boot-loader-spec: add devicetree-overlay key

Device tree overlays are a convenient way to patch device trees, e.g.,
add new devices to a device tree or enable/disable devices. This is
useful for non-discoverable but configurable hardware. Device tree
overlays are commonly used for displays on the Raspberry Pi or for
describing the content of FPGA bitstreams.

Add the devicetree-overlay key to boot loader specification entries to
allow boot loaders to apply overlays.

See #13537

docs/BOOT_LOADER_SPECIFICATION.md

@@ -112,6 +112,12 @@ These configuration snippets shall be Unix-style text files (i.e. line separatio
 * `devicetree` refers to the binary device tree to use when executing the
 kernel. This also shall be a path relative to the `$BOOT` directory. This
 key is optional. Example: `6a9857a393724b7a981ebb5b8495b9ea/3.8.0-2.fc19.armv7hl/tegra20-paz00.dtb`.
+* `devicetree-overlay` refers to a list of device tree overlays that should be
+applied by the boot loader. Multiple overlays are separated by spaces and
+applied in the same order as they are listed. This key is optional but depends
+on the `devicetree` key. Example:
+`/6a9857a393724b7a981ebb5b8495b9ea/overlays/overlay_A.dtbo
+/6a9857a393724b7a981ebb5b8495b9ea/overlays/overlay_B.dtbo`
 * `architecture` refers to the architecture this entry is defined for. The argument should be an architecture identifier, using the architecture vocabulary defined by the EFI specification (i.e. `IA32`, `x64`, `IA64`, `ARM`, `AA64`, …). If specified and this does not match (case insensitively) the local system architecture this entry should be hidden.
 
 Each configuration drop-in snippet must include at least a `linux` or an `efi` key and is otherwise not valid. Here's an example for a complete drop-in file:

src/core/mount.c

@@ -361,7 +361,7 @@ static int mount_add_device_dependencies(Mount *m) {
         /* We always use 'what' from /proc/self/mountinfo if mounted */
         mask = m->from_proc_self_mountinfo ? UNIT_DEPENDENCY_MOUNTINFO_IMPLICIT : UNIT_DEPENDENCY_FILE;
 
-        r = unit_add_node_dependency(UNIT(m), p->what, false, dep, mask);
+        r = unit_add_node_dependency(UNIT(m), p->what, dep, mask);
         if (r < 0)
                 return r;
 

src/core/socket.c

@@ -294,7 +294,7 @@ static int socket_add_device_dependencies(Socket *s) {
                 return 0;
 
         t = strjoina("/sys/subsystem/net/devices/", s->bind_to_device);
-        return unit_add_node_dependency(UNIT(s), t, false, UNIT_BINDS_TO, UNIT_DEPENDENCY_FILE);
+        return unit_add_node_dependency(UNIT(s), t, UNIT_BINDS_TO, UNIT_DEPENDENCY_FILE);
 }
 
 static int socket_add_default_dependencies(Socket *s) {

src/core/swap.c

@@ -197,12 +197,11 @@ static int swap_add_device_dependencies(Swap *s) {
                 return 0;
 
         if (is_device_path(s->what))
-                return unit_add_node_dependency(UNIT(s), s->what, MANAGER_IS_SYSTEM(UNIT(s)->manager), UNIT_BINDS_TO, UNIT_DEPENDENCY_FILE);
-        else
-                /* File based swap devices need to be ordered after
-                 * systemd-remount-fs.service, since they might need a
-                 * writable file system. */
-                return unit_add_dependency_by_name(UNIT(s), UNIT_AFTER, SPECIAL_REMOUNT_FS_SERVICE, true, UNIT_DEPENDENCY_FILE);
+                return unit_add_node_dependency(UNIT(s), s->what, UNIT_BINDS_TO, UNIT_DEPENDENCY_FILE);
+
+        /* File based swap devices need to be ordered after systemd-remount-fs.service,
+         * since they might need a writable file system. */
+        return unit_add_dependency_by_name(UNIT(s), UNIT_AFTER, SPECIAL_REMOUNT_FS_SERVICE, true, UNIT_DEPENDENCY_FILE);
 }
 
 static int swap_add_default_dependencies(Swap *s) {

src/core/unit.c

@@ -3832,7 +3832,7 @@ int unit_deserialize_skip(FILE *f) {
         }
 }
 
-int unit_add_node_dependency(Unit *u, const char *what, bool wants, UnitDependency dep, UnitDependencyMask mask) {
+int unit_add_node_dependency(Unit *u, const char *what, UnitDependency dep, UnitDependencyMask mask) {
         Unit *device;
         _cleanup_free_ char *e = NULL;
         int r;
@@ -3862,19 +3862,9 @@ int unit_add_node_dependency(Unit *u, const char *what, bool wants, UnitDependen
         if (dep == UNIT_REQUIRES && device_shall_be_bound_by(device, u))
                 dep = UNIT_BINDS_TO;
 
-        r = unit_add_two_dependencies(u, UNIT_AFTER,
-                                      MANAGER_IS_SYSTEM(u->manager) ? dep : UNIT_WANTS,
-                                      device, true, mask);
-        if (r < 0)
-                return r;
-
-        if (wants) {
-                r = unit_add_dependency(device, UNIT_WANTS, u, false, mask);
-                if (r < 0)
-                        return r;
-        }
-
-        return 0;
+        return unit_add_two_dependencies(u, UNIT_AFTER,
+                                         MANAGER_IS_SYSTEM(u->manager) ? dep : UNIT_WANTS,
+                                         device, true, mask);
 }
 
 int unit_coldplug(Unit *u) {

src/core/unit.h

@@ -733,7 +733,7 @@ int unit_serialize(Unit *u, FILE *f, FDSet *fds, bool serialize_jobs);
 int unit_deserialize(Unit *u, FILE *f, FDSet *fds);
 int unit_deserialize_skip(FILE *f);
 
-int unit_add_node_dependency(Unit *u, const char *what, bool wants, UnitDependency d, UnitDependencyMask mask);
+int unit_add_node_dependency(Unit *u, const char *what, UnitDependency d, UnitDependencyMask mask);
 
 int unit_coldplug(Unit *u);
 void unit_catchup(Unit *u);