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    SubjectRe: Alternatives to /sys/kernel/debug/wakeup_sources
    On Tue, Jun 18, 2019 at 7:15 PM Tri Vo <trong@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?

    thanks,

    - Joel

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