core: implement SwapContext/Runtime for io.systemd.Unit.List + tests

Add varlink context and runtime builders for .swap units:

SwapContext: What, Priority, Options, TimeoutUSec, ExecActivate, ExecDeactivate
SwapRuntime: ControlPID, Result, CleanResult, UID, GID (SwapResult enum)

SwapResult is exposed as a proper varlink enum type. Runtime follows the same pattern as MountRuntime (ControlPID, Result, CleanResult, ref UID/GID).

The integration test is conditional since swap units may not be present on all systems.

Co-developed-by: Claude Opus 4.6 <noreply@anthropic.com>

src/core/meson.build

@@ -75,6 +75,7 @@ libcore_sources = files(
         'varlink-mount.c',
         'varlink-path.c',
         'varlink-scope.c',
+        'varlink-swap.c',
         'varlink-unit.c',
 )
 

src/core/varlink-swap.c

@@ -0,0 +1,35 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include "sd-json.h"
+
+#include "json-util.h"
+#include "swap.h"
+#include "user-util.h"
+#include "varlink-common.h"
+#include "varlink-swap.h"
+
+int swap_context_build_json(sd_json_variant **ret, const char *name, void *userdata) {
+        Swap *s = ASSERT_PTR(SWAP(userdata));
+
+        return sd_json_buildo(
+                        ASSERT_PTR(ret),
+                        SD_JSON_BUILD_PAIR_STRING("What", s->what),
+                        JSON_BUILD_PAIR_INTEGER_NON_NEGATIVE("Priority", swap_get_priority(s)),
+                        JSON_BUILD_PAIR_STRING_NON_EMPTY("Options", swap_get_options(s)),
+                        JSON_BUILD_PAIR_FINITE_USEC("TimeoutUSec", s->timeout_usec),
+                        JSON_BUILD_PAIR_CALLBACK_NON_NULL("ExecActivate", exec_command_build_json, &s->exec_command[SWAP_EXEC_ACTIVATE]),
+                        JSON_BUILD_PAIR_CALLBACK_NON_NULL("ExecDeactivate", exec_command_build_json, &s->exec_command[SWAP_EXEC_DEACTIVATE]));
+}
+
+int swap_runtime_build_json(sd_json_variant **ret, const char *name, void *userdata) {
+        Unit *u = ASSERT_PTR(userdata);
+        Swap *s = ASSERT_PTR(SWAP(u));
+
+        return sd_json_buildo(
+                        ASSERT_PTR(ret),
+                        SD_JSON_BUILD_PAIR_CONDITION(pidref_is_set(&s->control_pid), "ControlPID", JSON_BUILD_PIDREF(&s->control_pid)),
+                        JSON_BUILD_PAIR_ENUM("Result", swap_result_to_string(s->result)),
+                        JSON_BUILD_PAIR_ENUM("CleanResult", swap_result_to_string(s->clean_result)),
+                        SD_JSON_BUILD_PAIR_CONDITION(uid_is_valid(u->ref_uid), "UID", SD_JSON_BUILD_UNSIGNED(u->ref_uid)),
+                        SD_JSON_BUILD_PAIR_CONDITION(gid_is_valid(u->ref_gid), "GID", SD_JSON_BUILD_UNSIGNED(u->ref_gid)));
+}

src/core/varlink-swap.h

@@ -0,0 +1,7 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+#pragma once
+
+#include "core-forward.h"
+
+int swap_context_build_json(sd_json_variant **ret, const char *name, void *userdata);
+int swap_runtime_build_json(sd_json_variant **ret, const char *name, void *userdata);

src/core/varlink-unit.c

@@ -31,6 +31,7 @@
 #include "varlink-mount.h"
 #include "varlink-path.h"
 #include "varlink-scope.h"
+#include "varlink-swap.h"
 #include "varlink-unit.h"
 #include "varlink-util.h"
 
@@ -167,6 +168,7 @@ static int unit_context_build_json(sd_json_variant **ret, const char *name, void
                 [UNIT_PATH]      = path_context_build_json,
                 [UNIT_SCOPE]     = scope_context_build_json,
                 [UNIT_SERVICE]   = service_context_build_json,
+                [UNIT_SWAP]      = swap_context_build_json,
         };
 
         return sd_json_buildo(
@@ -334,6 +336,7 @@ static int unit_runtime_build_json(sd_json_variant **ret, const char *name, void
                 [UNIT_MOUNT]     = mount_runtime_build_json,
                 [UNIT_PATH]      = path_runtime_build_json,
                 [UNIT_SCOPE]     = scope_runtime_build_json,
+                [UNIT_SWAP]      = swap_runtime_build_json,
         };
 
         return sd_json_buildo(