From b4be13823cc59d2a25a46c4a5554cd2476fc629d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Rafa=C5=82=20Harabie=C5=84?= <rafalh1992@o2.pl>
Date: Mon, 28 May 2018 00:03:42 +0200
Subject: [PATCH] Cache free clusters count

---
 src/fs.rs | 21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/src/fs.rs b/src/fs.rs
index d3f2791..ed1261a 100644
--- a/src/fs.rs
+++ b/src/fs.rs
@@ -272,6 +272,11 @@ impl FsInfoSector {
         self.next_free_cluster = Some(cluster);
         self.dirty = true;
     }
+
+    fn set_free_cluster_count(&mut self, free_cluster_count: u32) {
+        self.free_cluster_count = Some(free_cluster_count);
+        self.dirty = true;
+    }
 }
 
 /// FAT filesystem options.
@@ -493,12 +498,10 @@ impl <'a> FileSystem<'a> {
     /// For FAT32 volumes number of free clusters from FSInfo sector is returned (may be incorrect).
     /// For other filesystems number is computed on each call (scans entire FAT so it takes more time).
     pub fn stats(&self) -> io::Result<FileSystemStats> {
-        let free_clusters = match self.fs_info.borrow().free_cluster_count {
+        let free_clusters_option = self.fs_info.borrow().free_cluster_count;
+        let free_clusters = match free_clusters_option {
             Some(n) => n,
-            _ => {
-                let mut fat = self.fat_slice();
-                count_free_clusters(&mut fat, self.fat_type, self.total_clusters)?
-            }
+            _ => self.recalc_free_clusters()?,
         };
         Ok(FileSystemStats {
             cluster_size: self.cluster_size(),
@@ -507,6 +510,14 @@ impl <'a> FileSystem<'a> {
         })
     }
 
+    // Forces free clusters recalculation
+    fn recalc_free_clusters(&self) -> io::Result<u32> {
+        let mut fat = self.fat_slice();
+        let free_cluster_count = count_free_clusters(&mut fat, self.fat_type, self.total_clusters)?;
+        self.fs_info.borrow_mut().set_free_cluster_count(free_cluster_count);
+        Ok(free_cluster_count)
+    }
+
     /// Unmounts filesystem. Updates FSInfo sector if required in options.
     pub fn unmount(self) -> io::Result<()> {
         self.unmount_internal()