODEV (loop rest)))
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(('no-exec rest ...)
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(logior MS_NOEXEC (loop rest)))
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(()
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0))))
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(define (regular-file? file-name)
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"Return #t if FILE-NAME is a regular file."
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(eq? (stat:type (stat file-name)) 'regular))
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(define* (mount-file-system spec #:key (root "/root"))
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"Mount the file system described by SPEC under ROOT. SPEC must have the
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form:
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(DEVICE TITLE MOUNT-POINT TYPE (FLAGS ...) OPTIONS CHECK?)
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DEVICE, MOUNT-POINT, and TYPE must be strings; OPTIONS can be a string or #f;
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FLAGS must be a list of symbols. CHECK? is a Boolean indicating whether to
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run a file system check."
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(match spec
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((source title mount-point type (flags ...) options check?)
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(let ((source (canonicalize-device-spec source title))
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(mount-point (string-append root "/" mount-point))
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(flags (mount-flags->bit-mask flags)))
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(when check?
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(check-file-system source type))
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;; Create the mount point. Most of the time this is a directory, but
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;; in the case of a bind mount, a regular file may be needed.
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(if (and (= MS_BIND (logand flags MS_BIND))
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(regular-file? source))
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(unless (file-exists? mount-point)
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(mkdir-p (dirname mount-point))
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(call-with-output-file mount-point (const #t)))
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(mkdir-p mount-point))
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(mount source mount-point type flags options)
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;; For read-only bind mounts, an extra remount is needed, as per
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;; <http://lwn.net/Articles/281157/>, which still applies to Linux 4.0.
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(when (and (= MS_BIND (logand flags MS_BIND))
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(= MS_RDONLY (logand flags MS_RDONLY)))
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(let ((flags (logior MS_BIND MS_REMOUNT MS_RDONLY)))
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(mount source mount-point type flags #f)))))))
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;;; file-systems.scm ends here
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