chsst
change shared subtrees
Introduction
Shared subtree is a kernel feature which has a wide usage in conjunction with mount namespace. Android kernel does support this feature and it is already in use to propagate mount events between isolated namespaces. But unfortunately, Android has their own implementation of mount command in toybox, which doesn't support this feature yet. So this makes it hard to debug and play with shared subtrees. This is why chsst was born.
Usage
Get prebuilts from releases.
Push the binary matching your architecture via adb. For example arm64-v8a.
$ adb root
$ adb push <path-to-prebuilts>/arm64-v8a/chsst /data
Run it and see help.
$ adb shell chmod u+x /data/chsst
$ adb shell /data/chsst --help
chsst (CHange Shared SubTrees) by LibXZR <i@xzr.moe>
Usage:
chsst <mountpoint> <operation>
chsst <operation> <mountpoint>
Operations:
--make-shared mark a subtree as shared
--make-slave mark a subtree as slave
--make-private mark a subtree as private
--make-unbindable mark a subtree as unbindable
--make-rshared recursively mark a whole subtree as shared
--make-rslave recursively mark a whole subtree as slave
--make-rprivate recursively mark a whole subtree as private
--make-runbindable recursively mark a whole subtree as unbindable
The usage is basically same as that of mount in util-linux.
Building
It's easy to build it with Android NDK.
$ export PATH="/path/to/your/ndk:${PATH}"
$ git clone https://github.com/libxzr/chsst
......
$ cd chsst
$ ndk-build
......
$ tree libs
libs
├── arm64-v8a
│ └── chsst
├── armeabi-v7a
│ └── chsst
├── x86
│ └── chsst
└── x86_64
└── chsst