Documentation/trace/user_events.rst

2 user_events: User-based Event Tracing
9 User based trace events allow user processes to create events and trace data
18 delete user based events via the u: prefix. The format of the command to
37 Registering within a user process is done via ioctl() out to the
83   must be naturally aligned and write accessible within the user program.
119 User based events show up under tracefs like any other event under the
147 Basic types are supported (__data_loc, u32, u64, int, char, char[20], etc).
148 User programs are encouraged to use clearly sized types like u32.
150 **NOTE:** *Long is not supported since size can vary between user and kernel.*
153 This allows user programs to describe custom structs out to tools, if required.
158     char data[20];
163   struct mytype myname 20
167 Deleting an event from within a user process is done via ioctl() out to the
173 event (in both user and kernel space). User programs should use a separate file
229 When tools attach/record user based events the status of the event is updated
230 in realtime. This allows user programs to only incur the cost of the write() or
234 tools attach/detach from the event. User programs simply check if the bit is set
253 If a user enables the user event via ftrace, the output would change to this::
276 User programs might have well known structs that they wish to use to emit out
288 It's advised for user programs to do the following::