[systemd-devel] [PATCH] cryptsetup-generator: avoid ordering cycle on swap

[Tom Gundersen]

On Mon, Oct 17, 2011 at 4:24 PM, Lennart Poettering
<lennart at poettering.net> wrote:
> On Mon, 17.10.11 13:01, Tom Gundersen (teg at jklm.no) wrote:
>
>> Devices with random keys (swap), should not be ordered before local-fs.target,
>> as this creates a cycle with systemd-load-random-seed.service (and also it
>> does not make sense, a swap device is not a local-fs).
>
> Hmm, your patch makes some sense, but I believe we need to be careful
> here: we probably shouldn't try to boot up the machine without swap
> activated. Noawadays swap makes little sense unless you have a memory
> constrained system, and on those system it's probably quite important to
> activate swap before we begin with starting the full memory intensive
> snafu.

My understanding was that since dev-mapper-swap.device would only
appear after cryptsetup at swap.service has finished we have an implicit
ordering:

cryptsetup at swap.service -> dev-mapper-swap.device ->
dev-mapper-swap.swap -> swap.target

In case I got this wrong, let me know and I'll resubmit with
Before=swap.target for the swap devices.

> Could you rework the patch to order the activation of the crypto volumes
> before swap.target if they are to be sued for swapping? I think it would
> make a lot of sense to have all fs luks before local-fs.target still,
> and all swap luks before swap.target. I'll then merge the patch
> right-away.

If I understand correctly, one can use a random key to create a
temporary filesystem, so we cannot simply order all devices using a
random key before swap.target. However, if we order the swap devices
before swap.target and the tmp devices before local-fs.target, then
the latter will still have an ordering cycle. Come to think of it,
wouldn't any tmp device always end up in a cycle (following the same
reasoning as above)?

dev-mapper-tmp.device -> tmp.mount -> local-fs.target ->
systemd-random-seed-load.service -> cryptsetup at tmp.service

[where dev-mapper-tmp.device would only appear after
cryptsetup at tmp.service has finished].

Cheers,

-t