[cgl_discussion] Re: [cgl_tech_board] Use case - Live patching

[Mary Edie Meredith]

A few suggestions.  See below.


On Sun, 2005-03-27 at 18:14, Takashi Ikebe wrote:
> The following is a use case for a Live patching.  This
> addresses AVL10.0 Live patching on CGL Specification 3.0.
> Please feel free to comment / suggestion.
> 
> Takashi.
> -----------------------------------------------------------------------------------------------
> Description
> OSDL CGL specifies that carrier grade Linux shall provide the mechanism
> for dynamically replacing the symbols of a running process without
> restarting. Dynamic replacement of symbols allows a process to access
> patched functions or values without restarting and can improve process
> availability.
> 
> Desired Outcome
> Mainline kernel acceptance or distro acceptance

I suggest that CGL use this entry to state the desired outcome of the
steps being described in the use case.  In this case (I'll take a stab
here) it is "to increase system availability while staying in sync with
distro releases."

If you want to describe how you expect the solution to reach the
end-customer, I suggest you call that  "Target Acceptance"
> 
> Participants/Roles
> System administrators setup the requirements on installations. On
> operation, system administrators apply patch with the requirement.
> 
> Scenarios
> On operation, system administrators apply patch with the requirement as
> following scenario;
> 1.System administrators make patch file from diff file or new version's
> source code.
> 2.System administrators load patch to the process with provided live
> patch tool.
> 3.System administrators activate patch to the process with provided live
> patch tool.
> 4.Confirm that the patch is correctly applied or not.

I suggest you add something for backing out a patch that fails.

In light of the other suggestions, maybe you need a tool that tracks
what you have in memory with any given distro release.  The result might
be a comprehensive patch to that release so you can recover from
reboot.  That is yet another scenerio, perhaps.
> 
> Implementation Notes
> The requirement need to have following functions;
> - The function which loads the patch file to target process's memory area.
> - The function which overwrites the branch operation code to the patch,
> on the entry point of  target process's functions which wants to fix by
> patch.
> - The function which restores overwritten branch code.
> - The function which unload the patch files.
> Through above functions, the requirement realize on-line patch to target
> process.
> The requirement need to provide on-line patch even if the process is
> multi-thread model process, or environment is SMP, and stop time of
> target process should not over  100 milliseconds.
> 
> References
> Pannus project: http://pannus.sourceforge.net/
> Live patching implementation:
> http://prdownloads.sourceforge.net/pannus/pannus_en.pdf
-- 
Mary Edie Meredith 
maryedie at osdl.org
503-906-1942
Open Source Development Labs