deduplicate: Use 'sendfile' for small file copies.

* guix/store/deduplication.scm (dump-file/deduplicate): Use 'sendfile'
instead of 'dump-port'.
* tests/store-deduplication.scm ("copy-file/deduplicate, below %deduplication-minimum-size"):
New test.

2 files changed, 18 insertions, 3 deletions

diff --git a/guix/store/deduplication.scm b/guix/store/deduplication.scm
index ab982e3b3d2..9953675319a 100644
--- a/guix/store/deduplication.scm
+++ b/guix/store/deduplication.scm
@@ -1,6 +1,6 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2017 Caleb Ristvedt <caleb.ristvedt@cune.org>
-;;; Copyright © 2018-2021 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2018-2022 Ludovic Courtès <ludo@gnu.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -262,7 +262,7 @@ down the road."
       (deduplicate file (dump-and-compute-hash) #:store store)
       (call-with-output-file file
         (lambda (output)
-          (dump-port input output size)))))
+          (sendfile output input size 0)))))
 
 (define* (copy-file/deduplicate source target
                                 #:key (store (%store-directory)))
diff --git a/tests/store-deduplication.scm b/tests/store-deduplication.scm
index 2950fbc1a3e..f1845035d89 100644
--- a/tests/store-deduplication.scm
+++ b/tests/store-deduplication.scm
@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2018, 2020-2021 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2018, 2020-2022 Ludovic Courtès <ludo@gnu.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -136,6 +136,21 @@
        (cons (apply = (map (compose stat:ino stat) identical))
              (map (compose stat:nlink stat) identical))))))
 
+(test-assert "copy-file/deduplicate, below %deduplication-minimum-size"
+  (call-with-temporary-directory
+   (lambda (store)
+     (let ((source (string-append store "/input")))
+       (call-with-output-file source
+         (lambda (port)
+           (display "Hello!\n" port)))
+       (copy-file/deduplicate source
+                              (string-append store "/a")
+                              #:store store)
+       (and (not (directory-exists? (string-append store "/.links")))
+            (file=? source (string-append store "/a"))
+            (not (= (stat:ino (stat (string-append store "/a")))
+                    (stat:ino (stat source)))))))))
+
 (test-assert "copy-file/deduplicate"
   (call-with-temporary-directory
    (lambda (store)