[pbs-devel] [PATCH v5 proxmox-backup 44/62] client: pxar: add method for metadata comparison

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

Add method to compare metadata of current file entry against metadata
of the entry looked up in the previous backup snapshot. If the
metadata matched, the start offset pointing to the files payload
header in the payload steam is returned.

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

Signed-off-by: Christian Ebner <c.ebner@proxmox.com>
---
changes since version 4:
- refactor to `MetadataArchiveReader` type, reusable by tests with local
  accessor

 pbs-client/src/pxar/create.rs | 34 +++++++++++++++++++++++++++++++++-
 1 file changed, 33 insertions(+), 1 deletion(-)

diff --git a/pbs-client/src/pxar/create.rs b/pbs-client/src/pxar/create.rs
index 3248fd307..7e6402de5 100644
--- a/pbs-client/src/pxar/create.rs
+++ b/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::mem::size_of;
 use std::ops::Range;
 use std::os::unix::ffi::OsStrExt;
 use std::os::unix::io::{AsRawFd, FromRawFd, IntoRawFd, OwnedFd, RawFd};
@@ -21,7 +22,7 @@ use proxmox_sys::error::SysError;
 use pxar::accessor::aio::{Accessor, Directory};
 use pxar::accessor::ReadAt;
 use pxar::encoder::{LinkOffset, SeqWrite};
-use pxar::Metadata;
+use pxar::{EntryKind, Metadata};
 
 use proxmox_io::vec;
 use proxmox_lang::c_str;
@@ -344,6 +345,37 @@ impl Archiver {
         .boxed()
     }
 
+    async fn is_reusable_entry(
+        &mut self,
+        previous_metadata_accessor: &mut Directory<MetadataArchiveReader>,
+        file_name: &Path,
+        metadata: &Metadata,
+    ) -> Result<Option<Range<u64>>, Error> {
+        if let Some(file_entry) = previous_metadata_accessor.lookup(file_name).await? {
+            if metadata == file_entry.metadata() {
+                if let EntryKind::File {
+                    payload_offset: Some(offset),
+                    size,
+                    ..
+                } = file_entry.entry().kind()
+                {
+                    let range = *offset..*offset + size + size_of::<pxar::format::Header>() as u64;
+                    log::debug!(
+                        "reusable: {file_name:?} at range {range:?} has unchanged metadata."
+                    );
+                    return Ok(Some(range));
+                }
+                log::debug!("reencode: {file_name:?} not a regular file.");
+                return Ok(None);
+            }
+            log::debug!("reencode: {file_name:?} metadata did not match.");
+            return Ok(None);
+        }
+
+        log::debug!("reencode: {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



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