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Re: multiple dump devices

To: "Matt D. Robinson" <yakker@xxxxxxxxxxxxxx>
Subject: Re: multiple dump devices
From: "Masashige Kotani" <m-kotani@xxxxxxxxxxxxxxx>
Date: Fri, 7 Sep 2001 20:22:02 +0900
Cc: "Howell, David P" <david.p.howell@xxxxxxxxx>, <lkcd@xxxxxxxxxxx>
References: <10C8636AE359D4119118009027AE99870CE2F95B@FMSMSX34> <3B9563E8.9A432B7B@alacritech.com> <008401c136b6$05e00600$d64817ac@aoi.pst.fujitsu.com> <3B97CEE5.ED870202@alacritech.com>
Sender: owner-lkcd@xxxxxxxxxxx
> I guess what I mean is more like the following:
> 
> Assume there are multiple dump devices in /dev:
> 
> /dev/dump/dump0  (major 227, minor 0)
> /dev/dump/dump1  (major 227, minor 1)
> /dev/dump/dumpN  (major 227, minor N)
> 
> All of these are configurable via open() and ioctl(), and each can have
> their own individual dumping strategies based on configuration.  For
> example, let's say /dev/dump/dump0 is configured with dump method A,
> RLE compression, and is non-disruptive.  /dev/dump/dump1 is configured
> with dump method B (let's say it's Mission Critical Linux's MCLX crash
> utility), no compression, and is disruptive.  Etc., etc., etc.
> 
> Each can be triggered via dprobes, or a system crash, SysRQ, or
> any other mechanism.
> 
> As far as dump methods are concerned, we'd take dump_execute() and
> turn it into a dump method launch.  So, if it gets called, it walks
> through the dump methods and determines which one to execute based
> on what is configured.  The final step is to make each dump method
> a module rather than something statically built into the kernel.
> This eliminates the need for massive dump overhead in the kernel
> code -- each module can do its own thing with respect to method,
> compression, etc.  It can even determine whether it wants the kernel
> to go silent or not (like what IBM's trying to do).
> 
> So, 'lsmod' might show:
> 
> [root@watereye /root]# lsmod
> Module                  Size  Used by
> dump_rle                1104   0  (unused)
> dump_gzip               8906   0  (unused)
> dump_method_lkcd       89712   0  (unused)
> dump_method_mclx       22319   0  (unused)
> dump                   17248   0  [dump_rle]

Are the method modules and the compress modules used
two or more in once dumping?

> 
> So a dump method module, when loaded, can then be used by a dump
> device for crashing.  The only complexity is writing a nice user
> utility that configures how crashing is performed, and loads all
> the right modules for you (or sets them up to load).
> 
> Does this make any sense at all? :)  What do you think?
> Anyone have any thoughts on this?

I didn't imagine such construction. Since it comes to be simply changed
according to environment even if without rebuilding a kernel,
I think that it becomes easy to use LKCD for user.

Thank you for detailed explanation.

> 
> --Matt
> 

--Masashige



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