Thanks, Claudius.
On Wed, Feb 2, 2022 at 8:08 AM Claudius Heine <
ch@denx.de> wrote:
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.
If /dev/hwrng didn't exist, this feels like the original problem was a misconfigured
kernel or module that wasn't being loaded properly.
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.
Correct. Just because an `After` exists does not mean the service gets pulled into
the job queue, so prior to this change no other service was causing the deprecated
systemd-udev-settle.service to be run during boot. But now, every device including
openssh (which has a default PACKAGECONFIG option for rng-tools) now depends
on this deprecated service, which may cause unexpected boot delays.
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.
I'm more curious whether this change should be reverted from upstream. It seems
like a drop-in file could have been applied to your distro instead of adding a dependency
on a deprecated service for all openssh users.
Kyle
>
> 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
>
>
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