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file-systems: Add support for exFAT.
* gnu/build/file-systems.scm (%exfat-endianness): New syntax. (exfat-superblock?, exfat-bytes-per-sector-shift) (exfat-sectors-per-cluster-shift, exfat-root-directory-offset) (exfat-cluster-size, read-exfat-superblock+root-directory-cluster) (read-exfat-superblock, exfat-superblock-volume-name) (exfat-superblock-uuid, check-exfat-file-system): New procedures. (%partition-label-readers, %partition-uuid-readers): Register them. Change-Id: I08bd3147d2d67e5766c9381ae2159bc01530b814
This commit is contained in:
Tobias Geerinckx-Rice
parent
c9a28a87e8
commit
191e0f9e52
1 changed files with 116 additions and 1 deletions
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@ -3,7 +3,7 @@
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;;; Copyright © 2016, 2017 David Craven <david@craven.ch>
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;;; Copyright © 2017 Mathieu Othacehe <m.othacehe@gmail.com>
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;;; Copyright © 2019 Guillaume Le Vaillant <glv@posteo.net>
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;;; Copyright © 2019–2021 Tobias Geerinckx-Rice <me@tobias.gr>
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;;; Copyright © 2019–2021, 2024 Tobias Geerinckx-Rice <me@tobias.gr>
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;;; Copyright © 2019 David C. Trudgian <dave@trudgian.net>
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;;; Copyright © 2020 Maxim Cournoyer <maxim.cournoyer@gmail.com>
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;;; Copyright © 2022 Oleg Pykhalov <go.wigust@gmail.com>
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@ -448,6 +448,116 @@ (define (check-btrfs-file-system device force? repair)
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(_ 'fatal-error))
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'pass))
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;;;
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;;; exFAT file systems.
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;;;
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;; <https://learn.microsoft.com/en-us/windows/win32/fileio/exfat-specification>.
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(define-syntax %exfat-endianness
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(identifier-syntax (endianness little)))
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(define (exfat-superblock? sblock)
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"Return #t when SBLOCK, a bytevector of at least length 512, is an exFAT
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superblock, called main boot sector in the exFAT specification."
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(and (bytevector=? (string->utf8 "EXFAT ")
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(sub-bytevector sblock 3 8)) ;FileSystemName
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(bytevector=? (make-bytevector 53 0)
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(sub-bytevector sblock 11 53)) ;MustBeZero
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(bytevector=? #vu8(#x55 #xaa)
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(sub-bytevector sblock 510 2)))) ;BootSignature
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(define (exfat-bytes-per-sector-shift sblock)
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(bytevector-u8-ref sblock 108))
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(define (exfat-sectors-per-cluster-shift sblock)
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(bytevector-u8-ref sblock 109))
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(define (exfat-root-directory-offset sblock)
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(let ((cluster-heap-offset (bytevector-u32-ref sblock 88
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%exfat-endianness))
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(root-directory-cluster (bytevector-u32-ref sblock 96
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%exfat-endianness)))
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(define (cluster->sector cluster)
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(let ((first-data-cluster 2))
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(+ cluster-heap-offset (ash (- cluster first-data-cluster)
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(exfat-sectors-per-cluster-shift sblock)))))
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(ash (cluster->sector root-directory-cluster)
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(exfat-bytes-per-sector-shift sblock))))
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(define (exfat-cluster-size sblock)
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(ash 1 (+ (exfat-bytes-per-sector-shift sblock)
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(exfat-sectors-per-cluster-shift sblock))))
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;; exFAT stores the volume name in a directory entry with no fixed location. We
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;; search an arbitrary number of entries before giving up: 128 for devices <256M
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;; (4K clusters), 1024 for those <32G (32K clusters), or 4096 for others (128K).
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;; It's silly but mostly matches what util-linux's libblkid does with its higher
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;; arbitrary number of 10,000 tries. To match that, we'd not only have to look
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;; up subsequent clusters in the FAT, but redesign this entire module not to
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;; assume that all file systems have a `superblock' that both fits neatly into
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;; RAM, and just happens to politely contain all the metadata we'll ever need.
