Re: [pbs-devel] [PATCH proxmox v2 1/4] log: rename/move init functions

[Wolfgang Bumiller <w.bumiller@proxmox.com>]

On Mon, Feb 17, 2025 at 04:21:19PM +0100, Gabriel Goller wrote:
> > > > > <snip>
> > > > >
> > > > > I cooked up a simple builder type thingy to build layers:
> > > > >
> > > > >
> > > > >     struct LogBuilder {
> > > > >         global_log_level: LevelFilter,
> > > > >         layer: Vec<
> > > > >             Box<dyn tracing_subscriber::Layer<tracing_subscriber::Registry> + Send + Sync + 'static>,
> > > > >         >,
> > > > >     }
> > > > >
> > > > >
> > > > > And the implementation:
> > > > >
> > > > >     impl LogBuilder {
> > > > >         pub fn from_env(env_var: &str, default_log_level: LevelFilter) -> LogBuilder {
> > > > >             let log_level = get_env_variable(env_var, default_log_level);
> > > > >             LogBuilder {
> > > > >                 global_log_level: log_level,
> > > > >                 layer: vec![],
> > > > >             }
> > > > >         }
> > > > >
> > > > >         pub fn journald_or_stderr(mut self) -> LogBuilder {
> > > > >             self.layer.push(
> > > > >                 journald_or_stderr_layer()
> > > > >                     .with_filter(self.global_log_level)
> > > > >                     .boxed(),
> > > > >             );
> > > > >             self
> > > > >         }
> > > > >
> > > > >         pub fn journald_or_stderr_on_logcontext_and_error(mut self) -> LogBuilder {
> > > > >             self.layer.push(
> > > > >                 journald_or_stderr_layer()
> > > > >                     .with_filter(filter_fn(|metadata| {
> > > > >                         !LogContext::exists() || *metadata.level() == Level::ERROR
> > > > >                     }))
> > > > >                     .with_filter(self.global_log_level)
> > > > >                     .boxed(),
> > > > >             );
> > > > >             self
> > > > >         }
> > > > >
> > > > >         //...
> > > > >
> > > > >         pub fn init(self) -> Result<(), anyhow::Error> {
> > > > >             let registry = tracing_subscriber::registry().with(self.layer);
> > > > >             tracing::subscriber::set_global_default(registry)?;
> > > > >
> > > > >             LogTracer::init_with_filter(self.global_log_level.as_log())?;
> > > > >             Ok(())
> > > > >         }
> > > > >     }
> > > > >
> > > > > We could place this in a new builder module and then have the
> > > > > product-specific functions (e.g. init_pve_log, init_perlmod_log,
> > > > > init_pbs_log, etc.) in the init module.
> > > > >
> > > > > What do you think?
> > > >
> > > > Hmmm...
> > > > Those names are a bit long, and still as specific as before, so I'm not
> > > > sure we win a lot either way.
> > > >
> > > > I'm wondering - if we really have so many specific cases - do we really
> > > > need them implemented in this crate, rather than where they are used?
> > > > How many different types of logging layers do we have and where atm?
> > > 
> > > We currently have:
> > >  1) journald (with stderr fallback)
> > 
> > => builder.journald_logging()
> > 
> > (the fallback could just be implied, or do we ever not want that?)
> 
> true, I don't think we want to fail anywhere if there is no journald
> anyway.
> 
> > >  2) stderr
> > 
> > => builder.stderr_logging()
> > 
> > >  3) stderr (with pve formatting)
> > 
> > => builder.pve_logging() (#[cfg(feature = "pve")]?)
> 
> Maybe stderr_pve_logging? I'd like to mention 'stderr' somewhere in the
> case we add some different pve-format logging (e.g. pve-tasklog).

Sounds good.

> 
> > >  4) pbs tasklog
> > ^ I assume (4) is the "tasklog-or-journald" case?
> > Not sure where (1) is really the right choice.
> > 
> > Does (4) exist anywhere other than in the API daemons?
> > 
> > => builder.task_logging()
> > 
> > (the journal-if-not-in-task part could be implied - or do we ever need
> > to combine the tasklog part differently?)
> 
> Yes, in the proxmox-backup-manager. There we use stderr for all the
> normal logs and the tasklogger for when we a task is started.

