store-copy: 'populate-store' can optionally deduplicate files.

Until now deduplication was performed as an additional pass after
copying files, which involve re-traversing all the files that had just
been copied.

* guix/store/deduplication.scm (copy-file/deduplicate): New procedure.
* tests/store-deduplication.scm ("copy-file/deduplicate"): New test.
* guix/build/store-copy.scm (populate-store): Add #:deduplicate?
parameter and honor it.
* tests/gexp.scm ("gexp->derivation, store copy"): Pass #:deduplicate? #f
to 'populate-store'.
* gnu/build/image.scm (initialize-root-partition): Pass #:deduplicate?
to 'populate-store'.  Pass #:deduplicate? #f to 'register-closure'.
* gnu/build/vm.scm (root-partition-initializer): Likewise.
* gnu/build/install.scm (populate-single-profile-directory): Pass
 #:deduplicate? #f to 'populate-store'.
* gnu/build/linux-initrd.scm (build-initrd): Likewise.
* guix/scripts/pack.scm (self-contained-tarball)[import-module?]: New
procedure.
[build]: Pass it as an argument to 'source-module-closure'.
* guix/scripts/pack.scm (squashfs-image)[build]: Wrap in
'with-extensions'.
* gnu/system/linux-initrd.scm (expression->initrd)[import-module?]: New
procedure.
[builder]: Pass it to 'source-module-closure'.
* gnu/system/install.scm (cow-store-service-type)[import-module?]: New
procedure.  Pass it to 'source-module-closure'.

gnu/build/image.scm

@@ -186,7 +186,8 @@ rest of the store when registering the closures.  SYSTEM-DIRECTORY is the name
 of the directory of the 'system' derivation.  Pass WAL-MODE? to
 register-closure."
   (populate-root-file-system system-directory root)
-  (populate-store references-graphs root)
+  (populate-store references-graphs root
+                  #:deduplicate? deduplicate?)
 
   ;; Populate /dev.
   (when make-device-nodes
@@ -195,7 +196,7 @@ register-closure."
   (when register-closures?
     (for-each (lambda (closure)
                 (register-closure root closure
-                                  #:deduplicate? deduplicate?
+                                  #:deduplicate? #f
                                   #:wal-mode? wal-mode?))
               references-graphs))
 

gnu/build/install.scm

@@ -214,7 +214,8 @@ This is used to create the self-contained tarballs with 'guix pack'."
     (symlink old (scope new)))
 
   ;; Populate the store.
-  (populate-store (list closure) directory)
+  (populate-store (list closure) directory
+                  #:deduplicate? #f)
 
   (when database
     (install-database-and-gc-roots directory database profile

gnu/build/linux-initrd.scm

@@ -127,7 +127,8 @@ REFERENCES-GRAPHS."
   (mkdir "contents")
 
   ;; Copy the closures of all the items referenced in REFERENCES-GRAPHS.
-  (populate-store references-graphs "contents")
+  (populate-store references-graphs "contents"
+                  #:deduplicate? #f)
 
   (with-directory-excursion "contents"
     ;; Make '/init'.

gnu/build/vm.scm

@@ -395,7 +395,8 @@ system that is passed to 'populate-root-file-system'."
     (when copy-closures?
       ;; Populate the store.
       (populate-store (map (cut string-append "/xchg/" <>) closures)
-                      target))
+                      target
+                      #:deduplicate? deduplicate?))
 
     ;; Populate /dev.
     (make-device-nodes target)
@@ -412,7 +413,7 @@ system that is passed to 'populate-root-file-system'."
       (for-each (lambda (closure)
                   (register-closure target
                                     (string-append "/xchg/" closure)
-                                    #:deduplicate? deduplicate?))
+                                    #:deduplicate? #f))
                 closures)
       (unless copy-closures?
         (umount target-store)))