machined: add controlAddress field to Machine.Register and Machine.List

Follow the existing sshAddress pattern to add a controlAddress field
that allows machine registrants (like vmspawn) to advertise a varlink
socket address for direct VM control. machined stores and exposes
the address but never connects to it itself.

Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

src/machine/machine-varlink.c

@@ -142,6 +142,7 @@ int vl_method_register(sd_varlink *link, sd_json_variant *parameters, sd_varlink
                 { "vSockCid",            _SD_JSON_VARIANT_TYPE_INVALID, machine_cid,              offsetof(Machine, vsock_cid),            0                 },
                 { "sshAddress",          SD_JSON_VARIANT_STRING,        sd_json_dispatch_string,  offsetof(Machine, ssh_address),          SD_JSON_STRICT    },
                 { "sshPrivateKeyPath",   SD_JSON_VARIANT_STRING,        json_dispatch_path,       offsetof(Machine, ssh_private_key_path), 0                 },
+                { "controlAddress",      SD_JSON_VARIANT_STRING,        json_dispatch_path,       offsetof(Machine, control_address),      SD_JSON_STRICT    },
                 { "allocateUnit",        SD_JSON_VARIANT_BOOLEAN,       sd_json_dispatch_stdbool, offsetof(Machine, allocate_unit),        0                 },
                 VARLINK_DISPATCH_POLKIT_FIELD,
                 {}

src/machine/machine.c

@@ -154,6 +154,7 @@ Machine* machine_free(Machine *m) {
         free(m->netif);
         free(m->ssh_address);
         free(m->ssh_private_key_path);
+        free(m->control_address);
 
         return mfree(m);
 }
@@ -245,6 +246,7 @@ int machine_save(Machine *m) {
 
         env_file_fputs_assignment(f, "SSH_ADDRESS=", m->ssh_address);
         env_file_fputs_assignment(f, "SSH_PRIVATE_KEY_PATH=", m->ssh_private_key_path);
+        env_file_fputs_assignment(f, "CONTROL_ADDRESS=", m->control_address);
 
         r = flink_tmpfile(f, temp_path, m->state_file, LINK_TMPFILE_REPLACE);
         if (r < 0)
@@ -338,6 +340,7 @@ int machine_load(Machine *m) {
                            "VSOCK_CID",            &vsock_cid,
                            "SSH_ADDRESS",          &m->ssh_address,
                            "SSH_PRIVATE_KEY_PATH", &m->ssh_private_key_path,
+                           "CONTROL_ADDRESS",      &m->control_address,
                            "UID",                  &uid);
         if (r == -ENOENT)
                 return 0;

src/machine/machine.h

@@ -96,6 +96,7 @@ typedef struct Machine {
         unsigned vsock_cid;
         char *ssh_address;
         char *ssh_private_key_path;
+        char *control_address;
 
         LIST_HEAD(Operation, operations);
 

src/machine/machined-varlink.c

@@ -489,6 +489,7 @@ static int list_machine_one_and_maybe_read_metadata(sd_varlink *link, Machine *m
                         JSON_BUILD_PAIR_UNSIGNED_NOT_EQUAL("vSockCid", m->vsock_cid, VMADDR_CID_ANY),
                         JSON_BUILD_PAIR_STRING_NON_EMPTY("sshAddress", m->ssh_address),
                         JSON_BUILD_PAIR_STRING_NON_EMPTY("sshPrivateKeyPath", m->ssh_private_key_path),
+                        JSON_BUILD_PAIR_STRING_NON_EMPTY("controlAddress", m->control_address),
                         JSON_BUILD_PAIR_VARIANT_NON_NULL("addresses", addr_array),
                         JSON_BUILD_PAIR_STRV_ENV_PAIR_NON_EMPTY("OSRelease", os_release),
                         JSON_BUILD_PAIR_UNSIGNED_NOT_EQUAL("UIDShift", shift, UID_INVALID),

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

@@ -57,6 +57,8 @@ static SD_VARLINK_DEFINE_METHOD(
                 SD_VARLINK_DEFINE_INPUT(vSockCid,                SD_VARLINK_INT,    SD_VARLINK_NULLABLE),
                 SD_VARLINK_DEFINE_INPUT(sshAddress,              SD_VARLINK_STRING, SD_VARLINK_NULLABLE),
                 SD_VARLINK_DEFINE_INPUT(sshPrivateKeyPath,       SD_VARLINK_STRING, SD_VARLINK_NULLABLE),
+                SD_VARLINK_FIELD_COMMENT("Varlink socket address for direct machine control. The server at this address is expected to implement io.systemd.MachineInstance and optionally io.systemd.VirtualMachineInstance and io.systemd.QemuMachineInstance."),
+                SD_VARLINK_DEFINE_INPUT(controlAddress,          SD_VARLINK_STRING, SD_VARLINK_NULLABLE),
                 SD_VARLINK_FIELD_COMMENT("Controls whether to allocate a scope unit for the machine to register. If false, the client already took care of that and registered a service/scope specific to the machine."),
                 SD_VARLINK_DEFINE_INPUT(allocateUnit,            SD_VARLINK_BOOL,   SD_VARLINK_NULLABLE),
                 VARLINK_DEFINE_POLKIT_INPUT);
@@ -107,6 +109,8 @@ static SD_VARLINK_DEFINE_METHOD_FULL(
                 SD_VARLINK_DEFINE_OUTPUT(sshAddress, SD_VARLINK_STRING, SD_VARLINK_NULLABLE),
                 SD_VARLINK_FIELD_COMMENT("Path to private SSH key"),
                 SD_VARLINK_DEFINE_OUTPUT(sshPrivateKeyPath, SD_VARLINK_STRING, SD_VARLINK_NULLABLE),
+                SD_VARLINK_FIELD_COMMENT("Varlink socket address for direct machine control, implementing io.systemd.MachineInstance and optionally further interfaces"),
+                SD_VARLINK_DEFINE_OUTPUT(controlAddress, SD_VARLINK_STRING, SD_VARLINK_NULLABLE),
                 SD_VARLINK_FIELD_COMMENT("List of addresses of the machine"),
                 SD_VARLINK_DEFINE_OUTPUT_BY_TYPE(addresses, Address, SD_VARLINK_ARRAY | SD_VARLINK_NULLABLE),
                 SD_VARLINK_FIELD_COMMENT("OS release information of the machine. It contains an array of key value pairs read from the os-release(5) file in the image."),