Added caching with managed caches at the file level

This adds a fully independent layer between the rest of the filesystem
and the block device. This requires some additionally logic around cache
invalidation and flushing, but removes the need for any higher layer to
consider read/write sizes less than what is supported by the hardware.

Additionally, these caches can be used for possible speed improvements.
This is left up to the user to optimize for their use cases. For very
limited embedded systems with byte-level read/writes, the caches could
be omitted completely, or they could even be the size of a full block
for minimizing storage access.

(A full block may not be the best for speed, consider if only a small
portion of the read block is used, but I'll leave that evaluation as an
exercise for any consumers of this library)

lfs.c

@@ -9,46 +9,35 @@
 
 #include <string.h>
 #include <stdlib.h>
+#include <assert.h>
 
 
-/// Block device operations ///
-static int lfs_bd_flush(lfs_t *lfs) {
-    if (lfs->pcache.off != -1) {
-        int err = lfs->cfg->prog(lfs->cfg, lfs->pcache.block,
-                lfs->pcache.off, lfs->pcache.buffer, lfs->cfg->prog_size);
-        if (err) {
-            return err;
-        }
-
-        lfs->pcache.off = -1;
-    }
-
-    return 0;
-}
-
-static int lfs_bd_read(lfs_t *lfs, lfs_block_t block,
+/// Caching block device operations ///
+static int lfs_cache_read(lfs_t *lfs, lfs_cache_t *rcache,
+        const lfs_cache_t *pcache, lfs_block_t block,
         lfs_off_t off, void *buffer, lfs_size_t size) {
     uint8_t *data = buffer;
 
-    // flush overlapping programs
     while (size > 0) {
-        if (block == lfs->pcache.block && off >= lfs->pcache.off &&
-                off < lfs->pcache.off + lfs->cfg->prog_size) {
-            // is already in cache?
+        if (pcache && block == pcache->block && off >= pcache->off &&
+                off < pcache->off + lfs->cfg->prog_size) {
+            // is already in pcache?
             lfs_size_t diff = lfs_min(size,
-                    lfs->cfg->prog_size - (off-lfs->pcache.off));
-            memcpy(data, &lfs->pcache.buffer[off-lfs->pcache.off], diff);
+                    lfs->cfg->prog_size - (off-pcache->off));
+            memcpy(data, &pcache->buffer[off-pcache->off], diff);
 
             data += diff;
             off += diff;
             size -= diff;
             continue;
-        } else if (block == lfs->rcache.block && off >= lfs->rcache.off &&
-                off < lfs->rcache.off + lfs->cfg->read_size) {
-            // is already in cache?
+        }
+
+        if (block == rcache->block && off >= rcache->off &&
+                off < rcache->off + lfs->cfg->read_size) {
+            // is already in rcache?
             lfs_size_t diff = lfs_min(size,
-                    lfs->cfg->read_size - (off-lfs->rcache.off));
-            memcpy(data, &lfs->rcache.buffer[off-lfs->rcache.off], diff);
+                    lfs->cfg->read_size - (off-rcache->off));
+            memcpy(data, &rcache->buffer[off-rcache->off], diff);
 
             data += diff;
             off += diff;
@@ -56,14 +45,7 @@ static int lfs_bd_read(lfs_t *lfs, lfs_block_t block,
             continue;
         }
 
-        // write out pending programs
-        int err = lfs_bd_flush(lfs);
-        if (err) {
-            return err;
-        }
-
-        if (off % lfs->cfg->read_size == 0 &&
-                size >= lfs->cfg->read_size) {
+        if (off % lfs->cfg->read_size == 0 && size >= lfs->cfg->read_size) {
             // bypass cache?
             lfs_size_t diff = size - (size % lfs->cfg->read_size);
             int err = lfs->cfg->read(lfs->cfg, block, off, data, diff);
@@ -78,10 +60,10 @@ static int lfs_bd_read(lfs_t *lfs, lfs_block_t block,
         }
 
         // load to cache, first condition can no longer fail
-        lfs->rcache.block = block;
-        lfs->rcache.off = off - (off % lfs->cfg->read_size);
-        err = lfs->cfg->read(lfs->cfg, lfs->rcache.block,
-                lfs->rcache.off, lfs->rcache.buffer, lfs->cfg->read_size);
+        rcache->block = block;
+        rcache->off = off - (off % lfs->cfg->read_size);
+        int err = lfs->cfg->read(lfs->cfg, rcache->block,
+                rcache->off, rcache->buffer, lfs->cfg->read_size);
         if (err) {
             return err;
         }
@@ -90,34 +72,50 @@ static int lfs_bd_read(lfs_t *lfs, lfs_block_t block,
     return 0;
 }
 
-static int lfs_bd_prog(lfs_t *lfs, lfs_block_t block,
-        lfs_off_t off, const void *buffer, lfs_size_t size) {
-    const uint8_t *data = buffer;
+static int lfs_cache_flush(lfs_t *lfs, lfs_cache_t *cache) {
+    if (cache->off != -1) {
+        int err = lfs->cfg->prog(lfs->cfg, cache->block,
+                cache->off, cache->buffer, lfs->cfg->prog_size);
+        if (err) {
+            return err;
+        }
 
-    if (block == lfs->rcache.block) {
-        // invalidate read cache
-        lfs->rcache.off = -1;
+        cache->off = -1;
     }
 
