linux-kernel - Re: add devname module aliases to allow module on-demand auto-loading

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Message-Id: <201005211909.29326.knikanth@suse.de>
Date:	Fri, 21 May 2010 19:09:28 +0530
From:	Nikanth Karthikesan <knikanth@...e.de>
To:	Kay Sievers <kay.sievers@...y.org>
Cc:	Alasdair G Kergon <agk@...hat.com>,
	"linux-kernel" <linux-kernel@...r.kernel.org>,
	"Greg Kroah-Hartman" <gregkh@...e.de>,
	"David S. Miller" <davem@...emloft.net>,
	Miklos Szeredi <miklos@...redi.hu>,
	Chris Mason <chris.mason@...cle.com>,
	Tigran Aivazian <tigran@...azian.fsnet.co.uk>,
	Ian Kent <raven@...maw.net>
Subject: Re: add devname module aliases to allow module on-demand auto-loading

On Friday 21 May 2010 18:41:38 Kay Sievers wrote:
> On Fri, May 21, 2010 at 13:51, Kay Sievers <kay.sievers@...y.org> wrote:
> > On Fri, May 21, 2010 at 13:34, Alasdair G Kergon <agk@...hat.com> wrote:
> >
> > There is no harm to make a well-know device node static, it just
> > solves a lot of problems, and also makes it possible to work off of a
> > static /dev.
> 
> To illustrate:
> 
> On my box without this patch:
>   dmsetup version
>   Library version:   1.02.42 (2010-01-14)
>   /proc/misc: No entry for device-mapper found
>   Is device-mapper driver missing from kernel?
>   Failure to communicate with kernel device-mapper driver.
> 
> And the same box just with this patch, nothing else changed:
>   dmsetup version
>   Library version:   1.02.42 (2010-01-14)
>   Driver version:    4.17.0
> 
> But its up to you to care if device-mapper just works, or if there is
> stuff like an init script with modprobe needed to load stuff that
> might never be needed. :)
>

If this is needed, the dmsetup itself can do a `modprobe dm` instead of 
printing the message, "Is device-mapper driver missing from kernel?"?

> This is surely not about dynamic vs. static, it is about race-free
> on-demand activation of services and subsystems.
> 

Loading dm-mod alone is enough for `dmsetup version`. But for other operations 
dm-mod may not be enough, as various other modules like dm-crypt, dm-
mirror,... would also be required, depending on the dm table, which may or may 
not be installed.

Thanks
Nikanth

> Thanks,
> Kay
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