Re: Hot-patching

[Valdis . Kletnieks]

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....

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