>From c60913505af32c2005ffc9bb3ea7078de5379c54 Mon Sep 17 00:00:00 2001
From: Maxim Cournoyer <address@hidden>
Date: Tue, 11 Feb 2020 14:00:06 -0500
Subject: [PATCH 2/5] linux-boot: Refactor boot-system.

The --root option can now be omitted, and inferred from the root file system
declaration instead.

* gnu/build/linux-boot.scm (boot-system): Remove nested definitions for
root-fs-type, root-fs-flags and root-fs-options, and bind those inside the
let* instead.  Make "--root" take precedence over the device field string
representation of the root file system.
* doc/guix.texi (Initial RAM Disk): Document that "--root" can be left
unspecified.
---
 doc/guix.texi            |  7 +++--
 gnu/build/linux-boot.scm | 60 +++++++++++++++++++---------------------
 2 files changed, 32 insertions(+), 35 deletions(-)

diff --git a/doc/guix.texi b/doc/guix.texi
index d1fa8d033a..11b6884cab 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -26058,9 +26058,10 @@ service activation programs and then spawns the GNU@tie{}Shepherd, the
 initialization system.
 
 @item --root=@var{root}
-Mount @var{root} as the root file system.  @var{root} can be a
-device name like @code{/dev/sda1}, a file system label, or a file system
-UUID.
+Mount @var{root} as the root file system.  @var{root} can be a device
+name like @code{/dev/sda1}, a file system label, or a file system UUID.
+When unspecified, the device name from the root file system of the
+operating system declaration is used.
 
 @item --system=@var{system}
 Have @file{/run/booted-system} and @file{/run/current-system} point to
diff --git a/gnu/build/linux-boot.scm b/gnu/build/linux-boot.scm
index 4fb711b8f2..3a9c761a69 100644
--- a/gnu/build/linux-boot.scm
+++ b/gnu/build/linux-boot.scm
@@ -467,25 +467,13 @@ upon error."
   (define (root-mount-point? fs)
     (string=? (file-system-mount-point fs) "/"))
 
-  (define root-fs-type
-    (or (any (lambda (fs)
-               (and (root-mount-point? fs)
-                    (file-system-type fs)))
-             mounts)
-        "ext4"))
-
-  (define root-fs-flags
-    (mount-flags->bit-mask (or (any (lambda (fs)
-                                      (and (root-mount-point? fs)
-                                           (file-system-flags fs)))
-                                    mounts)
-                               '())))
-
-  (define root-fs-options
-    (any (lambda (fs)
-           (and (root-mount-point? fs)
-                (file-system-options fs)))
-         mounts))
+  (define (device-string->file-system-device device-string)
+    ;; The "--root=SPEC" kernel command-line option always provides a
+    ;; string, but the string can represent a device, a UUID, or a
+    ;; label.  So check for all three.
+    (cond ((string-prefix? "/" device-string) device-string)
+          ((uuid device-string) => identity)
+          (else (file-system-label device-string))))
 
   (display "Welcome, this is GNU's early boot Guile.\n")
   (display "Use '--repl' for an initrd REPL.\n\n")
@@ -495,7 +483,21 @@ upon error."
       (mount-essential-file-systems)
       (let* ((args    (linux-command-line))
              (to-load (find-long-option "--load" args))
-             (root    (find-long-option "--root" args)))
+             (root-fs (find root-mount-point? mounts))
+             (root-fs-type (or (and=> root-fs file-system-type)
+                               "ext4"))
+             (root-fs-device (and=> root-fs file-system-device))
+             (root-fs-flags (mount-flags->bit-mask
+                             (or (and=> root-fs file-system-flags)
+                                 '())))
+             (root-options (if root-fs
+                               (file-system-options root-fs)
+                               #f))
+             ;; --root takes precedence over the 'device' field of the root
+             ;; <file-system> record.
+             (root-device (or (and=> (find-long-option "--root" args)
+                                     device-string->file-system-device)
+                              root-fs-device)))
 
         (when (member "--repl" args)
           (start-repl))
@@ -530,18 +532,12 @@ upon error."
 
         (setenv "EXT2FS_NO_MTAB_OK" "1")
 
-        (if root
-            ;; The "--root=SPEC" kernel command-line option always provides a
-            ;; string, but the string can represent a device, a UUID, or a
-            ;; label.  So check for all three.
-            (let ((root (cond ((string-prefix? "/" root) root)
-                              ((uuid root) => identity)
-                              (else (file-system-label root)))))
-              (mount-root-file-system (canonicalize-device-spec root)
-                                      root-fs-type
-                                      #:volatile-root? volatile-root?
-                                      #:flags root-fs-flags
-                                      #:options root-fs-options))
+        (if root-device
+            (mount-root-file-system (canonicalize-device-spec root-device)
+                                    root-fs-type
+                                    #:volatile-root? volatile-root?
+                                    #:flags root-fs-flags
+                                    #:options root-options)
             (mount "none" "/root" "tmpfs"))
 
         ;; Mount the specified file systems.
-- 
2.25.1