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