[bug#75027] [PATCH 0/3] 'guix system reconfigure' loads system for kexec reboot

[bug#75027] [PATCH 0/3] 'guix system reconfigure' loads system for kexec reboot

[Ludovic Courtès]

Hello Guix,

Following work by Jakob Kirsch adding kexec support in the Shepherd
(the new ‘reboot -k’ option), here’s the Guix side of it: with these
patches, ‘guix system reconfigure’ loads the new system so that one
can run ‘reboot -k’ to quickly reboot into it.

Thoughts?

Ludo’.

PS: It took me a while to debug until I realized it was working
    very well: it’s just that I was booting a kernel with “quiet”
    on its command line, so I couldn’t see anything. 🤦

Ludovic Courtès (3):
  syscalls: Add ‘kexec-load-file’.
  system: Export ‘…-initrd-file’ and ‘…-root-file-system’.
  reconfigure: Call ‘kexec-load-file’.

 gnu/system.scm                      |  4 +-
 gnu/tests/reconfigure.scm           | 77 +++++++++++++++++++++++++++++
 guix/build/syscalls.scm             | 54 ++++++++++++++++++++
 guix/scripts/system/reconfigure.scm | 25 ++++++++++
 tests/syscalls.scm                  | 13 +++++
 5 files changed, 172 insertions(+), 1 deletion(-)


base-commit: 9f53e10235cced7a85697481c859829742b9912c
-- 
2.46.0

[bug#75027] [PATCH 1/3] syscalls: Add ‘kexec-load-file’.

[Ludovic Courtès]

* guix/build/syscalls.scm (string->utf-8/nul-terminated)
(kexec-load-file): New procedures.
* tests/syscalls.scm ("kexec-load-file"): New test.

Change-Id: I3724226a14ecc07f346e77519fb5b0591096c7f6
---
 guix/build/syscalls.scm | 54 +++++++++++++++++++++++++++++++++++++++++
 tests/syscalls.scm      | 13 ++++++++++
 2 files changed, 67 insertions(+)

diff --git a/guix/build/syscalls.scm b/guix/build/syscalls.scm
index 2c20edf058..f8c9937f54 100644
--- a/guix/build/syscalls.scm
+++ b/guix/build/syscalls.scm
@@ -146,6 +146,12 @@ (define-module (guix build syscalls)
             clone
             setns
 
+            kexec-load-file
+            KEXEC_FILE_UNLOAD
+            KEXEC_FILE_ON_CRASH
+            KEXEC_FILE_NO_INITRAMFS
+            KEXEC_FILE_DEBUG
+
             PF_PACKET
             AF_PACKET
             all-network-interface-names
@@ -765,6 +771,54 @@ (define-as-needed load-linux-module
                  (list (strerror err))
                  (list err)))))))
 
