linux-initrd: 'expression->initrd' returns the complete file name.

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.

gnu/build/linux-initrd.scm

@@ -72,11 +72,23 @@ COMPRESS? is true, compress it using GZIP.  On success, return OUTPUT."
                                #:file->header cpio:file->cpio-header*)))
 
   (or (not compress?)
+
+      ;; Gzip insists on adding a '.gz' suffix and does nothing if the input
+      ;; file already has that suffix.  Shuffle files around to placate it.
+      (let* ((gz-suffix? (string-suffix? ".gz" output))
+             (sans-gz    (if gz-suffix?
+                             (string-drop-right output 3)
+                             output)))
+        (when gz-suffix?
+          (rename-file output sans-gz))
         ;; Use '--no-name' so that gzip records neither a file name nor a time
         ;; stamp in its output.
-      (and (zero? (system* gzip "--best" "--no-name" output))
-           (rename-file (string-append output ".gz")
-                        output))
+        (and (zero? (system* gzip "--best" "--no-name" sans-gz))
+             (begin
+               (unless gz-suffix?
+                 (rename-file (string-append output ".gz") output))
+               output)))
+
       output))
 
 (define (cache-compiled-file-name file)

gnu/system.scm

@@ -870,12 +870,11 @@ hardware-related operations as necessary when booting a Linux container."
   (define make-initrd
     (operating-system-initrd os))
 
-  (let ((initrd (make-initrd boot-file-systems
+  (make-initrd boot-file-systems
                #:linux (operating-system-kernel os)
                #:linux-modules
                (operating-system-initrd-modules os)
-                             #:mapped-devices mapped-devices)))
-    (file-append initrd "/initrd")))
+               #:mapped-devices mapped-devices))
 
 (define (locale-name->definition* name)
   "Variant of 'locale-name->definition' that raises an error upon failure."

gnu/system/linux-initrd.scm

@@ -91,16 +91,17 @@ the derivations referenced by EXP are automatically copied to the initrd."
             (lambda (port)
               (simple-format port "~A\n" #$guile)))
 
-          (build-initrd (string-append #$output "/initrd")
+          (build-initrd (string-append #$output "/initrd.cpio.gz")
                         #:guile #$guile
                         #:init #$init
                         ;; Copy everything INIT refers to into the initrd.
                         #:references-graphs '("closure")
                         #:gzip (string-append #$gzip "/bin/gzip")))))
 
-  (computed-file name builder
+  (file-append (computed-file name builder
                               #:options
-                 `(#:references-graphs (("closure" ,init)))))
+                              `(#:references-graphs (("closure" ,init))))
+               "/initrd.cpio.gz"))
 
 (define (flat-linux-module-directory linux modules)
   "Return a flat directory containing the Linux kernel modules listed in

gnu/system/vm.scm

@@ -213,7 +213,7 @@ made available under the /xchg CIFS share."
               (let* ((inputs  '#$(list qemu (canonical-package coreutils)))
                      (linux   (string-append #$linux "/"
                                              #$(system-linux-image-file-name)))
-                     (initrd  (string-append #$initrd "/initrd"))
+                     (initrd  #$initrd)
                      (loader  #$loader)
                      (graphs  '#$(match references-graphs
                                    (((graph-files . _) ...) graph-files)