Allow a QEMU host to set the time and shutdown Guix guests.  Styled
after the patch from the Nix package:

https://github.com/NixOS/nixpkgs/blob/master/pkgs/applications/virtualization/qemu/fix-qemu-ga.patch

diff --git a/qga/commands-posix.c b/qga/commands-posix.c
--- a/qga/commands-posix.c
+++ b/qga/commands-posix.c
@@ -84,6 +84,7 @@ static void ga_wait_child(pid_t pid, int *status, Error **errp)
 void qmp_guest_shutdown(bool has_mode, const char *mode, Error **errp)
 {
     const char *shutdown_flag;
+    const char *command;
     Error *local_err = NULL;
     pid_t pid;
     int status;
@@ -101,10 +102,13 @@ void qmp_guest_shutdown(bool has_mode, const char *mode, Error **errp)
     slog("guest-shutdown called, mode: %s", mode);
     if (!has_mode || strcmp(mode, "powerdown") == 0) {
         shutdown_flag = powerdown_flag;
+        command = "shutdown";
     } else if (strcmp(mode, "halt") == 0) {
         shutdown_flag = halt_flag;
+        command = "halt";
     } else if (strcmp(mode, "reboot") == 0) {
         shutdown_flag = reboot_flag;
+        command = "reboot";
     } else {
         error_setg(errp,
                    "mode is invalid (valid values are: halt|powerdown|reboot");
@@ -123,6 +127,11 @@ void qmp_guest_shutdown(bool has_mode, const char *mode, Error **errp)
         execl("/sbin/shutdown", "shutdown", shutdown_flag, "-g0", "-y",
               "hypervisor initiated shutdown", (char *)NULL);
 #else
+        /* try Guix’s shutdown/halt/reboot first */
+        char *path = g_strdup_printf("/run/current-system/profile/sbin/%s", command);
+        execl(path, command, (char *)NULL);
+        g_free(path);
+
         execl("/sbin/shutdown", "shutdown", "-h", shutdown_flag, "+0",
                "hypervisor initiated shutdown", (char *)NULL);
 #endif
@@ -159,10 +168,12 @@ void qmp_guest_set_time(bool has_time, int64_t time_ns, Error **errp)
     Error *local_err = NULL;
     struct timeval tv;
     static const char hwclock_path[] = "/sbin/hwclock";
+    static const char hwclock_path_guix[] = "/run/current-system/profile/sbin/hwclock";
     static int hwclock_available = -1;
 
     if (hwclock_available < 0) {
-        hwclock_available = (access(hwclock_path, X_OK) == 0);
+        hwclock_available = (access(hwclock_path_guix, X_OK) == 0) ||
+                            (access(hwclock_path, X_OK) == 0);
     }
 
     if (!hwclock_available) {
@@ -208,6 +219,8 @@ void qmp_guest_set_time(bool has_time, int64_t time_ns, Error **errp)
 
         /* Use '/sbin/hwclock -w' to set RTC from the system time,
          * or '/sbin/hwclock -s' to set the system time from RTC. */
+        execl(hwclock_path_guix, "hwclock", has_time ? "-w" : "-s",
+               NULL);
         execl(hwclock_path, "hwclock", has_time ? "-w" : "-s", NULL);
         _exit(EXIT_FAILURE);
     } else if (pid < 0) {
mple.json?id=9608f4003dedd8dfe99327c15668ca1a43ebd93b'>tests: Fix malformed JSON.</a></td><td>Ludovic Courtès</td></tr>
<tr class='nohover-highlight'><td/><td colspan='3' class='logmsg'>
Guile-JSON 4.3.2 would parse in spite of these typos, but 4.4.1 is
stricter.

* tests/swh.scm (%directory-entries): Add missing comma.
* tests/cve-sample.json: Likewise.


</td></tr>
<tr class='logheader'><td><span title='2019-10-23 16:40:17 +0200'>2019-10-23</span></td><td class='logsubject'><a href='/guix/commit/tests/cve-sample.json?id=74afaa37d5dec1a9d1b83951529ba69d8947fb07'>cve: Rewrite to read the JSON feed instead of the XML feed.</a></td><td>Ludovic Courtès</td></tr>
<tr class='nohover-highlight'><td/><td colspan='3' class='logmsg'>
The XML feed was discontinued on Oct. 16th, 2019:

  &lt;https://nvd.nist.gov/General/News/XML-Vulnerability-Feed-Retirement-Phase-3&gt;

* guix/cve.scm (string-&gt;date*): New procedure.
(&lt;cve-item&gt;, &lt;cve&gt;, &lt;cve-reference&gt;): New record types.
(cpe-match-&gt;cve-configuration, configuration-data-&gt;cve-configurations)
(json-&gt;cve-items, version-matches?): New procedures.
(yearly-feed-uri): Change URL to refer to JSON feed.
(cpe-&gt;product-alist, %parse-vulnerability-feed)
(xml-&gt;vulnerabilities): Remove.
(cve-configuration-&gt;package-list, merge-package-lists)
(cve-item-&gt;vulnerability, json-&gt;vulnerabilities): New procedures.
(write-cache): Use 'json-&gt;vulnerabilities' instead of
'xml-&gt;vulnerabilities', and remove 'parameterize'.
(vulnerabilities-&gt;lookup-proc): Use 'version-matches?' when VERSION is
true.
* tests/cve.scm (%sample): Use 'tests/cve-sample.json'.
(%expected-vulnerabilities): Rewrite accordingly.
("json-&gt;cve-items", "cve-item-published-date")
("json-&gt;vulnerabilities"): New tests.
("xml-&gt;vulnerabilities"): Remove.
("vulnerabilities-&gt;lookup-proc"): Adjust to new vulnerabilities.
* tests/cve-sample.json: New file.
* tests/cve-sample.xml: Remove.
* Makefile.am (EXTRA_DIST): Adjust accordingly.
* doc/guix.texi (Invoking guix lint): Update nist.gov URLs.


</td></tr>