[Ce-android-mainline] [PATCH 04/10] android: ram_console: split out persistent ram

[Colin Cross]

On Mon, Feb 20, 2012 at 2:24 PM, john stultz <johnstul at us.ibm.com> wrote:
> On Sun, 2012-02-19 at 16:44 -0800, Colin Cross wrote:
>> Split ram_console into two halves.
>>
>> persistent_ram is a set of apis that handle a block of memory
>> that does not get erased across a reboot.  It provides functions
>> to fill it as a single buffer or a ring buffer, and to extract
>> the old data after a reboot.  It handles ecc on the data to
>> correct bit errors introduced during reboot.
>>
>> ram_console is now a small wrapper around persistent_ram that
>> feeds console data into the ringbuffer, and exports the old
>> data to /proc/last_kmsg after a reboot.
>
> This looks very cool (esp the ftrace bit), although have you looked at
> all into the pstore work to see how it might be able to be integrated?
>
> Kees (cc'ed) has apparently been working to get the ramoops driver
> (which writes oops and panic messages to a similar in-ram circular
> buffer) working with pstore and there seems like there is some overlap
> here.
>
> I'm not saying this should block this code going into staging, but just
> wanted to know if you had looked into the similar works and if so, could
> articulate why they couldn't be reused (so others can try to help
> integrate things if necessary).
>
> thanks
> -john
>
>

pstore is just an interface to write to a persistent storage, with a
tiny driver on it to dump console messages after a panic.  With the
number of crashes we see on ARM cpus that are not panics (mostly
watchdog resets), logging only after a panic is not appropriate, so it
can't replace ramconsole.  persistent_ram could easily be a pstore
driver, but that would not give any new useful functionality, since
ramconsole is better for us than pstore_dump.

Looking at ramoops, it is exactly the same as pstore on ioremapped
ram, but was originally implemented separately.  I see patches now
that convert it to a pstore backend, which leaves us in the same state
as above - only logging panics.