git-ref uses memmap2 (#293)

Author: Byron

Cargo.lock

@@ -38,7 +38,7 @@ serde = { version = "1.0.114", optional = true, default-features = false, featur
 os_str_bytes = "6.0.0"
 
 # packed refs
-filebuffer = "0.4.0"
+memmap2 = "0.5.0"
 
 [dev-dependencies]
 git-testtools = { path = "../tests/tools" }

git-ref/Cargo.toml

@@ -16,8 +16,7 @@
 //!     * references are stored in a single human-readable file, along with their targets if they are symbolic.
 //! * **ref-table**
 //!   * supersedes all of the above to allow handling hundreds of thousands of references.
-#![forbid(unsafe_code)]
-#![deny(missing_docs, rust_2018_idioms)]
+#![deny(unsafe_code, missing_docs, rust_2018_idioms)]
 
 use std::borrow::Cow;
 

git-ref/src/lib.rs

@@ -19,7 +19,7 @@ impl AsRef<[u8]> for packed::Backing {
 pub mod open {
     use std::path::PathBuf;
 
-    use filebuffer::FileBuffer;
+    use memmap2::Mmap;
 
     use crate::store_impl::packed;
 
@@ -35,7 +35,13 @@ pub mod open {
                 let backing = if std::fs::metadata(&path)?.len() <= use_memory_map_if_larger_than_bytes {
                     packed::Backing::InMemory(std::fs::read(&path)?)
                 } else {
-                    packed::Backing::Mapped(FileBuffer::open(&path)?)
+                    packed::Backing::Mapped(
+                        // SAFETY: we have to take the risk of somebody changing the file underneath. Git never writes into the same file.
+                        #[allow(unsafe_code)]
+                        unsafe {
+                            Mmap::map(&std::fs::File::open(&path)?)?
+                        },
+                    )
                 };
 
                 let (offset, sorted) = {

git-ref/src/store/packed/buffer.rs

@@ -1,9 +1,9 @@
 use std::path::PathBuf;
 
-use filebuffer::FileBuffer;
 use git_features::threading::OwnShared;
 use git_hash::ObjectId;
 use git_object::bstr::{BStr, BString};
+use memmap2::Mmap;
 
 use crate::{transaction::RefEdit, FullNameRef};
 
@@ -12,7 +12,7 @@ enum Backing {
     /// The buffer is loaded entirely in memory, along with the `offset` to the first record past the header.
     InMemory(Vec<u8>),
     /// The buffer is mapping the file on disk, along with the offset to the first record past the header
-    Mapped(FileBuffer),
+    Mapped(Mmap),
 }
 
 /// A buffer containing a packed-ref file that is either memory mapped or fully in-memory depending on a cutoff.