linux-kernel - Re: semi-regular plea for stable device mapping

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Message-ID: <477BD9DA.8030403@tmr.com>
Date:	Wed, 02 Jan 2008 13:37:14 -0500
From:	Bill Davidsen <davidsen@....com>
To:	Jan Engelhardt <jengelh@...putergmbh.de>
CC:	Gene Heskett <gene.heskett@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: semi-regular plea for stable device mapping

Jan Engelhardt wrote:
> On Jan 1 2008 10:54, Gene Heskett wrote:
>> BUT!  This defeats a fix I've had in my modprobe.conf for over a year now that 
>> gave the LVM stuff a stable major device # of 238, and now my LVM major is 
>> back to whatever mood the kernel is in, in this particular bootup case to 
>> #253.
>>
>> It may now be stable for a bit at that number because I see that pktcdvd has 
>> been given a stable address of its own, apparently with a major of 10.  That 
>> was the wedgie that fscked things up originally for me.  But what else lurks 
>> in the deep end of this experimental pool, to play piranna with us again when 
>> we least expect it?
> 
> Why exactly would you require a fixed major - not running udev or thelike?
> Use the boot parameter, dm_mod.major=238.
> 
What? And what happens when that gets used for something else? And if 
you say "we'll avoid using that" then you are treating it as a fixed 
value anyway.

>> This drives tar up a wall because it uses this device number as part of the 
>> file comparisons it does, and it thinks everything is therefore new and needs 
>> a full level 0 backup.  This is not at all practical, and requires that 
> 
> I wonder how FreeBSD gets around this, because they've got dynamic numbers
> everywhere.

Did they? I haven't tried using tar in the appropriate ways on BSD to 
see if it behaves in the same way. Of course on a system which doesn't 
change between backups I guess the dynamic number would be the same in 
any case.

-- 
Bill Davidsen <davidsen@....com>
   "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot
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