Add AppendVec::new_from_file_unchecked (#26795)

new_from_file_unchecked

runtime/src/append_vec.rs

@@ -321,32 +321,7 @@ impl AppendVec {
     }
 
     pub fn new_from_file<P: AsRef<Path>>(path: P, current_len: usize) -> io::Result<(Self, usize)> {
-        let data = OpenOptions::new()
-            .read(true)
-            .write(true)
-            .create(false)
-            .open(&path)?;
-
-        let file_size = std::fs::metadata(&path)?.len();
-        AppendVec::sanitize_len_and_size(current_len, file_size as usize)?;
-
-        let map = unsafe {
-            let result = MmapMut::map_mut(&data);
-            if result.is_err() {
-                // for vm.max_map_count, error is: {code: 12, kind: Other, message: "Cannot allocate memory"}
-                info!("memory map error: {:?}. This may be because vm.max_map_count is not set correctly.", result);
-            }
-            result?
-        };
-
-        let new = AppendVec {
-            path: path.as_ref().to_path_buf(),
-            map,
-            append_lock: Mutex::new(()),
-            current_len: AtomicUsize::new(current_len),
-            file_size,
-            remove_on_drop: true,
-        };
+        let new = Self::new_from_file_unchecked(path, current_len)?;
 
         let (sanitized, num_accounts) = new.sanitize_layout_and_length();
         if !sanitized {
@@ -359,6 +334,39 @@ impl AppendVec {
         Ok((new, num_accounts))
     }
 
+    /// Creates an appendvec from file without performing sanitize checks or counting the number of accounts
+    pub fn new_from_file_unchecked<P: AsRef<Path>>(
+        path: P,
+        current_len: usize,
+    ) -> io::Result<Self> {
+        let file_size = std::fs::metadata(&path)?.len();
+        Self::sanitize_len_and_size(current_len, file_size as usize)?;
+
+        let data = OpenOptions::new()
+            .read(true)
+            .write(true)
+            .create(false)
+            .open(&path)?;
+
+        let map = unsafe {
+            let result = MmapMut::map_mut(&data);
+            if result.is_err() {
+                // for vm.max_map_count, error is: {code: 12, kind: Other, message: "Cannot allocate memory"}
+                info!("memory map error: {:?}. This may be because vm.max_map_count is not set correctly.", result);
+            }
+            result?
+        };
+
+        Ok(AppendVec {
+            path: path.as_ref().to_path_buf(),
+            map,
+            append_lock: Mutex::new(()),
+            current_len: AtomicUsize::new(current_len),
+            file_size,
+            remove_on_drop: true,
+        })
+    }
+
     fn sanitize_layout_and_length(&self) -> (bool, usize) {
         let mut offset = 0;