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1What: /sys/.../uevent2Date: May 20173KernelVersion: 4.134Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>5Description:6 Enable passing additional variables for synthetic uevents that7 are generated by writing /sys/.../uevent file.8 9 Recognized extended format is::10 11 ACTION [UUID [KEY=VALUE ...]12 13 The ACTION is compulsory - it is the name of the uevent14 action (``add``, ``change``, ``remove``). There is no change15 compared to previous functionality here. The rest of the16 extended format is optional.17 18 You need to pass UUID first before any KEY=VALUE pairs.19 The UUID must be in ``xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx``20 format where 'x' is a hex digit. The UUID is considered to be21 a transaction identifier so it's possible to use the same UUID22 value for one or more synthetic uevents in which case we23 logically group these uevents together for any userspace24 listeners. The UUID value appears in uevent as25 ``SYNTH_UUID=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx`` environment26 variable.27 28 If UUID is not passed in, the generated synthetic uevent gains29 ``SYNTH_UUID=0`` environment variable automatically.30 31 The KEY=VALUE pairs can contain alphanumeric characters only.32 33 It's possible to define zero or more pairs - each pair is then34 delimited by a space character ' '. Each pair appears in35 synthetic uevent as ``SYNTH_ARG_KEY=VALUE``. That means the KEY36 name gains ``SYNTH_ARG_`` prefix to avoid possible collisions37 with existing variables.38 39 Example of valid sequence written to the uevent file::40 41 add fe4d7c9d-b8c6-4a70-9ef1-3d8a58d18eed A=1 B=abc42 43 This generates synthetic uevent including these variables::44 45 ACTION=add46 SYNTH_ARG_A=147 SYNTH_ARG_B=abc48 SYNTH_UUID=fe4d7c9d-b8c6-4a70-9ef1-3d8a58d18eed49 50Users:51 udev, userspace tools generating synthetic uevents52