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/linux-initrd.scm (write-cpio-archive): Mention timestamps in
docstring.
(build-initrd): Remove unnecessary timestamp reset phase.

* gnu/build/linux-initrd.scm (write-cpio-archive): Really return OUTPUT on
success, even when compression is disabled.

Previously 'expression->initrd' would return the directory that contains
the 'initrd' file; now it returns the complete file name for that file.

* gnu/system/linux-initrd.scm (expression->initrd)[builder]: Change
output file name to "initrd.cpio.gz".  Tail-call 'file-append' to return
the complete file name.
* gnu/system.scm (operating-system-initrd-file): Remove 'file-append'
call.
* gnu/build/linux-initrd.scm (write-cpio-archive): Check whether OUTPUT
already has the ".gz" suffix; rename if before invoking GZIP if it does,
and otherwise after.
* gnu/system/vm.scm (expression->derivation-in-linux-vm)[builder]: Do
not append "/initrd" to #$initrd.

Fixes <https://bugs.gnu.org/33297>.
Reported by Mark H Weaver <mhw@netris.org>.

This fixes a regression introduced in
72dc64f8f720268930eed448abfc15d2a0eca3cf, which made files read-only.

* gnu/build/linux-initrd.scm (build-initrd): Call 'make-file-writable'
on all the files under contents/.

* gnu/build/linux-initrd.scm (write-cpio-archive): Use '--no-name'.

* guix/cpio.scm (file->cpio-header*): New procedure.
* gnu/build/linux-initrd.scm (write-cpio-archive): Add #:file->header argument
  to 'cpio:write-cpio-archive'.

* gnu/build/linux-initrd.scm (write-cpio-archive)[files]: Use 'sort' instead
  of 'reverse'.

* gnu/build/linux-initrd.scm (write-cpio-archive): Remove 'open-pipe*' and
  related calls.  Compute list of files in 'files' variable.  Use
  'cpio:write-cpio-archive'.  Remove #:cpio parameter.
  (build-initrd): Remove #:cpio parameter.
* gnu/system/linux-initrd.scm (expression->initrd): Likewise, and adjust
  BUILDER accordingly.  Add (guix cpio) to #:modules.

* gnu/system/linux-initrd.scm (expression->initrd): Remove #:linux and
  #:linux-modules parameters.  Remove call to
  'float-linux-module-directory'.
  (base-initrd): Add call to 'float-linux-module-directory'.  Use it in
  #:linux-modules argument in the gexp.  Remove #:linux and
  #:linux-modules arguments to 'expression->initrd'.
* gnu/build/linux-initrd.scm (build-initrd): Remove
  #:linux-module-directory parameter.  Don't create 'modules'
  sub-directory.
* gnu/build/linux-boot.scm (boot-system): Mentin that LINUX-MODULES is a
  list of absolute file names.  Don't prepend "/modules/" to
  LINUX-MODULES.
* doc/guix.texi (Initial RAM Disk): Adjust accordingly.