updated readme
update introduction added most crucial dir info aosp-source-tree
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PROPGSP
@ -310,7 +310,7 @@ You can also make or modify and use your it as you wish but its kinda hardcoding
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## ***Deeper Look Into Some Important Directories***
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---
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Let’s roll on, Srinivasa — this time zooming into some of the ***most important internal folders*** of the AOSP tree. Since we finished the top-level overview, I’ll now guide you into the internal structures of key folders, one at a time.
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Let’s roll on, This time zooming into some of the ***most important internal folders*** of the AOSP tree. Since we finished the top-level overview, I’ll now guide you into the internal structures of key folders, one at a time.
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Let’s begin with:
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@ -337,12 +337,188 @@ Within `frameworks/base/`, you’ll find even more subdivisions:
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You’ll basically live inside `base/` if you're customizing Android behavior at the system level.
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Next one of the most foundational areas of AOSP.
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#### `system/` – Core Android System Components
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This folder is where much of Android’s **native system infrastructure** resides. It influences early boot, power management, process control, and security. Let’s break down its key subdirectories:
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| Subdirectory | Purpose |
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|----------------------|---------|
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| `core/` | Hosts `libcutils`, `liblog`, and native tools used system-wide. Also includes `toolbox` utilities (like `ls`, `ps`, etc.). |
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| `sepolicy/` | SELinux policy source files (`.te`, `.cil`, `.fc`), defining what services can do at runtime. |
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| `init/` | The `init` program implementation: parses `init.rc`, spawns daemons, mounts filesystems, applies permissions. |
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| `libvintf/` | Verifies system/vendor interface compatibility (VINTF), part of Treble. |
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| `libfmq/`, `libhidl/`| Fast message queues and legacy HIDL support libraries. |
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| `update_engine/` | OTA update mechanism used by Android (especially in A/B partitions). |
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| `netd/` | Manages Android’s networking stack — DNS, interfaces, tethering, etc. |
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| `logging/` | Logging subsystem (`logcat`, buffer management, etc.). |
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| `security/` | Key attestation, keystore, and related cryptography frameworks. |
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| `tools/` | Misc utilities for packaging and system dev (like `mksysimg`). |
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---
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##### Why `system/` Matters:
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- It's one of the **earliest initialized** parts of Android.
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- Many of Android’s core daemons (like `vold`, `servicemanager`, `lmkd`, etc.) live or are launched from here.
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- If you're working with **`init.rc`**, **SELinux**, or **system binaries**, this folder is your best friend.
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Next we’ll venture into the next big one: `packages/` — home to settings, UI, and the launcher you see on screen.
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Let’s dive into a folder that paints what you see on screen and holds the apps Android users interact with every day.
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#### `packages/` – System Apps & UI Components
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This folder contains the **built-in Android applications**, launchers, and essential UI layers. When you see Settings, SystemUI, or even the default Launcher — this is where the magic begins.
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| Subdirectory | Purpose |
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|------------------------|---------|
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| `apps/` | Official system apps like `Contacts`, `Dialer`, `DeskClock`, `Messaging`, etc. |
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| `Settings/` | The Android Settings app — from toggles to hidden developer options. |
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| `SystemUI/` | Status bar, notification panel, Quick Settings, lock screen, and more. |
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| `InputMethods/` | Default input methods like LatinIME (keyboard apps). |
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| `Screensavers/` | Built-in screen savers (aka “Daydreams” from older Androids). |
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| `Providers/` | Content providers (e.g., `MediaProvider`, `TelephonyProvider`). |
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| `WallpaperPicker/` | System wallpaper selector UI. |
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| `Launcher3/` | Reference launcher used by AOSP — the “home screen” experience. |
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---
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##### Why `packages/` Matters:
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- You’ll go here to **customize or replace stock apps**, like tweaking SystemUI for a custom ROM.
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- It's where **Java + XML combine**: you get layouts, drawables, logic, and resource overlays all working together.
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- If you're building a **modular or minimalist ROM**, this is the place to trim or enhance.
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Most apps here use a mix of:
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- Java/Kotlin for app logic
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- XML for layouts and UI
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- Gradle or Make/BP for build definitions
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Next through `vendor/` — where proprietary code lives, or `external/`, home of all the open-source third-party dependencies. Or if you're curious to enter the Android build pipeline soon, we can start looking at the `build/` and `prebuilts/` folders next.
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#### `vendor/` – Vendor-Specific Code & Proprietary Binaries
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This directory is crucial for any **device-specific AOSP build**. It houses all the **non-open-source blobs, configs, and binaries** provided by SoC vendors (like Qualcomm, MediaTek) and OEMs (like Motorola, Samsung).
