core: support percentage specifications on TasksMax=

This adds support for a TasksMax=40% syntax for specifying values relative to
the system's configured maximum number of processes. This is useful in order to
neatly subdivide the available room for tasks within containers.

2 files changed, 34 insertions, 3 deletions

diff --git a/src/core/dbus-cgroup.c b/src/core/dbus-cgroup.c
index 6167ce92cd..b3e2830c11 100644
--- a/src/core/dbus-cgroup.c
+++ b/src/core/dbus-cgroup.c
@@ -1060,6 +1060,8 @@ int bus_cgroup_set_property(
                 r = sd_bus_message_read(message, "t", &limit);
                 if (r < 0)
                         return r;
+                if (limit <= 0)
+                        return sd_bus_error_set_errnof(error, EINVAL, "%s= is too small", name);
 
                 if (mode != UNIT_CHECK) {
                         c->tasks_max = limit;
@@ -1072,6 +1074,26 @@ int bus_cgroup_set_property(
                 }
 
                 return 1;
+        } else if (streq(name, "TasksMaxScale")) {
+                uint64_t limit;
+                uint32_t raw;
+
+                r = sd_bus_message_read(message, "u", &raw);
+                if (r < 0)
+                        return r;
+
+                limit = system_tasks_max_scale(raw, UINT32_MAX);
+                if (limit <= 0 || limit >= UINT64_MAX)
+                        return sd_bus_error_set_errnof(error, EINVAL, "%s= is out of range", name);
+
+                if (mode != UNIT_CHECK) {
+                        c->tasks_max = limit;
+                        unit_invalidate_cgroup(u, CGROUP_MASK_PIDS);
+                        unit_write_drop_in_private_format(u, mode, name, "TasksMax=%" PRIu32 "%%",
+                                                          (uint32_t) (DIV_ROUND_UP((uint64_t) raw * 100U, (uint64_t) UINT32_MAX)));
+                }
+
+                return 1;
         }
 
         if (u->transient && u->load_state == UNIT_STUB) {
diff --git a/src/core/load-fragment.c b/src/core/load-fragment.c
index 782e420e4c..cd7bf9c707 100644
--- a/src/core/load-fragment.c
+++ b/src/core/load-fragment.c
@@ -2861,9 +2861,18 @@ int config_parse_tasks_max(
                 return 0;
         }
 
-        r = safe_atou64(rvalue, &u);
-        if (r < 0 || u < 1) {
-                log_syntax(unit, LOG_ERR, filename, line, r, "Maximum tasks value '%s' invalid. Ignoring.", rvalue);
+        r = parse_percent(rvalue);
+        if (r < 0) {
+                r = safe_atou64(rvalue, &u);
+                if (r < 0) {
+                        log_syntax(unit, LOG_ERR, filename, line, r, "Maximum tasks value '%s' invalid. Ignoring.", rvalue);
+                        return 0;
+                }
+        } else
+                u = system_tasks_max_scale(r, 100U);
+
+        if (u <= 0 || u >= UINT64_MAX) {
+                log_syntax(unit, LOG_ERR, filename, line, 0, "Maximum tasks value '%s' out of range. Ignoring.", rvalue);
                 return 0;
         }