[bug#45643] [PATCH 1/3] gnu, doc: Create and document procedure to compile ZFS for specific kernel.

[raid5atemyhomework via Guix-patches via <guix-patches@gnu.org>]

From 004a84a38266eb8735f1e127f5794bf6d66b9272 Mon Sep 17 00:00:00 2001
From: raid5atemyhomework <raid5atemyhomework@protonmail.com>
Date: Fri, 1 Jan 2021 20:26:42 +0800
Subject: [PATCH 1/3] gnu, doc: Create and document procedure to compile ZFS
 for specific kernel.

---
 doc/guix.texi                 | 100 ++++++++++++++++++++++++++++++++++
 gnu/local.mk                  |   1 +
 gnu/packages/file-systems.scm |  25 ++++++++-
 gnu/services/file-systems.scm |  72 ++++++++++++++++++++++++
 4 files changed, 196 insertions(+), 2 deletions(-)
 create mode 100644 gnu/services/file-systems.scm

diff --git a/doc/guix.texi b/doc/guix.texi
index 1081ed26a3..5ad3907dbe 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -13885,6 +13885,106 @@ a file system declaration such as:
 compress-force=zstd,space_cache=v2"))
 @end lisp

+@node ZFS file system
+@subsection ZFS file system
+
+The ZFS on Linux file system cannot legally be downloaded as part of the
+Linux kernel, but you as a user can do anything on hardware you own,
+including download ZFS as source code, compile ZFS as a kernel module,
+and link it into Linux.
+
+As a large and complex kernel module, ZFS has to be compiled for a
+specific version of Linux. Often the latest ZFS package available in Guix
+cannot be compiled with the latest Linux kernel available in Guix, so
+installing the @code{zfs} package in your system configuration file will
+fail.
+
+Instead, you have to check the
+@url{https://github.com/openzfs/zfs/releases,OpenZFS release notes} for
+the specific version of ZFS that Guix has packaged to determine what
+Linux kernels you can use, then check the @code{linux-libre} packages
+that Guix has packaged, and select one you can use on your system.
+
+Then, you have to modify your system configuration file, and create a
+ZFS package that compiles using the specific Linux version you chose.
+Below is a sketch of how you would modify your @code{operating-system}
+declaration in order to set up ZFS:
+
+@lisp
+(use-modules (gnu))
+;; @dots{}
+(use-service-modules
+  ; @dots{}
+  file-systems)
+(use-package-modules
+  ; @dots{}
+  linux
+  file-systems)
+
+;; @dots{}
+
+;;; (1) Select a specific kernel.
+(define system-kernel linux-libre-5.4)
+;;; (2) Define a ZFS package for your kernel.
+(define system-zfs (make-zfs-package system-kernel))
+
+;; @dots{}
+
+(operating-system
+  ;;; (3) Specify your selected kernel.
+  (kernel system-kernel)
+  ;;; (4) Add the "module" output of the system ZFS package to
+  ;;; the kernel-loadable modules.
+  (kernel-loadable-modules (list (list system-zfs "module")))
+
+  ;; @dots{}
+
+  (packages
+    ;;; (5) Add the system ZFS package to global packages so that
+    ;;; "zfs", "zpool" etc. commands are available.
+    (cons* system-zfs
+           ; @dots{}
+           %base-packages))
+
+  ;; @dots{}
+
+  (services
+    ;;; (6) Add a service that loads ZFS and all ZFS pools at boot.
+    (cons* (service zfs-loader-service-type
+                    system-zfs)
+           ; @dots{}
+           %base-services))
+  ;; @dots{}
+  )
+@end lisp
+
+@deffn (Scheme Procedure) make-zfs-package @var{kernel}
+This procedure creates a package which, when included as a package
+in your system, can be loaded as a kernel module for the specified
+@var{kernel}, a Linux kernel package.
+It is intended to create a system-specific ZFS kernel module for
+the Linux kernel you will use in your system.
+@end deffn
+
+@deffn (Scheme Variable) zfs-loader-service-type
+This is the service that loads the ZFS kernel module and imports all
+ZFS pools. The value associated with @code{zfs-loader-service-type}
+services must be the ZFS package you defined for your system, and
+whose @code{"module"} output you have included as a loadable kernel
+module.
+@end deffn
+
+When you have modified your @code{operating-system} to include ZFS
+as in the above and reconfigured and rebooted, you will now be able
+to create, mount, and manage ZFS pools. At each boot, ZFS will
+automatically open any ZFS pools it detects in your system, and will
+mount ZFS pools that have a non-@code{legacy} mountpoint. If ZFS
+finds mountable ZFS filesystems that are encrypted by passphrase, it
+will prompt for passphrases on the console.
+
+ZFS as root filesystem is not supported yet. ZFS for @code{/home} is
+also probably not easily doable yet.
+
 @node Mapped Devices
 @section Mapped Devices