+(define (string->utf-8/nul-terminated str)
+  "Serialize STR to UTF-8; return the resulting bytevector, including
+terminating nul character."
+  (let* ((source (string->utf8 str))
+         (bv     (make-bytevector (+ (bytevector-length source) 1) 0)))
+    (bytevector-copy! source 0 bv 0 (bytevector-length source))
+    bv))
+
+;; Constants from <linux/kexec.h>.
+(define KEXEC_FILE_UNLOAD	#x00000001)
+(define KEXEC_FILE_ON_CRASH	#x00000002)
+(define KEXEC_FILE_NO_INITRAMFS	#x00000004)
+(define KEXEC_FILE_DEBUG	#x00000008)
+
+(define kexec-load-file
+  (let* ((proc (syscall->procedure int "syscall"
+                                   (list long             ;sysno
+                                         int              ;kernel fd
+                                         int              ;initrd fd
+                                         unsigned-long    ;cmdline length
+                                         '*               ;cmdline
+                                         unsigned-long))) ;flags
+         ;; TODO: Don't do this.
+         (syscall-id (match (utsname:machine (uname))
+                       ("i686"    320)
+                       ("x86_64"  320)
+                       ("armv7l"  401)
+                       ("aarch64" 401)
+                       ;; XXX: There's apparently no support for ppc64le and
+                       ;; riscv64.
+                       (_ #f))))
+    (lambda* (kernel-fd initrd-fd command-line #:optional (flags 0))
+      "Load for eventual use of kexec(8) the Linux kernel from
+@var{kernel-fd}, its initial RAM disk from @var{initrd-fd}, with the given
+@var{command-line} (a string).  Optionally, @var{flags} can be a bitwise or of
+the KEXEC_FILE_* constants."
+      (let*-values (((command-line)
+                     (string->utf-8/nul-terminated command-line))
+                    ((ret err)
+                     (proc syscall-id kernel-fd initrd-fd
+                           (bytevector-length command-line)
+                           (bytevector->pointer command-line)
+                           flags)))
+        (when (= ret -1)
+          (throw 'system-error "kexec-load-file" "~A"
+                 (list (strerror err))
+                 (list err)))))))
+
 (define (linux-process-flags pid)                 ;copied from the Shepherd
   "Return the process flags of @var{pid} (or'd @code{PF_} constants), assuming
 the Linux /proc file system is mounted; raise a @code{system-error} exception
diff --git a/tests/syscalls.scm b/tests/syscalls.scm
index 13f4f11721..eef864d097 100644
--- a/tests/syscalls.scm
+++ b/tests/syscalls.scm
@@ -679,6 +679,19 @@ (define perform-container-tests?
         (lambda args
           (system-error-errno args))))))
 
+(when (or (zero? (getuid))
+          (not (string-contains %host-type "linux")))
+  (test-skip 1))
+(test-equal "kexec-load-file"
+  EPERM
+  (catch 'system-error
+    (lambda ()
+      (let ((fd1 (open-fdes "/dev/null" O_RDONLY))
+            (fd2 (open-fdes "/dev/null" O_RDONLY)))
+        (kexec-load-file fd1 fd2 "gnu.repl=yes")))
+    (lambda args
+      (system-error-errno args))))
+
 (test-end)
 
 (false-if-exception (delete-file temp-file))
-- 
2.46.0

[bug#75027] [PATCH 2/3] system: Export ‘…-initrd-file’ and ‘…-root-file-system’.

[Ludovic Courtès]

* gnu/system.scm (operating-system-initrd-file): Fix docstring and
export.
(operating-system-root-file-system): Export.

Change-Id: I5254d82ce547e8014027ed20675b8bfe5a5847c5
---
 gnu/system.scm | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/gnu/system.scm b/gnu/system.scm
index dfcb8fb279..252a26cac3 100644
--- a/gnu/system.scm
+++ b/gnu/system.scm
@@ -110,6 +110,7 @@ (define-module (gnu system)
             operating-system-default-label
             operating-system-initrd-modules
             operating-system-initrd
+            operating-system-initrd-file
             operating-system-users
             operating-system-groups
             operating-system-issue
@@ -119,6 +120,7 @@ (define-module (gnu system)
             operating-system-locale-libcs
             operating-system-mapped-devices
             operating-system-file-systems
+            operating-system-root-file-system
             operating-system-store-file-system
             operating-system-user-mapped-devices
             operating-system-boot-mapped-devices
@@ -1355,7 +1357,7 @@ (define (operating-system-root-file-system os)
                (location (operating-system-location os)))))))
 
 (define (operating-system-initrd-file os)
-  "Return a gexp denoting the initrd file of OS."
+  "Return a file-like object for the initrd file of OS."
   (define boot-file-systems
     (filter file-system-needed-for-boot?
             (operating-system-file-systems os)))
-- 
2.46.0

[bug#75027] [PATCH 3/3] reconfigure: Call ‘kexec-load-file’.

[Ludovic Courtès]

This allows rebooting straight into the new system with ‘reboot -k’.

