From 9d2b4f74db11fb7d938a2cab9edeeb49a3e92fe0 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: 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
-- 
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