Re: [pbs-devel] [PATCH proxmox-backup v2] datastore: simplify update-datastore-cache socket command

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

On Mon, Aug 19, 2024 at 11:45:22AM GMT, Hannes Laimer wrote:
> ... by always dropping the cache entry and not allowing it to be
> re-added based on the maintenance mode. The check is only needed for

What "check are you referring to here?

> `Lookup` operations since lookups with those wouldn't fail based on
> maintenance mode alone. Already running tasks won't be affected and
> since they're the only ones holding a reference to a DataStore, it,
> and the file handles it holds will be dropped automatically once the
> (last) task finishes.
> 
> Signed-off-by: Hannes Laimer <h.laimer@proxmox.com>
> ---
> v2:
>  - rebase onto master
> 
>  pbs-datastore/src/datastore.rs  | 26 ++++++++++----------------
>  src/api2/config/datastore.rs    |  7 +++----
>  src/bin/proxmox-backup-proxy.rs |  6 +++---
>  3 files changed, 16 insertions(+), 23 deletions(-)
> 
> diff --git a/pbs-datastore/src/datastore.rs b/pbs-datastore/src/datastore.rs
> index d0f3c53a..69b4c83e 100644
> --- a/pbs-datastore/src/datastore.rs
> +++ b/pbs-datastore/src/datastore.rs
> @@ -183,10 +183,15 @@ impl DataStore {
>              )?)
>          };
>  
> +        let is_offline = config
> +            .get_maintenance_mode()
> +            .map_or(false, |m| m.is_offline());
>          let datastore = DataStore::with_store_and_config(chunk_store, config, Some(digest))?;
>  
>          let datastore = Arc::new(datastore);
> -        datastore_cache.insert(name.to_string(), datastore.clone());
> +        if !is_offline {
> +            datastore_cache.insert(name.to_string(), datastore.clone());
> +        }

So previously we always only ever had 1 DataStore+ChunkStore pair. Now,
we can have multiple instances for an offline data store, as well as
after receiving an "update-datastore-cache" command, which now forces
multiple instances.

This seems to go against the original idea here. Why do we want this?

>  
>          if let Some(operation) = operation {
>              update_active_operations(name, operation, 1)?;
> @@ -208,21 +213,10 @@ impl DataStore {
>          Ok(())
>      }
>  
> -    /// trigger clearing cache entry based on maintenance mode. Entry will only
> -    /// be cleared iff there is no other task running, if there is, the end of the
> -    /// last running task will trigger the clearing of the cache entry.
> -    pub fn update_datastore_cache(name: &str) -> Result<(), Error> {
> -        let (config, _digest) = pbs_config::datastore::config()?;
> -        let datastore: DataStoreConfig = config.lookup("datastore", name)?;
> -        if datastore
> -            .get_maintenance_mode()
> -            .map_or(false, |m| m.is_offline())
> -        {
> -            // the datastore drop handler does the checking if tasks are running and clears the
> -            // cache entry, so we just have to trigger it here
> -            let _ = DataStore::lookup_datastore(name, Some(Operation::Lookup));
> -        }
> -
> +    /// removes datastore from cache
> +    pub fn drop_from_datastore_cache(name: &str) -> Result<(), Error> {

There's no remaining error case here, so we wouldn't need a `Result`.

> +        let mut datastore_cache = DATASTORE_MAP.lock().unwrap();
> +        datastore_cache.remove(name);
>          Ok(())
>      }
>  
> diff --git a/src/api2/config/datastore.rs b/src/api2/config/datastore.rs
> index ca6edf05..65d88265 100644
> --- a/src/api2/config/datastore.rs
> +++ b/src/api2/config/datastore.rs
> @@ -396,16 +396,15 @@ pub fn update_datastore(
>          data.tuning = update.tuning;
>      }
>  
> -    let mut maintenance_mode_changed = false;
> +    let mut drop_store_from_cache = false;
>      if update.maintenance_mode.is_some() {
> -        maintenance_mode_changed = data.maintenance_mode != update.maintenance_mode;
> -
>          let maintenance_mode = match update.maintenance_mode {
>              Some(mode_str) => Some(MaintenanceMode::deserialize(
>                  proxmox_schema::de::SchemaDeserializer::new(mode_str, &MaintenanceMode::API_SCHEMA),
>              )?),
>              None => None,
>          };
> +        drop_store_from_cache = maintenance_mode.as_ref().map_or(false, |m| m.is_offline());

(This could be set in the `Some` match arm more efficiently as it
already defaults to false)

>          data.set_maintenance_mode(maintenance_mode)?;
>      }
>  
> @@ -420,7 +419,7 @@ pub fn update_datastore(
>      }
>  
>      // tell the proxy it might have to clear a cache entry

The comment is now wrong.

> -    if maintenance_mode_changed {
> +    if drop_store_from_cache {
>          tokio::spawn(async move {
>              if let Ok(proxy_pid) =
>                  proxmox_rest_server::read_pid(pbs_buildcfg::PROXMOX_BACKUP_PROXY_PID_FN)
> diff --git a/src/bin/proxmox-backup-proxy.rs b/src/bin/proxmox-backup-proxy.rs
> index 041f3aff..04622d43 100644
> --- a/src/bin/proxmox-backup-proxy.rs
> +++ b/src/bin/proxmox-backup-proxy.rs
> @@ -274,11 +274,11 @@ async fn run() -> Result<(), Error> {
>          Ok(Value::Null)
>      })?;
>  
> -    // clear cache entry for datastore that is in a specific maintenance mode
> +    // clear cache entry for datastore
>      command_sock.register_command("update-datastore-cache".to_string(), |value| {
>          if let Some(name) = value.and_then(Value::as_str) {
> -            if let Err(err) = DataStore::update_datastore_cache(name) {
> -                log::error!("could not trigger update datastore cache: {err}");
> +            if let Err(err) = DataStore::drop_from_datastore_cache(name) {
> +                log::error!("could not drop datastore from cache: {err}");
>              }
>          }
>          Ok(Value::Null)
> -- 
> 2.39.2


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