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file-systems: Add FAT32 support.

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* gnu/build/file-systems.scm (%fat32-endianness, fat32-superblock?,
read-fat32-superblock, fat32-superblock-uuid, fat32-uuid->string,
fat32-superblock-volume-name, check-fat32-file-system): New variables.
(%partition-label-readers, %partition-uuid-readers, check-file-system): Add
fat support.
(latin1->string): New variable.
(null-terminated-latin1->string): Use latin1->string.
This commit is contained in:
David Craven 2017-02-14 16:28:26 +01:00 committed by Danny Milosavljevic
parent bd9f8869b1
commit b0377e58c3
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GPG key ID: E71A35542C30BAA5
1 changed files with 59 additions and 7 deletions
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66
gnu/build/file-systems.scm
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@ -106,15 +106,17 @@ (define (sub-bytevector bv start 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))))
(define (latin1->string bv terminator)
"Return a string of BV, a latin1 bytevector, or #f. TERMINATOR is a predicate
that takes a number and returns #t when a termination character is found."
(let ((bytes (take-while (negate terminator) (bytevector->u8-list bv))))
(if (null? bytes)
#f
(list->string (map integer->char bytes)))))
(define null-terminated-latin1->string
(cut latin1->string <> zero?))
;;;
;;; Ext2 file systems.
@ -192,6 +194,51 @@ (define (check-btrfs-file-system device)
(0 'pass)
(_ 'fatal-error)))
;;;
;;; FAT32 file systems.
;;;
;; <http://www.ecma-international.org/publications/files/ECMA-ST/Ecma-107.pdf>.
(define-syntax %fat32-endianness
;; Endianness of fat file systems.
(identifier-syntax (endianness little)))
(define (fat32-superblock? sblock)
"Return #t when SBLOCK is a fat32 superblock."
(bytevector=? (sub-bytevector sblock 82 8)
(string->utf8 "FAT32 ")))
(define (read-fat32-superblock device)
"Return the raw contents of DEVICE's fat32 superblock as a bytevector, or
#f if DEVICE does not contain a fat32 file system."
(read-superblock device 0 90 fat32-superblock?))
(define (fat32-superblock-uuid sblock)
"Return the Volume ID of a fat superblock SBLOCK as a 4-byte bytevector."
(sub-bytevector sblock 67 4))
(define (fat32-uuid->string uuid)
"Convert fat32 UUID, a 4-byte bytevector, to its string representation."
(let ((high (bytevector-uint-ref uuid 0 %fat32-endianness 2))
(low (bytevector-uint-ref uuid 2 %fat32-endianness 2)))
(format #f "~:@(~x-~x~)" low high)))
(define (fat32-superblock-volume-name sblock)
"Return the volume name of SBLOCK as a string of at most 11 characters, or
#f if SBLOCK has no volume name. The volume name is a latin1 string.
Trailing spaces are trimmed."
(string-trim-right (latin1->string (sub-bytevector sblock 71 11) (lambda (c) #f)) #\space))
(define (check-fat32-file-system device)
"Return the health of a fat file system on DEVICE."
(match (status:exit-val
(system* "fsck.vfat" "-v" "-a" device))
(0 'pass)
(1 'errors-corrected)
(_ 'fatal-error)))
;;;
;;; LUKS encrypted devices.
@ -307,13 +354,17 @@ (define %partition-label-readers
(list (partition-field-reader read-ext2-superblock
ext2-superblock-volume-name)
(partition-field-reader read-btrfs-superblock
btrfs-superblock-volume-name)))
btrfs-superblock-volume-name)
(partition-field-reader read-fat32-superblock
fat32-superblock-volume-name)))
(define %partition-uuid-readers
(list (partition-field-reader read-ext2-superblock
ext2-superblock-uuid)
(partition-field-reader read-btrfs-superblock
btrfs-superblock-uuid)))
btrfs-superblock-uuid)
(partition-field-reader read-fat32-superblock
fat32-superblock-uuid)))
(define read-partition-label
(cut read-partition-field <> %partition-label-readers))
@ -481,6 +532,7 @@ (define check-procedure
(cond
((string-prefix? "ext" type) check-ext2-file-system)
((string-prefix? "btrfs" type) check-btrfs-file-system)
((string-suffix? "fat" type) check-fat32-file-system)
(else #f)))
(if check-procedure