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From:   Alexander Potapenko <glider@google.com>
Date:   Fri, 15 Jan 2021 16:26:21 +0100
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Subject: Re: [PATCH v2 3/5] docs: ABI: add /sys/kernel/error_report/ documentation
To:     Greg KH <gregkh@linuxfoundation.org>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andrey Konovalov <andreyknvl@google.com>,
        Dmitriy Vyukov <dvyukov@google.com>,
        Ingo Molnar <mingo@redhat.com>, Marco Elver <elver@google.com>,
        Petr Mladek <pmladek@suse.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Linux Memory Management List <linux-mm@kvack.org>
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> sysfs is "one value per file"
What about existing interfaces that even export binary blobs through
sysfs (e.g. /sys/firmware, /sys/boot_params)?
What qualifies as a "value" in that case?

> please put something like this in
> tracefs, as there is no such rules there.  Or debugfs, but please, not
> sysfs.
Does tracefs have anything similar to sysfs_notify() or any other way
to implement a poll() handler?
Our main goal is to let users wait on poll(), so that they don't have
to check the file for new contents every now and then. Is it possible
with tracefs or debugfs?

Also, for our goal debugfs isn't a particularly good fit, as Android
kernels do not enable debugfs.
Not sure about tracefs, they seem to have it, need to check.

Do you think it is viable to keep
/sys/kernel/error_report/report_count in sysfs and use it for
notifications, but move last_report somewhere else?
(I'd probably prefer procfs, but it could be tracefs as well, if you
find that better).
This way it will still be possible to easily notify userspace about
new reports, but the report itself won't have any atomicity
guarantees. Users will have to check the report count to ensure it
didn't change under their feet.

> Also, any reason you didn't cc: the sysfs maintainers?
Only my lack of common sense :)
I'll add them should the following patches rely on sysfs, thank you!

Alex


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Alexander Potapenko
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