1What: /sys/.../uevent 2Date: May 2017 3KernelVersion: 4.13 4Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 5Description: 6 Enable passing additional variables for synthetic uevents that 7 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 uevent 14 action (``add``, ``change``, ``remove``). There is no change 15 compared to previous functionality here. The rest of the 16 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 be 21 a transaction identifier so it's possible to use the same UUID 22 value for one or more synthetic uevents in which case we 23 logically group these uevents together for any userspace 24 listeners. The UUID value appears in uevent as 25 ``SYNTH_UUID=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx`` environment 26 variable. 27 28 If UUID is not passed in, the generated synthetic uevent gains 29 ``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 then 34 delimited by a space character ' '. Each pair appears in 35 synthetic uevent as ``SYNTH_ARG_KEY=VALUE``. That means the KEY 36 name gains ``SYNTH_ARG_`` prefix to avoid possible collisions 37 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=abc 42 43 This generates synthetic uevent including these variables:: 44 45 ACTION=add 46 SYNTH_ARG_A=1 47 SYNTH_ARG_B=abc 48 SYNTH_UUID=fe4d7c9d-b8c6-4a70-9ef1-3d8a58d18eed 49 50Users: 51 udev, userspace tools generating synthetic uevents 52