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Diffstat (limited to 'Documentation/media/uapi/v4l/open.rst')
| -rw-r--r-- | Documentation/media/uapi/v4l/open.rst | 12 |
1 files changed, 6 insertions, 6 deletions
diff --git a/Documentation/media/uapi/v4l/open.rst b/Documentation/media/uapi/v4l/open.rst index a3e39df91e9d..afd116edb40d 100644 --- a/Documentation/media/uapi/v4l/open.rst +++ b/Documentation/media/uapi/v4l/open.rst @@ -99,12 +99,12 @@ linux-media mailing list: Multiple Opens ============== -V4L2 devices can be opened more than once. [1]_ When this is supported +V4L2 devices can be opened more than once. [#f1]_ When this is supported by the driver, users can for example start a "panel" application to change controls like brightness or audio volume, while another application captures video and audio. In other words, panel applications are comparable to an ALSA audio mixer application. Just opening a V4L2 -device should not change the state of the device. [2]_ +device should not change the state of the device. [#f2]_ Once an application has allocated the memory buffers needed for streaming data (by calling the :ref:`VIDIOC_REQBUFS` @@ -117,7 +117,7 @@ that would affect the buffer sizes (e.g. by calling the no longer allowed to allocate buffers or start or stop streaming. The EBUSY error code will be returned instead. -Merely opening a V4L2 device does not grant exclusive access. [3]_ +Merely opening a V4L2 device does not grant exclusive access. [#f3]_ Initiating data exchange however assigns the right to read or write the requested type of data, and to change related properties, to this file descriptor. Applications can request additional access privileges using @@ -142,17 +142,17 @@ respectively. Devices are programmed using the :ref:`ioctl() <func-ioctl>` function as explained in the following sections. -.. [1] +.. [#f1] There are still some old and obscure drivers that have not been updated to allow for multiple opens. This implies that for such drivers :ref:`open() <func-open>` can return an ``EBUSY`` error code when the device is already in use. -.. [2] +.. [#f2] Unfortunately, opening a radio device often switches the state of the device to radio mode in many drivers. This behavior should be fixed eventually as it violates the V4L2 specification. -.. [3] +.. [#f3] Drivers could recognize the ``O_EXCL`` open flag. Presently this is not required, so applications cannot know if it really works. |