machined: make List() varlink method return a full pidref JSON object for leader

This new call has not been released yet, hence we can still change the
encoding of the "leader" field.

src/shared/varlink-idl-common.c

@@ -10,3 +10,12 @@ SD_VARLINK_DEFINE_STRUCT_TYPE(
                 SD_VARLINK_DEFINE_FIELD(realtime, SD_VARLINK_INT, SD_VARLINK_NULLABLE),
                 SD_VARLINK_FIELD_COMMENT("Timestamp in µs in the CLOCK_MONOTONIC clock"),
                 SD_VARLINK_DEFINE_FIELD(monotonic, SD_VARLINK_INT, SD_VARLINK_NULLABLE));
+
+SD_VARLINK_DEFINE_STRUCT_TYPE(
+                ProcessId,
+                SD_VARLINK_FIELD_COMMENT("Numeric UNIX PID value"),
+                SD_VARLINK_DEFINE_FIELD(pid, SD_VARLINK_INT, 0),
+                SD_VARLINK_FIELD_COMMENT("64bit inode number of pidfd if known"),
+                SD_VARLINK_DEFINE_FIELD(pidfdId, SD_VARLINK_INT, SD_VARLINK_NULLABLE),
+                SD_VARLINK_FIELD_COMMENT("Boot ID of the system the inode number belongs to"),
+                SD_VARLINK_DEFINE_FIELD(bootId, SD_VARLINK_INT, SD_VARLINK_NULLABLE));

src/shared/varlink-idl-common.h

@@ -4,3 +4,4 @@
 #include "sd-varlink-idl.h"
 
 extern const sd_varlink_symbol vl_type_Timestamp;
+extern const sd_varlink_symbol vl_type_ProcessId;

src/shared/varlink-io.systemd.Machine.c

@@ -57,7 +57,7 @@ static SD_VARLINK_DEFINE_METHOD_FULL(
                 SD_VARLINK_FIELD_COMMENT("The class of this machine"),
                 SD_VARLINK_DEFINE_OUTPUT(class, SD_VARLINK_STRING, 0),
                 SD_VARLINK_FIELD_COMMENT("Leader process PID of this machine"),
-                SD_VARLINK_DEFINE_OUTPUT(leader, SD_VARLINK_INT, SD_VARLINK_NULLABLE),
+                SD_VARLINK_DEFINE_OUTPUT_BY_TYPE(leader, ProcessId, SD_VARLINK_NULLABLE),
                 SD_VARLINK_FIELD_COMMENT("Root directory of this machine, if known, relative to host file system"),
                 SD_VARLINK_DEFINE_OUTPUT(rootDirectory, SD_VARLINK_STRING, SD_VARLINK_NULLABLE),
                 SD_VARLINK_FIELD_COMMENT("The service manager unit this machine resides in"),
@@ -77,6 +77,8 @@ static SD_VARLINK_DEFINE_ERROR(MachineExists);
 SD_VARLINK_DEFINE_INTERFACE(
                 io_systemd_Machine,
                 "io.systemd.Machine",
+                SD_VARLINK_SYMBOL_COMMENT("An object for referencing UNIX processes"),
+                &vl_type_ProcessId,
                 SD_VARLINK_SYMBOL_COMMENT("A timestamp object consisting of both CLOCK_REALTIME and CLOCK_MONOTONIC timestamps"),
                 &vl_type_Timestamp,
                 &vl_method_Register,