Re: [gentoo-user] activating swap by udev event

[Albert Hopkins <marduk@letterboxes.org>]

On Thu, 2010-07-01 at 18:06 +0200, Nils Larsson wrote:
> tor 2010-07-01 klockan 08:49 -0700 skrev Bill Longman:
> > On 07/01/2010 08:44 AM, SpaceCake wrote:
> > > So, it solves the first problem, identifiying the device, but how can I
> > > tell to udev to use always /dev/sds (for example) for this device?
> 
> You need to have the udev rule or the script that it runs look at
> something specific(the swaplabel for instance).
> 
> > > I'm thinking how can I instruct udev to turn off swap when the device is
> > > removed, but this is another story :)
> 
> I tried doing exactly what you're doing now awhile ago and this is where
> I got stuck, swapoff needs the deivce node(path) to still exist, it
> can't disable swap without it. I could never get swapoff to run before
> udev removed the device node, so I ended up with the system thinking(or
> at least reporting) that it had loads more swap than it actually did.

This is a bad thing to do.  If you have pages swapped out to the device
and you remove the device before putting those pages elsewhere then you
have effectively hosed your system.  If it doesn't fail immediately then
as soon as the kernel tries to swap in those pages and finds out the
device it's on can't be accessed then you are in for a world of pain.

I guess the deeper question (although entirely rhetorical AFAIC) is why
would someone want to swap out to a removable device?