On Mon, Jan 30, 2023 at 11:59 AM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > > On Mon, 30 Jan 2023 11:52:03 -0800 > Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> wrote: > > > 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. > > Could we add a way to try to mount it? > > If anything, the tests should not have the path hard coded. It should then > look to see if it is mounted and use the path that is found. Otherwise it > should try mounting it at the correct location. > > Feel free to take the code from libtracefs (and modify it): > > https://git.kernel.org/pub/scm/libs/libtrace/libtracefs.git/tree/src/tracefs-utils.c#n89 > > It will make the test code much more robust. The point is not about tests. The point is that this change might break some users that are working today with /sys/kernel/debug/tracing. It also might be mounted differently. For example from another system: cat /proc/mounts|grep trace tracefs /sys/kernel/tracing tracefs rw,nosuid,nodev,noexec,relatime 0 0 tracefs /sys/kernel/debug/tracing tracefs rw,relatime 0 0 So I suggest leaving the code as-is.
