[PATCH proxmox-backup v2 2/3] api: datastore: add option to run garbage collection before unmount

[Hannes Laimer <h.laimer@proxmox.com>]

Removable datastores set up for auto-unmount have no natural point at
which to run garbage collection, since the drive is unmounted right
after jobs finish. Expose a gc-on-unmount option so GC can be triggered
as part of the unmount for those setups.

Relies on the active write operation by garbage collection to block
the unmount task until GC completes (among possible other active
operations). No other active operation can occur in the meantime
since the datastore remains in 'unmount' maintenance mode.

Signed-off-by: Hannes Laimer <h.laimer@proxmox.com>
---
 src/api2/admin/datastore.rs  | 23 ++++++++++++++++++++---
 src/api2/config/datastore.rs |  9 +++++++++
 2 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/src/api2/admin/datastore.rs b/src/api2/admin/datastore.rs
index 757b3114..212a48da 100644
--- a/src/api2/admin/datastore.rs
+++ b/src/api2/admin/datastore.rs
@@ -2641,9 +2641,8 @@ fn do_unmount_device(
 }
 
 async fn do_unmount(store: String, auth_id: Authid, to_stdout: bool) -> Result<Value, Error> {
-    let _lock = pbs_config::datastore::lock_config()?;
-    let (mut section_config, _digest) = pbs_config::datastore::config()?;
-    let mut datastore: DataStoreConfig = section_config.lookup("datastore", &store)?;
+    let (section_config, _digest) = pbs_config::datastore::config()?;
+    let datastore: DataStoreConfig = section_config.lookup("datastore", &store)?;
 
     if datastore.backing_device.is_none() {
         bail!("datastore '{store}' is not removable");
@@ -2651,6 +2650,24 @@ async fn do_unmount(store: String, auth_id: Authid, to_stdout: bool) -> Result<V
 
     ensure_datastore_is_mounted(&datastore)?;
 
+    // Setting gc-on-unmount requires Datastore.Modify (or Datastore.Allocate at creation), the
+    // same level needed to start GC directly, so no privilege escalation from triggering it here.
+    if datastore.gc_on_unmount.unwrap_or(false) {
+        let client = crate::client_helpers::connect_to_localhost()
+            .context("failed to connect to localhost for starting GC")?;
+        match client
+            .post(&format!("api2/json/admin/datastore/{store}/gc"), None)
+            .await
+        {
+            Ok(_) => info!("started garbage collection, unmount will wait for it to finish"),
+            Err(err) => warn!("unable to start garbage collection before unmount: {err}"),
+        }
+    }
+
+    let _lock = pbs_config::datastore::lock_config()?;
+    let (mut section_config, _digest) = pbs_config::datastore::config()?;
+    let mut datastore: DataStoreConfig = section_config.lookup("datastore", &store)?;
+
     datastore.set_maintenance_mode(Some(MaintenanceMode {
         ty: MaintenanceType::Unmount,
         message: None,
diff --git a/src/api2/config/datastore.rs b/src/api2/config/datastore.rs
index c44d50d1..c0be0296 100644
--- a/src/api2/config/datastore.rs
+++ b/src/api2/config/datastore.rs
@@ -409,6 +409,8 @@ pub enum DeletableProperty {
     Comment,
     /// Delete the garbage collection schedule.
     GcSchedule,
+    /// Delete the gc-on-unmount property.
+    GcOnUnmount,
     /// Delete the prune job schedule.
     PruneSchedule,
     /// Delete the keep-last property
@@ -495,6 +497,9 @@ pub fn update_datastore(
                 DeletableProperty::GcSchedule => {
                     data.gc_schedule = None;
                 }
+                DeletableProperty::GcOnUnmount => {
+                    data.gc_on_unmount = None;
+                }
                 DeletableProperty::PruneSchedule => {
                     data.prune_schedule = None;
                 }
@@ -560,6 +565,10 @@ pub fn update_datastore(
         data.gc_schedule = update.gc_schedule;
     }
 
+    if update.gc_on_unmount.is_some() {
+        data.gc_on_unmount = update.gc_on_unmount;
+    }
+
     macro_rules! prune_disabled {
         ($(($param:literal, $($member:tt)+)),+) => {
             $(
-- 
2.47.3