Reserve space for crypt metadata on data tier for online reencryption…

… in the future

src/engine/strat_engine/backstore/backstore/v2.rs

@@ -166,17 +166,14 @@ impl InternalBackstore for Backstore {
     }
 
     fn datatier_usable_size(&self) -> Sectors {
-        self.data_tier.usable_size()
-            - if self.encryption_info.is_some() {
-                crypt_metadata_size().sectors()
-            } else {
-                Sectors(0)
-            }
+        self.data_tier.usable_size() - crypt_metadata_size().sectors()
     }
 
     fn available_in_backstore(&self) -> Sectors {
         self.data_tier.usable_size()
             - self.next
+            // This subtraction needs to be maintained because for encrypted devices, next is 0
+            // while it is set to after the crypt metadata size for unencrypted devices.
             - if self.encryption_info.is_some() {
                 crypt_metadata_size().sectors()
             } else {
@@ -388,12 +385,15 @@ impl Backstore {
         let mut data_tier = DataTier::<StratBlockDev>::new(
             BlockDevMgr::<StratBlockDev>::initialize(pool_uuid, devices, mda_data_size)?,
         );
-        if encryption_info.is_some() {
-            let request = data_tier.alloc_request(&[crypt_metadata_size().sectors()])?.ok_or_else(|| {
-                StratisError::Msg("There was not enough space on the device to satisfy the allocation request".to_string())
+        let request = data_tier
+            .alloc_request(&[crypt_metadata_size().sectors()])?
+            .ok_or_else(|| {
+                StratisError::Msg(
+                    "There was not enough space on the device to satisfy the allocation request"
+                        .to_string(),
+                )
             })?;
-            data_tier.alloc_commit(request)?;
-        }
+        data_tier.alloc_commit(request)?;
 
         Ok(Backstore {
             data_tier,
@@ -403,7 +403,11 @@ impl Backstore {
             cap_linear: None,
             handle: None,
             encryption_info: encryption_info.cloned(),
-            next: Sectors(0),
+            next: if encryption_info.is_some() {
+                Sectors(0)
+            } else {
+                crypt_metadata_size().sectors()
+            },
         })
     }