initrd: Honor rootfstype and rootflags command-line parameters.

* gnu/build/linux-boot.scm (boot-system): Honor rootfstype and rootflags
arguments.  Update doc.  Error out in case there is insufficient information
with regard to the root file system.
Restore the behavior of inferring the root device from the root file system
from the operating system in case the root argument is not provided.
* doc/guix.texi (Initial RAM Disk): Document the new command-line parameters.

2 files changed, 46 insertions, 19 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index ce44eb3b47..dc6cb9842e 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -34973,6 +34973,16 @@ 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 rootfstype=@var{type}
+Set the type of the root file system.  It overrides the @code{type}
+field of the root file system specified via the @code{operating-system}
+declaration, if any.
+
+@item rootflags=@var{options}
+Set the mount @emph{options} of the root file system.  It overrides the
+@code{options} field of the root file system specified via the
+@code{operating-system} declaration, if any.
+
 @item fsck.mode=@var{mode}
 Whether to check the @var{root} file system for errors before mounting
 it.  @var{mode} is one of @code{skip} (never check), @code{force} (always
diff --git a/gnu/build/linux-boot.scm b/gnu/build/linux-boot.scm
index cfa1ab2fcb..7d41537652 100644
--- a/gnu/build/linux-boot.scm
+++ b/gnu/build/linux-boot.scm
@@ -500,9 +500,9 @@ LINUX-MODULE-DIRECTORY, then installing KEYMAP-FILE with 'loadkeys' (if
 KEYMAP-FILE is true), then setting up QEMU guest networking if
 QEMU-GUEST-NETWORKING? is true, calling PRE-MOUNT, mounting the file systems
 specified in MOUNTS, and finally booting into the new root if any.  The initrd
-supports kernel command-line parameters 'gnu.load' and 'gnu.repl'.  It also
+supports the kernel command-line options 'gnu.load' and 'gnu.repl'.  It also
 honors a subset of the Linux kernel command-line parameters such as
-'fsck.mode', 'resume', 'root' and 'rootdelay'.
+'fsck.mode', 'resume', 'rootdelay', rootflags and rootfstype.
 
 Mount the root file system, specified by the 'root' command-line argument, if
 any.
@@ -538,13 +538,30 @@ upon error."
              ;; over the ‘device’ field of the root <file-system> record.
              (root-device (and=> (find-long-option "root" args)
                                  device-string->file-system-device))
-             (root-fs (or (find root-mount-point? mounts)
-                          ;; Fall back to fictitious defaults.
-                          (file-system (device (or root-device "/dev/root"))
-                                       (mount-point "/")
-                                       (type "ext4"))))
+             (rootfstype  (find-long-option "rootfstype" args))
+             (rootflags   (find-long-option "rootflags" args))
+             (root-fs*    (find root-mount-point? mounts))
              (fsck.mode (find-long-option "fsck.mode" args)))
 
+        (unless (or root-fs* (and root-device rootfstype))
+          (error "no root file system or 'root' and 'rootfstype' parameters"))
+
+        ;; If present, ‘root’ on the kernel command line takes precedence over
+        ;; the ‘device’ field of the root <file-system> record; likewise for
+        ;; the 'rootfstype' and 'rootflags' arguments.
+        (define root-fs
+          (if root-fs*
+              (file-system
+                (inherit root-fs*)
+                (device (or root-device (file-system-device root-fs*)))
+                (type (or rootfstype (file-system-type root-fs*)))
+                (options (or rootflags (file-system-options root-fs*))))
+              (file-system
+                (device root-device)
+                (mount-point "/")
+                (type rootfstype)
+                (options rootflags))))
+
         (define (check? fs)
           (match fsck.mode
             ("skip"  #f)
@@ -616,18 +633,18 @@ the root file system...\n" root-delay)
 
         (setenv "EXT2FS_NO_MTAB_OK" "1")
 
-        (if root-device
-            (mount-root-file-system (canonicalize-device-spec root-device)
-                                    (file-system-type root-fs)
-                                    #:volatile-root? volatile-root?
-                                    #:flags (mount-flags->bit-mask
-                                             (file-system-flags root-fs))
-                                    #:options (file-system-options root-fs)
-                                    #:check? (check? root-fs)
-                                    #:skip-check-if-clean?
-                                    (skip-check-if-clean? root-fs)
-                                    #:repair (repair root-fs))
-            (mount "none" "/root" "tmpfs"))
+        ;; Mount the root file system.
+        (mount-root-file-system (canonicalize-device-spec
+                                 (file-system-device root-fs))
+                                (file-system-type root-fs)
+                                #:volatile-root? volatile-root?
+                                #:flags (mount-flags->bit-mask
+                                         (file-system-flags root-fs))
+                                #:options (file-system-options root-fs)
+                                #:check? (check? root-fs)
+                                #:skip-check-if-clean?
+                                (skip-check-if-clean? root-fs)
+                                #:repair (repair root-fs))
 
         ;; Mount the specified non-root file systems.
         (for-each (lambda (fs)