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| author | Kees Cook <kees+treewide@kernel.org> | 2026-09-02 15:31:14 -0700 |
|---|---|---|
| committer | Kees Cook <kees@kernel.org> | 2026-09-04 21:37:00 -0700 |
| commit | 3a2c4d55e32ad65efebdb6de44eef3bfa08bb49d (patch) | |
| tree | c65086f9bdcd48c6360fb7cb4598bca084da1f32 /Documentation/admin-guide/binderfs.rst | |
| download | linux-stable-3a2c4d55e32ad65efebdb6de44eef3bfa08bb49d.tar.gz linux-stable-3a2c4d55e32ad65efebdb6de44eef3bfa08bb49d.zip | |
treewide: refresh kmalloc_obj() conversionsgrafted
This is another run of the Coccinelle script for converting kmalloc()
family of allocations to kmalloc_obj() via the existing rules in
scripts/coccinelle/api/kmalloc_objs.cocci
This catches both the set of kmalloc() uses added since the first
kmalloc_obj() conversions in v7.0 and adds a large group missed in the
first pass due to Coccinelle not interacting well with the cleanup.h
scoped_...() family of macros[1]. I worked around this with spatch's
"--macro-file" argument to a file with all the scoped_...() macros mapped
to Coccinelle's YACFE_ITERATOR[2] as that was the closest viable control
flow indicator I could find.
Build tested allmodconfig on x86, arm64, arm, loongarch, mips, powerpc,
riscv, and s390 with no new warnings.
Link: https://lore.kernel.org/lkml/202609021314.8A9C0B8@keescook/ [1]
Link: https://github.com/coccinelle/coccinelle/blob/master/standard.h [2]
Signed-off-by: Kees Cook <kees+treewide@kernel.org>
Diffstat (limited to 'Documentation/admin-guide/binderfs.rst')
| -rw-r--r-- | Documentation/admin-guide/binderfs.rst | 87 |
1 files changed, 87 insertions, 0 deletions
diff --git a/Documentation/admin-guide/binderfs.rst b/Documentation/admin-guide/binderfs.rst new file mode 100644 index 000000000..41a4db00d --- /dev/null +++ b/Documentation/admin-guide/binderfs.rst @@ -0,0 +1,87 @@ +.. 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 unusable. The ``binder-control`` device will be deleted when the +binderfs instance is unmounted and all references to it have been dropped. + +Binder features +--------------- + +Assuming an instance of binderfs has been mounted at ``/dev/binderfs``, the +features supported by the binder driver can be located under +``/dev/binderfs/features/``. The presence of individual files can be tested +to determine whether a particular feature is supported by the driver. + +Example:: + + cat /dev/binderfs/features/oneway_spam_detection + 1 |
