guix-kreyren/guix/store/deduplication.scm
Ricardo Wurmus e35c08d2f9
guix: Remove duplicate definitions of dump-port.
* guix/store.scm (dump-port): Remove procedure; autoload from (guix build
utils) instead.
* guix/store/deduplication.scm (dump-port): Remove procedure; unhide dump-port
from (guix build utils).
2022-05-20 20:42:53 +02:00

279 lines
12 KiB
Scheme

;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2017 Caleb Ristvedt <caleb.ristvedt@cune.org>
;;; Copyright © 2018-2021 Ludovic Courtès <ludo@gnu.org>
;;;
;;; This file is part of GNU Guix.
;;;
;;; GNU Guix is free software; you can redistribute it and/or modify it
;;; under the terms of the GNU General Public License as published by
;;; the Free Software Foundation; either version 3 of the License, or (at
;;; your option) any later version.
;;;
;;; GNU Guix is distributed in the hope that it will be useful, but
;;; WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
;;; GNU General Public License for more details.
;;;
;;; You should have received a copy of the GNU General Public License
;;; along with GNU Guix. If not, see <http://www.gnu.org/licenses/>.
;;; This houses stuff we do to files when they arrive at the store - resetting
;;; timestamps, deduplicating, etc.
(define-module (guix store deduplication)
#:use-module (gcrypt hash)
#:use-module (guix build utils)
#:use-module (guix build syscalls)
#:use-module (guix base32)
#:use-module (srfi srfi-11)
#:use-module (srfi srfi-34)
#:use-module (srfi srfi-35)
#:use-module (rnrs bytevectors)
#:use-module (rnrs io ports)
#:use-module (ice-9 ftw)
#:use-module (ice-9 match)
#:use-module (guix serialization)
#:export (nar-sha256
deduplicate
dump-file/deduplicate
copy-file/deduplicate))
(define (nar-sha256 file)
"Gives the sha256 hash of a file and the size of the file in nar form."
(let-values (((port get-hash) (open-sha256-port)))
(write-file file port)
(force-output port)
(let ((hash (get-hash))
(size (port-position port)))
(close-port port)
(values hash size))))
(define (tempname-in directory)
"Gives an unused temporary name under DIRECTORY. Not guaranteed to still be
unused by the time you create anything with that name, but a good shot."
(let ((const-part (string-append directory "/.tmp-link-"
(number->string (getpid)))))
(let try ((guess-part
(number->string (random most-positive-fixnum) 16)))
(if (file-exists? (string-append const-part "-" guess-part))
(try (number->string (random most-positive-fixnum) 16))
(string-append const-part "-" guess-part)))))
(define* (get-temp-link target #:optional (link-prefix (dirname target)))
"Like mkstemp!, but instead of creating a new file and giving you the name,
it creates a new hardlink to TARGET and gives you the name. Since
cross-file-system hardlinks don't work, the temp link must be created on the
same file system - where in that file system it is can be controlled by
LINK-PREFIX."
(let try ((tempname (tempname-in link-prefix)))
(catch 'system-error
(lambda ()
(link target tempname)
tempname)
(lambda args
(if (= (system-error-errno args) EEXIST)
(try (tempname-in link-prefix))
(apply throw args))))))
(define (call-with-writable-file file store thunk)
(if (string=? file store)
(thunk) ;don't meddle with the store's permissions
(let ((stat (lstat file)))
(dynamic-wind
(lambda ()
(make-file-writable file))
thunk
(lambda ()
(set-file-time file stat)
(chmod file (stat:mode stat)))))))
(define-syntax-rule (with-writable-file file store exp ...)
"Make FILE writable for the dynamic extent of EXP..., except if FILE is the
store."
(call-with-writable-file file store (lambda () exp ...)))
;; There are 3 main kinds of errors we can get from hardlinking: "Too many
;; things link to this" (EMLINK), "this link already exists" (EEXIST), and
;; "can't fit more stuff in this directory" (ENOSPC).
(define* (replace-with-link target to-replace
#:key (swap-directory (dirname target))
(store (%store-directory)))
"Atomically replace the file TO-REPLACE with a link to TARGET. Use
SWAP-DIRECTORY as the directory to store temporary hard links. Upon ENOSPC
and EMLINK, TO-REPLACE is left unchanged.
Note: TARGET, TO-REPLACE, and SWAP-DIRECTORY must be on the same file system."
(define temp-link
(catch 'system-error
(lambda ()
(get-temp-link target swap-directory))
(lambda args
;; We get ENOSPC when we can't fit an additional entry in
;; SWAP-DIRECTORY. If it's EMLINK, then TARGET has reached its
;; maximum number of links.
(if (memv (system-error-errno args) `(,ENOSPC ,EMLINK))
#f
(apply throw args)))))
;; If we couldn't create TEMP-LINK, that's OK: just don't do the
;; replacement, which means TO-REPLACE won't be deduplicated.