* guix/scripts/system/reconfigure.scm (kexec-loading-program): New
procedure.
(upgrade-shepherd-services): Use it.
* gnu/tests/reconfigure.scm (run-kexec-test): New procedure.
(%test-upgrade-kexec): New variable.

Change-Id: I86d11f1c348e4359bc9e73c86e5aebff60fe875c
---
 gnu/tests/reconfigure.scm           | 77 +++++++++++++++++++++++++++++
 guix/scripts/system/reconfigure.scm | 25 ++++++++++
 2 files changed, 102 insertions(+)

diff --git a/gnu/tests/reconfigure.scm b/gnu/tests/reconfigure.scm
index bcc7645fa3..8d33bdac9b 100644
--- a/gnu/tests/reconfigure.scm
+++ b/gnu/tests/reconfigure.scm
@@ -1,5 +1,6 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2019 Jakob L. Kreuze <zerodaysfordays@sdf.org>
+;;; Copyright © 2024 Ludovic Courtès <ludo@gnu.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -18,9 +19,12 @@
 
 (define-module (gnu tests reconfigure)
   #:use-module (gnu bootloader)
+  #:use-module (gnu services)
+  #:use-module (gnu services base)
   #:use-module (gnu services shepherd)
   #:use-module (gnu system)
   #:use-module (gnu system accounts)
+  #:use-module (gnu system file-systems)
   #:use-module (gnu system shadow)
   #:use-module (gnu system vm)
   #:use-module (gnu tests)
@@ -31,6 +35,7 @@ (define-module (gnu tests reconfigure)
   #:use-module (guix store)
   #:export (%test-switch-to-system
             %test-upgrade-services
+            %test-upgrade-kexec
             %test-install-bootloader))
 
 ;;; Commentary:
@@ -178,6 +183,72 @@ (define* (run-upgrade-services-test)
           (disable (upgrade-services-program '() '() '(dummy) '())))
      (test enable disable))))
 
+(define* (run-kexec-test)
+  (define os
+    (marionette-operating-system
+     (operating-system
+       (inherit %simple-os)
+       (services (modify-services %base-services
+                   (syslog-service-type
+                    config => (syslog-configuration
+                               (inherit config)
+                               (config-file
+                                (plain-file
+                                 "syslog.conf"
+                                 "*.* /dev/console\n")))))))
+     #:imported-modules '((gnu services herd)
+                          (guix combinators))))
+
+  (define new-os
+    (marionette-operating-system
+     (virtualized-operating-system               ;run as with "guix system vm"
+      (operating-system
+        (inherit %simple-os)
+        (host-name "the-new-os")
+        (kernel-arguments '("console=ttyS0")))    ;be verbose
+      #:volatile? #t)                             ;mount root read-only
+     #:imported-modules '((gnu services herd)
+                          (guix combinators))))
+
+  (define vm (virtual-machine os))
+
+  (define test
+    (with-imported-modules '((gnu build marionette))
+      #~(begin
+          (use-modules (gnu build marionette)
+                       (srfi srfi-64))
+
+          (define marionette
+            (make-marionette (list #$vm)))
+
+          (test-runner-current (system-test-runner #$output))
+          (test-begin "kexec")
+
+          (test-equal "host name"
+            #$(operating-system-host-name os)
+            (marionette-eval '(gethostname) marionette))
+
+          (test-assert "kexec-loading-program"
+            (marionette-eval
+             '(primitive-load #$(kexec-loading-program new-os))
+             marionette))
+
+          (test-assert "reboot/kexec"
+            (marionette-eval
+             '(begin
+                (use-modules (gnu services herd))
+                (with-shepherd-action 'root ('kexec) result
+                  (pk 'reboot-kexec result)))
+             marionette))
+
+          (test-equal "host name of new OS"
+            #$(operating-system-host-name new-os)
+            (marionette-eval '(gethostname) marionette))
+
+          (test-end))))
+
+  (gexp->derivation "kexec-test" test))
+
 (define* (run-install-bootloader-test)
   "Run a test of an OS running INSTALL-BOOTLOADER-PROGRAM, which installs a
 bootloader's configuration file."
@@ -268,6 +339,12 @@ (define %test-upgrade-services
 loading new services.")
    (value (run-upgrade-services-test))))
 