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| Subdirectory | Purpose |
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|------------------------|---------|
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| `vendor/<oem>/` | Top-level vendor folder, e.g., `vendor/google/`, `vendor/motorola/`. |
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| `proprietary/` | Closed-source firmware blobs — camera libs, WiFi drivers, etc. |
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| `prebuilt/` | Precompiled binaries needed during the build. |
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| `sepolicy/` | Vendor-specific SELinux extensions to complement system policies. |
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| `init/` | Vendor init RC scripts (like `init.vendor.rc`), executed by Android `init`. |
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| `lib64/`, `lib/` | Vendor-shipped native shared libraries. |
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| `bin/` | Daemons or executables (e.g., `thermal_engine`, `imsd`). |
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| `etc/` | Config files for RIL, audio, graphics, etc. |
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| `modules/` | Kernel modules (`.ko` files) required at runtime. |
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##### Why `vendor/` Is Essential:
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- **Required for real hardware builds**: Without this, AOSP runs only on generic emulators.
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- **Partition separation** (Treble): It's split from `/system` and mounted as `/vendor`, isolating hardware code.
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- For ROM devs like you, **extracting vendor blobs** is key for porting AOSP to new devices.
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Next we continue with `external/`, which houses all third-party open-source libraries.
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#### `external/` – Third-Party Open Source Libraries
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This directory is Android’s curated collection of open-source projects it depends on. These aren’t developed by Google but are **vital for system functionality**.
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| Subdirectory Examples | Purpose |
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|-----------------------------|---------|
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| `openssl/`, `boringssl/` | Cryptographic libraries. |
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| `libxml2/`, `jsoncpp/` | XML and JSON parsing. |
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| `clang/`, `llvm-project/` | Android’s compiler and tooling stack. |
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| `f2fs-tools/`, `e2fsprogs/` | Filesystem utilities. |
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| `icu/` | Unicode and internationalization support. |
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| `protobuf/` | Google’s Protocol Buffers serialization. |
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| `libziparchive/`, `zlib/` | Archiving and compression. |
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These folders are regularly updated to sync with upstream versions, but with **patches to fit Android’s needs** (like BoringSSL replacing OpenSSL).
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#### `build/` (revisited) – Android Build Logic
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While we already mentioned it briefly, let’s look deeper.
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| Subdirectory | Role |
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|---------------------------|------|
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| `make/` | Legacy Make-based system. Includes `envsetup.sh`, `lunch`, product configs. |
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| `soong/` | Modern Go-based build engine (`Android.bp`, `blueprint`) — much faster and more modular. |
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| `kati/`, `ninja/` | Makefile-to-ninja converters for optimized builds. |
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| `tools/` | Scripts for packaging OTAs, generating `system.img`, etc. |
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This folder orchestrates **how the entire source tree gets transformed into flashable images**.
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#### `prebuilts/` – Precompiled Tools and Artifacts
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| Subdirectory | Purpose |
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|------------------------|---------|
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| `clang/`, `gcc/`, `ndk/` | Prebuilt compilers and toolchains — used instead of building them from source. |
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| `sdk/`, `gradle-plugin/` | Android SDK and build tools for app developers. |
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| `misc/`, `tools/` | Helper binaries and scripts (e.g., `aapt`, `adb`, `fastboot`). |
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**Why it matters:** These binaries are version-locked and optimized — saving hours of build time. For example, building LLVM/Clang from scratch would be a nightmare without this.
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#### `toolchain/` – Compiler Source Trees
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| Subdirectory | Purpose |
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|----------------------------|---------|
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| `llvm/`, `riscv/`, `arm/` | Source for platform-specific compilers and assembler/linker utilities. |
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| `binutils/`, `gcc/` | Older toolchain components, still used on some branches. |
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**Why it matters:** If you're modifying native C/C++ build behavior, targeting exotic architectures, or tinkering with LLVM itself, this is the forge.
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#### `soong/` – Soong Build System Engine
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- The brains behind the `Android.bp` system — written in Go.
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- Interprets Blueprint files to produce Ninja build rules.
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- Works side by side with Makefiles (especially during legacy-to-Soong transitions).
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This is what powers modern AOSP builds — lightning-fast, modular, and dependency-aware.
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#### `vndk/` & `product/` – Partitioned Modularity
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| Folder | Role |
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|------------|------|
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| `vndk/` | Shared native libraries (Vendor Native Development Kit) for Treble compliance. |
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| `product/` | Extra product-specific apps, overlays, or configs (goes into `/product` partition). |
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These ensure **modularization** between the system (`/system`), vendor (`/vendor`), and product (`/product`) partitions — giving manufacturers flexibility without breaking compatibility.
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And that’s it — **you’ve now mapped the entire AOSP source tree.** Every folder, from the cryptic internals to the user-facing polish, the aosp source is now yours to explore.
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#### Quick Recap: What You Now Know
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- You understand the **entire top-level AOSP directory tree**.
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- You’ve explored each key folder like `frameworks/`, `system/`, `packages/`, `vendor/`, `external/`, and more.
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- You know when and why to explore subfolders — based on your goals (custom ROMs, HAL integration, boot mods, etc.).
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