Document the plugin API in Documentation/manual.txt and provide an
example plugin.
Signed-off-by: Andrei Ziureaev <andrei.ziureaev@xxxxxxx>
Signed-off-by: Andrei Ziureaev <andreiziureaev@xxxxxxxxx>
---
Changes in v3:
- plugins have to implement prototypes
- added license tags to the example
- copied some definitions from dtc-plugin.h to the manual
- better wording
Changes in v2:
- better structure
- information about the data model under "5.2) Exporting Functionality"
- plugins must register with the build system
- the "validate_fn_t" hook can return a status
Documentation/manual.txt | 146 +++++++++++++++++++++++++++++++
plugins/example/Makefile.example | 27 ++++++
plugins/example/example.c | 33 +++++++
3 files changed, 206 insertions(+)
create mode 100644 plugins/example/Makefile.example
create mode 100644 plugins/example/example.c
diff --git a/Documentation/manual.txt b/Documentation/manual.txt
index adf5ccb..c87d1f3 100644
--- a/Documentation/manual.txt
+++ b/Documentation/manual.txt
@@ -10,6 +10,9 @@ I - "dtc", the device tree compiler
4.1) Overview
4.2) Properties
4.3) Labels and References
+ 5) Plugins
+ 5.1) Building and Installing
+ 5.2) Exporting Functionality
II - The DT block format
1) Header
@@ -115,6 +118,16 @@ Options:
-d <dependency_filename>
Generate a dependency file during compilation.
+ -l, --plugin <plugin name>[,key[,value]]
+ Load a plugin and, optionally, pass it an argument.
+ plugin name - the name of the shared object without the extension (can contain a path)
+ key - the name of the argument
+ value - the value of the argument (can be omitted)
+ Example: dtc -l some-plugin,o,out.dts -l some-plugin,help -l another-plugin [...]
+
+ -L, --plugin-dir <arg>
+ The directory in which to search for plugins
+
-q
Quiet: -q suppress warnings, -qq errors, -qqq all
@@ -272,6 +285,139 @@ And used in properties, labels may appear before or after any value:
};
+5) Plugins
+
+Plugins are shared libraries that DTC loads at runtime using
+
+ dlopen(path, RTLD_NOW | RTLD_GLOBAL | RTLD_DEEPBIND)
+
+RTLD_NOW means they are loaded immediately (right before the parsing
+stage).
+
+RTLD_GLOBAL means their symbols can be used by other plugins.
+
+RTLD_DEEPBIND means the dynamic linker will look for symbols within the
+plugin first, before searching in the main program and other plugins.
+
+All plugins must include the "dtc-plugin.h" header.
+
+
+5.1) Building and Installing
+
+Plugins are built and installed using the command "make plugins".
+
+Suppose your plugin is called "example" and its source code is in
+"plugins/example/example.c". To register it with the build system,
+create a file "plugins/example/Makefile.example" with the following
+line as its contents:
+
+PLUGIN_LIBS += $(PLUGIN_dir)/example/example.so
+
+This means "make plugins" will try to build
+
+ plugins/example/example.so
+
+from
+
+ plugins/example/example.c
+
+It will also make a symlink
+
+ plugins/example.so
+
+for convenience. You could then call DTC like this:
+
+ ./dtc -Onull some-file.dts -l plugins/example
+
+Please, see "plugins/example/Makefile.example" for how to override the
+default behavior, add GCC flags, etc.
+
+
+5.2) Exporting Functionality
+
+- From "dtc-plugin.h":
+
+```
+/*
+ * Plugins export functionality by implementing one or more of the
+ * functions below. DTC tries to call each function exactly once for
+ * each plugin.
+ *
+ * The typedefs are there for conveniently storing pointers to these
+ * functions.
+ */
+
+/**
+ * Initialize the plugin.
+ *
+ * Called right after the plugin is loaded.
+ *
+ * Every plugin must implement this. At the very least, it should
+ * perform a version check.
+ *
+ * @param dtc_ver DTC's plugin API version
+ * @param argc Length of argv
+ * @param argv Array of plugin arguments
+ * @return 0 on success, or 1 on failure
+ */
+int dtc_init(struct plugin_version dtc_ver, int argc, struct plugin_arg *argv);
+typedef int (*dtc_init_fn_t)(struct plugin_version dtc_ver, int argc,
+ struct plugin_arg *argv);
+
+/**
+ * Validate a device tree.
