Re: [PATCH 3/9] selftests/bpf: use canonical ftrace path

[Alexei Starovoitov]

On Mon, Jan 30, 2023 at 10:19 AM Ross Zwisler <zwisler@xxxxxxxxxxxx> wrote:
>
> The canonical location for the tracefs filesystem is at /sys/kernel/tracing.
>
> But, from Documentation/trace/ftrace.rst:
>
>   Before 4.1, all ftrace tracing control files were within the debugfs
>   file system, which is typically located at /sys/kernel/debug/tracing.
>   For backward compatibility, when mounting the debugfs file system,
>   the tracefs file system will be automatically mounted at:
>
>   /sys/kernel/debug/tracing
>
> Many tests in the bpf selftest code still refer to this older debugfs
> path, so let's update them to avoid confusion.

I wish that was the case, but in reality there are still systems
out there where tracefs is only mounted in that old location.
For example in one my VMs:

$ cat /proc/mounts |grep tracefs
tracefs /sys/kernel/debug/tracing tracefs rw,relatime 0 0
$ ls /sys/kernel/tracing/
$ uname -r
6.2.0-rc5-01030-gc1a3daf7363b

So this change will break the tests. We cannot do it.