units: introduce new Documentation= field and make use of it everywhere

This should help making the boot process a bit easier to explore and
understand for the administrator. The simple idea is that "systemctl
status" now shows a link to documentation alongside the other status and
decriptionary information of a service.

This patch adds the necessary fields to all our shipped units if we have
proper documentation for them.

src/core/dbus-unit.c

@@ -808,6 +808,7 @@ const BusProperty bus_unit_properties[] = {
         { "PropagateReloadTo",    bus_unit_append_dependencies,      "as", offsetof(Unit, dependencies[UNIT_PROPAGATE_RELOAD_TO]),     true },
         { "PropagateReloadFrom",  bus_unit_append_dependencies,      "as", offsetof(Unit, dependencies[UNIT_PROPAGATE_RELOAD_FROM]),   true },
         { "RequiresMountsFor",    bus_property_append_strv,          "as", offsetof(Unit, requires_mounts_for),                        true },
+        { "Documentation",        bus_property_append_strv,          "as", offsetof(Unit, documentation),                              true },
         { "Description",          bus_unit_append_description,        "s", 0 },
         { "LoadState",            bus_unit_append_load_state,         "s", offsetof(Unit, load_state)                         },
         { "ActiveState",          bus_unit_append_active_state,       "s", 0 },

src/core/dbus-unit.h

@@ -87,6 +87,7 @@
         "  <property name=\"PropagateReloadFrom\" type=\"as\" access=\"read\"/>\n" \
         "  <property name=\"RequiresMountsFor\" type=\"as\" access=\"read\"/>\n" \
         "  <property name=\"Description\" type=\"s\" access=\"read\"/>\n" \
+        "  <property name=\"Documentation\" type=\"as\" access=\"read\"/>\n" \
         "  <property name=\"LoadState\" type=\"s\" access=\"read\"/>\n" \
         "  <property name=\"ActiveState\" type=\"s\" access=\"read\"/>\n" \
         "  <property name=\"SubState\" type=\"s\" access=\"read\"/>\n"  \

src/core/load-fragment-gperf.gperf.m4

@@ -92,6 +92,7 @@ $1.ControlGroupPersistent,       config_parse_tristate,              0,
 )m4_dnl
 Unit.Names,                      config_parse_unit_names,            0,                             0
 Unit.Description,                config_parse_unit_string_printf,    0,                             offsetof(Unit, description)
+Unit.Documentation,              config_parse_documentation,         0,                             offsetof(Unit, documentation)
 Unit.Requires,                   config_parse_unit_deps,             UNIT_REQUIRES,                 0
 Unit.RequiresOverridable,        config_parse_unit_deps,             UNIT_REQUIRES_OVERRIDABLE,     0
 Unit.Requisite,                  config_parse_unit_deps,             UNIT_REQUISITE,                0

src/core/load-fragment.c

@@ -2063,6 +2063,43 @@ int config_parse_unit_requires_mounts_for(
         return r;
 }
 
+int config_parse_documentation(
+                const char *filename,
+                unsigned line,
+                const char *section,
+                const char *lvalue,
+                int ltype,
+                const char *rvalue,
+                void *data,
+                void *userdata) {
+
+        Unit *u = userdata;
+        int r;
+        char **a, **b;
+
+        assert(filename);
+        assert(lvalue);
+        assert(rvalue);
+        assert(u);
+
+        r = config_parse_unit_strv_printf(filename, line, section, lvalue, ltype, rvalue, data, userdata);
+        if (r < 0)
+                return r;
+
+        for (a = b = u->documentation; a && *a; a++) {
+
+                if (is_valid_documentation_url(*a))
+                        *(b++) = *a;
+                else {
+                        log_error("[%s:%u] Invalid URL, ignoring: %s", filename, line, *a);
+                        free(*a);
+                }
+        }
+        *b = NULL;
+
+        return r;
+}
+
 #define FOLLOW_MAX 8
 
 static int open_follow(char **filename, FILE **_f, Set *names, char **_final) {

src/core/load-fragment.h

@@ -36,6 +36,7 @@ int config_parse_unit_names(const char *filename, unsigned line, const char *sec
 int config_parse_unit_string_printf(const char *filename, unsigned line, const char *section, const char *lvalue, int ltype, const char *rvalue, void *data, void *userdata);
 int config_parse_unit_strv_printf(const char *filename, unsigned line, const char *section, const char *lvalue, int ltype, const char *rvalue, void *data, void *userdata);
 int config_parse_unit_path_printf(const char *filename, unsigned line, const char *section, const char *lvalue, int ltype, const char *rvalue, void *data, void *userdata);
+int config_parse_documentation(const char *filename, unsigned line, const char *section, const char *lvalue, int ltype, const char *rvalue, void *data, void *userdata);
 int config_parse_socket_listen(const char *filename, unsigned line, const char *section, const char *lvalue, int ltype, const char *rvalue, void *data, void *userdata);
 int config_parse_socket_bind(const char *filename, unsigned line, const char *section, const char *lvalue, int ltype, const char *rvalue, void *data, void *userdata);
 int config_parse_exec_nice(const char *filename, unsigned line, const char *section, const char *lvalue, int ltype, const char *rvalue, void *data, void *userdata);

src/core/unit.c

@@ -397,6 +397,7 @@ void unit_free(Unit *u) {
         cgroup_attribute_free_list(u->cgroup_attributes);
 
         free(u->description);
+        strv_free(u->documentation);
         free(u->fragment_path);
         free(u->instance);
 
@@ -624,7 +625,7 @@ const char *unit_description(Unit *u) {
 }
 
 void unit_dump(Unit *u, FILE *f, const char *prefix) {
-        char *t;
+        char *t, **j;
         UnitDependency d;
         Iterator i;
         char *p2;
@@ -672,6 +673,9 @@ void unit_dump(Unit *u, FILE *f, const char *prefix) {
         SET_FOREACH(t, u->names, i)
                 fprintf(f, "%s\tName: %s\n", prefix, t);
 
+        STRV_FOREACH(j, u->documentation)
+                fprintf(f, "%s\tDocumentation: %s\n", prefix, *j);
+
         if ((following = unit_following(u)))
                 fprintf(f, "%s\tFollowing: %s\n", prefix, following->id);
 
@@ -698,8 +702,6 @@ void unit_dump(Unit *u, FILE *f, const char *prefix) {
         }
 
         if (!strv_isempty(u->requires_mounts_for)) {
-                char **j;
-
                 fprintf(f,
                         "%s\tRequiresMountsFor:", prefix);
 

src/core/unit.h

@@ -157,6 +157,7 @@ struct Unit {
         char **requires_mounts_for;
 
         char *description;
+        char **documentation;
 
         char *fragment_path; /* if loaded from a config file this is the primary path to it */
         usec_t fragment_mtime;