system: Take kernel modules from the user-specified kernel.

* gnu/system/linux-initrd.scm (base-initrd): Add #:linux option to
  specify the linux kernel to use.
* gnu/system/vm.scm (expression->derivation-in-linux-vm): Propagate
  #:linux to base-initrd.
* gnu/system.scm (operating-system-initrd-file): Pass #:linux to
  'make-initrd'.

Co-authored-by: Ludovic Courtès <ludo@gnu.org>

gnu/system.scm

@@ -737,6 +737,7 @@ (define make-initrd
     (operating-system-initrd os))
 
   (mlet %store-monad ((initrd (make-initrd boot-file-systems
+                                           #:linux (operating-system-kernel os)
                                            #:mapped-devices mapped-devices)))
     (return #~(string-append #$initrd "/initrd"))))
 

gnu/system/linux-initrd.scm

@@ -143,16 +143,17 @@ (define (file-system->spec fs)
 
 (define* (base-initrd file-systems
                       #:key
+                      (linux linux-libre)
                       (mapped-devices '())
                       qemu-networking?
                       virtio?
                       volatile-root?
                       (extra-modules '()))
-  "Return a monadic derivation that builds a generic initrd.  FILE-SYSTEMS is
-a list of file-systems to be mounted by the initrd, possibly in addition to
-the root file system specified on the kernel command line via '--root'.
-MAPPED-DEVICES is a list of device mappings to realize before FILE-SYSTEMS are
-mounted.
+  "Return a monadic derivation that builds a generic initrd, with kernel
+modules taken from LINUX.  FILE-SYSTEMS is a list of file-systems to be
+mounted by the initrd, possibly in addition to the root file system specified
+on the kernel command line via '--root'.  MAPPED-DEVICES is a list of device
+mappings to realize before FILE-SYSTEMS are mounted.
 
 When QEMU-NETWORKING? is true, set up networking with the standard QEMU
 parameters.  When VIRTIO? is true, load additional modules so the initrd can
@@ -224,7 +225,7 @@ (define device-mapping-commands
              (open source target)))
          mapped-devices))
 
-  (mlet %store-monad ((kodir (flat-linux-module-directory linux-libre
+  (mlet %store-monad ((kodir (flat-linux-module-directory linux
                                                           linux-modules)))
     (expression->initrd
      #~(begin

gnu/system/vm.scm

@@ -149,6 +149,7 @@ (define* (expression->derivation-in-linux-vm name exp
        (initrd       (if initrd                   ; use the default initrd?
                          (return initrd)
                          (base-initrd %linux-vm-file-systems
+                                      #:linux linux
                                       #:virtio? #t
                                       #:qemu-networking? #t))))