[pbs-devel] [PATCH v3 proxmox-backup 45/58] client: pxar: add method for metadata comparison

[Christian Ebner]

Adds a method to compare the metadata of the current file entry
against the metadata of the entry looked up in the previous backup
snapshot.

If the metadata matched, the start offset for the payload stream is
returned.

This is in preparation for reusing payload chunks for unchanged files.

Signed-off-by: Christian Ebner <c.ebner at proxmox.com>
---
changes since version 2:
- refactored to new padding based threshold

 pbs-client/src/pxar/create.rs | 31 ++++++++++++++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

diff --git a/pbs-client/src/pxar/create.rs b/pbs-client/src/pxar/create.rs
index 79925bba2..c64084a74 100644
--- a/pbs-client/src/pxar/create.rs
+++ b/pbs-client/src/pxar/create.rs
@@ -21,7 +21,7 @@ use pbs_datastore::index::IndexFile;
 use proxmox_sys::error::SysError;
 use pxar::accessor::aio::{Accessor, Directory};
 use pxar::encoder::{LinkOffset, PayloadOffset, SeqWrite};
-use pxar::Metadata;
+use pxar::{EntryKind, Metadata};
 
 use proxmox_io::vec;
 use proxmox_lang::c_str;
@@ -466,6 +466,35 @@ impl Archiver {
         .boxed()
     }
 
+    async fn is_reusable_entry(
+        &mut self,
+        previous_metadata_accessor: &mut Directory<LocalDynamicReadAt<RemoteChunkReader>>,
+        file_name: &Path,
+        stat: &FileStat,
+        metadata: &Metadata,
+    ) -> Result<Option<u64>, Error> {
+        if stat.st_nlink > 1 {
+            log::debug!("re-encode: {file_name:?} has hardlinks.");
+            return Ok(None);
+        }
+
+        if let Some(file_entry) = previous_metadata_accessor.lookup(file_name).await? {
+            if metadata == file_entry.metadata() {
+                if let EntryKind::File { payload_offset, .. } = file_entry.entry().kind() {
+                    log::debug!("possible re-use: {file_name:?} at offset {payload_offset:?} has unchanged metadata.");
+                    return Ok(*payload_offset);
+                }
+                log::debug!("re-encode: {file_name:?} not a regular file.");
+                return Ok(None);
+            }
+            log::debug!("re-encode: {file_name:?} metadata did not match.");
+            return Ok(None);
+        }
+
+        log::debug!("re-encode: {file_name:?} not found in previous archive.");
+        Ok(None)
+    }
+
     /// openat() wrapper which allows but logs `EACCES` and turns `ENOENT` into `None`.
     ///
     /// The `existed` flag is set when iterating through a directory to note that we know the file
-- 
2.39.2