Re: [OE-core] [PATCH] rng-tools: add systemd-udev-settle wants to service

[Claudius Heine <ch@denx.de>]

Hi Kyle,

On 2022-02-02 13:38, Kyle Russell wrote:
> Is this the correct approach?  Even the systemd-udev-settle.service man 
> pages recommends not using its service.  Were the kernel modules really 
> not loaded when rngd started?  Or is the original problem just a matter 
> of waiting for sufficient entropy?

IIRC, the rngd could not find any random source device node (/dev/hwrng 
in that case), so the service failed to start.

The patch you are commenting on only adds `Wants` weak dependency to 
make sure `systemd-udev-settle.service` is pulled in to the job queue, 
the `After` ordering rule was already there.

So changing this service file to be triggered by a udev event or maybe 
wrap it in a script, which makes sure the right modules are loaded and 
device nodes are available, could be an improvement, but it would be out 
of scope of this patch IMO.

regards,
Claudius

> 
> On Fri, Sep 17, 2021 at 4:08 AM Claudius Heine <ch@denx.de 
> <mailto:ch@denx.de>> wrote:
> 
>     rngd needs to start after `systemd-udev-settle` in order for the kernel
>     modules of the random source hardware to be loaded before it is started.
> 
>     However, since the `rngd.service` does not require or want
>     `systemd-udev-settle.service` it might not be scheduled for start and
>     the `After=systemd-udev-settle.service` there has no effect.
> 
>     Adding `Wants=systemd-udev-settle.service` provides a weak requirement
>     to it, so that the `rngd` is started after it, if possible.
> 
>     Signed-off-by: Claudius Heine <ch@denx.de <mailto:ch@denx.de>>
>     ---
> 
>     Hi,
> 
>     this is a fix, which should probably be backported to the maintained
>     releases.
> 
>     regards,
>     Claudius
> 
>       meta/recipes-support/rng-tools/rng-tools/rngd.service | 1 +
>       1 file changed, 1 insertion(+)
> 
>     diff --git a/meta/recipes-support/rng-tools/rng-tools/rngd.service
>     b/meta/recipes-support/rng-tools/rng-tools/rngd.service
>     index 0559b97991..568686e80e 100644
>     --- a/meta/recipes-support/rng-tools/rng-tools/rngd.service
>     +++ b/meta/recipes-support/rng-tools/rng-tools/rngd.service
>     @@ -3,6 +3,7 @@ Description=Hardware RNG Entropy Gatherer Daemon
>       DefaultDependencies=no
>       After=systemd-udev-settle.service
>       Before=sysinit.target shutdown.target
>     +Wants=systemd-udev-settle.service
>       Conflicts=shutdown.target
> 
>       [Service]
>     -- 
>     2.33.0
> 
> 
>     -=-=-=-=-=-=-=-=-=-=-=-
>     Links: You receive all messages sent to this group.
>     View/Reply Online (#156129):
>     https://lists.openembedded.org/g/openembedded-core/message/156129
>     <https://lists.openembedded.org/g/openembedded-core/message/156129>
>     Mute This Topic: https://lists.openembedded.org/mt/85671578/4454381
>     <https://lists.openembedded.org/mt/85671578/4454381>
>     Group Owner: openembedded-core+owner@lists.openembedded.org
>     <mailto:openembedded-core%2Bowner@lists.openembedded.org>
>     Unsubscribe:
>     https://lists.openembedded.org/g/openembedded-core/unsub
>     <https://lists.openembedded.org/g/openembedded-core/unsub>
>     [bkylerussell@gmail.com <mailto:bkylerussell@gmail.com>]
>     -=-=-=-=-=-=-=-=-=-=-=-
>