Re: [pbs-devel] [PATCH proxmox-backup v9 36/46] api/datastore: implement refresh endpoint for stores with s3 backend

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

On 7/21/25 4:16 PM, Hannes Laimer wrote:
> On Sat Jul 19, 2025 at 2:50 PM CEST, Christian Ebner wrote:
>> Allows to easily refresh the contents on the local cache store for
>> datastores backed by an S3 object store.
>>
>> In order to guarantee that no read or write operations are ongoing,
>> the store is first set into the maintenance mode `S3Refresh`. Objects
>> are then fetched into a temporary directory to avoid loosing contents
>> and consistency in case of an error. Once all objects have been
>> fetched, clears out existing contents and moves the newly fetched
>> contents in place.
>>
>> Signed-off-by: Christian Ebner <c.ebner@proxmox.com>
>> ---
>> changes since version 8:
>> - refactor s3 refresh into more compact methods
>> - drop un-necessary drop(_lock)
>> - use missing tokio::task::spawn_blocking context for blocking
>>    maintenance mode setting
>>
>>   pbs-datastore/src/datastore.rs | 175 +++++++++++++++++++++++++++++++++
>>   src/api2/admin/datastore.rs    |  34 +++++++
>>   2 files changed, 209 insertions(+)
>>
>> diff --git a/pbs-datastore/src/datastore.rs b/pbs-datastore/src/datastore.rs
>> index a524d7b32..b2af05eac 100644
>> --- a/pbs-datastore/src/datastore.rs
>> +++ b/pbs-datastore/src/datastore.rs
>> @@ -10,6 +10,7 @@ use anyhow::{bail, format_err, Context, Error};
>>   use http_body_util::BodyExt;
>>   use nix::unistd::{unlinkat, UnlinkatFlags};
>>   use pbs_tools::lru_cache::LruCache;
>> +use tokio::io::AsyncWriteExt;
>>   use tracing::{info, warn};
>>   
>>   use proxmox_human_byte::HumanByte;
>> @@ -2200,4 +2201,178 @@ impl DataStore {
>>       pub fn old_locking(&self) -> bool {
>>           *OLD_LOCKING
>>       }
>> +
>> +    /// Set the datastore's maintenance mode to `S3Refresh`, fetch from S3 object store, clear and
>> +    /// replace the local cache store contents. Once finished disable the maintenance mode again.
>> +    /// Returns with error for other datastore backends without setting the maintenance mode.
>> +    pub async fn s3_refresh(self: &Arc<Self>) -> Result<(), Error> {
>> +        match self.backend()? {
>> +            DatastoreBackend::Filesystem => bail!("store '{}' not backed by S3", self.name()),
>> +            DatastoreBackend::S3(s3_client) => {
>> +                let self_clone = Arc::clone(self);
>> +                tokio::task::spawn_blocking(move || {
>> +                    self_clone.maintenance_mode(Some(MaintenanceMode {
>> +                        ty: MaintenanceType::S3Refresh,
>> +                        message: None,
>> +                    }))
>> +                })
>> +                .await?
>> +                .context("failed to set maintenance mode")?;
> 
> I think we should hold the config lock, so it can't be changed while we
> refresh, no?

Yes, but that is handled by the method itself, also to limit lock scope.

See further below...

> 
>> +
>> +                let tmp_base = proxmox_sys::fs::make_tmp_dir(&self.base_path(), None)
>> +                    .context("failed to create temporary content folder in {store_base}")?;
>> +
>> +                self.fetch_tmp_contents(&tmp_base, &s3_client).await?;
>> +                self.move_tmp_contents_in_place(&tmp_base).await?;
>> +
>> +                let self_clone = Arc::clone(self);
>> +                tokio::task::spawn_blocking(move || self_clone.maintenance_mode(None))
>> +                    .await?
>> +                    .context("failed to clear maintenance mode")?;
>> +            }
>> +        }
>> +        Ok(())
>> +    }
>> +
>> +    // Set or clear the datastores maintenance mode by locking and updating the datastore config
>> +    fn maintenance_mode(&self, maintenance_mode: Option<MaintenanceMode>) -> Result<(), Error> {
>> +        let _lock = pbs_config::datastore::lock_config()?;

... here the config is locked and the scope limited by the method.

