[PATCH] base-files: add option to make /var persistent

[Stijn Tintel]

On 7/08/2021 10:05, Alberto Bursi wrote:
>
>
> On 07/08/21 02:46, Stijn Tintel wrote:
>> On 7/08/2021 02:56, Alberto Bursi wrote:
>>>
>>>
>>> On 06/08/21 21:27, Stijn Tintel wrote:
>>>> In OpenWrt, /var is symlinked to /tmp by default. This is done to 
>>>> reduce
>>>> the amount of writes to the flash chip, which often don't have the
>>>> greatest durability. As a result, things like DHCP or UPnP lease 
>>>> files,
>>>> are not persistent across reboots.
>>>>
>>>> Since OpenWrt can run on devices with more durable storage, it makes
>>>> sense to have an option for a persistent /var. Add an option to make
>>>> /var persistent. When enabled, /var will no longer be symlinked to 
>>>> /tmp,
>>>> but /var/run will be symlink to /tmp/run, as it should contain only
>>>> files that should not be kept during reboot. The option is off by
>>>> default, to maintain the current behaviour.
>>>>
>>>
>>> Since it does not really need to recompile anything, I think it
>>> can/should be handled as a package, not as a compile option.
>>>
>>> When you install the package these operations are executed, if you
>>> remove the package they are undone.
>>
>> Removing /var at runtime, which basically happens when you remove the
>> symlink, is very ugly and has a huge potential for breakage. Having it
>> as a build option also avoids users from accidentally installing it as a
>> package. If you disagree, please elaborate further, including measures
>> to avoid random breakage caused by removing /var at runtime.
>>
>
> My focus was more on "not using a compile option", I don't think it's 
> necessary to do this at runtime.
>
> A simple measure to avoid breakage would be to add something that runs 
> on boot (either initscript or preinitscript) to do these changes 
> before any other service that needs that folder is started.
> So you install the package and then reboot.
>
> This approach also allows to make this a permanent change (not an 
> optional package) and control this function with UCI config, just 
> change the setting and reboot.
>
> IMHO this is good enough for most users, and much better than having 
> to recompile or do the change manually.
>
>
> For the sake of completeness, (also shameless plug about my project):
> A more complex way to do it at runtime that avoids breakage is bind 
> mounting the original folder somewhere else so you can sync the 
> contents with the new/empty folder, then restarting all services that 
> need it.
> See
> https://github.com/bobafetthotmail/folder2ram/blob/master/debian_package/sbin/folder2ram#L658 
>
> (the service restart is not included in that script since it has no 
> way of knowing what services need the folders, this operation is left 
> to the user or for OpenMediaVault it's handled by the plugin that also 
> writes the configuration)
>

Appreciate the input. It still sounds overly complex compared to my 
suggestion, especially for something that most users will probably not 
use. I don't feel comfortable implementing something like that. I'll 
just keep using my patch locally then, as I have done for almost five years.

Thanks,
Stijn