[bug#40927] [PATCH] Allow resume from swap device during boot

[Jean-Baptiste Note <jean-baptiste.note@m4x.org>]

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Dear GUIX maintainers,

Current the GUIX SD boot process does not allow resuming from sleep,
even thought sleep options are available through loginctl, eg:

loginctl hybrid-sleep
loginctl hibernate

This is a very important feature for people like me using GUIX SD on a
laptop (yes, it is possible, mine is a corebooted X230 running
linux-libre!)

This patch is based on a patch floating around. The core functionality
has been isolated, the resume function isolated, the patch rebased and
tested. I'm not taking credit for it, even though tracing the exact
origin is hard.

The resume hook is called if the resume= kernel argument is provided,
which one can do during system configuration.

My scheme level is zero, so please bear with me. In particular, some
conditionals could maybe be moved within the function, or the function
itself called within some already-available hooks. Also it is not clear
if the commit log is adequate for such a change.

Please let me know how to improve this and get this merged; I can also
write some documentation (probably once the mechanism is in place) to
explain how the feature can be used.

Kind regards,
Jean-Baptiste


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From 2531d1d08dabb53ff15020aedcec2ad5d8e6c600 Mon Sep 17 00:00:00 2001
From: Jean-Baptiste Note <jean-baptiste.note@m4x.org>
Date: Mon, 27 Apr 2020 20:42:03 +0000
Subject: [PATCH] linux-boot: Add support for resuming from swap device.

* gnu/build/linux-boot.scm (resume-from-device): Add function.

* gnu/build/linux-boot.scm (boot-system): Add hook calling resume-from-device
  if specified on commandline, before mounting any actual disk filesystems.
---
 gnu/build/linux-boot.scm | 43 +++++++++++++++++++++++++++++++++++++---
 1 file changed, 40 insertions(+), 3 deletions(-)

diff --git a/gnu/build/linux-boot.scm b/gnu/build/linux-boot.scm
index 4fb711b8f2..907c84276f 100644
--- a/gnu/build/linux-boot.scm
+++ b/gnu/build/linux-boot.scm
@@ -357,6 +357,37 @@ the last argument of `mknod'."
                      (compose (cut string=? program <>) basename))))
           (filter-map string->number (scandir "/proc")))))
 
+(define (resume-from-device resume-device)
+  "Resume from hibernation state on device DEVICE. This *must* happen before
+we mount any filesystems on disk. See
+linux-libre/Documentation/swsusp.txt. Please note that this function will not
+return if resume happens successfully, and will return if swap device does not
+contain a valid resume signature."
+  (false-if-exception
+   (let* ((device-base-name
+           ;; The base name of the device file, after resolving
+           ;; symlinks.
+           (let loop ((file resume-device))
+             (match (stat:type (lstat file))
+               ('symlink
+                (let ((target (readlink file)))
+                  (if (string-prefix? "/" target)
+                      (loop target)
+                      (loop (string-append (dirname file) "/" target)))))
+               (_ (basename file)))))
+          (major+minor
+           ;; The major:minor string (e.g. "8:2") corresponding
+           ;; to the resume device.
+           (call-with-input-file (string-append "/sys/class/block/"
+                                                device-base-name
+                                                "/dev")
+             read-line)))
+     ;; Write the major:minor string to /sys/power/resume
+     ;; to attempt resume from hibernation.
+     (when major+minor
+       (call-with-output-file "/sys/power/resume"
+         (cut display major+minor <>))))))
+
 (define* (mount-root-file-system root type
                                  #:key volatile-root? (flags 0) options)
   "Mount the root file system of type TYPE at device ROOT. If VOLATILE-ROOT? is
@@ -493,9 +524,10 @@ upon error."
   (call-with-error-handling
     (lambda ()
       (mount-essential-file-systems)
-      (let* ((args    (linux-command-line))
-             (to-load (find-long-option "--load" args))
-             (root    (find-long-option "--root" args)))
+      (let* ((args          (linux-command-line))
+             (to-load       (find-long-option "--load" args))
+             (root          (find-long-option "--root" args))
+             (resume-device (find-long-option "resume" args)))
 
         (when (member "--repl" args)
           (start-repl))
@@ -528,6 +560,11 @@ upon error."
           (unless (pre-mount)
             (error "pre-mount actions failed")))
 
+        (when (and resume-device
+                   (file-exists? resume-device)
+                   (file-exists? "/sys/power/resume"))
+          (resume-from-device resume-device))
+
         (setenv "EXT2FS_NO_MTAB_OK" "1")
 
         (if root
-- 
2.26.1


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