Use the ftrace buffer instances

[phantez]

If ftrace is already in use without instances, options are inherited and it prevents the logging to work as expected for the pertf-tools CLIs.

@brendangregg : It's a very simplistic approach to the problem, not sure you want to merge that like it, but it's mainly a heads up if some other people are running into the same issues as I did.

[phantez]

BTW, if you are interested I can clean that pull request to make it a bit nicer, like variables to avoid duplication of the long path, etc..

[brendangregg]

Thanks; I'll eventually switch perf-tools over to use buffer instances when they are available (Linux version ??). Since every tool is going to get a chunk of boilerplate, it might be time to move it into its own library. Although I'll try hard not to break the copy-n-paste virtue of stand-alone tools: perhaps I'll make perf-tools "build" stand-alone tools which are committed in github, but we actually develop them in a src directory.

[psanford]

This would have been useful for me this week. Specifically, I wanted to run uprobe multiple times. If there was an option to make a new (ephemeral) trace instance per invocation that would have made things a lot easier for me.

[psanford]

This would have been useful for me this week. Specifically, I wanted to run uprobe multiple times. If there was an option to make a new (ephemeral) trace instance per invocation that would have made things a lot easier for me.

Hmm. Looking at this some more it doesn't seem like you can set uprobes on a trace instance (at least on my 5.4 kernel).