From 2c68e31c3ccef1cee7267bfa91ae044a37337489 Mon Sep 17 00:00:00 2001
From: Andrei Gherzan <andrei.gherzan@huawei.com>
Date: Tue, 1 Jun 2021 12:02:01 +0100
Subject: [PATCH] docs: Add OS topic on partition table
Signed-off-by: Andrei Gherzan <andrei.gherzan@huawei.com>
---
docs/index.rst | 1 +
docs/os/index.rst | 14 ++++
docs/os/linux/index.rst | 11 ++++
docs/os/linux/partition-table.rst | 105 ++++++++++++++++++++++++++++++
4 files changed, 131 insertions(+)
create mode 100644 docs/os/index.rst
create mode 100644 docs/os/linux/index.rst
create mode 100644 docs/os/linux/partition-table.rst
diff --git a/docs/index.rst b/docs/index.rst
index 9dc32766..9ac6552e 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -13,6 +13,7 @@ Build System Guide
repo-workspace
build-flavours/index
ohos-build/index
+ os/index
ci/index
blueprints/index
supported-images
diff --git a/docs/os/index.rst b/docs/os/index.rst
new file mode 100644
index 00000000..507188a5
--- /dev/null
+++ b/docs/os/index.rst
@@ -0,0 +1,14 @@
+.. SPDX-FileCopyrightText: Huawei Inc.
+..
+.. SPDX-License-Identifier: CC-BY-4.0
+
+Operating System
+################
+
+All Scenarios OS provides support for a set of kernels. This documentation
+details various aspects for each kernel type.
+
+.. toctree::
+ :maxdepth: 2
+
+ linux/index
diff --git a/docs/os/linux/index.rst b/docs/os/linux/index.rst
new file mode 100644
index 00000000..e57e6b9a
--- /dev/null
+++ b/docs/os/linux/index.rst
@@ -0,0 +1,11 @@
+.. SPDX-FileCopyrightText: Huawei Inc.
+..
+.. SPDX-License-Identifier: CC-BY-4.0
+
+All Scenarios OS - Linux
+########################
+
+.. toctree::
+ :maxdepth: 1
+
+ partition-table
diff --git a/docs/os/linux/partition-table.rst b/docs/os/linux/partition-table.rst
new file mode 100644
index 00000000..22b6ca9f
--- /dev/null
+++ b/docs/os/linux/partition-table.rst
@@ -0,0 +1,105 @@
+.. SPDX-FileCopyrightText: Huawei Inc.
+..
+.. SPDX-License-Identifier: CC-BY-4.0
+
+Disk Partition Table
+####################
+
+.. contents::
+ :depth: 2
+
+Overview
+********
+
+The OS defines the partitions included as part of the Linux-based distro as it
+follows:
+
+* boot
+
+ * filesystem label: x-boot (partition name when relevant)
+
+ * It provides boot artefacts required by the lower bootloader assumptions. It
+ is device-specific both in terms of filesystem and content.
+
+* sys-a
+
+ * filesystem label: x-sys-a (partition name when relevant)
+
+ * It provides the root filesystem hierarchy.
+
+ * Filesystem type, configuration and structure are device-independent.
+
+ * This partition is the only one provided with a redundant counterpart (see
+ below).
+
+* sys-b
+
+ * filesystem label: x-sys-b (partition name when relevant)
+
+ * It provides a redundant root filesystem hierarchy used as part of the
+ system update strategies.
+
+ * Filesystem type, configuration and structure are device-independent.
+
+* dev-data
+
+ * filesystem label: x-dev-data (partition name when relevant)
+
+ * Device-specific data meant to be preserved over system reset (factory
+ reset).
+
+ * The runtime will completely treat this data read-only.
+
+* sys-data
+
+ * filesystem label: x-sys-data (partition name when relevant)
+
+ * This partition holds the system state to deal with the root filesystem as a
+ read-only asset.
+
+ * It ties closely into the system update strategies.
+
+ * Data is kept over system updates (subject to state transition hooks) but
+ discarded over factory reset.
+
+* app-data
+
+ * filesystem label: x-app-data (partition name when relevant)
+
+ * This partition provides application data storage.
+
+ * Data is kept over system updates (subject to state transition hooks) but
+ discarded over factory reset.
+
+The build system tries to unify the partition as much as possible, leaving
+upper layers (for example, the system update layers) with as few deviations to
+deal with as feasible. This means that filesystem labels and partition names
+are to be assumed by the OS components.
+
+Partition Table
+***************
+
+The OS will support both MBR and GPT as partition table type. In this way, the
+OS can achieve more extensive device support.
+
+The OS assumes a GPT disk layout as it follows:
+
+* 4MiB is left untouched at the start of the disk (to accommodate for
+ hardware-specific requirements).
+
+* All partitions are aligned to 4MiB.
+
+* The filesystem labels and partition names are as described above.
+
+On the MBR side, the disk layout is similar to GPT. The design mainly
+workarounds the four physical partitions limitation:
+
+* 4MiB is left untouched at the start of the disk (to accommodate for
+ hardware-specific requirements).
+
+* All partitions are aligned to 4MiB.
+
+* The filesystem labels and partition names are as described above.
+
+* The 4th partition is defined as extended and contains all the data partitions
+ (dev-data, sys-data and app-data).
--
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