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author | Linus Torvalds <torvalds@linux-foundation.org> | 2019-07-09 12:34:26 -0700 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2019-07-09 12:34:26 -0700 |
commit | e9a83bd2322035ed9d7dcf35753d3f984d76c6a5 (patch) | |
tree | 66dc466ff9aec0f9bb7f39cba50a47eab6585559 /Documentation/admin-guide/binderfs.rst | |
parent | 7011b7e1b702cc76f9e969b41d9a95969f2aecaa (diff) | |
parent | 454f96f2b738374da4b0a703b1e2e7aed82c4486 (diff) |
Merge tag 'docs-5.3' of git://git.lwn.net/linux
Pull Documentation updates from Jonathan Corbet:
"It's been a relatively busy cycle for docs:
- A fair pile of RST conversions, many from Mauro. These create more
than the usual number of simple but annoying merge conflicts with
other trees, unfortunately. He has a lot more of these waiting on
the wings that, I think, will go to you directly later on.
- A new document on how to use merges and rebases in kernel repos,
and one on Spectre vulnerabilities.
- Various improvements to the build system, including automatic
markup of function() references because some people, for reasons I
will never understand, were of the opinion that
:c:func:``function()`` is unattractive and not fun to type.
- We now recommend using sphinx 1.7, but still support back to 1.4.
- Lots of smaller improvements, warning fixes, typo fixes, etc"
* tag 'docs-5.3' of git://git.lwn.net/linux: (129 commits)
docs: automarkup.py: ignore exceptions when seeking for xrefs
docs: Move binderfs to admin-guide
Disable Sphinx SmartyPants in HTML output
doc: RCU callback locks need only _bh, not necessarily _irq
docs: format kernel-parameters -- as code
Doc : doc-guide : Fix a typo
platform: x86: get rid of a non-existent document
Add the RCU docs to the core-api manual
Documentation: RCU: Add TOC tree hooks
Documentation: RCU: Rename txt files to rst
Documentation: RCU: Convert RCU UP systems to reST
Documentation: RCU: Convert RCU linked list to reST
Documentation: RCU: Convert RCU basic concepts to reST
docs: filesystems: Remove uneeded .rst extension on toctables
scripts/sphinx-pre-install: fix out-of-tree build
docs: zh_CN: submitting-drivers.rst: Remove a duplicated Documentation/
Documentation: PGP: update for newer HW devices
Documentation: Add section about CPU vulnerabilities for Spectre
Documentation: platform: Delete x86-laptop-drivers.txt
docs: Note that :c:func: should no longer be used
...
Diffstat (limited to 'Documentation/admin-guide/binderfs.rst')
-rw-r--r-- | Documentation/admin-guide/binderfs.rst | 68 |
1 files changed, 68 insertions, 0 deletions
diff --git a/Documentation/admin-guide/binderfs.rst b/Documentation/admin-guide/binderfs.rst new file mode 100644 index 000000000000..c009671f8434 --- /dev/null +++ b/Documentation/admin-guide/binderfs.rst @@ -0,0 +1,68 @@ +.. 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. + +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. |