mirror of
https://mirrors.bfsu.edu.cn/git/linux.git
synced 2024-12-01 08:04:22 +08:00
befacdcf47
Add documentation of the binderfs 'stats' mount option. Description taken from the commit message. Signed-off-by: Randy Dunlap <rdunlap@infradead.org> Acked-by: Christian Brauner <christian.brauner@ubuntu.com> Link: https://lore.kernel.org/r/baa0aa81-007d-af46-16a5-91fead0bd1b9@infradead.org Signed-off-by: Jonathan Corbet <corbet@lwn.net>
75 lines
3.2 KiB
ReStructuredText
75 lines
3.2 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
|
|
|
|
The Android binderfs Filesystem
|
|
===============================
|
|
|
|
Android binderfs is a filesystem for the Android binder IPC mechanism. It
|
|
allows to dynamically add and remove binder devices at runtime. Binder devices
|
|
located in a new binderfs instance are independent of binder devices located in
|
|
other binderfs instances. Mounting a new binderfs instance makes it possible
|
|
to get a set of private binder devices.
|
|
|
|
Mounting binderfs
|
|
-----------------
|
|
|
|
Android binderfs can be mounted with::
|
|
|
|
mkdir /dev/binderfs
|
|
mount -t binder binder /dev/binderfs
|
|
|
|
at which point a new instance of binderfs will show up at ``/dev/binderfs``.
|
|
In a fresh instance of binderfs no binder devices will be present. There will
|
|
only be a ``binder-control`` device which serves as the request handler for
|
|
binderfs. Mounting another binderfs instance at a different location will
|
|
create a new and separate instance from all other binderfs mounts. This is
|
|
identical to the behavior of e.g. ``devpts`` and ``tmpfs``. The Android
|
|
binderfs filesystem can be mounted in user namespaces.
|
|
|
|
Options
|
|
-------
|
|
max
|
|
binderfs instances can be mounted with a limit on the number of binder
|
|
devices that can be allocated. The ``max=<count>`` mount option serves as
|
|
a per-instance limit. If ``max=<count>`` is set then only ``<count>`` number
|
|
of binder devices can be allocated in this binderfs instance.
|
|
|
|
stats
|
|
Using ``stats=global`` enables global binder statistics.
|
|
``stats=global`` is only available for a binderfs instance mounted in the
|
|
initial user namespace. An attempt to use the option to mount a binderfs
|
|
instance in another user namespace will return a permission error.
|
|
|
|
Allocating binder Devices
|
|
-------------------------
|
|
|
|
.. _ioctl: http://man7.org/linux/man-pages/man2/ioctl.2.html
|
|
|
|
To allocate a new binder device in a binderfs instance a request needs to be
|
|
sent through the ``binder-control`` device node. A request is sent in the form
|
|
of an `ioctl() <ioctl_>`_.
|
|
|
|
What a program needs to do is to open the ``binder-control`` device node and
|
|
send a ``BINDER_CTL_ADD`` request to the kernel. Users of binderfs need to
|
|
tell the kernel which name the new binder device should get. By default a name
|
|
can only contain up to ``BINDERFS_MAX_NAME`` chars including the terminating
|
|
zero byte.
|
|
|
|
Once the request is made via an `ioctl() <ioctl_>`_ passing a ``struct
|
|
binder_device`` with the name to the kernel it will allocate a new binder
|
|
device and return the major and minor number of the new device in the struct
|
|
(This is necessary because binderfs allocates a major device number
|
|
dynamically.). After the `ioctl() <ioctl_>`_ returns there will be a new
|
|
binder device located under /dev/binderfs with the chosen name.
|
|
|
|
Deleting binder Devices
|
|
-----------------------
|
|
|
|
.. _unlink: http://man7.org/linux/man-pages/man2/unlink.2.html
|
|
.. _rm: http://man7.org/linux/man-pages/man1/rm.1.html
|
|
|
|
Binderfs binder devices can be deleted via `unlink() <unlink_>`_. This means
|
|
that the `rm() <rm_>`_ tool can be used to delete them. Note that the
|
|
``binder-control`` device cannot be deleted since this would make the binderfs
|
|
instance unuseable. The ``binder-control`` device will be deleted when the
|
|
binderfs instance is unmounted and all references to it have been dropped.
|