On Tue, 3 Sep 2019 at 23:48, Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > On Tue, Sep 03, 2019 at 04:51:40PM -0600, Mathieu Poirier wrote: > > On Tue, 3 Sep 2019 at 13:59, Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > > > > > On Thu, Aug 29, 2019 at 10:33:19PM +0100, Mike Leach wrote: > > > > Update document to include the new sysfs features added during this > > > > patchset. > > > > > > > > Updated to reflect the new sysfs component nameing schema. > > > > > > > > Signed-off-by: Mike Leach <mike.leach@xxxxxxxxxx> > > > > --- > > > > .../testing/sysfs-bus-coresight-devices-etm4x | 183 +++++++++++------- > > > > 1 file changed, 115 insertions(+), 68 deletions(-) > > > > > > > > diff --git a/Documentation/ABI/testing/sysfs-bus-coresight-devices-etm4x b/Documentation/ABI/testing/sysfs-bus-coresight-devices-etm4x > > > > index 36258bc1b473..112c50ae9986 100644 > > > > --- a/Documentation/ABI/testing/sysfs-bus-coresight-devices-etm4x > > > > +++ b/Documentation/ABI/testing/sysfs-bus-coresight-devices-etm4x > > > > @@ -1,4 +1,4 @@ > > > > -What: /sys/bus/coresight/devices/<memory_map>.etm/enable_source > > > > +What: /sys/bus/coresight/devices/etm<N>/enable_source > > > > > > You are renaming sysfs directories that have been around since: > > > > > > > Date: April 2015 > > > > > > ??? > > > > > > Really? > > > > > > That's brave. > > > > > > When I worked on the coresight sysfs ABI a while back I specifically > > added it at the "testing" level as I was well aware that things could > > change in the future. According to the guidelines in the > > documentation userspace can rely on it which was accurate since the > > interface didn't change for 4 years. But the guidelines also mention > > that changes can occur before the interfaces are move to stables, and > > that programs are encouraged to manifest their interest by adding > > their name to the "users" field. > > > > The interface was changed in 5.2 to support coresight from ACPI and > > make things easier to understand for users. It is a lot more > > intuitive to associate an ETM tracer with the CPU it belongs to by > > referring to the CPU number than the memory mapped address. Given the > > "testing" status of the interface and the absence of registered users > > I decided to move forward with the change. If "testing" is too strict > > for that I suggest to add an "experimental" category where it would be > > more acceptable to change things as subsystems mature. > > "testing" is not really "testing" if you have userspace tools/programs > assuming the location and contents of specific files in sysfs. > > You can change things in sysfs by creating new files, but to do > wholesale renaming like you did here can be very dangerous as you might > be breaking things. Yes, something I have definitely considered. > Usually new files are created, not existing ones > moved. In this case it would have meant a new symbolic link for every coresight device, so twice a many entries under $(SYS)/bus/coresight/device/. That would have been a lot of clutter and an increasing source of problems as the number of CPU and sinks increases. To me, and given the permissive definition of "testing" found in the documentation, a clean break was a better option. > > What tools use these today? What is going to break? Other than local shell scripts I am not aware of any tools using these today. I am certainly open to discuss a better alternative but right now, I just don't see one. > > thanks, > greg k-h
