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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
commit | 5d1646d90e1f2cceb9f0828f4b28318cd0ec7744 (patch) | |
tree | a94efe259b9009378be6d90eb30d2b019d95c194 /Documentation/userspace-api/media/v4l/app-pri.rst | |
parent | Initial commit. (diff) | |
download | linux-upstream/5.10.209.tar.xz linux-upstream/5.10.209.zip |
Adding upstream version 5.10.209.upstream/5.10.209upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to '')
-rw-r--r-- | Documentation/userspace-api/media/v4l/app-pri.rst | 30 |
1 files changed, 30 insertions, 0 deletions
diff --git a/Documentation/userspace-api/media/v4l/app-pri.rst b/Documentation/userspace-api/media/v4l/app-pri.rst new file mode 100644 index 000000000..626a42f2e --- /dev/null +++ b/Documentation/userspace-api/media/v4l/app-pri.rst @@ -0,0 +1,30 @@ +.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later + +.. _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. |