+ *
+ * Called after DTC's parsing stage, but before the output stage.
+ *
+ * @param dti The unflattened device tree. Implementations can modify
+ * it and "pass it back" to DTC and to subsequent plugins.
+ * The header "dt.h" contains functionality for accessing
+ * "struct dt_info".
+ * @return 1 on a fatal failure, otherwise 0
+ */
+int dtc_validate(struct dt_info *dti);
+typedef int (*dtc_validate_fn_t)(struct dt_info *dti);
+```
+
+- "struct plugin_version" is defined as:
+
+```
+struct plugin_version {
+ int major; /* Incompatible changes */
+ int minor; /* Compatible changes, such as adding a new field
+ * to the end of a struct */
+};
+```
+
+- A version check can be performed by calling this function:
+
+```
+/**
+ * The strictest possible version check.
+ *
+ * @param dtc_ver The version passed by DTC
+ * @return true on success, false on failure
+ */
+static inline bool dtc_plugin_default_version_check(struct plugin_version dtc_ver)
+{
+ struct plugin_version plugin_ver = DTC_PLUGIN_API_VERSION;
+ return dtc_ver.major == plugin_ver.major && dtc_ver.minor == plugin_ver.minor;
+}
+```
+
+- "struct plugin_arg" is defined as:
+
+```
+struct plugin_arg {
+ char *key; /* A non-empty string */
+ char *value; /* NULL or a non-empty string */
+};
+```
+
+Please, see an example of a "dtc_init" implementation in
+"plugins/example/example.c".
+
+
II - The DT block format
========================
diff --git a/plugins/example/Makefile.example b/plugins/example/Makefile.example
new file mode 100644
index 0000000..9dc06e1
--- /dev/null
+++ b/plugins/example/Makefile.example
@@ -0,0 +1,27 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+# Makefile.example
+#
+# This is not a complete Makefile of itself. Instead, it is designed to
+# be easily embeddable into other systems of Makefiles.
+#
+
+# Allow "make plugins" to discover the plugin
+PLUGIN_LIBS += $(PLUGIN_dir)/example/example.$(SHAREDLIB_EXT)
+
+# Add GCC flags:
+# PLUGIN_CFLAGS_example = -some-flag
+
+# Add libraries:
+# PLUGIN_LDLIBS_example = -lsome-lib
+
+# Add files to clean:
+# PLUGIN_CLEANFILES += $(PLUGIN_dir)/example/*.tmp
+
+# Override the default rules:
+# $(PLUGIN_dir)/example/example.$(SHAREDLIB_EXT): $(PLUGIN_dir)/example/example.o
+# @$(VECHO) LD $@
+# ...
+#
+# $(PLUGIN_dir)/example/example.o: $(PLUGIN_dir)/example/example.c
+# @$(VECHO) CC $@
+# ...
diff --git a/plugins/example/example.c b/plugins/example/example.c
new file mode 100644
index 0000000..4d4e7f3
--- /dev/null
+++ b/plugins/example/example.c
@@ -0,0 +1,33 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * (C) Copyright Arm Holdings. 2020
+ */
+
+#include <stdio.h>
+#include <string.h>
+
+#include "dtc-plugin.h"
+
+#define NAME "example: "
+
+int dtc_init(struct plugin_version dtc_ver, int argc, struct plugin_arg *argv)
+{
+ if (!dtc_plugin_default_version_check(dtc_ver)) {
+ fprintf(stderr, NAME"Plugin is incompatible with this version of DTC\n");
+ return 1;
+ }
+
+ for (int i = 0; i < argc; i++) {
+ if (strcmp(argv[i].key, "h") == 0
+ || strcmp(argv[i].key, "help") == 0) {
+ printf(NAME"This is an example plugin. It prints its arguments.\n");
+ return 1;
+ } else {
+ printf(NAME"%s: %s\n", argv[i].key,
+ argv[i].value ? argv[i].value : "");
+ }
+ }
+
+ printf(NAME"Loaded plugin 'example'\n");
+ return 0;
+}
--
2.17.1
