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 ACTION [UUID [KEY=VALUE ...].
10
11                The ACTION is compulsory - it is the name of the uevent action
12                ("add", "change", "remove"). There is no change compared to
13                previous functionality here. The rest of the extended format
14                is optional.
15
16                You need to pass UUID first before any KEY=VALUE pairs.
17                The UUID must be in "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx"
18                format where 'x' is a hex digit. The UUID is considered to be
19                a transaction identifier so it's possible to use the same UUID
20                value for one or more synthetic uevents in which case we
21                logically group these uevents together for any userspace
22                listeners. The UUID value appears in uevent as
23                "SYNTH_UUID=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx" environment
24                variable.
25
26                If UUID is not passed in, the generated synthetic uevent gains
27                "SYNTH_UUID=0" environment variable automatically.
28
29                The KEY=VALUE pairs can contain alphanumeric characters only.
30                It's possible to define zero or more pairs - each pair is then
31                delimited by a space character ' '. Each pair appears in
32                synthetic uevent as "SYNTH_ARG_KEY=VALUE". That means the KEY
33                name gains "SYNTH_ARG_" prefix to avoid possible collisions
34                with existing variables.
35
36                Example of valid sequence written to the uevent file:
37
38                    add fe4d7c9d-b8c6-4a70-9ef1-3d8a58d18eed A=1 B=abc
39
40                This generates synthetic uevent including these variables:
41
42                    ACTION=add
43                    SYNTH_ARG_A=1
44                    SYNTH_ARG_B=abc
45                    SYNTH_UUID=fe4d7c9d-b8c6-4a70-9ef1-3d8a58d18eed
46Users:
47                udev, userspace tools generating synthetic uevents
48