build(packaging): add PX4 SITL .deb packages

Add cmake/cpack infrastructure for building .deb packages from
px4_sitl_sih and px4_sitl_default targets. Includes install rules,
package scripts, Gazebo wrapper, and CI workflow.

Signed-off-by: Ramon Roche <mrpollo@gmail.com>

platforms/posix/CMakeLists.txt

@@ -23,6 +23,9 @@ px4_posix_generate_alias(
 
 add_definitions(-DPX4_SOURCE_DIR="${PX4_SOURCE_DIR}" -DPX4_BINARY_DIR="${PX4_BINARY_DIR}")
 
+# PX4_INSTALL_PREFIX is set by cmake/package.cmake after this file is processed.
+# It is passed via target_compile_definitions on the px4 target from package.cmake.
+
 add_executable(px4
 	src/px4/common/main.cpp
 	apps.cpp
@@ -80,10 +83,16 @@ target_link_libraries(px4 PRIVATE uORB)
 # install
 #
 
+# Detect dpkg early so install rules can branch on it.
+# find_program caches the result, so the later call in package.cmake is a no-op.
+find_program(DPKG_PROGRAM dpkg)
+
 # Generic install rules (skipped when board provides its own install.cmake)
 if(NOT EXISTS "${PX4_BOARD_DIR}/cmake/install.cmake")
 
-# px4 dirs
+# Legacy top-level install (posix-configs, test data, etc into px4/ prefix).
+# Skip when building .deb packages which use a clean /opt/px4-sitl{,-sih}/ layout.
+if(NOT DPKG_PROGRAM)
 install(
 	DIRECTORY
 		${PROJECT_SOURCE_DIR}/posix-configs
@@ -94,6 +103,7 @@ install(
 		${PROJECT_NAME}
 	USE_SOURCE_PERMISSIONS
 )
+endif()
 
 endif() # NOT board install.cmake
 
@@ -163,6 +173,11 @@ elseif("${PX4_BOARD}" MATCHES "sitl")
 
 	# install
 
+	# Legacy install rules (used by ROS launch, existing CPack tarball workflow).
+	# Skip when building .deb packages: the .deb rules below provide a clean
+	# /opt/px4-sitl{,-sih}/ layout and these would duplicate/bloat the package.
+	if(NOT DPKG_PROGRAM)
+
 	# px4 dirs
 	install(
 		DIRECTORY
@@ -227,4 +242,82 @@ elseif("${PX4_BOARD}" MATCHES "sitl")
 		OPTIONAL
 		)
 
+	endif() # NOT DPKG_PROGRAM
+
+	####################################################################
+	# Install rules for .deb package (only when dpkg is available)
+	####################################################################
+	if(DPKG_PROGRAM AND NOT CMAKE_C_COMPILER MATCHES "emcc$")
+
+	# px4 binary
+	install(TARGETS px4
+		RUNTIME DESTINATION bin
+		)
+
+	# module symlinks and alias script
+	install(
+		DIRECTORY ${CMAKE_RUNTIME_OUTPUT_DIRECTORY}/
+		DESTINATION bin
+		USE_SOURCE_PERMISSIONS
+		FILES_MATCHING
+			PATTERN "px4-*"
+			PATTERN "px4-alias.sh"
+		)
+
+	# ROMFS (init scripts, mixers, etc.)
+	install(
+		DIRECTORY ${PX4_BINARY_DIR}/etc
+		DESTINATION .
+		USE_SOURCE_PERMISSIONS
+		)
+
+	if(CONFIG_MODULES_SIMULATION_GZ_BRIDGE)
+	# Gazebo wrapper script (sets GZ_SIM_* env vars pointing at installed resources)
+	install(
+		PROGRAMS ${PROJECT_SOURCE_DIR}/Tools/packaging/px4-gazebo.sh
+		DESTINATION bin
+		RENAME px4-gazebo
+		)
+	endif()
+
+	if(CONFIG_MODULES_SIMULATION_GZ_BRIDGE)
+	# Gazebo models
+	install(
+		DIRECTORY ${PROJECT_SOURCE_DIR}/Tools/simulation/gz/models
+		DESTINATION share/gz
+		OPTIONAL
+		)
+
+	# Gazebo worlds
+	install(
+		DIRECTORY ${PROJECT_SOURCE_DIR}/Tools/simulation/gz/worlds
+		DESTINATION share/gz
+		OPTIONAL
+		)
+
+	# Gazebo server config
+	install(
+		FILES ${PROJECT_SOURCE_DIR}/Tools/simulation/gz/server.config
+		DESTINATION share/gz
+		OPTIONAL
+		)
+
+	# Gazebo plugins (built .so files)
+	install(
+		DIRECTORY ${CMAKE_BINARY_DIR}/src/modules/simulation/gz_plugins/
+		DESTINATION lib/gz/plugins
+		FILES_MATCHING PATTERN "*.so"
+		PATTERN "CMakeFiles" EXCLUDE
+		)
+
+	# OpticalFlow external library (runtime dep of OpticalFlowSystem plugin)
+	install(
+		FILES ${CMAKE_BINARY_DIR}/OpticalFlow/install/lib/libOpticalFlow.so
+		DESTINATION lib/gz/plugins
+		OPTIONAL
+		)
+	endif()
+
+	endif() # DPKG_PROGRAM AND NOT emcc
+
 endif()