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(define (read-exfat-superblock+root-directory-cluster device sblock)
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"Return as a bytevector the raw contents of DEVICE's exFAT `superblock' from
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main boot sector up to the RootDirectoryCluster expected to contain the volume
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label."
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(let* ((span (+ (exfat-root-directory-offset sblock)
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(exfat-cluster-size sblock))))
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(read-superblock device 0 span (const #t))))
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(define (read-exfat-superblock device)
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"Return the raw contents of DEVICE's exFAT superblock as a bytevector, or #f
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if DEVICE does not contain an exFAT file system."
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(and=> (read-superblock device 0 512 exfat-superblock?)
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(cut read-exfat-superblock+root-directory-cluster device <>)))
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(define (exfat-superblock-volume-name sblock)
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"Return as a string the volume name belonging to an exFAT file system
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beginning with bytevector SBLOCK, which includes directory entries.
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Return #f if no volume name was found within our arbitrary limit."
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;; Defined in section 7.3 of the exFAT specification.
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(let ((root-directory (exfat-root-directory-offset sblock))
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(cluster-size (exfat-cluster-size sblock))
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(entry-size 32)) ;bytes
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(let loop ((cluster-offset 0))
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(if (< cluster-offset cluster-size)
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(let ((offset (+ root-directory cluster-offset)))
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(match (bytevector-u8-ref sblock offset)
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((or #x00 ;end of directory
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#x03) ;type 3 & not in use
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#f)
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(#x83 ;type 3 & in use
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(let* ((length (min 11 (bytevector-u8-ref sblock (+ 1 offset))))
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(label (sub-bytevector sblock (+ 2 offset) (* 2 length))))
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(utf16->string label %exfat-endianness)))
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(_ (loop (+ entry-size offset)))))
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#f))))
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(define (exfat-superblock-uuid sblock)
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"Return the Volume Serial Number of exFAT superblock SBLOCK as a bytevector.
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This 4-byte identifier is guaranteed to exist, unlike the optional 16-byte
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Volume GUID from section 7.5 of the exFAT specification."
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(sub-bytevector sblock 100 4))
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(define (check-exfat-file-system device force? repair)
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"Return the health of an unmounted exFAT file system on DEVICE. If FORCE?
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is true, check the file system even if it's marked as clean. If REPAIR is
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false, do not write to the file system to fix errors. If it's #t, fix all
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errors. Otherwise, fix only those considered safe to repair automatically."
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(match (status:exit-val
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(apply system*/tty "fsck.exfat" "-sv"
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`(,@(if force? '("-b") '())
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,@(match repair
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(#f '("-n"))
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(#t '("-y"))
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(_ '("-p")))
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,device)))
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(0 'pass)
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(1 'errors-corrected)
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(2 'reboot-required)
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(_ 'fatal-error)))
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;;;
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;;; FAT32 file systems.
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@ -937,6 +1047,8 @@ (define %partition-label-readers
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bcachefs-superblock-volume-name)
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(partition-field-reader read-btrfs-superblock
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btrfs-superblock-volume-name)
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(partition-field-reader read-exfat-superblock
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exfat-superblock-volume-name)
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(partition-field-reader read-fat32-superblock
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fat32-superblock-volume-name)
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(partition-field-reader read-fat16-superblock
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@ -959,6 +1071,8 @@ (define %partition-uuid-readers
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bcachefs-superblock-external-uuid)
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(partition-field-reader read-btrfs-superblock
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btrfs-superblock-uuid)
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(partition-field-reader read-exfat-superblock
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exfat-superblock-uuid)
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(partition-field-reader read-fat32-superblock
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fat32-superblock-uuid)
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(partition-field-reader read-fat16-superblock
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@ -1079,6 +1193,7 @@ (define check-procedure
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((string-prefix? "ext" type) check-ext2-file-system)
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((string-prefix? "bcachefs" type) check-bcachefs-file-system)
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((string-prefix? "btrfs" type) check-btrfs-file-system)
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((string-suffix? "exfat" type) check-exfat-file-system)
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((string-suffix? "fat" type) check-fat-file-system)
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((string-prefix? "jfs" type) check-jfs-file-system)
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((string-prefix? "f2fs" type) check-f2fs-file-system)
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