From: Tri Vo <email@example.com> To: "Rafael J. Wysocki" <firstname.lastname@example.org> Cc: Joel Fernandes <email@example.com>, "Rafael J. Wysocki" <firstname.lastname@example.org>, Sandeep Patil <email@example.com>, Viresh Kumar <firstname.lastname@example.org>, Hridya Valsaraju <email@example.com>, Linux PM <firstname.lastname@example.org>, "Cc: Android Kernel" <email@example.com>, Greg Kroah-Hartman <firstname.lastname@example.org>, LKML <email@example.com> Subject: Re: Alternatives to /sys/kernel/debug/wakeup_sources Date: Sun, 23 Jun 2019 18:48:43 -0700 Message-ID: <CANA+-vCBW=P=dpJGfcKTt7SoNKzWcpP5pwZHSDMU6MkwBKoC9A@mail.gmail.com> (raw) In-Reply-To: <CAJZ5v0gvzCx-7qS9qkxB=sGKjQJKMR7yCc21f=_vqrbZxMSWNg@mail.gmail.com> On Wed, Jun 19, 2019 at 1:35 AM Rafael J. Wysocki <firstname.lastname@example.org> wrote: > > On Wed, Jun 19, 2019 at 1:52 AM Joel Fernandes <email@example.com> wrote: > > > > On Tue, Jun 18, 2019 at 7:15 PM Tri Vo <firstname.lastname@example.org> 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. I only see kobject to kobject symlinks around. And I don't think we can make /sys/devices/.../power/ directory a symlink to where our new wakeup stats will be, since the former contains attributes other than wakeup ones. Thanks!
next prev parent reply index Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-06-05 0:23 Tri Vo 2019-06-11 17:31 ` Tri Vo 2019-06-18 20:17 ` Sandeep Patil 2019-06-18 21:23 ` Rafael J. Wysocki 2019-06-18 23:15 ` Tri Vo 2019-06-18 23:52 ` Joel Fernandes 2019-06-19 8:35 ` Rafael J. Wysocki 2019-06-19 10:33 ` Joel Fernandes 2019-06-19 16:51 ` Sandeep Patil 2019-06-19 16:53 ` Joel Fernandes 2019-06-19 17:07 ` Greg Kroah-Hartman 2019-06-19 18:01 ` Joel Fernandes 2019-06-19 18:31 ` Tri Vo 2019-06-19 18:35 ` Greg Kroah-Hartman 2019-06-19 18:55 ` Joel Fernandes [not found] ` <CAGETcx-ZZRc_jtBws2cFTe1wjiWeBowdqfqOhcCJV_7AUyBEVw@mail.gmail.com> 2019-06-19 20:09 ` Joel Fernandes 2019-06-19 20:40 ` Saravana Kannan 2019-06-19 20:52 ` Joel Fernandes 2019-06-24 1:48 ` Tri Vo [this message] 2019-06-24 7:36 ` Greg Kroah-Hartman 2019-06-24 12:27 ` Joel Fernandes 2019-06-24 21:55 ` Rafael J. Wysocki 2019-06-24 22:14 ` Tri Vo
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