[PATCH proxmox-backup 4/9] datastore: fix inconsistent implementation of index_size method

[Robert Obkircher <r.obkircher@proxmox.com>]

Return the file size of fixed index files, just like for dynamic ones.
Previously, the size of the referenced backup contents was returned,
which is still available via the index_bytes method.

The impact of this change should be fairly small, as this only seems
to be used by "proxmox-backup-debug inspect file". The original
intention was probably to show the file size there, because it also
does that for blobs.

Fixes: f0d23e537 ("add ctime and size function to IndexFile trait")
Signed-off-by: Robert Obkircher <r.obkircher@proxmox.com>
---
 pbs-datastore/src/fixed_index.rs | 4 ++--
 pbs-datastore/src/index.rs       | 5 +++++
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/pbs-datastore/src/fixed_index.rs b/pbs-datastore/src/fixed_index.rs
index 8104cbe72..0145f93d3 100644
--- a/pbs-datastore/src/fixed_index.rs
+++ b/pbs-datastore/src/fixed_index.rs
@@ -187,7 +187,7 @@ impl IndexFile for FixedIndexReader {
     }
 
     fn index_size(&self) -> usize {
-        self.size as usize
+        size_of::<FixedIndexHeader>() + self.index_length * 32
     }
 
     fn compute_csum(&self) -> ([u8; 32], u64) {
@@ -658,7 +658,7 @@ mod tests {
         fs::write(&path, &data).unwrap();
         let reader = FixedIndexReader::open(&path).unwrap();
         assert_eq!(reader.index_bytes(), size);
-        assert_eq!(reader.index_size(), size as usize);
+        assert_eq!(reader.index_size(), 4096 + 64);
         assert_eq!(reader.chunk_size, chunk_size as usize);
         assert_eq!(reader.index_count(), 2);
         assert_eq!(
diff --git a/pbs-datastore/src/index.rs b/pbs-datastore/src/index.rs
index b5d20ad91..4c0e9aefb 100644
--- a/pbs-datastore/src/index.rs
+++ b/pbs-datastore/src/index.rs
@@ -20,9 +20,14 @@ impl ChunkReadInfo {
 pub trait IndexFile {
     fn index_count(&self) -> usize;
     fn index_digest(&self, pos: usize) -> Option<&[u8; 32]>;
+
+    /// The total size of the referenced backup content.
     fn index_bytes(&self) -> u64;
+
     fn chunk_info(&self, pos: usize) -> Option<ChunkReadInfo>;
     fn index_ctime(&self) -> i64;
+
+    /// The size of the index file including the header.
     fn index_size(&self) -> usize;
 
     /// Get the chunk index and the relative offset within it for a byte offset
-- 
2.47.3