fix: assure memory maps are created with MAP_PRIVATE (#1312)

That way, the mmap process should work under more circumstances.

gix-commitgraph/src/file/init.rs

@@ -4,16 +4,14 @@ use std::{
     path::Path,
 };
 
-use bstr::ByteSlice;
-use memmap2::Mmap;
-
 use crate::{
     file::{
         ChunkId, BASE_GRAPHS_LIST_CHUNK_ID, COMMIT_DATA_CHUNK_ID, COMMIT_DATA_ENTRY_SIZE_SANS_HASH,
         EXTENDED_EDGES_LIST_CHUNK_ID, FAN_LEN, HEADER_LEN, OID_FAN_CHUNK_ID, OID_LOOKUP_CHUNK_ID, SIGNATURE,
     },
     File,
 };
+use bstr::ByteSlice;
 
 /// The error used in [`File::at()`].
 #[derive(thiserror::Error, Debug)]
@@ -246,7 +244,7 @@ impl TryFrom<&Path> for File {
                 // 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(&file)
+                    memmap2::MmapOptions::new().map_copy_read_only(&file)
                 }
             })
             .map_err(|e| Error::Io {

gix-index/src/file/init.rs

@@ -2,8 +2,6 @@
 
 use std::path::{Path, PathBuf};
 
-use memmap2::Mmap;
-
 use crate::{decode, extension, File, State};
 
 mod error {
@@ -64,7 +62,7 @@ impl File {
             let mut file = std::fs::File::open(&path)?;
             // SAFETY: we have to take the risk of somebody changing the file underneath. Git never writes into the same file.
             #[allow(unsafe_code)]
-            let data = unsafe { Mmap::map(&file)? };
+            let data = unsafe { memmap2::MmapOptions::new().map_copy_read_only(&file)? };
 
             if !skip_hash {
                 // Note that even though it's trivial to offload this into a thread, which is worth it for all but the smallest

gix-pack/src/lib.rs

@@ -55,7 +55,7 @@ mod mmap {
         // SAFETY: we have to take the risk of somebody changing the file underneath. Git never writes into the same file.
         #[allow(unsafe_code)]
         unsafe {
-            memmap2::Mmap::map(&file)
+            memmap2::MmapOptions::new().map_copy_read_only(&file)
         }
     }
 }

gix-pack/tests/pack/index.rs

@@ -148,7 +148,7 @@ mod version {
                     desired_kind,
                     || {
                         let file = std::fs::File::open(fixture_path(data_path))?;
-                        let map = unsafe { memmap2::Mmap::map(&file)? };
+                        let map = unsafe { memmap2::MmapOptions::map_copy_read_only(&file)? };
                         Ok((slice_map, map))
                     },
                     pack_iter,

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

@@ -19,7 +19,6 @@ impl AsRef<[u8]> for packed::Backing {
 pub mod open {
     use std::path::PathBuf;
 
-    use memmap2::Mmap;
     use winnow::{prelude::*, stream::Offset};
 
     use crate::store_impl::packed;
@@ -81,7 +80,7 @@ pub mod open {
                     // 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)?)?
+                        memmap2::MmapOptions::new().map_copy_read_only(&std::fs::File::open(&path)?)?
                     },
                 )
             };