On Mon, Jun 24, 2019 at 2:27 PM Joel Fernandes <joe...@google.com> wrote: > > On Mon, Jun 24, 2019 at 3:37 AM Greg Kroah-Hartman > <gre...@linuxfoundation.org> wrote: > > > > On Sun, Jun 23, 2019 at 06:48:43PM -0700, Tri Vo wrote: > > > On Wed, Jun 19, 2019 at 1:35 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). > > > > > > This may be a dumb question. Is it appropriate to make symbolic links > > > in sysfs from one attribute to another attribute? For example, > > > /sys/devices/.../power/wakeup_count -> > > > /sys/power/wakeup_sources/.../wakeup_count. > > > > Why? would you want that? > > This sounds like what Rafael suggested (quoted above), right?
I did, basically to avoid exposing the same information in two places via different code paths. I tend to forget about this limitation, sorry for the confusion. That's not a big deal, though, the attributes under /sys/devices/.../power/ just need to stay the way they are (for backwards compatibility).
