0001 What: /sys/.../uevent
0002 Date: May 2017
0003 KernelVersion: 4.13
0004 Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
0005 Description:
0006 Enable passing additional variables for synthetic uevents that
0007 are generated by writing /sys/.../uevent file.
0008
0009 Recognized extended format is::
0010
0011 ACTION [UUID [KEY=VALUE ...]
0012
0013 The ACTION is compulsory - it is the name of the uevent
0014 action (``add``, ``change``, ``remove``). There is no change
0015 compared to previous functionality here. The rest of the
0016 extended format is optional.
0017
0018 You need to pass UUID first before any KEY=VALUE pairs.
0019 The UUID must be in ``xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx``
0020 format where 'x' is a hex digit. The UUID is considered to be
0021 a transaction identifier so it's possible to use the same UUID
0022 value for one or more synthetic uevents in which case we
0023 logically group these uevents together for any userspace
0024 listeners. The UUID value appears in uevent as
0025 ``SYNTH_UUID=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx`` environment
0026 variable.
0027
0028 If UUID is not passed in, the generated synthetic uevent gains
0029 ``SYNTH_UUID=0`` environment variable automatically.
0030
0031 The KEY=VALUE pairs can contain alphanumeric characters only.
0032
0033 It's possible to define zero or more pairs - each pair is then
0034 delimited by a space character ' '. Each pair appears in
0035 synthetic uevent as ``SYNTH_ARG_KEY=VALUE``. That means the KEY
0036 name gains ``SYNTH_ARG_`` prefix to avoid possible collisions
0037 with existing variables.
0038
0039 Example of valid sequence written to the uevent file::
0040
0041 add fe4d7c9d-b8c6-4a70-9ef1-3d8a58d18eed A=1 B=abc
0042
0043 This generates synthetic uevent including these variables::
0044
0045 ACTION=add
0046 SYNTH_ARG_A=1
0047 SYNTH_ARG_B=abc
0048 SYNTH_UUID=fe4d7c9d-b8c6-4a70-9ef1-3d8a58d18eed
0049
0050 Users:
0051 udev, userspace tools generating synthetic uevents
