162 lines
5.2 KiB
Scheme
162 lines
5.2 KiB
Scheme
(import
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(fmt fmt)
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(matchable))
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;;;;---------------------------------------------------
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;;;; Constants
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;;;;---------------------------------------------------
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;; FIXME: duplicate with main.scm
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(define (current-metadata)
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"./metadata.bin")
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(define metadata-block-size 4096)
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(define superblock-magic 27022010)
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(define superblock-salt 160774)
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(define uuid-size 16)
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(define space-map-root-size 128)
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;;;;---------------------------------------------------
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;;;; Metadata IO
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;;;;---------------------------------------------------
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(define (open-metadata path)
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(open-file-input-port path (file-options) (buffer-mode none)))
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(define-syntax with-metadata
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(syntax-rules ()
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((_ (port path) body ...) (let ((port (open-metadata path)))
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(dynamic-wind
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(lambda () #f)
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(lambda () body ...)
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(lambda () (close-port port)))))))
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;; FIXME: return our own condition?
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(define (io-error msg)
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(raise (condition
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(make-error)
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(make-message-condition msg))))
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;;; Returns a boolean indicating success
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(define (read-exact! port offset len bv start)
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(set-port-position! port offset)
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(let ((nr (get-bytevector-n! port bv start len)))
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(and (not (eof-object? nr))
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(= len nr))))
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;;; Returns a 4k bytevector or #f
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(define (read-exact port offset len)
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(let ((bv (make-bytevector len)))
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(if (read-exact! port offset len bv 0) bv #f)))
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(define (read-block port b)
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(or (read-exact port (* b metadata-block-size) metadata-block-size)
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(io-error (fmt #f (dsp "Unable to read metadata block: ") (num b)))))
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;;; FIXME: implement a little block cache.
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;;;;---------------------------------------------------
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;;;; CRC32
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;;;;---------------------------------------------------
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;; FIXME: move to own library
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(load-shared-object "libz.so")
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(define crc32
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(foreign-procedure "crc32" (unsigned-long u8* unsigned-int) unsigned-long))
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(define crc32-combine
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(foreign-procedure "crc32_combine" (unsigned-long unsigned-long unsigned-long) unsigned-long))
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;; FIXME: stop copying the bytevector. I'm not sure how to pass an offset into
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;; the bv.
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(define (crc32-region salt bv start end)
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(assert (< start end))
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(let ((len (- end start)))
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(let ((copy (make-bytevector len)))
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(bytevector-copy! bv start copy 0 len)
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(let ((crc (crc32 salt copy 0)))
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(crc32 crc copy len)))))
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;;;;---------------------------------------------------
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;;;; Decoding
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;;;;---------------------------------------------------
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(define-syntax unpack-type
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(syntax-rules (le32 le64 bytes)
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((_ bv offset le32)
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(bytevector-u32-ref bv offset (endianness little)))
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((_ bv offset le64)
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(bytevector-u64-ref bv offset (endianness little)))
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((_ bv offset (bytes count))
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(let ((copy (make-bytevector count)))
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(bytevector-copy! bv offset copy 0 count)
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copy))))
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(define (size-type t)
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(syntax-case t (le32 le64 bytes)
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(le32 #'4)
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(le64 #'8)
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((bytes count) #'count)))
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;;; FIXME: (bytes <count>) has to use a literal rather than a symbol.
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(define-syntax binary-format
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(lambda (x)
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(syntax-case x ()
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((_ (name pack-name unpack-name) (field type) ...)
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(with-syntax ((((t o) ...)
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(let f ((acc 0) (types #'(type ...)))
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(if (null? types)
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'()
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(cons (list (car types) acc)
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(f (+ (syntax->datum (size-type (car types))) acc) (cdr types)))))))
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#`(begin
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(define-record-type name (fields field ...))
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(define (unpack-name bv offset)
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((record-constructor (record-type-descriptor name))
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(unpack-type bv (+ offset o) t) ...))))))))
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(binary-format (superblock pack-superblock unpack-superblock)
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(csum le32)
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(flags le32)
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(block-nr le64)
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(uuid (bytes 16))
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(magic le64)
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(version le32)
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(time le32)
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(trans-id le64)
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(metadata-snap le64)
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(data-space-map-root (bytes 128))
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(metadata-space-map-root (bytes 128))
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(data-mapping-root le64)
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(device-details-root le64)
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(data-block-size le32)
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(metadata-block-size le32)
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(metadata-nr-blocks le64)
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(compat-flags le32)
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(compat-ro-flags le32)
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(incompat-flags le32))
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;;;;---------------------------------------------------
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;;;; Top level
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;;;;---------------------------------------------------
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(define (check-magic sb)
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((let ((m (bytevector-u32-ref sb 32 (endianness little))))
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(fmt #t (dsp "on disk magic: ") (num m) nl)
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)))
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(define (read-superblock)
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(with-metadata (md (current-metadata))
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(unpack-superblock (read-block md 0) 0)))
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(define (check-superblock)
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(with-metadata (md (current-metadata))
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(let ((superblock (read-block md 0)))
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(fmt #t (dsp "checksum on disk: ") (dsp (bytevector-u32-ref superblock 0 (endianness little))) nl)
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(fmt #t (dsp "calculated checksum: ") (dsp (crc32-region superblock-salt superblock 4 4092)) nl)
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(check-magic superblock))))
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