From 9863a22986912c0a1ebbe866a53f11d3a7c9720f Mon Sep 17 00:00:00 2001
From: Ben Hutchings <ben@decadent.org.uk>
Date: Thu, 19 Jul 2018 21:34:08 +0100
Subject: [PATCH] resume: Backward compatibility for resume_offset

Forwarded: not-needed

In Debian we will need to maintain backward compatibility with Linux
4.9 at least until after the "buster" release.  Therefore we need to
accept that /sys/power/resume_offset might not exist.

If we can't open that file because it doesn't exist, we should check
whether the offset we are trying to set is the offset that the kernel
would use anyway.  In that case, continue.


Gbp-Pq: Name resume-backward-compatibility-for-resume_offset.patch
---
 usr/kinit/resume/resumelib.c | 82 +++++++++++++++++++++++++++++++++++-
 1 file changed, 81 insertions(+), 1 deletion(-)

diff --git a/usr/kinit/resume/resumelib.c b/usr/kinit/resume/resumelib.c
index 03e596a..c9add45 100644
--- a/usr/kinit/resume/resumelib.c
+++ b/usr/kinit/resume/resumelib.c
@@ -2,6 +2,8 @@
  * Handle resume from suspend-to-disk
  */
 
+#include <ctype.h>
+#include <errno.h>
 #include <fcntl.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -41,6 +43,70 @@ int do_resume(int argc, char *argv[])
 	return resume(resume_file, resume_offset);
 }
 
+/*
+ * Get the default resume_offset set on the kernel command line.
+ * Return 0 (built-in default) if it is not set, or -1 on failure.
+ */
+static unsigned long long default_resume_offset(void)
+{
+	static const char str_hibernate_noresume[] = "hibernate=noresume";
+	static const char str_resume_offset[] = "resume_offset=";
+	unsigned long long offset = -1;
+	/*
+	 * Max length of the kernel command line is arch-dependent,
+	 * but currently no more than 4K.
+	 */
+	char buf[4096], *param;
+	ssize_t len;
+	int fd;
+
+	fd = open("/proc/cmdline", O_RDONLY);
+	if (fd < 0)
+		goto out;
+
+	len = read(fd, buf, sizeof buf - 1);
+	if (len < 0)
+		goto out;
+	buf[len] = 0;
+
+	offset = 0;
+	param = buf;
+	for (;;) {
+		/* Skip white space and check for end of string */
+		param += strspn(param, " \t\r\n");
+		if (!*param)
+			break;
+
+		/* Get param length */
+		len = strcspn(param, " \t\r\n");
+
+		/*
+		 * Check for hibernate=(noresume|no) which inhibits
+		 * parsing of the resume_offset parameter
+		 */
+		if ((len == sizeof str_hibernate_noresume - 1 ||
+		     len == sizeof str_hibernate_noresume - 1 - 6) &&
+		    strncmp(param, str_hibernate_noresume, len) == 0) {
+			offset = 0;
+			break;
+		}
+
+		/* Check for resume_offset=... */
+		if (strncmp(param, str_resume_offset,
+			    sizeof str_resume_offset - 1) == 0)
+			sscanf(param + sizeof str_resume_offset - 1,
+			       "%llu", &offset);
+
+		/* Advance over param */
+		param += len;
+	}
+
+out:
+	if (fd >= 0)
+		close(fd);
+	return offset;
+}
+
 int resume(const char *resume_file, unsigned long long resume_offset)
 {
 	dev_t resume_device;
@@ -55,8 +121,21 @@ int resume(const char *resume_file, unsigned long long resume_offset)
 		goto failure;
 	}
 
-	if ((attr_fd = open("/sys/power/resume_offset", O_WRONLY)) < 0)
+	if ((attr_fd = open("/sys/power/resume_offset", O_WRONLY)) < 0) {
+		if (errno == ENOENT) {
+			/*
+			 * We can't change the offset, but maybe we don't
+			 * need to.  In that case, continue.
+			 */
+			unsigned long long default_offset =
+				default_resume_offset();
+
+			if (default_offset != (unsigned long long)(-1) &&
+			    default_offset == resume_offset)
+				goto skip_offset;
+		}
 		goto fail_offset;
+	}
 
 	len = snprintf(attr_value, sizeof attr_value,
 		       "%llu",
@@ -71,6 +150,7 @@ int resume(const char *resume_file, unsigned long long resume_offset)
 
 	close(attr_fd);
 
+skip_offset:
 	if ((attr_fd = open("/sys/power/resume", O_WRONLY)) < 0)
 		goto fail_r;
 
-- 
2.30.2