>> +        let (mut section_config, _digest) = pbs_config::datastore::config()?;
>> +        let mut datastore: DataStoreConfig = section_config.lookup("datastore", self.name())?;
>> +        datastore.set_maintenance_mode(maintenance_mode)?;
>> +        section_config.set_data(self.name(), "datastore", &datastore)?;
>> +        pbs_config::datastore::save_config(&section_config)?;
>> +        Ok(())
>> +    }
>> +
>> +    // Fetch the contents (metadata, no chunks) of the datastore from the S3 object store to the
>> +    // provided temporaray directory
>> +    async fn fetch_tmp_contents(&self, tmp_base: &Path, s3_client: &S3Client) -> Result<(), Error> {
>> +        let backup_user = pbs_config::backup_user().context("failed to get backup user")?;
>> +        let mode = nix::sys::stat::Mode::from_bits_truncate(0o0644);
>> +        let file_create_options = CreateOptions::new()
>> +            .perm(mode)
>> +            .owner(backup_user.uid)
>> +            .group(backup_user.gid);
>> +        let mode = nix::sys::stat::Mode::from_bits_truncate(0o0755);
>> +        let dir_create_options = CreateOptions::new()
>> +            .perm(mode)
>> +            .owner(backup_user.uid)
>> +            .group(backup_user.gid);
>> +
>> +        let list_prefix = S3PathPrefix::Some(S3_CONTENT_PREFIX.to_string());
>> +        let store_prefix = format!("{}/{S3_CONTENT_PREFIX}/", self.name());
>> +        let mut next_continuation_token: Option<String> = None;
>> +        loop {
>> +            let list_objects_result = s3_client
>> +                .list_objects_v2(&list_prefix, next_continuation_token.as_deref())
>> +                .await
>> +                .context("failed to list object")?;
>> +
>> +            let objects_to_fetch: Vec<S3ObjectKey> = list_objects_result
>> +                .contents
>> +                .into_iter()
>> +                .map(|item| item.key)
>> +                .collect();
>> +
>> +            for object_key in objects_to_fetch {
>> +                let object_path = format!("{object_key}");
>> +                let object_path = object_path.strip_prefix(&store_prefix).with_context(|| {
>> +                    format!("failed to strip store context prefix {store_prefix} for {object_key}")
>> +                })?;
>> +                if object_path.ends_with(NAMESPACE_MARKER_FILENAME) {
>> +                    continue;
>> +                }
>> +
>> +                info!("Fetching object {object_path}");
>> +
>> +                let file_path = tmp_base.join(object_path);
>> +                if let Some(parent) = file_path.parent() {
>> +                    proxmox_sys::fs::create_path(
>> +                        parent,
>> +                        Some(dir_create_options),
>> +                        Some(dir_create_options),
>> +                    )?;
>> +                }
>> +
>> +                let mut target_file = tokio::fs::OpenOptions::new()
>> +                    .write(true)
>> +                    .create(true)
>> +                    .truncate(true)
>> +                    .read(true)
>> +                    .open(&file_path)
>> +                    .await
>> +                    .with_context(|| format!("failed to create target file {file_path:?}"))?;
>> +
>> +                if let Some(response) = s3_client
>> +                    .get_object(object_key)
>> +                    .await
>> +                    .with_context(|| format!("failed to fetch object {object_path}"))?
>> +                {
>> +                    let data = response
>> +                        .content
>> +                        .collect()
>> +                        .await
>> +                        .context("failed to collect object contents")?;
>> +                    target_file
>> +                        .write_all(&data.to_bytes())
>> +                        .await
>> +                        .context("failed to write to target file")?;
>> +                    file_create_options
>> +                        .apply_to(&mut target_file, &file_path)
>> +                        .context("failed to set target file create options")?;
>> +                    target_file
>> +                        .flush()
