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, 143 insertions, 0 deletions

diff --git a/src/core/dbus-unit.c b/src/core/dbus-unit.c
index c507265070..ed207f15b9 100644
--- a/src/core/dbus-unit.c
+++ b/src/core/dbus-unit.c
@@ -24,8 +24,10 @@
 #include "cgroup-util.h"
 #include "dbus-unit.h"
 #include "dbus.h"
+#include "fd-util.h"
 #include "locale-util.h"
 #include "log.h"
+#include "process-util.h"
 #include "selinux-access.h"
 #include "signal-util.h"
 #include "special.h"
@@ -841,6 +843,146 @@ static int property_get_cgroup(
         return sd_bus_message_append(reply, "s", t);
 }
 
+static int append_process(sd_bus_message *reply, const char *p, pid_t pid, Set *pids) {
+        _cleanup_free_ char *buf = NULL, *cmdline = NULL;
+        int r;
+
+        assert(reply);
+        assert(pid > 0);
+
+        r = set_put(pids, PID_TO_PTR(pid));
+        if (r == -EEXIST || r == 0)
+                return 0;
+        if (r < 0)
+                return r;
+
+        if (!p) {
+                r = cg_pid_get_path(SYSTEMD_CGROUP_CONTROLLER, pid, &buf);
+                if (r == -ESRCH)
+                        return 0;
+                if (r < 0)
+                        return r;
+
+                p = buf;
+        }
+
+        (void) get_process_cmdline(pid, 0, true, &cmdline);
+
+        return sd_bus_message_append(reply,
+                                     "(sus)",
+                                     p,
+                                     (uint32_t) pid,
+                                     cmdline);
+}
+
+static int append_cgroup(sd_bus_message *reply, const char *p, Set *pids) {
+        _cleanup_closedir_ DIR *d = NULL;
+        _cleanup_fclose_ FILE *f = NULL;
+        int r;
+
+        assert(reply);
+        assert(p);
+
+        r = cg_enumerate_processes(SYSTEMD_CGROUP_CONTROLLER, p, &f);
+        if (r == ENOENT)
+                return 0;
+        if (r < 0)
+                return r;
+
+        for (;;) {
+                pid_t pid;
+
+                r = cg_read_pid(f, &pid);
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        break;
+
+                if (is_kernel_thread(pid) > 0)
+                        continue;
+
+                r = append_process(reply, p, pid, pids);
+                if (r < 0)
+                        return r;
+        }
+
+        r = cg_enumerate_subgroups(SYSTEMD_CGROUP_CONTROLLER, p, &d);
+        if (r == -ENOENT)
+                return 0;
+        if (r < 0)
+                return r;
+
+        for (;;) {
+                _cleanup_free_ char *g = NULL, *j = NULL;
+
+                r = cg_read_subgroup(d, &g);
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        break;
+
+                j = strjoin(p, "/", g, NULL);
+                if (!j)
+                        return -ENOMEM;
+
+                r = append_cgroup(reply, j, pids);
+                if (r < 0)
+                        return r;
+        }
+
+        return 0;
+}
+
+int bus_unit_method_get_processes(sd_bus_message *message, void *userdata, sd_bus_error *error) {
+        _cleanup_(sd_bus_message_unrefp) sd_bus_message *reply = NULL;
+        _cleanup_(set_freep) Set *pids = NULL;
+        _cleanup_free_ char *p = NULL;
+        Unit *u = userdata;
+        pid_t pid;
+        int r;
+
+        assert(message);
+
+        pids = set_new(NULL);
+        if (!pids)
+                return -ENOMEM;
+
+        r = sd_bus_message_new_method_return(message, &reply);
+        if (r < 0)
+                return r;
+
+        r = sd_bus_message_open_container(reply, 'a', "(sus)");
+        if (r < 0)
+                return r;
+
+        if (u->cgroup_path) {
+                r = append_cgroup(reply, u->cgroup_path, pids);
+                if (r < 0)
+                        return r;
+        }
+
+        /* The main and control pids might live outside of the cgroup, hence fetch them separately */
+        pid = unit_main_pid(u);
+        if (pid > 0) {
+                r = append_process(reply, NULL, pid, pids);
+                if (r < 0)
+                        return r;
+        }
+
+        pid = unit_control_pid(u);
+        if (pid > 0) {
+                r = append_process(reply, NULL, pid, pids);
+                if (r < 0)
+                        return r;
+        }
+
+        r = sd_bus_message_close_container(reply);
+        if (r < 0)
+                return r;
+
+        return sd_bus_send(NULL, reply, NULL);
+}
+
 const sd_bus_vtable bus_unit_cgroup_vtable[] = {
         SD_BUS_VTABLE_START(0),
         SD_BUS_PROPERTY("Slice", "s", property_get_slice, 0, 0),
@@ -848,6 +990,7 @@ const sd_bus_vtable bus_unit_cgroup_vtable[] = {
         SD_BUS_PROPERTY("MemoryCurrent", "t", property_get_current_memory, 0, 0),
         SD_BUS_PROPERTY("CPUUsageNSec", "t", property_get_cpu_usage, 0, 0),
         SD_BUS_PROPERTY("TasksCurrent", "t", property_get_current_tasks, 0, 0),
+        SD_BUS_METHOD("GetProcesses", NULL, "a(sus)", bus_unit_method_get_processes, SD_BUS_VTABLE_UNPRIVILEGED),
         SD_BUS_VTABLE_END
 };