75 lines
2.5 KiB
ReStructuredText
75 lines
2.5 KiB
ReStructuredText
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.. 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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