Re: [pbs-devel] [RFC proxmox-backup 0/3] Encode creation parameters into pxar archive

[Christian Ebner <c.ebner@proxmox.com>]

> On 06.03.2024 15:34 CET Gabriel Goller <g.goller@proxmox.com> wrote:
> 
>  
> To better debug the creation of the pxar archive, we encode the 
> creation_params (the parameters passed to the cli) inside the pxar
> archive. Like this we just need to locate the `.pxar_creation_params`
> file in the archive and we can check which arguments have been used. 
> 
> To realize this, we unify all the parameters of the `create_backup`
> function so that we don't need an additional struct (which in turn
> introduces additional maintenance efforts).
> 
> An example `.pxar_creation_params` file would look like this:
> 
>     {
>       "backupspec": [
>         "test.pxar:linux"
>       ],
>       "chunk-size": 4096,
>       "exclude": [
>         "MAINTAINERS"
>       ],
>       "skip-e2big-xattr": true
>     }
>

While this approach has already been used up until now for storing the
pxar cli exclude patterns, allowing to encode such metadata inside the
archive as regular file without having any means other than the filename
to find and distinguish this information from other files seems not
ideal to me.

Wouldn't it make sense to extend the pxar file format by a dedicated
entry type to store such information? And handle these entries in a
dedicated manner? E.g. by a `PXAR_CLI_PARAMS` entry header?

This would of course require an updated pxar format version 2, which we
might need anyways if the patches regarding metadata based change
detection should be applied.

Cheers,
Chris