A new trigger type for global control

[namhyung]

I remember there were some suggestions using file size or elapsed time as a trigger point and associate (global) actions to it (But I cannot find where). For example, we might do things like:

• tracing is off by default, and turn it on after 10 seconds
• similarly, trace only the first 3 seconds of execution
• or trace only from 5 second to 10 second of execution
• finish the tracing when file size reaches to 100 MB

There's --signal option for the similar purpose, but it only handles signals. Maybe we can add time and size support there, or have a new option to handle it separately.

[honggyukim]

This is related to #1699.

[namhyung]

Actually we can use timeout command to send a signal at given time: #1598 (comment).

For the first case above, this would do the job (but much more verbose).

$ timeout -s RTMIN 10  uftrace --trace=off --signal RTMIN@trace_on <target-program>

[namhyung]

This could be

$ uftrace --trace=off --signal time=10s@trace_on <target-program>

[honggyukim]

How about the following interface as mentioned at #1699?

# trace target program since 10s elapsed from the beginning.
$ uftrace --trace=10s~ ./prog

This can be much simpler.

[namhyung]

Yep, that looks better. I think we also need data size support (maybe only needed for finish action).