Message-ID: <46AC5576.2050602@linux.vnet.ibm.com>
Date:	Sun, 29 Jul 2007 14:23:10 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Neil Horman <nhorman@...driver.com>
CC:	Martin Pitt <martin.pitt@...ntu.com>, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, jeremy@...p.org, wwoods@...hat.com,
	Ben Collins <ben.collins@...ntu.com>
Subject: Re: [PATCH 2/3] core_pattern: allow passing of arguments to user
 mode helper when core_pattern is a pipe



Neil Horman wrote:
> On Sat, Jul 28, 2007 at 06:17:25PM +0200, Martin Pitt wrote:
>> Hi Neil,
>>
>> Neil Horman [2007-07-28  9:46 -0400]:
>>>> I just want to mention a potential problem with this: If you first
>>>> expand the macros (from pattern to corename) and then split
>>>> corename into an argv, then this breaks macro expansions
>>>> containing spaces.  This mostly affects the executable name, of
>>>> course.
>>>>
>>> I never intended for this core_pattern argument passing to be able
>>> to expand macros, other than the macros specified by the
>>> core_pattern code.  If you want it to do that, we can address that
>>> with a later patch.
>> No, I specifically mean the standard ones provided by
>> format_corename(), such as %p (pid), %s (signal), or %e (executable
>> name). I don't see a reason to provide additional functionality.
>>
> Ahh, well then you should have nothing to worry about, this patch expands them
> just fine.  And none of those macros will ever have spaces in them.  I suppose
> it would be possible for the executable name to have spaces in it, but honestly,
> thats going rather out of your way to do something that you arguably shouldn't
> do anyway.
> 
>>>> In fact we considered this macro approach when doing the original
>>>> patches in the Ubuntu kernel, but we eventually used environment
>>>> variables because they are much easier and more robust to
>>>> implement than doing a robust macro expansion (i. e. first split
>>>> core_pattern into an argv and then call the macro expansion for
>>>> each element).
>>>>
>>> I disagree. While it might be nice to be able to specify environment
>>> variables as command line arguments, it would be much easier to just
>>> let the core_pattern executable inherit the crashing processes
>>> environment.  we don't do that currently, but we easily could.  That
>>> way any information that the crashing process wants the dying
>>> process to know can be inherited and vetted easily by apport (or
>>> whatever the core_pattern points to).  I'll do a patch later for
>>> that if you don't like it.
>> I don't think that this will be necessary. After all, the crash
>> handler can read all the environment from /proc/<pid>/ (and that's
>> indeed what apport does to figure out relevant parts from the
>> environment like the locale).
>>
> Agreed, /proc/<pid of crashing process>/* will be available while the helper app
> runs.
> 
>> It seems we misunderstood each other, I don't expect or want any new
>> functionality in core_pattern. AN example might make it more clear:
>>
> I think you're correct, I misundersood you previously.  Apologies.
> 
>> The original problem that we are trying to solve is the current
>> behaviour of core_pattern expansion with pipes:
>>
>>   |/bin/crash --pid %p
>>
>> would try to execute the program '/bin/crash --pid 1234' instead of
>> calling /bin/crash with ['--pid', '1234'] as argv, right? Your patch
>> achieves the latter by splitting the formatted core dump string into
>> an array (at spaces).
>>
> Yes, that is exactly correct.
> 
>> I pointed out that this leads to problems when macro values contain
>> spaces. This currently affects hostname (%h) (although this really
>> should not happen in practice) and executable name (%e) (rare, but at
>> least valid).  I. e. for an executable name "foo bar" your patch would
>> expand
>>
>>   |/bin/crash %e
>>
>> to ['/bin/crash', 'foo', 'bar'] instead of ['/bin/crash', 'foo bar'].
>>
> Also correct.  Thats a pretty big corner case, and I personally don't think an
> executable name with spaces is/should be valid anyway, but it can be done.
> 
>> Of course this is a corner case, and personally I don't really care.
>> I strive to keep the assumptions about the interface at a minimum, so
>> right now Apport's only required input is the core dump itself (over
>> stdin); signal and pid can be read from the environment, and if not
>> present, they are read from the core dump.
>>
> 
> Jeremy asked that I make a patch next week to address split_argv's requirement
> that the argc parameter be non-NULL.  I'll be fixing that next week, and what I
> can do is further enhance it such that it ignores spaces in quoted strings,
> which should address the case that concerns you.  I.E I can make split_argv
> behave such that:
> echo "|\"foo bar\" --pid %p" > /proc/sys/kernel/core_pattern
> results in the following argv:
> {{"foo bar"}, {"--pid"}, {"1234"}}
> 
> Which I think handles what you are looking for.
> 


One would also need to quote the expansion of %e  as Martin listed in the previous mail
So a %e should expand to \"my executable\". So that it get passed as single argument.

I guess we should only do it when "|" is specified in core pattern. Otherwise we would
have core file as 

core."my exectutable" 


-aneesh
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