Added optional block-level caching

This adds caching of the most recent read/program blocks, allowing
support of devices that don't have byte-level read+writes, along
with reduced device access on devices that do support byte-level
read+writes.

Note: The current implementation is a bit eager to drop caches where
it simplifies the cache layer. This layer is already complex enough.

Note: It may be worthwhile to add a compile switch for caching to
reduce code size, note sure.

Note: This does add a dependency on malloc, which could have a porting
layer, but I'm just using the functions from stdlib for now. These can be
overwritten with noops if the user controls the system, and keeps things
simple for now.

1 files changed, 13 insertions, 0 deletions

diff --git a/lfs.h b/lfs.h
index 505c60b..7efa6de 100644
--- a/lfs.h
+++ b/lfs.h
@@ -20,6 +20,7 @@ enum lfs_error {
     LFS_ERROR_IS_DIR   = -7,
     LFS_ERROR_INVALID  = -8,
     LFS_ERROR_NO_SPACE = -9,
+    LFS_ERROR_NO_MEM   = -10,
 };
 
 enum lfs_type {
@@ -74,6 +75,12 @@ struct lfs_config {
 
     // Number of erasable blocks on the device.
     lfs_size_t block_count;
+
+    // Optional, statically allocated read buffer. Must be read sized.
+    void *read_buffer;
+
+    // Optional, statically allocated program buffer. Must be program sized.
+    void *prog_buffer;
 };
 
 // File info structure
@@ -159,6 +166,12 @@ typedef struct lfs {
         lfs_block_t end;
     } free;
 
+    struct {
+        lfs_block_t block;
+        lfs_off_t off;
+        uint8_t *buffer;
+    } rcache, pcache;
+
     uint32_t lookahead[LFS_CFG_LOOKAHEAD/32];
 } lfs_t;