core,systemctl: add bus API to retrieve processes of a unit

This adds a new GetProcesses() bus call to the Unit object which returns an
array consisting of all PIDs, their process names, as well as their full cgroup
paths. This is then used by "systemctl status" to show the per-unit process
tree.

This has the benefit that the client-side no longer needs to access the
cgroupfs directly to show the process tree of a unit. Instead, it now uses this
new API, which means it also works if -H or -M are used correctly, as the
information from the specific host is used, and not the one from the local
system.

Fixes: #2945

1 files changed, 20 insertions, 15 deletions

diff --git a/src/systemctl/systemctl.c b/src/systemctl/systemctl.c
index 04205411dd..c74fc11ca6 100644
--- a/src/systemctl/systemctl.c
+++ b/src/systemctl/systemctl.c
@@ -39,6 +39,7 @@
 #include "bus-common-errors.h"
 #include "bus-error.h"
 #include "bus-message.h"
+#include "bus-unit-util.h"
 #include "bus-util.h"
 #include "cgroup-show.h"
 #include "cgroup-util.h"
@@ -3434,6 +3435,7 @@ typedef struct UnitStatusInfo {
 } UnitStatusInfo;
 
 static void print_status_info(
+                sd_bus *bus,
                 UnitStatusInfo *i,
                 bool *ellipsized) {
 
@@ -3444,6 +3446,7 @@ static void print_status_info(
         char since2[FORMAT_TIMESTAMP_MAX], *s2;
         const char *path;
         char **t, **t2;
+        int r;
 
         assert(i);
 
@@ -3716,25 +3719,26 @@ static void print_status_info(
                 printf("      CPU: %s\n", format_timespan(buf, sizeof(buf), i->cpu_usage_nsec / NSEC_PER_USEC, USEC_PER_MSEC));
         }
 
-        if (i->control_group &&
-            (i->main_pid > 0 || i->control_pid > 0 ||
-             (!IN_SET(arg_transport, BUS_TRANSPORT_LOCAL, BUS_TRANSPORT_MACHINE) || cg_is_empty_recursive(SYSTEMD_CGROUP_CONTROLLER, i->control_group) == 0))) {
+        if (i->control_group)
+                printf("   CGroup: %s\n", i->control_group);
+
+        {
+                _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
+                static const char prefix[] = "           ";
                 unsigned c;
 
-                printf("   CGroup: %s\n", i->control_group);
+                c = columns();
+                if (c > sizeof(prefix) - 1)
+                        c -= sizeof(prefix) - 1;
+                else
+                        c = 0;
 
-                if (IN_SET(arg_transport,
-                           BUS_TRANSPORT_LOCAL,
-                           BUS_TRANSPORT_MACHINE)) {
+                r = unit_show_processes(bus, i->id, i->control_group, prefix, c, get_output_flags(), &error);
+                if (r == -EBADR) {
                         unsigned k = 0;
                         pid_t extra[2];
-                        static const char prefix[] = "           ";
 
-                        c = columns();
-                        if (c > sizeof(prefix) - 1)
-                                c -= sizeof(prefix) - 1;
-                        else
-                                c = 0;
+                        /* Fallback for older systemd versions where the GetUnitProcesses() call is not yet available */
 
                         if (i->main_pid > 0)
                                 extra[k++] = i->main_pid;
@@ -3743,7 +3747,8 @@ static void print_status_info(
                                 extra[k++] = i->control_pid;
 
                         show_cgroup_and_extra(SYSTEMD_CGROUP_CONTROLLER, i->control_group, prefix, c, false, extra, k, get_output_flags());
-                }
+                } else if (r < 0)
+                        log_warning_errno(r, "Failed to dump process list, ignoring: %s", bus_error_message(&error, r));
         }
 
         if (i->id && arg_transport == BUS_TRANSPORT_LOCAL)
@@ -4504,7 +4509,7 @@ static int show_one(
                 if (streq(verb, "help"))
                         show_unit_help(&info);
                 else
-                        print_status_info(&info, ellipsized);
+                        print_status_info(bus, &info, ellipsized);
         }
 
         strv_free(info.documentation);