shared: add generic logic for waiting for a unit to enter some state

This is a generic implementation of a client-side logic of waiting until
a unit enters or leaves some state.

This is a more generic implementation of the WaitContext logic currently
in systemctl.c, and is supposed to replace it (a later commit does
this). It's similar to bus-wait-for-jobs.c and we probably should fold
that one into it later on.

This code is more powerful and cleaner than the WaitContext logic
however. In addition to waiting for a unit to exit this also allows us
to wait for a unit to leave the "maintainance" state.

This commit only implements the generic logic, and adds no users of it
yet.

1 files changed, 35 insertions, 0 deletions

diff --git a/src/shared/bus-wait-for-units.h b/src/shared/bus-wait-for-units.h
new file mode 100644
index 0000000000..a20f3d8fd7
--- /dev/null
+++ b/src/shared/bus-wait-for-units.h
@@ -0,0 +1,35 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+#pragma once
+
+#include "macro.h"
+#include "sd-bus.h"
+
+typedef struct BusWaitForUnits BusWaitForUnits;
+
+typedef enum BusWaitForUnitsState {
+        BUS_WAIT_SUCCESS,    /* Nothing to wait for anymore and nothing failed */
+        BUS_WAIT_FAILURE,    /* dito, but something failed */
+        BUS_WAIT_RUNNING,    /* Still something to wait for */
+        _BUS_WAIT_FOR_UNITS_STATE_MAX,
+        _BUS_WAIT_FOR_UNITS_STATE_INVALID = -1,
+} BusWaitForUnitsState;
+
+typedef enum BusWaitForUnitsFlags {
+        BUS_WAIT_FOR_MAINTENANCE_END = 1 << 0, /* Wait until the unit is no longer in maintenance state */
+        BUS_WAIT_FOR_INACTIVE        = 1 << 1, /* Wait until the unit is back in inactive or dead state */
+        BUS_WAIT_NO_JOB              = 1 << 2, /* Wait until there's no more job pending */
+        BUS_WAIT_REFFED              = 1 << 3, /* The unit is already reffed with RefUnit() */
+} BusWaitForUnitsFlags;
+
+typedef void (*bus_wait_for_units_ready_callback)(BusWaitForUnits *d, BusWaitForUnitsState state, void *userdata);
+typedef void (*bus_wait_for_units_unit_callback)(BusWaitForUnits *d, const char *unit_path, bool good, void *userdata);
+
+int bus_wait_for_units_new(sd_bus *bus, BusWaitForUnits **ret);
+BusWaitForUnits* bus_wait_for_units_free(BusWaitForUnits *d);
+
+BusWaitForUnitsState bus_wait_for_units_state(BusWaitForUnits *d);
+void bus_wait_for_units_set_ready_callback(BusWaitForUnits *d, bus_wait_for_units_ready_callback callback, void *userdata);
+int bus_wait_for_units_add_unit(BusWaitForUnits *d, const char *unit, BusWaitForUnitsFlags flags, bus_wait_for_units_unit_callback callback, void *userdata);
+int bus_wait_for_units_run(BusWaitForUnits *d);
+
+DEFINE_TRIVIAL_CLEANUP_FUNC(BusWaitForUnits*, bus_wait_for_units_free);