platforms/posix/src/px4/common/main.cpp

@@ -259,6 +259,32 @@ int main(int argc, char **argv)
 			PX4_INFO("instance: %i", instance);
 		}
 
+#if defined(PX4_INSTALL_PREFIX)
+
+		// When installed as a .deb package, default to the baked-in install prefix.
+		// Working directory defaults to XDG_DATA_HOME/px4/rootfs/<instance>.
+		if (commands_file.empty() && data_path.empty() && working_directory.empty()
+		    && dir_exists(PX4_INSTALL_PREFIX"/etc")
+		   ) {
+			data_path = PX4_INSTALL_PREFIX"/etc";
+
+			const char *xdg_data_home = getenv("XDG_DATA_HOME");
+			std::string state_base;
+
+			if (xdg_data_home) {
+				state_base = xdg_data_home;
+
+			} else {
+				const char *home = getenv("HOME");
+				state_base = std::string(home ? home : "/tmp") + "/.local/share";
+			}
+
+			working_directory = state_base + "/px4/rootfs";
+			working_directory_default = true;
+		}
+
+#endif // PX4_INSTALL_PREFIX
+
 #if defined(PX4_BINARY_DIR)
 
 		// data_path & working_directory: if no commands specified or in current working directory),
@@ -745,13 +771,34 @@ std::string pwd()
 	return (getcwd(temp, PATH_MAX) ? std::string(temp) : std::string(""));
 }
 
+static int mkdir_p(const std::string &path)
+{
+	std::string tmp = path;
+
+	for (size_t i = 1; i < tmp.size(); ++i) {
+		if (tmp[i] == '/') {
+			tmp[i] = '\0';
+
+			if (mkdir(tmp.c_str(), S_IRWXU | S_IRWXG | S_IRWXO) != 0 && errno != EEXIST) {
+				return -1;
+			}
+
+			tmp[i] = '/';
+		}
+	}
+
+	if (mkdir(tmp.c_str(), S_IRWXU | S_IRWXG | S_IRWXO) != 0 && errno != EEXIST) {
+		return -1;
+	}
+
+	return 0;
+}
+
 int change_directory(const std::string &directory)
 {
-	// create directory
+	// create directory (including intermediate components)
 	if (!dir_exists(directory)) {
-		int ret = mkdir(directory.c_str(), S_IRWXU | S_IRWXG | S_IRWXO);
-
-		if (ret == -1) {
+		if (mkdir_p(directory) != 0) {
 			PX4_ERR("Error creating directory: %s (%s)", directory.c_str(), strerror(errno));
 			return -1;
 		}