1*4882a593SmuzhiyunWhat: /sys/.../uevent 2*4882a593SmuzhiyunDate: May 2017 3*4882a593SmuzhiyunKernelVersion: 4.13 4*4882a593SmuzhiyunContact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 5*4882a593SmuzhiyunDescription: 6*4882a593Smuzhiyun Enable passing additional variables for synthetic uevents that 7*4882a593Smuzhiyun are generated by writing /sys/.../uevent file. 8*4882a593Smuzhiyun 9*4882a593Smuzhiyun Recognized extended format is:: 10*4882a593Smuzhiyun 11*4882a593Smuzhiyun ACTION [UUID [KEY=VALUE ...] 12*4882a593Smuzhiyun 13*4882a593Smuzhiyun The ACTION is compulsory - it is the name of the uevent 14*4882a593Smuzhiyun action (``add``, ``change``, ``remove``). There is no change 15*4882a593Smuzhiyun compared to previous functionality here. The rest of the 16*4882a593Smuzhiyun extended format is optional. 17*4882a593Smuzhiyun 18*4882a593Smuzhiyun You need to pass UUID first before any KEY=VALUE pairs. 19*4882a593Smuzhiyun The UUID must be in ``xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx`` 20*4882a593Smuzhiyun format where 'x' is a hex digit. The UUID is considered to be 21*4882a593Smuzhiyun a transaction identifier so it's possible to use the same UUID 22*4882a593Smuzhiyun value for one or more synthetic uevents in which case we 23*4882a593Smuzhiyun logically group these uevents together for any userspace 24*4882a593Smuzhiyun listeners. The UUID value appears in uevent as 25*4882a593Smuzhiyun ``SYNTH_UUID=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx`` environment 26*4882a593Smuzhiyun variable. 27*4882a593Smuzhiyun 28*4882a593Smuzhiyun If UUID is not passed in, the generated synthetic uevent gains 29*4882a593Smuzhiyun ``SYNTH_UUID=0`` environment variable automatically. 30*4882a593Smuzhiyun 31*4882a593Smuzhiyun The KEY=VALUE pairs can contain alphanumeric characters only. 32*4882a593Smuzhiyun 33*4882a593Smuzhiyun It's possible to define zero or more pairs - each pair is then 34*4882a593Smuzhiyun delimited by a space character ' '. Each pair appears in 35*4882a593Smuzhiyun synthetic uevent as ``SYNTH_ARG_KEY=VALUE``. That means the KEY 36*4882a593Smuzhiyun name gains ``SYNTH_ARG_`` prefix to avoid possible collisions 37*4882a593Smuzhiyun with existing variables. 38*4882a593Smuzhiyun 39*4882a593Smuzhiyun Example of valid sequence written to the uevent file:: 40*4882a593Smuzhiyun 41*4882a593Smuzhiyun add fe4d7c9d-b8c6-4a70-9ef1-3d8a58d18eed A=1 B=abc 42*4882a593Smuzhiyun 43*4882a593Smuzhiyun This generates synthetic uevent including these variables:: 44*4882a593Smuzhiyun 45*4882a593Smuzhiyun ACTION=add 46*4882a593Smuzhiyun SYNTH_ARG_A=1 47*4882a593Smuzhiyun SYNTH_ARG_B=abc 48*4882a593Smuzhiyun SYNTH_UUID=fe4d7c9d-b8c6-4a70-9ef1-3d8a58d18eed 49*4882a593Smuzhiyun 50*4882a593SmuzhiyunUsers: 51*4882a593Smuzhiyun udev, userspace tools generating synthetic uevents 52