(when temp-link
(with-writable-file (dirname to-replace) store
(catch 'system-error
(lambda ()
(rename-file temp-link to-replace))
(lambda args
(delete-file temp-link)
(unless (= EMLINK (system-error-errno args))
(apply throw args)))))))
(define %deduplication-minimum-size
;; Size below which files are not deduplicated. This avoids adding too many
;; entries to '.links', which would slow down 'removeUnusedLinks' while
;; saving little space. Keep in sync with optimize-store.cc.
8192)
(define* (deduplicate path hash #:key (store (%store-directory)))
"Check if a store item with sha256 hash HASH already exists. If so,
replace PATH with a hardlink to the already-existing one. If not, register
PATH so that future duplicates can hardlink to it. PATH is assumed to be
under STORE."
;; Lightweight promises.
(define-syntax-rule (delay exp)
(let ((value #f))
(lambda ()
(unless value
(set! value exp))
value)))
(define-syntax-rule (force promise)
(promise))
(define links-directory
(string-append store "/.links"))
(let loop ((path path)
(type (stat:type (lstat path)))
(hash hash))
(if (eq? 'directory type)
;; Can't hardlink directories, so hardlink their atoms.
(for-each (match-lambda
((file . properties)
(unless (member file '("." ".."))
(let* ((file (string-append path "/" file))
(st (delay (lstat file)))
(type (match (assoc-ref properties 'type)
((or 'unknown #f)
(stat:type (force st)))
(type type))))
(when (or (eq? 'directory type)
(and (eq? 'regular type)
(>= (stat:size (force st))
%deduplication-minimum-size)))
(loop file type
(and (not (eq? 'directory type))
(nar-sha256 file))))))))
(scandir* path))
(let ((link-file (string-append links-directory "/"
(bytevector->nix-base32-string hash))))
(if (file-exists? link-file)
(replace-with-link link-file path
#:swap-directory links-directory
#:store store)
(catch 'system-error
(lambda ()
(link path link-file))
(lambda args
(let ((errno (system-error-errno args)))
(cond ((= errno EEXIST)
;; Someone else put an entry for PATH in
;; LINKS-DIRECTORY before we could. Let's use it.
(replace-with-link path link-file
#:swap-directory
links-directory
#:store store))
((= errno ENOENT)
;; This most likely means that LINKS-DIRECTORY does
;; not exist. Attempt to create it and try again.
(mkdir-p links-directory)
(loop path type hash))
((= errno ENOSPC)
;; There's not enough room in the directory index for
;; more entries in .links, but that's fine: we can
;; just stop.
#f)
((= errno EMLINK)
;; PATH has reached the maximum number of links, but
;; that's OK: we just can't deduplicate it more.
#f)
(else (apply throw args)))))))))))
(define (tee input len output)
"Return a port that reads up to LEN bytes from INPUT and writes them to
OUTPUT as it goes."
(define bytes-read 0)
(define (fail)
;; Reached EOF before we had read LEN bytes from INPUT.
(raise (condition
(&nar-error (port input)
(file (port-filename output))))))
(define (read! bv start count)
;; Read at most LEN bytes in total.
(let ((count (min count (- len bytes-read))))
(let loop ((ret (get-bytevector-n! input bv start count)))
(cond ((eof-object? ret)
(if (= bytes-read len)
0 ; EOF
(fail)))
((and (zero? ret) (> count 0))
;; Do not return zero since zero means EOF, so try again.
(loop (get-bytevector-n! input bv start count)))
(else
(put-bytevector output bv start ret)
(set! bytes-read (+ bytes-read ret))
ret)))))
(make-custom-binary-input-port "tee input port" read! #f #f #f))
(define* (dump-file/deduplicate file input size type
#:key (store (%store-directory)))
"Write SIZE bytes read from INPUT to FILE. TYPE is a symbol, either
'regular or 'executable.
This procedure is suitable as a #:dump-file argument to 'restore-file'. When
used that way, it deduplicates files on the fly as they are restored, thereby
removing the need for a deduplication pass that would re-read all the files
down the road."
(define (dump-and-compute-hash)
(call-with-output-file file
(lambda (output)
(let-values (((hash-port get-hash)
(open-hash-port (hash-algorithm sha256))))
(write-file-tree file hash-port
#:file-type+size (lambda (_) (values type size))
#:file-port
(const (tee input size output)))
(close-port hash-port)
(get-hash)))))
(if (>= size %deduplication-minimum-size)
(deduplicate file (dump-and-compute-hash) #:store store)
(call-with-output-file file
(lambda (output)
(dump-port input output size)))))
(define* (copy-file/deduplicate source target
#:key (store (%store-directory)))
"Like 'copy-file', but additionally deduplicate TARGET in STORE."
(call-with-input-file source
(lambda (input)
(let ((stat (stat input)))
(dump-file/deduplicate target input (stat:size stat)
(if (zero? (logand (stat:mode stat)
#o100))
'regular
'executable)
#:store store)))))