Re: [OE-core][PATCH] rng-tools: Replace obsolete "wants systemd-udev-settle"

[Claudius Heine <ch@denx.de>]

Hi Drew,

On 2022-08-01 20:44, Drew Moseley wrote:
> On 7/26/22 9:17 AM, drew.moseley@gmail.com wrote:
> 
>> From: Drew Moseley <drew@moseleynet.net>
>>
>> The systemd-udev-settle service is listed as obsolete and does in
>> some cases result in a significant boot time.  Replace that with
>> "after systemd-modules-load" to allow the random source hardware
>> to be loaded in the proper sequence.
>>
>> Before this change:
>>
>>     Startup finished in 4.025s (kernel) + 2min 13.236s (userspace) = 
>> 2min 17.262s
>>     multi-user.target reached after 2min 8.153s in userspace
>>
>> After this change:
>>
>>     Startup finished in 3.956s (kernel) + 13.294s (userspace) = 17.250s
>>     multi-user.target reached after 9.522s in userspace
>>
>> Signed-off-by: Drew Moseley <drew@moseleynet.net>
>> ---
>>   meta/recipes-support/rng-tools/rng-tools/rngd.service | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/meta/recipes-support/rng-tools/rng-tools/rngd.service 
>> b/meta/recipes-support/rng-tools/rng-tools/rngd.service
>> index 568686e80e..e818cfcf78 100644
>> --- a/meta/recipes-support/rng-tools/rng-tools/rngd.service
>> +++ b/meta/recipes-support/rng-tools/rng-tools/rngd.service
>> @@ -3,7 +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
>> +After=systemd-modules-load.service
>>   Conflicts=shutdown.target
>>   [Service]
> 
> 
> Hi Khem, Claudius,
> 
> Any thoughts on this change? Obviously I cannot verify if the original 
> hardware combination issue is resolved and unfortunately it sounds like 
> you cannot either but I'm using this successfully to work around the 
> delayed boots I was seeing here.

Well as I said, `systemd-modules-load.service` just waits until all 
statically configured modules are loaded, however not until the 
`/dev/hwrng` device node is available. `systemd-udev-settle.service` 
waits until all udev rules are applied, and that means it includes 
loading of all dynamically loaded modules as well as executing code that 
creates symlinks, etc.

Instead of waiting for modules to be loaded, that might be unrelated or 
waiting for all (mostly unrelated) udev rules to be settled, I think 
waiting directly for the `/dev/hwrng` device node might be more explicit 
and specific.

regards,
Claudius