diff --git a/gnu/local.mk b/gnu/local.mk
index c03a8b9f51..e59a3bb9f7 100644
--- a/gnu/local.mk
+++ b/gnu/local.mk
@@ -601,6 +601,7 @@ GNU_SYSTEM_MODULES =				\
   %D%/services/dict.scm				\
   %D%/services/dns.scm				\
   %D%/services/docker.scm			\
+  %D%/services/file-systems.scm			\
   %D%/services/authentication.scm		\
   %D%/services/games.scm			\
   %D%/services/ganeti.scm			\
diff --git a/gnu/packages/file-systems.scm b/gnu/packages/file-systems.scm
index 895ad069c5..e8f49a59fa 100644
--- a/gnu/packages/file-systems.scm
+++ b/gnu/packages/file-systems.scm
@@ -944,16 +944,37 @@ APFS.")
        ("openssl" ,openssl)
        ("python" ,python)
        ("python-cffi" ,python-cffi)
-       ("util-linux" ,util-linux "lib")
+       ("util-linux" ,util-linux)
+       ("util-linux-lib" ,util-linux "lib")
        ("zlib" ,zlib)))
     (home-page "https://zfsonlinux.org/")
     (synopsis "Native ZFS on Linux")
     (description
      "ZFS on Linux is an advanced file system and volume manager which was
 originally developed for Solaris and is now maintained by the OpenZFS
-community.")
+community.
+
+DO NOT INSTALL THIS PACKAGE. Instead, refer to the 'ZFS file system' section
+of the Guix info manual for how to install ZFS.")
     (license license:cddl1.0)))

+(define-public (make-zfs-package kernel)
+  (package
+    (inherit zfs)
+    (name (string-append "zfs-for-"
+                         (package-name kernel)
+                         "-"
+                         (package-version kernel)
+                         "-version"))
+    (arguments
+      (cons* #:linux kernel (package-arguments zfs)))
+    (description
+     "ZFS on Linux is an advanced file system and volume manager which was
+originally developed for Solaris and is now maintained by the OpenZFS
+community.
+
+This package has been compiled for a specific Linux kernel.")))
+
 (define-public mergerfs
   (package
     (name "mergerfs")
diff --git a/gnu/services/file-systems.scm b/gnu/services/file-systems.scm
new file mode 100644
index 0000000000..bdc33f4028
--- /dev/null
+++ b/gnu/services/file-systems.scm
@@ -0,0 +1,72 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2021 raid5atemyhomework <raid5atemyhomework@protonmail.com>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; GNU Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (gnu services file-systems)
+  #:use-module (guix gexp)
+  #:use-module (gnu services)
+  #:use-module (gnu services shepherd))
+
+;;; ZFS
+(define (zfs-loader-shepherd-service system-zfs)
+  (let* ((zpool (file-append system-zfs "/sbin/zpool")))
+    (list
+      (shepherd-service
+       (documentation "Load ZFS kernel module and import ZFS pools.")
+       (provision '(zfs-loader))
+       (requirement '(file-systems))
+       (one-shot? #t)
+       (modules `((srfi srfi-1)
+                  (srfi srfi-34)
+                  (srfi srfi-35)
+                  (rnrs io ports)
+                  ,@%default-modules))
+       (start #~(lambda _
+                  (if (not (file-exists? "/proc/sys/kernel/modprobe"))
+                      (begin (format (current-error-port) "error: ~a~%"
+                                     "Kernel is missing loadable module support.")
+                             #f)
+                      (and
+                        (let ((modprobe (call-with-input-file
+                                          "/proc/sys/kernel/modprobe" get-line)))
+                          (guard (c ((message-condition? c)
+                                     (format (current-error-port)
+                                             "error loading 'zfs' kernel module: ~a~%"
+                                             (condition-message c))
+                                     #f))
+                            (invoke/quiet modprobe "--" "zfs")))
+                        (guard (c ((message-condition? c)
+                                   (format (current-error-port)
+                                           "error importing zpools: ~a~%"
+                                           (condition-message c))
+                                   #f))
+                          ;; 'current-output-port' is typically connected to /dev/klog
+                          ;; in PID 1, so redirect it to the console so we are talking
+                          ;; to the user if zpool sees an encrpyted fs that needs a
+                          ;; passphrase.
+                          (with-output-to-port (current-error-port)
+                            (lambda ()
+                              (invoke #$zpool "import" "-a" "-l"))))))))))))
+
+(define-public zfs-loader-service-type
+  (service-type
+   (name 'zfs-loader)
+   (description "Load ZFS kernel module and import ZFS pools.")
+   (extensions
+    (list (service-extension shepherd-root-service-type zfs-loader-shepherd-service)
+          (service-extension user-processes-service-type (const '(zfs-loader)))))))
+
--
2.29.2