+(define %test-upgrade-kexec
+  (system-test
+   (name "upgrade-kexec")
+   (description "FIXME")
+   (value (run-kexec-test))))
+
 (define %test-install-bootloader
   (system-test
    (name "install-bootloader")
diff --git a/guix/scripts/system/reconfigure.scm b/guix/scripts/system/reconfigure.scm
index ddb561d28c..9e08179613 100644
--- a/guix/scripts/system/reconfigure.scm
+++ b/guix/scripts/system/reconfigure.scm
@@ -31,6 +31,7 @@ (define-module (guix scripts system reconfigure)
   #:use-module (gnu services herd)
   #:use-module (gnu services shepherd)
   #:use-module (gnu system)
+  #:autoload   (gnu system file-systems) (file-system-device)
   #:use-module (guix gexp)
   #:use-module (guix modules)
   #:use-module (guix monads)
@@ -51,6 +52,7 @@ (define-module (guix scripts system reconfigure)
 
             upgrade-services-program
             upgrade-shepherd-services
+            kexec-loading-program
 
             install-bootloader-program
             install-bootloader
@@ -176,6 +178,27 @@ (define (upgrade-services-program service-files to-start to-unload to-restart)
         (for-each unload-service '#$to-unload)
         (for-each start-service '#$to-start)))))
 
+(define (kexec-loading-program os)
+  "Return a program that calls 'kexec_file_load' to allow rebooting into OS
+via 'kexec'."
+  (let ((root-device (file-system-device
+                      (operating-system-root-file-system os))))
+    (program-file
+     "kexec-load-system.scm"
+     (with-imported-modules '((guix build syscalls))
+       #~(begin
+           (use-modules (guix build syscalls))
+
+           (let ((kernel (open-fdes #$(operating-system-kernel-file os)
+                                    O_RDONLY))
+                 (initrd (open-fdes #$(operating-system-initrd-file os)
+                                    O_RDONLY)))
+             (kexec-load-file kernel initrd
+                              (string-join
+                               (list #$@(operating-system-kernel-arguments
+                                         os root-device)))
+                              KEXEC_FILE_DEBUG)))))))
+
 (define* (upgrade-shepherd-services eval os)
   "Using EVAL, a monadic procedure taking a single G-Expression as an argument,
 upgrade the Shepherd (PID 1) by unloading obsolete services and loading new
@@ -200,6 +223,8 @@ (define* (upgrade-shepherd-services eval os)
                                         running))
            (service-files (map shepherd-service-file target-services)))
       (eval #~(parameterize ((current-warning-port (%make-void-port "w")))
+                (when (string-contains %host-type "-linux")
+                  (primitive-load #$(kexec-loading-program os)))
                 (primitive-load #$(upgrade-services-program service-files
                                                             to-start
                                                             to-unload
-- 
2.46.0

[bug#75027] [PATCH 0/3] 'guix system reconfigure' loads system for kexec reboot

[Jakob Kirsch via Guix-patches via]

Would it be possible to expose the output of kexec-loading-program as a file in the output directory of the operating system (e.g. as /run/current-system/kexec)?

[bug#75027] [PATCH 0/3] 'guix system reconfigure' loads system for kexec reboot

[Jakob Kirsch via Guix-patches via]

On Mon, Dec 23, 2024 at 12:22:20PM +0100, Ludovic Courtès wrote:
> In addition to or instead of running it by default?

I would say in addition to but with a flag to not load it (like with "--no-bootloader" for the bootloader).

Btw I've also noticed that the framebuffer is only initialized after something graphical (gdm in my case) has been started. This usually isn't an issue for most users but my disks are encrypted so I can't see the password prompt but I can still type in my password.