[PATCH] tools/xl: add suspend-to-ram and resume subcommands

["zithro / Cyril Rébert" <slack@rabbit.lu>]

The xl command doesn't provide suspend/resume, so add them :
  xl suspend-to-ram <Domain>
  xl resume <Domain>

This patch follows a discussion on XenDevel: when you want the
virtualized equivalent of "sleep"-ing a host, it's better to
suspend/resume than to pause/unpause a domain.

Suggested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Suggested-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>

---
- Tested on v4.17, x86
- the function "libxl_domain_resume" is called like libvirt does, so
  using a "co-operative resume", but I don't know what it means (:
- there may be a problem with the words resume <-> restore, like
  for "LIBXL_HAVE_NO_SUSPEND_RESUME"
- for the docs, I only slightly adapted a copy/paste from xl pause ...
---
---
 docs/man/xl.1.pod.in    | 10 ++++++++++
 tools/xl/xl.h           |  2 ++
 tools/xl/xl_cmdtable.c  | 10 ++++++++++
 tools/xl/xl_vmcontrol.c | 36 ++++++++++++++++++++++++++++++++++++
 4 files changed, 58 insertions(+)

diff --git a/docs/man/xl.1.pod.in b/docs/man/xl.1.pod.in
index bed8393473..63d80f1449 100644
--- a/docs/man/xl.1.pod.in
+++ b/docs/man/xl.1.pod.in
@@ -682,6 +682,10 @@ Pass the VNC password to vncviewer via stdin.
 
 =back
 
+=item B<resume> I<domain-id>
+
+Resume a domain, after having been suspended to RAM.
+
 =item B<save> [I<OPTIONS>] I<domain-id> I<checkpointfile> [I<configfile>]
 
 Saves a running domain to a state file so that it can be restored
@@ -760,6 +764,12 @@ in response to this event.
 
 =back
 
+=item B<suspend-to-ram> I<domain-id>
+
+Suspend a domain to RAM.  When in a suspended state the domain will still
+consume allocated resources (such as memory), but will not be eligible for
+scheduling by the Xen hypervisor. It is in a shutdown state, but not dying.
+
 =item B<sysrq> I<domain-id> I<letter>
 
 Send a <Magic System Request> to the domain, each type of request is
diff --git a/tools/xl/xl.h b/tools/xl/xl.h
index 9c86bb1d98..716ad32423 100644
--- a/tools/xl/xl.h
+++ b/tools/xl/xl.h
@@ -133,6 +133,8 @@ int main_migrate(int argc, char **argv);
 int main_dump_core(int argc, char **argv);
 int main_pause(int argc, char **argv);
 int main_unpause(int argc, char **argv);
+int main_suspendtoram(int argc, char **argv);
+int main_resume(int argc, char **argv);
 int main_destroy(int argc, char **argv);
 int main_shutdown(int argc, char **argv);
 int main_reboot(int argc, char **argv);
diff --git a/tools/xl/xl_cmdtable.c b/tools/xl/xl_cmdtable.c
index 62bdb2aeaa..1382282252 100644
--- a/tools/xl/xl_cmdtable.c
+++ b/tools/xl/xl_cmdtable.c
@@ -136,6 +136,16 @@ const struct cmd_spec cmd_table[] = {
       "Unpause a paused domain",
       "<Domain>",
     },
+    { "suspend-to-ram",
+      &main_suspendtoram, 0, 1,
+      "Suspend a domain to RAM",
+      "<Domain>",
+    },
+    { "resume",
+      &main_resume, 0, 1,
+      "Resume a domain from RAM",
+      "<Domain>",
+    },
     { "console",
       &main_console, 0, 0,
       "Attach to domain's console",
diff --git a/tools/xl/xl_vmcontrol.c b/tools/xl/xl_vmcontrol.c
index 98f6bd2e76..ba45f89c5a 100644
--- a/tools/xl/xl_vmcontrol.c
+++ b/tools/xl/xl_vmcontrol.c
@@ -42,6 +42,16 @@ static void unpause_domain(uint32_t domid)
     libxl_domain_unpause(ctx, domid, NULL);
 }
 
+static void suspend_domain_toram(uint32_t domid)
+{
+    libxl_domain_suspend_only(ctx, domid, NULL);
+}
+
+static void resume_domain(uint32_t domid)
+{
+    libxl_domain_resume(ctx, domid, 1, NULL);
+}
+
 static void destroy_domain(uint32_t domid, int force)
 {
     int rc;
@@ -82,6 +92,32 @@ int main_unpause(int argc, char **argv)
     return EXIT_SUCCESS;
 }
 
+int main_suspendtoram(int argc, char **argv)
+{
+    int opt;
+
+    SWITCH_FOREACH_OPT(opt, "", NULL, "suspend-to-ram", 1) {
+        /* No options */
+    }
+
+    suspend_domain_toram(find_domain(argv[optind]));
+
+    return EXIT_SUCCESS;
+}
+
+int main_resume(int argc, char **argv)
+{
+    int opt;
+
+    SWITCH_FOREACH_OPT(opt, "", NULL, "resume", 1) {
+        /* No options */
+    }
+
+    resume_domain(find_domain(argv[optind]));
+
+    return EXIT_SUCCESS;
+}
+
 int main_destroy(int argc, char **argv)
 {
     int opt;
-- 
2.39.2