[pbs-devel] [RFC proxmox-backup 30/36] client: pxar: add method for metadata comparison

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

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@proxmox.com>
---
 pbs-client/src/pxar/create.rs | 33 +++++++++++++++++++++++++++++++--
 1 file changed, 31 insertions(+), 2 deletions(-)

diff --git a/pbs-client/src/pxar/create.rs b/pbs-client/src/pxar/create.rs
index 6713daf3..39864483 100644
--- a/pbs-client/src/pxar/create.rs
+++ b/pbs-client/src/pxar/create.rs
@@ -17,9 +17,9 @@ use nix::sys::stat::{FileStat, Mode};
 
 use pathpatterns::{MatchEntry, MatchFlag, MatchList, MatchType, PatternFlag};
 use proxmox_sys::error::SysError;
-use pxar::accessor::aio::Accessor;
+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;
@@ -422,6 +422,35 @@ impl Archiver {
         .boxed()
     }
 
+    async fn is_reusable_entry(
+        &mut self,
+        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) = accessor.lookup(file_name).await? {
+            if metadata == file_entry.metadata() {
+                if let EntryKind::File { payload_offset, .. } = file_entry.entry().kind() {
+                    log::debug!("re-use: {file_name:?} has unchanged metadata.");
+                    return Ok(payload_offset.clone());
+                }
+                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