From: Yu Watanabe <watanabe.yu+github@gmail.com>
Date: Sun, 13 Jan 2019 07:44:38 +0900
Subject: [PATCH] udevadm: add --ping option to 'control' command

This exposes `udev_ctrl_send_ping()`.
---
Ported from upstream commit a82340cc0312e2a946ac5c797fa57e98fe613ce7:
https://github.com/systemd/systemd/commit/a82340cc0312e2a946ac5c797fa57e98fe613ce7

 * Minor changes required to match context that changed in between
   v225 and the upstream commit.
 * using 'rc' vs. 'r' variable, plus different return/break conventions

 man/udevadm.xml            |  7 +++++++
 src/udev/udevadm-control.c | 35 ++++++++++++++++++++++++-----------
 2 files changed, 31 insertions(+), 11 deletions(-)

diff --git a/man/udevadm.xml b/man/udevadm.xml
index 484cbac84dc4..f3c62fba6b1d 100644
--- a/man/udevadm.xml
+++ b/man/udevadm.xml
@@ -450,6 +450,13 @@
             same time.</para>
           </listitem>
         </varlistentry>
+        <varlistentry>
+          <term><option>--ping</option></term>
+          <listitem>
+            <para>Send a ping message to systemd-udevd and wait for the reply. This may be useful to check that
+            systemd-udevd daemon is running.</para>
+          </listitem>
+        </varlistentry>
         <varlistentry>
           <term><option>--timeout=</option><replaceable>seconds</replaceable></term>
           <listitem>
diff --git a/src/udev/udevadm-control.c b/src/udev/udevadm-control.c
index 78170463b653..edda91d2906d 100644
--- a/src/udev/udevadm-control.c
+++ b/src/udev/udevadm-control.c
@@ -35,6 +35,7 @@ static void print_help(void) {
                "  -R --reload              Reload rules and databases\n"
                "  -p --property=KEY=VALUE  Set a global property for all events\n"
                "  -m --children-max=N      Maximum number of children\n"
+               "     --ping                Wait for udev to respond to a ping message\n"
                "     --timeout=SECONDS     Maximum time to block for a reply\n"
                , program_invocation_short_name);
 }
@@ -44,18 +45,23 @@ static int adm_control(struct udev *udev, int argc, char *argv[]) {
         int timeout = 60;
         int rc = 1, c;
 
+        enum {
+                ARG_PING = 0x100,
+        };
+
         static const struct option options[] = {
-                { "exit",             no_argument,       NULL, 'e' },
-                { "log-priority",     required_argument, NULL, 'l' },
-                { "stop-exec-queue",  no_argument,       NULL, 's' },
-                { "start-exec-queue", no_argument,       NULL, 'S' },
-                { "reload",           no_argument,       NULL, 'R' },
-                { "reload-rules",     no_argument,       NULL, 'R' }, /* alias for -R */
-                { "property",         required_argument, NULL, 'p' },
-                { "env",              required_argument, NULL, 'p' }, /* alias for -p */
-                { "children-max",     required_argument, NULL, 'm' },
-                { "timeout",          required_argument, NULL, 't' },
-                { "help",             no_argument,       NULL, 'h' },
+                { "exit",             no_argument,       NULL, 'e'      },
+                { "log-priority",     required_argument, NULL, 'l'      },
+                { "stop-exec-queue",  no_argument,       NULL, 's'      },
+                { "start-exec-queue", no_argument,       NULL, 'S'      },
+                { "reload",           no_argument,       NULL, 'R'      },
+                { "reload-rules",     no_argument,       NULL, 'R'      }, /* alias for -R */
+                { "property",         required_argument, NULL, 'p'      },
+                { "env",              required_argument, NULL, 'p'      }, /* alias for -p */
+                { "children-max",     required_argument, NULL, 'm'      },
+                { "ping",             no_argument,       NULL, ARG_PING },
+                { "timeout",          required_argument, NULL, 't'      },
+                { "help",             no_argument,       NULL, 'h'      },
                 {}
         };
 
@@ -133,6 +139,15 @@ static int adm_control(struct udev *udev, int argc, char *argv[]) {
                                 rc = 0;
                         break;
                 }
+                case ARG_PING:
+                        rc = udev_ctrl_send_ping(uctrl, timeout);
+                        if (rc < 0) {
+                                log_error_errno(rc, "Failed to connect to udev daemon: %m");
+                                rc = 2;
+                        } else {
+                                rc = 0;
+                        }
+                        break;
                 case 't': {
                         int seconds;
 
-- 
2.29.2