From b56aea9c62b015c8a8b48827f9587b1578c83af3 Mon Sep 17 00:00:00 2001
From: Maxim Cournoyer <address@hidden>
Date: Thu, 18 Jul 2019 04:59:25 +0900
Subject: [PATCH 4/4] linux-boot: Honor "rootflags" kernel argument.

* gnu/build/linux-boot.scm (mount-root-file-system): Add the optional FLAGS
and OPTIONS arguments; and document them.  Pass those to the `mount' calls.
(boot-system): Parse the "rootflags" kernel argument, and use it when calling
`mount-root-file-system'.
* doc/guix.texi (Initial RAM Disk): Document the use of the "rootflags"
argument.
---
 doc/guix.texi            | 19 +++++++++++++++++++
 gnu/build/linux-boot.scm | 22 +++++++++++++---------
 2 files changed, 32 insertions(+), 9 deletions(-)

diff --git a/doc/guix.texi b/doc/guix.texi
index cc7c91ac92..1e093b38a0 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -24761,6 +24761,25 @@ Instruct the initial RAM disk as well as the @command{modprobe} command
 must be a comma-separated list of module names---e.g.,
 @code{usbkbd,9pnet}.
 
+@item rootflags=@var{options}@dots{}
+@cindex mount options, passed to initrd
+@cindex rootflags, initrd
+This argument allows passing one or multiple file system specific mount
+options to the @code{mount} procedure used by the init script.  @var{options}
+must be a comma-separated list of option names or option-value pairs.  The
+following example instructs the initial RAM disk to mount the Btrfs subvolume
+named ``rootfs'' as the root file system, and to enable automatic file
+defragmentation:
+
+@example
+rootflags=subvol=rootfs,autodefrag
+@end example
+
+Specifying the subvolume to mount by its name, as shown above, is also used in
+Guix to produce a working Grub configuration for the Grub-based bootloaders
+when using a Btrfs subvolume for the root file system (@xref{Bootloader
+Configuration}).
+
 @item --repl
 Start a read-eval-print loop (REPL) from the initial RAM disk before it
 tries to load kernel modules and to mount the root file system.  Our
diff --git a/gnu/build/linux-boot.scm b/gnu/build/linux-boot.scm
index b4e6421b27..b2d8f74a71 100644
--- a/gnu/build/linux-boot.scm
+++ b/gnu/build/linux-boot.scm
@@ -1,6 +1,7 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2013, 2014, 2015, 2016, 2017, 2018, 2019 Ludovic Courtès <address@hidden>
 ;;; Copyright © 2017 Mathieu Othacehe <address@hidden>
+;;; Copyright © 2019 Maxim Cournoyer <address@hidden>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -360,15 +361,16 @@ the last argument of `mknod'."
           (filter-map string->number (scandir "/proc")))))
 
 (define* (mount-root-file-system root type
+                                 #:optional (flags 0) options
                                  #:key volatile-root?)
-  "Mount the root file system of type TYPE at device ROOT.  If VOLATILE-ROOT?
-is true, mount ROOT read-only and make it an overlay with a writable tmpfs
-using the kernel built-in overlayfs."
-
+  "Mount the root file system of type TYPE at device ROOT.  The optional FLAGS
+and OPTIONS arguments behave the same as for the `mount' procedure.  If
+VOLATILE-ROOT?  is true, mount ROOT read-only and make it an overlay with a
+writable tmpfs using the kernel built-in overlayfs."
   (if volatile-root?
       (begin
         (mkdir-p "/real-root")
-        (mount root "/real-root" type MS_RDONLY)
+        (mount root "/real-root" type (logior MS_RDONLY flags) options)
         (mkdir-p "/rw-root")
         (mount "none" "/rw-root" "tmpfs")
 
@@ -385,11 +387,11 @@ using the kernel built-in overlayfs."
                "lowerdir=/real-root,upperdir=/rw-root/upper,workdir=/rw-root/work"))
       (begin
         (check-file-system root type)
-        (mount root "/root" type)))
+        (mount root "/root" type flags options)))
 
   ;; Make sure /root/etc/mtab is a symlink to /proc/self/mounts.
   (false-if-exception
-    (delete-file "/root/etc/mtab"))
+   (delete-file "/root/etc/mtab"))
   (mkdir-p "/root/etc")
   (symlink "/proc/self/mounts" "/root/etc/mtab"))
 
@@ -483,7 +485,8 @@ 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    (find-long-option "--root" args))
+            (rootflags (find-long-option "rootflags" args)))
 
        (when (member "--repl" args)
          (start-repl))
@@ -526,7 +529,8 @@ upon error."
                              ((uuid root) => identity)
                              (else (file-system-label root)))))
              (mount-root-file-system (canonicalize-device-spec root)
-                                     root-fs-type
+                                     root-fs-type 0
+                                     rootflags
                                      #:volatile-root? volatile-root?))
            (mount "none" "/root" "tmpfs"))
 
-- 
2.23.0