[pbs-devel] [PATCH v7 proxmox-backup 48/69] pxar: caching: add look-ahead cache

[Christian Ebner]

Add a lookahead cache and the neccessary types to store the required
data and keep track of directory boundaries while traversing the
filesystem tree, in order to postpone a decision if to reuse or
reencode a given regular file with unchanged metadata.

Signed-off-by: Christian Ebner <c.ebner at proxmox.com>
---
changes since version 6:
- add PxarLookaheadCache and refactor some of the logic to be contained
  within this patch

 pbs-client/src/pxar/create.rs           |   2 +-
 pbs-client/src/pxar/look_ahead_cache.rs | 165 ++++++++++++++++++++++++
 pbs-client/src/pxar/mod.rs              |   1 +
 3 files changed, 167 insertions(+), 1 deletion(-)
 create mode 100644 pbs-client/src/pxar/look_ahead_cache.rs

diff --git a/pbs-client/src/pxar/create.rs b/pbs-client/src/pxar/create.rs
index ac8827bb2..6127aa88f 100644
--- a/pbs-client/src/pxar/create.rs
+++ b/pbs-client/src/pxar/create.rs
@@ -131,7 +131,7 @@ impl fmt::Display for ArchiveError {
 }
 
 #[derive(Eq, PartialEq, Hash)]
-struct HardLinkInfo {
+pub(crate) struct HardLinkInfo {
     st_dev: u64,
     st_ino: u64,
 }
diff --git a/pbs-client/src/pxar/look_ahead_cache.rs b/pbs-client/src/pxar/look_ahead_cache.rs
new file mode 100644
index 000000000..539586271
--- /dev/null
+++ b/pbs-client/src/pxar/look_ahead_cache.rs
@@ -0,0 +1,165 @@
+use std::collections::HashSet;
+use std::ffi::CString;
+use std::ops::Range;
+use std::os::unix::io::OwnedFd;
+use std::path::PathBuf;
+
+use nix::sys::stat::FileStat;
+
+use pxar::encoder::PayloadOffset;
+use pxar::Metadata;
+
+use super::create::*;
+
+const DEFAULT_CACHE_SIZE: usize = 512;
+
+pub(crate) struct CacheEntryData {
+    pub(crate) fd: OwnedFd,
+    pub(crate) c_file_name: CString,
+    pub(crate) stat: FileStat,
+    pub(crate) metadata: Metadata,
+    pub(crate) payload_offset: PayloadOffset,
+}
+
+pub(crate) enum CacheEntry {
+    RegEntry(CacheEntryData),
+    DirEntry(CacheEntryData),
+    DirEnd,
+}
+
+pub(crate) struct PxarLookaheadCache {
+    // Current state of the cache
+    enabled: bool,
+    // Cached entries
+    entries: Vec<CacheEntry>,
+    // Entries encountered having more than one link given by stat
+    hardlinks: HashSet<HardLinkInfo>,
+    // Payload range covered by the currently cached entries
+    range: Range<u64>,
+    // Possible held back last chunk from last flush, used for possible chunk continuation
+    last_chunk: Option<ReusableDynamicEntry>,
+    // Path when started caching
+    start_path: PathBuf,
+    // Number of entries with file descriptors
+    fd_entries: usize,
+    // Max number of entries with file descriptors
+    cache_size: usize,
+}
+
+impl PxarLookaheadCache {
+    pub(crate) fn new(size: Option<usize>) -> Self {
+        Self {
+            enabled: false,
+            entries: Vec::new(),
+            hardlinks: HashSet::new(),
+            range: 0..0,
+            last_chunk: None,
+            start_path: PathBuf::new(),
+            fd_entries: 0,
+            cache_size: size.unwrap_or(DEFAULT_CACHE_SIZE),
+        }
+    }
+
+    pub(crate) fn is_full(&self) -> bool {
+        self.fd_entries >= self.cache_size
+    }
+
+    pub(crate) fn caching_enabled(&self) -> bool {
+        self.enabled
+    }
+
+    pub(crate) fn insert(
+        &mut self,
+        fd: OwnedFd,
+        c_file_name: CString,
+        stat: FileStat,
+        metadata: Metadata,
+        payload_offset: PayloadOffset,
+    ) {
+        self.enabled = true;
+        self.fd_entries += 1;
+        if metadata.is_dir() {
+            self.entries.push(CacheEntry::DirEntry(CacheEntryData {
+                fd,
+                c_file_name,
+                stat,
+                metadata,
+                payload_offset,
+            }))
+        } else {
+            self.entries.push(CacheEntry::RegEntry(CacheEntryData {
+                fd,
+                c_file_name,
+                stat,
+                metadata,
+                payload_offset,
+            }))
+        }
+    }
+
+    pub(crate) fn insert_dir_end(&mut self) {
+        self.entries.push(CacheEntry::DirEnd);
+    }
+
+    pub(crate) fn take_and_reset(&mut self) -> Vec<CacheEntry> {
+        self.fd_entries = 0;
+        self.enabled = false;
+        self.start_path.clear();
+        self.clear_range();
+        std::mem::take(&mut self.entries)
+    }
+
+    pub(crate) fn update_start_path(&mut self, path: PathBuf) {
+        self.start_path = path;
+    }
+
+    pub(crate) fn start_path(&self) -> &PathBuf {
+        &self.start_path
+    }
+
+    pub(crate) fn contains_hardlink(&self, info: &HardLinkInfo) -> bool {
+        self.hardlinks.contains(info)
+    }
+
+    pub(crate) fn insert_hardlink(&mut self, info: HardLinkInfo) -> bool {
+        self.hardlinks.insert(info)
+    }
+
+    pub(crate) fn range(&self) -> &Range<u64> {
+        &self.range
+    }
+
+    pub(crate) fn update_range(&mut self, range: Range<u64>) {
+        self.range = range;
+    }
+
+    pub(crate) fn clear_range(&mut self) {
+        // keep end for possible continuation if cache has been cleared because
+        // it was full, but further caching would be fine
+        self.range = self.range.end..self.range.end
+    }
+
+    pub(crate) fn try_extend_range(&mut self, range: Range<u64>) -> bool {
+        if self.range.end == 0 {
+            // initialize first range to start and end with start of new range
+            self.range.start = range.start;
+            self.range.end = range.start;
+        }
+
+        // range continued, update end
+        if self.range.end == range.start {
+            self.range.end = range.end;
+            return true;
+        }
+
+        false
+    }
+
+    pub(crate) fn take_last_chunk(&mut self) -> Option<ReusableDynamicEntry> {
+        self.last_chunk.take()
+    }
+
+    pub(crate) fn update_last_chunk(&mut self, chunk: Option<ReusableDynamicEntry>) {
+        self.last_chunk = chunk;
+    }
+}
diff --git a/pbs-client/src/pxar/mod.rs b/pbs-client/src/pxar/mod.rs
index 5248a1956..334759df6 100644
--- a/pbs-client/src/pxar/mod.rs
+++ b/pbs-client/src/pxar/mod.rs
@@ -50,6 +50,7 @@
 pub(crate) mod create;
 pub(crate) mod dir_stack;
 pub(crate) mod extract;
+pub(crate) mod look_ahead_cache;
 pub(crate) mod metadata;
 pub(crate) mod tools;
 
-- 
2.39.2