linux-kernel - Re: RFC: android logger feedback request

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Date:	Wed, 21 Dec 2011 21:07:14 -0800 (PST)
From:	david@...g.hm
To:	Brian Swetland <swetland@...gle.com>
cc:	Kay Sievers <kay.sievers@...y.org>, Greg KH <gregkh@...e.de>,
	Tim Bird <tim.bird@...sony.com>,
	linux-embedded <linux-embedded@...r.kernel.org>,
	linux kernel <linux-kernel@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>,
	john stultz <johnstul@...ibm.com>,
	Lennart Poettering <lennart@...ttering.net>
Subject: Re: RFC: android logger feedback request

On Wed, 21 Dec 2011, Brian Swetland wrote:

> On Wed, Dec 21, 2011 at 8:47 PM,  <david@...g.hm> wrote:
>> On Wed, 21 Dec 2011, Brian Swetland wrote:
>>> Any thoughts as to how one could allow N userspace agents to log to a
>>> single shared buffer without one agent, if buggy or malicious,
>>> spamming out all the other contents of the log?  This is one of the
>>> main reasons we maintain separate logs in Android today, and are
>>> likely to continue doing so until we figure out how resolve the issue.
>>
>> note that you still don't prevent one app from blowing out the logs, all you
>> do is separate the logs into a handfulof categories and limit the app
>> (through standard filesystem permissions) to only blowing out one category
>> of logs.
>>
>> or do I misunderstand this and you actually keep a separate queue for each
>> pid (which would seem to be a problem as you no longer know how much space
>> you need)
>
> You're correct -- that's the model at present.  We'd like to move to a
> model where we have better control and are kicking around ideas for
> how to do this for the next platform version.
>
> The rate at which apps push data into logs is pretty amazing at times.
> The system booting (maybe 10-20 services and 10+ apps starting up)
> can blow through 256K of ringbuffer in seconds.
>
> Having enough context available when something crashes to be able to
> diagnose what went wrong, especially when problems could involve
> interaction between multiple agents in multiple processes is important
> for the frameworks and apps teams.

this makes it sound more like this belongs in userspace instead of the 
kernel. if something crashes and they can flip a flag in userspace to say 
'keep more logs now' and try to duplicate the crash is going to be far 
easier than having to compile a new kernel to extend the size of the log.

> Trying to get individual developers to be frugal with their logging
> has turned out to be mostly a losing battle.

that's for sure, anything that's success depends on developers doing 
things right that aren't visible to the user are pretty much doomed.

David Lang