image: Initial work on backend support

5 files changed, 135 insertions, 5 deletions

diff --git a/image/backends/CMakeLists.txt b/image/backends/CMakeLists.txt
new file mode 100644
index 0000000..f3c7f5d
--- /dev/null
+++ b/image/backends/CMakeLists.txt
@@ -0,0 +1,4 @@
+set(BACKEND_SRCS
+        ${CMAKE_CURRENT_SOURCE_DIR}/basic.cc
+        PARENT_SCOPE
+)
diff --git a/image/backends/README.rst b/image/backends/README.rst
index ca510b9..acb44ef 100644
--- a/image/backends/README.rst
+++ b/image/backends/README.rst
@@ -41,17 +41,19 @@ Design
 
 Image creation backends shall derive from the Horizon::Image::BasicBackend
 class.  Concrete backends can exist in any namespace.  To be used with the
-Image Creation utility, the backend must be registered in the ``backends.hh``
+Image Creation utility, the backend must be registered in the ``basic.cc``
 file along with a unique Type Code.  This Type Code can then be passed to
 the Image Creation utility with the ``-t`` parameter for use.
 
 The Horizon::Image::BasicBackend is an abstract (pure virtual) class that
 has a single method that you must implement: ``create()``.  This will be
-called on a constructed object of your concrete backend class, with two
-parameters: ``std::string ir_dir``, which is the base directory for the
-installed system (like ``/target`` during a normal installation), and
+called on a constructed object of your concrete backend class, which has two
+instance variables: ``std::string ir_dir``, which is the base directory for
+the installed system (like ``/target`` during a normal installation), and
 ``std::string out_path``, which is the user's desired output path and file
-name.
+name.  You may also implement ``prepare()``, which is called before create,
+and ``finalise()``, which is called after.  Default no-op implementations
+are provided for you in BasicBackend.
 
 
 
diff --git a/image/backends/backends.hh b/image/backends/backends.hh
new file mode 100644
index 0000000..3199ee0
--- /dev/null
+++ b/image/backends/backends.hh
@@ -0,0 +1,33 @@
+/*
+ * backends.hh - Horizon Image Creation backend table
+ * image, the image processing utilities for
+ * Project Horizon
+ *
+ * Copyright (c) 2020 Adélie Linux and contributors.  All rights reserved.
+ * This code is licensed under the AGPL 3.0 license, as noted in the
+ * LICENSE-code file in the root directory of this repository.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+#pragma once
+
+#include <functional>
+#include <string>
+#include <vector>
+
+namespace Horizon {
+namespace Image {
+
+class BasicBackend;
+
+struct BackendDescriptor {
+    std::string type_code;
+    std::string description;
+    std::function<BasicBackend *(std::string, std::string)> creation_fn;
+};
+
+extern std::vector<BackendDescriptor> known_backends;
+
+}
+}
diff --git a/image/backends/basic.cc b/image/backends/basic.cc
new file mode 100644
index 0000000..908f1d9
--- /dev/null
+++ b/image/backends/basic.cc
@@ -0,0 +1,37 @@
+/*
+ * basic.cc - Implementation of the abstract Horizon Image Creation backend
+ * image, the image processing utilities for
+ * Project Horizon
+ *
+ * Copyright (c) 2020 Adélie Linux and contributors.  All rights reserved.
+ * This code is licensed under the AGPL 3.0 license, as noted in the
+ * LICENSE-code file in the root directory of this repository.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+#include "basic.hh"
+#include "backends.hh"
+
+namespace Horizon {
+namespace Image {
+
+std::vector<BackendDescriptor> known_backends = {
+   {"tar", "Create a tarball (.tar)", [](std::string, std::string){ return nullptr; } },
+   {"squashfs", "Create a SquashFS image (.squashfs)", [](std::string, std::string){ return nullptr; } }
+};
+
+int BasicBackend::prepare() {
+    /* The default implementation returns success immediately;
+     * no preparation is required. */
+    return 0;
+}
+
+int BasicBackend::finalise() {
+    /* The default implementation returns success immediately;
+     * no finalisation is required. */
+    return 0;
+}
+
+}
+}
diff --git a/image/backends/basic.hh b/image/backends/basic.hh
new file mode 100644
index 0000000..d39c57e
--- /dev/null
+++ b/image/backends/basic.hh
@@ -0,0 +1,54 @@
+/*
+ * basic.hh - Definition of the abstract Horizon Image Creation backend
+ * image, the image processing utilities for
+ * Project Horizon
+ *
+ * Copyright (c) 2020 Adélie Linux and contributors.  All rights reserved.
+ * This code is licensed under the AGPL 3.0 license, as noted in the
+ * LICENSE-code file in the root directory of this repository.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+#pragma once
+
+#include <string>
+
+namespace Horizon {
+namespace Image {
+
+class BasicBackend {
+public:
+    /*! Create the backend object.
+     * @param _ir_dir   The intermediate directory the image should contain.
+     * @param _out_path The path to write the image.
+     */
+    BasicBackend(const std::string &_ir_dir, const std::string &_out_path) :
+        ir_dir(_ir_dir), out_path(_out_path) {};
+    virtual ~BasicBackend() {};
+
+    /*! Prepare for creating the image.
+     * @returns 0 if preparation succeeded; otherwise, an error code.
+     */
+    virtual int prepare();
+
+    /*! Create the image.
+     * @returns 0 if the image is created successfully; otherwise, an error
+     *          code which explains the failure.
+     */
+    virtual int create() = 0;
+
+    /*! Finalise the image.
+     * @returns 0 if the image is finalised; otherwise, an error code.
+     */
+    virtual int finalise();
+
+    /*! The intermediate directory which contains the sysroot the image
+     *  should contain. */
+    const std::string &ir_dir;
+    /*! The path at which to write the image. */
+    const std::string &out_path;
+};
+
+}
+}