client: pxar: helper for lookup of reusable dynamic entries

The helper method allows to lookup the entries of a dynamic index
which fully cover a given offset range. Further, the helper returns
the start padding from the start offset of the dynamic index entry
to the start offset of the given range and the end padding.

This will be used to lookup size and digest for chunks covering the
payload range of a regular file in order to re-use found chunks by
indexing them in the archives index file instead of re-encoding the
payload.

Signed-off-by: Christian Ebner <c.ebner@proxmox.com>

pbs-client/src/pxar/create.rs

@@ -2,6 +2,7 @@ use std::collections::{HashMap, HashSet};
 use std::ffi::{CStr, CString, OsStr};
 use std::fmt;
 use std::io::{self, Read};
+use std::ops::Range;
 use std::os::unix::ffi::OsStrExt;
 use std::os::unix::io::{AsRawFd, FromRawFd, IntoRawFd, OwnedFd, RawFd};
 use std::path::{Path, PathBuf};
@@ -25,6 +26,8 @@ use proxmox_lang::c_str;
 use proxmox_sys::fs::{self, acl, xattr};
 
 use pbs_datastore::catalog::BackupCatalogWriter;
+use pbs_datastore::dynamic_index::DynamicIndexReader;
+use pbs_datastore::index::IndexFile;
 
 use crate::pxar::metadata::errno_is_unsupported;
 use crate::pxar::tools::assert_single_path_component;
@@ -780,6 +783,73 @@ impl Archiver {
     }
 }
 
+/// Dynamic entry reusable by payload references
+#[derive(Clone, Debug)]
+#[repr(C)]
+pub struct ReusableDynamicEntry {
+    size: u64,
+    padding: u64,
+    digest: [u8; 32],
+}
+
+impl ReusableDynamicEntry {
+    #[inline]
+    pub fn size(&self) -> u64 {
+        self.size
+    }
+
+    #[inline]
+    pub fn digest(&self) -> [u8; 32] {
+        self.digest
+    }
+}
+
+/// List of dynamic entries containing the data given by an offset range
+fn lookup_dynamic_entries(
+    index: &DynamicIndexReader,
+    range: &Range<u64>,
+) -> Result<(Vec<ReusableDynamicEntry>, u64, u64), Error> {
+    let end_idx = index.index_count() - 1;
+    let chunk_end = index.chunk_end(end_idx);
+    let start = index.binary_search(0, 0, end_idx, chunk_end, range.start)?;
+
+    let mut prev_end = if start == 0 {
+        0
+    } else {
+        index.chunk_end(start - 1)
+    };
+    let padding_start = range.start - prev_end;
+    let mut padding_end = 0;
+
+    let mut indices = Vec::new();
+    for dynamic_entry in &index.index()[start..] {
+        let end = dynamic_entry.end();
+
+        let reusable_dynamic_entry = ReusableDynamicEntry {
+            size: (end - prev_end),
+            padding: 0,
+            digest: dynamic_entry.digest(),
+        };
+        indices.push(reusable_dynamic_entry);
+
+        if range.end < end {
+            padding_end = end - range.end;
+            break;
+        }
+        prev_end = end;
+    }
+
+    if let Some(first) = indices.first_mut() {
+        first.padding += padding_start;
+    }
+
+    if let Some(last) = indices.last_mut() {
+        last.padding += padding_end;
+    }
+
+    Ok((indices, padding_start, padding_end))
+}
+
 fn get_metadata(
     fd: RawFd,
     stat: &FileStat,