[PATCH proxmox-backup v2 12/14] api: admin: add endpoint to fetch fine-grained datastore usage stats

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

Provides the endpoint to read the per-namespace/group/snapshot usage
statistics as persisted during the last garbage collection run.

Signed-off-by: Christian Ebner <c.ebner@proxmox.com>
---
 pbs-datastore/src/datastore.rs | 13 ++++++++++++-
 src/api2/admin/datastore.rs    | 35 +++++++++++++++++++++++++++++++---
 2 files changed, 44 insertions(+), 4 deletions(-)

diff --git a/pbs-datastore/src/datastore.rs b/pbs-datastore/src/datastore.rs
index f568ea2b3..a35b3721f 100644
--- a/pbs-datastore/src/datastore.rs
+++ b/pbs-datastore/src/datastore.rs
@@ -24,7 +24,7 @@ use proxmox_s3_client::{
 use proxmox_schema::ApiType;
 
 use proxmox_sys::error::SysError;
-use proxmox_sys::fs::{CreateOptions, file_read_optional_string, replace_file};
+use proxmox_sys::fs::{CreateOptions, file_get_contents, file_read_optional_string, replace_file};
 use proxmox_sys::linux::procfs::MountInfo;
 use proxmox_sys::process_locker::{ProcessLockExclusiveGuard, ProcessLockSharedGuard};
 use proxmox_time::{TimeSpan, epoch_i64};
@@ -3546,6 +3546,17 @@ impl DataStore {
         replace_file(&path, &contents, CreateOptions::new(), true)?;
         Ok(())
     }
+
+    pub fn read_statistics(&self) -> Result<Vec<StatisticsListItem>, Error> {
+        let path = self.base_path().join(DATASTORE_STATISTICS_FILENAME);
+        if !path.exists() {
+            // no statistics generated yet
+            return Ok(Vec::new());
+        }
+        let contents = file_get_contents(&path)?;
+        let list = serde_json::from_slice(&contents)?;
+        Ok(list)
+    }
 }
 
 /// Track S3 object keys to be deleted by garbage collection while holding their file lock.
diff --git a/src/api2/admin/datastore.rs b/src/api2/admin/datastore.rs
index 3367fb2c1..b111af5fa 100644
--- a/src/api2/admin/datastore.rs
+++ b/src/api2/admin/datastore.rs
@@ -44,9 +44,10 @@ use pbs_api_types::{
     IGNORE_VERIFIED_BACKUPS_SCHEMA, JobScheduleStatus, KeepOptions, MAX_NAMESPACE_DEPTH,
     MaintenanceMode, MaintenanceType, NS_MAX_DEPTH_SCHEMA, Operation, PRIV_DATASTORE_AUDIT,
     PRIV_DATASTORE_BACKUP, PRIV_DATASTORE_MODIFY, PRIV_DATASTORE_PRUNE, PRIV_DATASTORE_READ,
-    PRIV_DATASTORE_VERIFY, PRIV_SYS_MODIFY, PruneJobOptions, SnapshotListItem, SyncJobConfig, UPID,
-    UPID_SCHEMA, VERIFICATION_OUTDATED_AFTER_SCHEMA, VERIFY_JOB_READ_THREADS_SCHEMA,
-    VERIFY_JOB_VERIFY_THREADS_SCHEMA, print_ns_and_snapshot, print_store_and_ns,
+    PRIV_DATASTORE_VERIFY, PRIV_SYS_MODIFY, PruneJobOptions, SnapshotListItem, StatisticsListItem,
+    SyncJobConfig, UPID, UPID_SCHEMA, VERIFICATION_OUTDATED_AFTER_SCHEMA,
+    VERIFY_JOB_READ_THREADS_SCHEMA, VERIFY_JOB_VERIFY_THREADS_SCHEMA, print_ns_and_snapshot,
+    print_store_and_ns,
 };
 use pbs_client::pxar::{create_tar, create_zip};
 use pbs_config::CachedUserInfo;
@@ -523,6 +524,30 @@ pub async fn list_snapshots(
     .map_err(|err| format_err!("failed to await blocking task: {err}"))?
 }
 
+#[api(
+    input: {
+        properties: {
+            store: { schema: DATASTORE_SCHEMA },
+        },
+    },
+    access: {
+        permission: &Permission::Privilege(&["datastore", "{store}"], PRIV_DATASTORE_AUDIT, false),
+    },
+    returns: pbs_api_types::ADMIN_DATASTORE_LIST_STATISTICS_RETURN_TYPE,
+)]
+/// List backup usage statistics.
+pub fn list_statistics(
+    store: String,
+    _info: &ApiMethod,
+    _rpcenv: &mut dyn RpcEnvironment,
+) -> Result<Vec<StatisticsListItem>, Error> {
+    let datastore = DataStore::lookup_datastore(lookup_with(&store, Operation::Read))?;
+    let stats = datastore
+        .read_statistics()
+        .map_err(|err| format_err!("failed to read statistics: {err}"))?;
+    Ok(stats)
+}
+
 fn get_group_owner(
     store: &str,
     ns: &BackupNamespace,
@@ -2984,6 +3009,10 @@ const DATASTORE_INFO_SUBDIRS: SubdirMap = &[
             .get(&API_METHOD_LIST_GROUPS)
             .delete(&API_METHOD_DELETE_GROUP),
     ),
+    (
+        "list-statistics",
+        &Router::new().get(&API_METHOD_LIST_STATISTICS),
+    ),
     ("mount", &Router::new().post(&API_METHOD_MOUNT)),
     ("move-group", &Router::new().post(&API_METHOD_MOVE_GROUP)),
     (
-- 
2.47.3