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337a21080b
Reusing content from the master branch which underwent this change earlier. This change makes it much easier to backport manual updates to the kirkstone LTS branch. To make the change and future updates simpler, reused file contents from master, only excluding changes which don't apply to kirkstone. (From yocto-docs rev: 95171233f0e96c00d55ed40cf713c62e6df57b8d) Signed-off-by: Michael Opdenacker <michael.opdenacker@bootlin.com> Signed-off-by: Steve Sakoman <steve@sakoman.com>
75 lines
2.5 KiB
ReStructuredText
75 lines
2.5 KiB
ReStructuredText
.. SPDX-License-Identifier: CC-BY-SA-2.0-UK
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.. _device-manager:
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Selecting a Device Manager
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**************************
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The Yocto Project provides multiple ways to manage the device manager
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(``/dev``):
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- Persistent and Pre-Populated ``/dev``: For this case, the ``/dev``
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directory is persistent and the required device nodes are created
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during the build.
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- Use ``devtmpfs`` with a Device Manager: For this case, the ``/dev``
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directory is provided by the kernel as an in-memory file system and
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is automatically populated by the kernel at runtime. Additional
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configuration of device nodes is done in user space by a device
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manager like ``udev`` or ``busybox-mdev``.
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Using Persistent and Pre-Populated ``/dev``
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===========================================
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To use the static method for device population, you need to set the
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:term:`USE_DEVFS` variable to "0"
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as follows::
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USE_DEVFS = "0"
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The content of the resulting ``/dev`` directory is defined in a Device
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Table file. The
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:term:`IMAGE_DEVICE_TABLES`
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variable defines the Device Table to use and should be set in the
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machine or distro configuration file. Alternatively, you can set this
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variable in your ``local.conf`` configuration file.
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If you do not define the :term:`IMAGE_DEVICE_TABLES` variable, the default
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``device_table-minimal.txt`` is used::
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IMAGE_DEVICE_TABLES = "device_table-mymachine.txt"
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The population is handled by the ``makedevs`` utility during image
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creation:
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Using ``devtmpfs`` and a Device Manager
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=======================================
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To use the dynamic method for device population, you need to use (or be
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sure to set) the :term:`USE_DEVFS`
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variable to "1", which is the default::
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USE_DEVFS = "1"
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With this
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setting, the resulting ``/dev`` directory is populated by the kernel
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using ``devtmpfs``. Make sure the corresponding kernel configuration
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variable ``CONFIG_DEVTMPFS`` is set when building you build a Linux
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kernel.
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All devices created by ``devtmpfs`` will be owned by ``root`` and have
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permissions ``0600``.
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To have more control over the device nodes, you can use a device manager
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like ``udev`` or ``busybox-mdev``. You choose the device manager by
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defining the ``VIRTUAL-RUNTIME_dev_manager`` variable in your machine or
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distro configuration file. Alternatively, you can set this variable in
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your ``local.conf`` configuration file::
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VIRTUAL-RUNTIME_dev_manager = "udev"
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# Some alternative values
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# VIRTUAL-RUNTIME_dev_manager = "busybox-mdev"
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# VIRTUAL-RUNTIME_dev_manager = "systemd"
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