| 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 |
