52 lines
2.3 KiB
Plaintext
52 lines
2.3 KiB
Plaintext
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What: /sys/.../uevent
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Date: May 2017
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KernelVersion: 4.13
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Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
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Description:
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Enable passing additional variables for synthetic uevents that
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are generated by writing /sys/.../uevent file.
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Recognized extended format is::
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ACTION [UUID [KEY=VALUE ...]
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The ACTION is compulsory - it is the name of the uevent
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action (``add``, ``change``, ``remove``). There is no change
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compared to previous functionality here. The rest of the
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extended format is optional.
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You need to pass UUID first before any KEY=VALUE pairs.
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The UUID must be in ``xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx``
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format where 'x' is a hex digit. The UUID is considered to be
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a transaction identifier so it's possible to use the same UUID
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value for one or more synthetic uevents in which case we
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logically group these uevents together for any userspace
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listeners. The UUID value appears in uevent as
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``SYNTH_UUID=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx`` environment
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variable.
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If UUID is not passed in, the generated synthetic uevent gains
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``SYNTH_UUID=0`` environment variable automatically.
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The KEY=VALUE pairs can contain alphanumeric characters only.
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It's possible to define zero or more pairs - each pair is then
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delimited by a space character ' '. Each pair appears in
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synthetic uevent as ``SYNTH_ARG_KEY=VALUE``. That means the KEY
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name gains ``SYNTH_ARG_`` prefix to avoid possible collisions
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with existing variables.
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Example of valid sequence written to the uevent file::
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add fe4d7c9d-b8c6-4a70-9ef1-3d8a58d18eed A=1 B=abc
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This generates synthetic uevent including these variables::
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ACTION=add
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SYNTH_ARG_A=1
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SYNTH_ARG_B=abc
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SYNTH_UUID=fe4d7c9d-b8c6-4a70-9ef1-3d8a58d18eed
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Users:
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udev, userspace tools generating synthetic uevents
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