[pbs-devel] [PATCH v6 proxmox-backup 10/29] fix #3174: index: add fn index list from start/end-offsets

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

Adds a function to get a list of DynamicEntry's from a chunk index by
given start and end offset, which should be contained within these
chunks.
This is needed in order to reference file payloads and reuse the
chunks containing them from a previous backup run.

The index entries are normalized, meaning each entries end() is equal to
the chunk size.

In addition to the list of index entries, the padding to the start of
the requested start offset from the first chunk is returned. This is
needed for calculation of the appendix section offsets during
decoding.

Signed-off-by: Christian Ebner <c.ebner@proxmox.com>
---
Changes since v5:
- Introduce dedicated `AppendableDynamicEntry` to distinguish from
  regular `DynamicEntry` objects. Refactor accordingly.

 pbs-datastore/src/dynamic_index.rs | 55 ++++++++++++++++++++++++++++++
 1 file changed, 55 insertions(+)

diff --git a/pbs-datastore/src/dynamic_index.rs b/pbs-datastore/src/dynamic_index.rs
index 71a5082e..a4d8ceec 100644
--- a/pbs-datastore/src/dynamic_index.rs
+++ b/pbs-datastore/src/dynamic_index.rs
@@ -74,6 +74,26 @@ impl DynamicEntry {
     }
 }
 
+/// Dynamic Entry appendable as pxar Appendix entry
+#[derive(Clone, Debug)]
+#[repr(C)]
+pub struct AppendableDynamicEntry {
+    size_le: u64,
+    digest: [u8; 32],
+}
+
+impl AppendableDynamicEntry {
+    #[inline]
+    pub fn size(&self) -> u64 {
+        u64::from_le(self.size_le)
+    }
+
+    #[inline]
+    pub fn digest(&self) -> [u8; 32] {
+        self.digest.clone()
+    }
+}
+
 pub struct DynamicIndexReader {
     _file: File,
     pub size: usize,
@@ -188,6 +208,41 @@ impl DynamicIndexReader {
             self.binary_search(middle_idx + 1, middle_end, end_idx, end, offset)
         }
     }
+
+    /// List of chunk indices containing the data from start_offset to end_offset
+    pub fn indices(
+        &self,
+        start_offset: u64,
+        end_offset: u64,
+    ) -> Result<(Vec<AppendableDynamicEntry>, u64, u64), Error> {
+        let end_idx = self.index.len() - 1;
+        let chunk_end = self.chunk_end(end_idx);
+        let start = self.binary_search(0, 0, end_idx, chunk_end, start_offset)?;
+        let end = self.binary_search(0, 0, end_idx, chunk_end, end_offset)?;
+
+        let offset_first = if start == 0 {
+            0
+        } else {
+            self.index[start - 1].end()
+        };
+
+        let padding_start = start_offset - offset_first;
+        let padding_end = self.index[end].end() - end_offset;
+
+        let mut indices = Vec::new();
+        let mut prev_end = offset_first;
+        for dynamic_entry in &self.index[start..end + 1] {
+            let size = dynamic_entry.end() - prev_end;
+            let appendable_dynamic_entry = AppendableDynamicEntry {
+                size_le: size.to_le(),
+                digest: dynamic_entry.digest.clone(),
+            };
+            prev_end += size;
+            indices.push(appendable_dynamic_entry);
+        }
+
+        Ok((indices, padding_start, padding_end))
+    }
 }
 
 impl IndexFile for DynamicIndexReader {
-- 
2.39.2