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, 51 insertions, 19 deletions

diff --git a/src/shared/cgroup-show.c b/src/shared/cgroup-show.c
index f3039b23f7..65a2c554d5 100644
--- a/src/shared/cgroup-show.c
+++ b/src/shared/cgroup-show.c
@@ -37,23 +37,13 @@
 #include "string-util.h"
 #include "terminal-util.h"
 
-static int compare(const void *a, const void *b) {
-        const pid_t *p = a, *q = b;
-
-        if (*p < *q)
-                return -1;
-        if (*p > *q)
-                return 1;
-        return 0;
-}
-
 static void show_pid_array(pid_t pids[], unsigned n_pids, const char *prefix, unsigned n_columns, bool extra, bool more, bool kernel_threads, OutputFlags flags) {
         unsigned i, j, pid_width;
 
         if (n_pids == 0)
                 return;
 
-        qsort(pids, n_pids, sizeof(pid_t), compare);
+        qsort(pids, n_pids, sizeof(pid_t), pid_compare_func);
 
         /* Filter duplicates */
         for (j = 0, i = 1; i < n_pids; i++) {
@@ -86,8 +76,14 @@ static void show_pid_array(pid_t pids[], unsigned n_pids, const char *prefix, un
         }
 }
 
+static int show_cgroup_one_by_path(
+                const char *path,
+                const char *prefix,
+                unsigned n_columns,
+                bool more,
+                bool kernel_threads,
+                OutputFlags flags) {
 
-static int show_cgroup_one_by_path(const char *path, const char *prefix, unsigned n_columns, bool more, bool kernel_threads, OutputFlags flags) {
         char *fn;
         _cleanup_fclose_ FILE *f = NULL;
         size_t n = 0, n_allocated = 0;
@@ -125,7 +121,13 @@ static int show_cgroup_one_by_path(const char *path, const char *prefix, unsigne
         return 0;
 }
 
-int show_cgroup_by_path(const char *path, const char *prefix, unsigned n_columns, bool kernel_threads, OutputFlags flags) {
+int show_cgroup_by_path(
+                const char *path,
+                const char *prefix,
+                unsigned n_columns,
+                bool kernel_threads,
+                OutputFlags flags) {
+
         _cleanup_free_ char *fn = NULL, *p1 = NULL, *last = NULL, *p2 = NULL;
         _cleanup_closedir_ DIR *d = NULL;
         char *gn = NULL;
@@ -137,8 +139,7 @@ int show_cgroup_by_path(const char *path, const char *prefix, unsigned n_columns
         if (n_columns <= 0)
                 n_columns = columns();
 
-        if (!prefix)
-                prefix = "";
+        prefix = strempty(prefix);
 
         r = cg_mangle_path(path, &fn);
         if (r < 0)
@@ -202,7 +203,13 @@ int show_cgroup_by_path(const char *path, const char *prefix, unsigned n_columns
         return 0;
 }
 
-int show_cgroup(const char *controller, const char *path, const char *prefix, unsigned n_columns, bool kernel_threads, OutputFlags flags) {
+int show_cgroup(const char *controller,
+                const char *path,
+                const char *prefix,
+                unsigned n_columns,
+                bool kernel_threads,
+
+                OutputFlags flags) {
         _cleanup_free_ char *p = NULL;
         int r;
 
@@ -215,7 +222,15 @@ int show_cgroup(const char *controller, const char *path, const char *prefix, un
         return show_cgroup_by_path(p, prefix, n_columns, kernel_threads, flags);
 }
 
-static int show_extra_pids(const char *controller, const char *path, const char *prefix, unsigned n_columns, const pid_t pids[], unsigned n_pids, OutputFlags flags) {
+static int show_extra_pids(
+                const char *controller,
+                const char *path,
+                const char *prefix,
+                unsigned n_columns,
+                const pid_t pids[],
+                unsigned n_pids,
+                OutputFlags flags) {
+
         _cleanup_free_ pid_t *copy = NULL;
         unsigned i, j;
         int r;
@@ -252,7 +267,16 @@ static int show_extra_pids(const char *controller, const char *path, const char
         return 0;
 }
 
-int show_cgroup_and_extra(const char *controller, const char *path, const char *prefix, unsigned n_columns, bool kernel_threads, const pid_t extra_pids[], unsigned n_extra_pids, OutputFlags flags) {
+int show_cgroup_and_extra(
+                const char *controller,
+                const char *path,
+                const char *prefix,
+                unsigned n_columns,
+                bool kernel_threads,
+                const pid_t extra_pids[],
+                unsigned n_extra_pids,
+                OutputFlags flags) {
+
         int r;
 
         assert(path);
@@ -264,7 +288,15 @@ int show_cgroup_and_extra(const char *controller, const char *path, const char *
         return show_extra_pids(controller, path, prefix, n_columns, extra_pids, n_extra_pids, flags);
 }
 
-int show_cgroup_and_extra_by_spec(const char *spec, const char *prefix, unsigned n_columns, bool kernel_threads, const pid_t extra_pids[], unsigned n_extra_pids, OutputFlags flags) {
+int show_cgroup_and_extra_by_spec(
+                const char *spec,
+                const char *prefix,
+                unsigned n_columns,
+                bool kernel_threads,
+                const pid_t extra_pids[],
+                unsigned n_extra_pids,
+                OutputFlags flags) {
+
         _cleanup_free_ char *controller = NULL, *path = NULL;
         int r;