file-systems: Implement partition lookup by UUID.
* gnu/build/file-systems.scm (read-ext2-superblock*, partition-predicate): New procedures. (partition-label-predicate): Rewrite in terms of 'partition-predicate'. (partition-uuid-predicate, find-partition-by-uuid, uuid->string): New procedures. (%network-byte-order): New macro. (canonicalize-device-spec)[canonical-title]: Check whether SPEC is a string. [resolve]: New procedure. Add 'uuid' case and use it.
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@ -22,13 +22,16 @@
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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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@ -159,12 +162,10 @@ if DEVICE does not contain an ext2 file system."
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(loop (cons name parts))
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(loop parts))))))))))
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(define (partition-label-predicate label)
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"Return a procedure that, when applied to a partition name such as \"sda1\",
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return #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 (catch 'system-error
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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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@ -174,14 +175,29 @@ return #t if that partition's volume name is LABEL."
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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~%"
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device)
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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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(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 ((volume (ext2-superblock-volume-name sblock)))
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(and volume
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(string=? volume label)))))))
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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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@ -190,6 +206,28 @@ were found."
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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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@ -198,6 +236,8 @@ the following:
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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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@ -210,30 +250,36 @@ the following:
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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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(let loop ((count 0))
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(let ((device (find-partition-by-label 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 label" spec)
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(begin
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(format #t "waiting for partition '~a' to appear...~%"
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spec)
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(sleep 1)
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(loop (+ 1 count))))))))
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;; TODO: Add support for UUIDs.
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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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