Documentation/userspace-api/media/v4l/app-pri.rst
Source file repositories/reference/linux-study-clean/Documentation/userspace-api/media/v4l/app-pri.rst
File Facts
- System
- Linux kernel
- Corpus path
Documentation/userspace-api/media/v4l/app-pri.rst- Extension
.rst- Size
- 1381 bytes
- Lines
- 32
- Domain
- Support Tooling And Documentation
- Bucket
- Documentation
- Inferred role
- Support Tooling And Documentation: documentation
- Status
- atlas-only
Why This File Exists
Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.
- Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.
Dependency Surface
- No C-style include directives detected by the generator.
Detected Declarations
- No top-level syscall, struct, function, initcall, or export declaration detected by the generator.
Annotated Snippet
.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
.. c:namespace:: V4L
.. _app-pri:
********************
Application Priority
********************
When multiple applications share a device it may be desirable to assign
them different priorities. Contrary to the traditional "rm -rf /" school
of thought, a video recording application could for example block other
applications from changing video controls or switching the current TV
channel. Another objective is to permit low priority applications
working in background, which can be preempted by user controlled
applications and automatically regain control of the device at a later
time.
Since these features cannot be implemented entirely in user space V4L2
defines the :ref:`VIDIOC_G_PRIORITY <VIDIOC_G_PRIORITY>` and
:ref:`VIDIOC_S_PRIORITY <VIDIOC_G_PRIORITY>` ioctls to request and
query the access priority associate with a file descriptor. Opening a
device assigns a medium priority, compatible with earlier versions of
V4L2 and drivers not supporting these ioctls. Applications requiring a
different priority will usually call :ref:`VIDIOC_S_PRIORITY
<VIDIOC_G_PRIORITY>` after verifying the device with the
:ref:`VIDIOC_QUERYCAP` ioctl.
Ioctls changing driver properties, such as
:ref:`VIDIOC_S_INPUT <VIDIOC_G_INPUT>`, return an ``EBUSY`` error code
after another application obtained higher priority.Annotation
- Atlas domain: Support Tooling And Documentation / Documentation.
- Implementation status: atlas-only.
Implementation Notes
- This generated page is the file-by-file coverage layer; curated subsystem chapters should link here when they synthesize a multi-file control flow.
- Core OS pages should be promoted from atlas-only to deep-reviewed when they explain data structures, invariants, locking, lifecycle, and C implementation snippets.
- Driver-family pages are intentionally pattern-oriented unless they are part of the selected PCIe/NVMe representative device path.