(I think this could be considered a special case, but if its case is
covered by the builder that's fine.)

> 
> > > But the problem is we have different combinations and filters as well:
> > > journald and stderr (perlmod), stderr and pbs tasklog (but only when we
> > > are in a tasklog or when the level is error) (pbs-client), etc.
> > 
> > ^ Why is "pbs-client" the example here? IMO this sounds like the API
> > daemons. The pbs-client *CLI* tool certainly should just log to stderr,
> > and the "crate" otherwise doesn't decide this.
> 
> Oops, my bad I meant the proxmox-backup-manager.
> 
> > > The logging gets initiated in:
> > 
> > (list below is reordered)
> > 
> > >  * pbs proxy daemon
> > >  * pbs api daemon
> > 
> > ^ API daemons - so those are case (4) - are they different from one
> > another?
> 
> Nope, this is case 4. (To be exact case 1 + 4, journald + tasklog.)
> Also you need to add filters here, this isn't just a "print everything
> to journald", we only print to journald when the level is error or we
> are *not* in a tasklog.

I did say 4 ;-)
But okay, the filters are annoying.

> 
> > >  * pbs proxmox-file-restore
> > 
> > ^ The VM side? Not sure what it needs, but seems special-enough to have
> > its own code, unless we just log to the journal anyway
> 
> As far as I remember this one should print to stderr only. (This is
> wrong in this patch.)
> 
> > >  * pbs tape pmt
> > >  * pbs tape pmtx
> > >  * pbs client
> > >  * pbs pxar
> > >  * pbs proxmox-backup-debug
> > >  * pbs proxmox-backup-manager
> > >  * pbs proxmox-backup-tape
> > >  * pbs sg-tape-cmd
> > 
> > ^ IIRC all of these are CLI tools and should therefore all be case (2) -
> > although I don't know about how the tape stuff works.
> > If they do anything else, it would be good to know why and have this
> > documented either in proxmox-log or in their logging-init functions.
> 
> All except the proxmox-backup-manager as far as I can see, because that
> one starts pbs tasks directly.
> 
> > >  * pbs proxmox-daily-update
> > 
> > The 'daily-update' may be a special case and could use the journal
> > directly, but may as well be stderr->journald via its `.service`.
> > But, yeah, obviously it would make actual tracing/debugging easier with
> > a proper journald-logger here. So another user of case (1).
> 
> Agree.
> 
> > >  * perlmod
> > ^ For the lack of a better place (as pve, pmg and nftables code probably
> > all want to share it), having this as a special function in proxmox-log
> > makes some sense I suppose (but could be feature-guarded).
> 
> There is already a shared common::init_logger function in perlmod I think.

I don't think the nft firewall code (and potential additional new
rust-only things we might add in the future) can access this. We have a
`proxmox-ve-rs.git` now, but that one won't be used by *pmg*.
Anyway, that part is for later.

> 
> > > Exposing the builder directly without any helper functions would be fine
> > > as well I reckon. The downside is that the initiation gets more
> > > "complicated", e.g. (the pbs daemon):
> > > 
> > >     LogBuilder::from_env("PBS_LOG", LevelFilter::INFO)
> > >         .journald_on_no_tasklog_or_error()
> > >         .tasklog().init()?;
> > 
> > So yes this is probably okay to have, but I really don't think we need
> > these huge names - like I said, it doesn't make sense to me that
> > `.tasklog()` should be combined with anything other than this exact one
> > other thing anyway, so the middle line there could just be left out IMO.
> 
> See above.
> Also either we use a helper function which does everything for us (e.g.
> init_perlmod_logger, init_journald_and_tasklog) or we use the builder
> where we *need* to mention every layer separately. Otherwise you have different
> builder functions, some which add a single layer and others that add
> multiple layers + magic (which IMO is a mess).

Yeah. I suppose we can proceed with the builder.
It might be good to have the 4 types above summarised in the builder
type's doc comments.

As for a builder *module* (which you mentioned in an earlier mail) - I
*think* API-wise, the builder type itself could very well live (as in be
re-exported) at the top level, but implementation wise it could be in
its own module for sure, if it makes the code more tidy/organized in
your opinion.


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