>> +                        .await
>> +                        .context("failed to flush target file")?;
>> +                } else {
>> +                    bail!("failed to download {object_path}, not found");
>> +                }
>> +            }
>> +
>> +            if list_objects_result.is_truncated {
>> +                next_continuation_token = list_objects_result
>> +                    .next_continuation_token
>> +                    .as_ref()
>> +                    .cloned();
>> +                continue;
>> +            }
>> +            break;
>> +        }
>> +        Ok(())
>> +    }
>> +
>> +    // Fetch the contents (metadata, no chunks) of the datastore from the S3 object store to the
>> +    // provided temporaray directory
>> +    async fn move_tmp_contents_in_place(&self, tmp_base: &PathBuf) -> Result<(), Error> {
>> +        for ty in ["vm", "ct", "host", "ns"] {
>> +            let store_base_clone = self.base_path().clone();
>> +            let tmp_base_clone = tmp_base.clone();
>> +            tokio::task::spawn_blocking(move || {
>> +                let type_dir = store_base_clone.join(ty);
>> +                if let Err(err) = std::fs::remove_dir_all(&type_dir) {
>> +                    if err.kind() != io::ErrorKind::NotFound {
>> +                        return Err(err).with_context(|| {
>> +                            format!("failed to remove old contents in {type_dir:?}")
>> +                        });
>> +                    }
>> +                }
>> +                let tmp_type_dir = tmp_base_clone.join(ty);
>> +                if let Err(err) = std::fs::rename(&tmp_type_dir, &type_dir) {
>> +                    if err.kind() != io::ErrorKind::NotFound {
>> +                        return Err(err)
>> +                            .with_context(|| format!("failed to rename {tmp_type_dir:?}"));
>> +                    }
>> +                }
>> +                Ok::<(), Error>(())
>> +            })
>> +            .await?
>> +            .with_context(|| format!("failed to refresh {:?}", self.base_path()))?;
>> +        }
>> +
>> +        std::fs::remove_dir_all(&tmp_base)
>> +            .with_context(|| format!("failed to cleanup temporary content in {tmp_base:?}"))?;
>> +
>> +        Ok(())
>> +    }
>>   }
>> diff --git a/src/api2/admin/datastore.rs b/src/api2/admin/datastore.rs
>> index 87a8641bd..23b216bef 100644
>> --- a/src/api2/admin/datastore.rs
>> +++ b/src/api2/admin/datastore.rs
>> @@ -2707,6 +2707,39 @@ pub async fn unmount(store: String, rpcenv: &mut dyn RpcEnvironment) -> Result<V
>>       Ok(json!(upid))
>>   }
>>   
>> +#[api(
>> +    protected: true,
>> +    input: {
>> +        properties: {
>> +            store: {
>> +                schema: DATASTORE_SCHEMA,
>> +            },
>> +        }
>> +    },
>> +    returns: {
>> +        schema: UPID_SCHEMA,
>> +    },
>> +    access: {
>> +        permission: &Permission::Privilege(&["datastore", "{store}"], PRIV_DATASTORE_MODIFY, false),
>> +    },
>> +)]
>> +/// Refresh datastore contents from S3 to local cache store.
>> +pub async fn s3_refresh(store: String, rpcenv: &mut dyn RpcEnvironment) -> Result<Value, Error> {
>> +    let datastore = DataStore::lookup_datastore(&store, Some(Operation::Lookup))?;
>> +    let auth_id: Authid = rpcenv.get_auth_id().unwrap().parse()?;
>> +    let to_stdout = rpcenv.env_type() == RpcEnvironmentType::CLI;
>> +
>> +    let upid = WorkerTask::spawn(
>> +        "s3-refresh",
>> +        Some(store),
>> +        auth_id.to_string(),
>> +        to_stdout,
>> +        move |_worker| async move { datastore.s3_refresh().await },
>> +    )?;
>> +
>> +    Ok(json!(upid))
>> +}
>> +
>>   #[sortable]
>>   const DATASTORE_INFO_SUBDIRS: SubdirMap = &[
>>       (
>> @@ -2773,6 +2806,7 @@ const DATASTORE_INFO_SUBDIRS: SubdirMap = &[
>>           &Router::new().download(&API_METHOD_PXAR_FILE_DOWNLOAD),
>>       ),
>>       ("rrd", &Router::new().get(&API_METHOD_GET_RRD_STATS)),
>> +    ("s3-refresh", &Router::new().put(&API_METHOD_S3_REFRESH)),
>>       (
>>           "snapshots",
>>           &Router::new()
> 
> 
> 
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