In-Reply-To: <426C51C4.9040902@lab.ntt.co.jp>
References: <4263275A.2020405@lab.ntt.co.jp> <m1y8b9xyaw.fsf@muc.de> <426C51C4.9040902@lab.ntt.co.jp>
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Cc: linux-kernel@vger.kernel.org, Andi Kleen <ak@muc.de>
From: Kyle Moffett <mrmacman_g4@mac.com>
Subject: Re: [PATCH x86_64] Live Patching Function on 2.6.11.7
Date: Sun, 24 Apr 2005 22:48:15 -0400
To: Takashi Ikebe <ikebe.takashi@lab.ntt.co.jp>
Sender: linux-kernel-owner@vger.kernel.org
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If you want that exact functionality, do this:

At program start, spawn a new thread:
	1) Open a UNIX socket (/var/run/someapp_live_patch.sock)
	2) poll() that socket for a connection.
	3) When you get a connection, do your own security checks
	4) If it's ok, then map the specified file into memory
	5) Read a table of crap to patch from the file
	6) Do the patching, being careful to avoid the millions of
	   races involved for each CPU, *especially* regarding the
	   separate icache and dcache on CPUs like PPC and such.
	7) Go back to step 2

If you want equivalent functionality but much safer and not CPU
dependent and full of hand-coded assembly:

1) open(), mmap(), and mlock() the file (/var/lib/someapp/data)
2) Spawn normal operation threads
3) Spawn a new hot-patch thread:
	1) Open a UNIX socket (/var/run/someapp_live_patch.sock)
	2) poll() that socket for a connection.
	3) When you get one, coordinate with the new process as it
	   attaches itself to /var/lib/someapp/data
	4) Handle shared locking of parts of /var/lib/someapp/data
	5) Send it your listen() file-descriptors over the socket.
	6) Wait for the other process to signal it's ready.
	7) Stop accepting new connections on the socket.
	8) Send file-descriptors for current connections
	9) Cleanup and quit

When live-patching:
1)  connect to the socket /var/run/someapp_live_patch.sock
2)  open(), mmap() and mlock() /var/lib/someapp/data
3)  Coordinate with the other process via the socket
4)  Receive the listen() file-descriptors over the socket.
5)  Set up the shared data locking
6)  Spawn normal operation threads
7)  Signal readiness
8)  Receive file-descriptors for current connections
9)  Spawn threads for them too.
10) Spawn a new hot-patch thread as above

Cheers,
Kyle Moffett

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