Make metadata_max configurable through the Storage trait

src/driver.rs

@@ -44,6 +44,12 @@ pub trait Storage {
     /// Value zero is invalid, must be positive or -1.
     const BLOCK_CYCLES: isize = -1;
 
+    // Optional upper limit on total space given to metadata pairs in bytes. On
+    // devices with large blocks (e.g. 128kB) setting this to a low size (2-8kB)
+    // can help bound the metadata compaction time. Must be <= block_size.
+    // Defaults to block_size when zero.
+    const METADATA_MAX: u32 = 0;
+
     /// littlefs uses a read cache, a write cache, and one cache per per file.
     /// Must be a multiple of `READ_SIZE` and `WRITE_SIZE`.
     /// Must be a factor of `BLOCK_SIZE`.

src/fs.rs

@@ -61,6 +61,7 @@ impl<Storage: driver::Storage> Allocation<Storage> {
         let lookahead_size: u32 = 8 * <Storage as driver::Storage>::LOOKAHEAD_SIZE::U32;
         let block_cycles: i32 = Storage::BLOCK_CYCLES as _;
         let block_count: u32 = Storage::BLOCK_COUNT as _;
+        let metadata_max = Storage::METADATA_MAX;
 
         debug_assert!(block_cycles >= -1);
         debug_assert!(block_cycles != 0);
@@ -132,7 +133,7 @@ impl<Storage: driver::Storage> Allocation<Storage> {
             name_max: filename_max_plus_one.wrapping_sub(1),
             file_max,
             attr_max,
-            metadata_max: 0,
+            metadata_max,
         };
 
         Self {

src/tests.rs

@@ -42,8 +42,8 @@ ram_storage!(
 
 #[test]
 fn version() {
-    assert_eq!(crate::version().format, (2, 0));
-    assert_eq!(crate::version().backend, (2, 2));
+    assert_eq!(crate::version().format, (2, 1));
+    assert_eq!(crate::version().backend, (2, 6));
 }
 
 #[test]