On Wed, Jun 19, 2019 at 4:35 AM Rafael J. Wysocki <raf...@kernel.org> wrote: > > On Wed, Jun 19, 2019 at 1:52 AM Joel Fernandes <joe...@google.com> wrote: > > > > On Tue, Jun 18, 2019 at 7:15 PM Tri Vo <tr...@android.com> wrote: > > [snip] > > > > > > > > > > > > > > Android userspace reading wakeup_sources is not ideal because: > > > > > > > - Debugfs API is not stable, i.e. Android tools built on top of > > > > > > > it are > > > > > > > not guaranteed to be backward/forward compatible. > > > > > > > - This file requires debugfs to be mounted, which itself is > > > > > > > undesirable for security reasons. > > > > > > > > > > > > > > To address these problems, we want to contribute a way to expose > > > > > > > these > > > > > > > statistics that doesn't depend on debugfs. > > > > > > > > > > > > > > Some initial thoughts/questions: Should we expose the stats in > > > > > > > sysfs? > > > > > > > Or maybe implement eBPF-based solution? What do you think? > > > > > > > > > > We are going through Android's out-of-tree kernel dependencies along > > > > > with > > > > > userspace APIs that are not necessarily considered "stable and forever > > > > > supported" upstream. The debugfs dependencies showed up on our radar > > > > > as a > > > > > result and so we are wondering if we should worry about changes in > > > > > debugfs > > > > > interface and hence the question(s) below. > > > > > > > > > > So, can we rely on /d/wakeup_sources to be considered a userspace API > > > > > and > > > > > hence maintained stable as we do for other /proc and /sys entries? > > > > > > > > > > If yes, then we will go ahead and add tests for this in LTP or > > > > > somewhere else suitable. > > > > > > > > No, debugfs is not ABI. > > > > > > > > > If no, then we would love to hear suggestions for any changes that > > > > > need to be > > > > > made or we simply just move the debugfs entry into somewhere like > > > > > /sys/power/ ? > > > > > > > > No, moving that entire file from debugfs into sysfs is not an option > > > > either. > > > > > > > > The statistics for the wakeup sources associated with devices are > > > > already there > > > > under /sys/devices/.../power/ , but I guess you want all wakeup sources? > > > > > > > > That would require adding a kobject to struct wakeup_source and exposing > > > > all of the statistics as separate attributes under it. In which case > > > > it would be > > > > good to replace the existing wakeup statistics under > > > > /sys/devices/.../power/ > > > > with symbolic links to the attributes under the wakeup_source kobject. > > > > > > Thanks for your input, Rafael! Your suggestion makes sense. I'll work > > > on a patch for this. > > > > Does that entail making each wake up source, a new sysfs node under a > > particular device, and then adding stats under that new node? > > Not under a device, because there are wakeup source objects without > associated devices. > > It is conceivable to have a "wakeup_sources" directory under > /sys/power/ and sysfs nodes for all wakeup sources in there. > > Then, instead of exposing wakeup statistics directly under > /sys/devices/.../power/, there can be symbolic links from there to the > new wakeup source nodes under "wakeup_sources" (so as to avoid > exposing the same data in two different places in sysfs, which may be > confusing).
Makes sense to me, thanks! - Joel
