Message-ID: <43309243.3050100@comcast.net>
Date: Tue, 20 Sep 2005 18:50:43 -0400
From: John Richard Moser <nigelenki@comcast.net>
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To: Valdis.Kletnieks@vt.edu
CC: linux-kernel@vger.kernel.org
Subject: Re: Hot-patching
References: <43308815.1000200@comcast.net> <200509202221.j8KMLhcr032238@turing-police.cc.vt.edu>
In-Reply-To: <200509202221.j8KMLhcr032238@turing-police.cc.vt.edu>
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Valdis.Kletnieks@vt.edu wrote:
> On Tue, 20 Sep 2005 18:07:17 EDT, John Richard Moser said:
> 
> 
>>These bugfixes don't typically change the exported binary interface of
>>the existing functions being corrected, and so it would be feasible to
>>halt all processors and execute an atomic codepath to switch the symbols
>>in the running kernel to point to the replacement functions from the old
>>ones.  If big functions are split up into smaller ones, as long as the
>>interface is the same for all existing functions, it shouldn't matter as
>>well.
> 
> 
> I believe telco switch software has been doing patch-on-the-fly for quite
> a long time.  It's a royal pain in the butt, especially if you have any
> dynamic 'struct foo_ops' lurking.
> 
> And you can't just plop the code in either - let's say the fix includes "add
> a state bit to the 'struct foo_ctl' to track XYZ".  Now you need to think about
> the fact that there's likely kmalloc'ed struct foo_ctl's already out there
> that don't know about this bit.  Hilarity ensues....

In which case you can't make a hot-patch, unless you like watching your
kernel take a crap.

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