+    return 0;
+}
+
+static int lfs_cache_prog(lfs_t *lfs, lfs_cache_t *cache, lfs_block_t block,
+        lfs_off_t off, const void *buffer, lfs_size_t size) {
+    const uint8_t *data = buffer;
+
     while (size > 0) {
-        if (block == lfs->pcache.block && off >= lfs->pcache.off &&
-                off < lfs->pcache.off + lfs->cfg->prog_size) {
+        if (block == cache->block && off >= cache->off &&
+                off < cache->off + lfs->cfg->prog_size) {
             // is already in cache?
             lfs_size_t diff = lfs_min(size,
-                    lfs->cfg->prog_size - (off-lfs->pcache.off));
-            memcpy(&lfs->pcache.buffer[off-lfs->pcache.off], data, diff);
+                    lfs->cfg->prog_size - (off-cache->off));
+            memcpy(&cache->buffer[off-cache->off], data, diff);
 
             data += diff;
             off += diff;
             size -= diff;
+
+            if (off % lfs->cfg->prog_size == 0) {
+                // eagerly flush out cache if we fill up
+                int err = lfs_cache_flush(lfs, cache);
+                if (err) {
+                    return err;
+                }
+            }
+
             continue;
         }
 
-        // write out pending programs
-        int err = lfs_bd_flush(lfs);
-        if (err) {
-            return err;
-        }
+        // cache must have been flushed, either by programming and
+        // entire block or manually flushing the cache
+        assert(cache->off == -1);
 
         if (off % lfs->cfg->prog_size == 0 &&
                 size >= lfs->cfg->prog_size) {
@@ -135,19 +133,35 @@ static int lfs_bd_prog(lfs_t *lfs, lfs_block_t block,
         }
 
         // prepare cache, first condition can no longer fail
-        lfs->pcache.block = block;
-        lfs->pcache.off = off - (off % lfs->cfg->prog_size);
+        cache->block = block;
+        cache->off = off - (off % lfs->cfg->prog_size);
     }
 
     return 0;
 }
 
-static int lfs_bd_erase(lfs_t *lfs, lfs_block_t block) {
+
+/// General lfs block device operations ///
+static int lfs_read(lfs_t *lfs, lfs_block_t block,
+        lfs_off_t off, void *buffer, lfs_size_t size) {
+    // if we ever do more than writes to alternating pairs,
+    // this may need to consider pcache
+    return lfs_cache_read(lfs, &lfs->rcache, NULL,
+            block, off, buffer, size);
+}
+
+static int lfs_prog(lfs_t *lfs, lfs_block_t block,
+        lfs_off_t off, const void *buffer, lfs_size_t size) {
+    return lfs_cache_prog(lfs, &lfs->pcache,
+            block, off, buffer, size);
+}
+
+static int lfs_erase(lfs_t *lfs, lfs_block_t block) {
     return lfs->cfg->erase(lfs->cfg, block);
 }
 
-static int lfs_bd_sync(lfs_t *lfs) {
-    int err = lfs_bd_flush(lfs);
+static int lfs_sync(lfs_t *lfs) {
+    int err = lfs_cache_flush(lfs, &lfs->pcache);
     if (err) {
         return err;
     }
@@ -155,13 +169,13 @@ static int lfs_bd_sync(lfs_t *lfs) {
     return lfs->cfg->sync(lfs->cfg);
 }
 
-static int lfs_bd_cmp(lfs_t *lfs, lfs_block_t block,
+static int lfs_cmp(lfs_t *lfs, lfs_block_t block,
         lfs_off_t off, lfs_size_t size, const void *buffer) {
     const uint8_t *data = buffer;
 
     for (lfs_off_t i = 0; i < size; i++) {
         uint8_t c;
-        int err = lfs_bd_read(lfs, block, off+i, &c, 1);
+        int err = lfs_read(lfs, block, off+i, &c, 1);
         if (err) {
             return err;
         }
@@ -250,7 +264,7 @@ static inline void lfs_pairswap(lfs_block_t pair[2]) {
 }
 
 static inline bool lfs_pairisnull(const lfs_block_t pair[2]) {
-    return !pair[0] || !pair[1];
+    return !pair[0] && !pair[1];
 }
 
 static inline int lfs_paircmp(
@@ -276,7 +290,7 @@ static int lfs_dir_alloc(lfs_t *lfs, lfs_dir_t *dir) {
 
     // rather than clobbering one of the blocks we just pretend
     // the revision may be valid
-    int err = lfs_bd_read(lfs, dir->pair[0], 0, &dir->d.rev, 4);
+    int err = lfs_read(lfs, dir->pair[0], 0, &dir->d.rev, 4);
     if (err) {
         return err;
     }
@@ -301,7 +315,7 @@ static int lfs_dir_fetch(lfs_t *lfs,
     // check both blocks for the most recent revision
     for (int i = 0; i < 2; i++) {
         struct lfs_disk_dir test;
-        int err = lfs_bd_read(lfs, tpair[i], 0, &test, sizeof(test));
+        int err = lfs_read(lfs, tpair[i], 0, &test, sizeof(test));
         if (err) {
             return err;
         }
@@ -315,7 +329,7 @@ static int lfs_dir_fetch(lfs_t *lfs,
 
         for (lfs_off_t j = sizeof(test); j < lfs->cfg->block_size; j += 4) {
             uint32_t word;
-            int err = lfs_bd_read(lfs, tpair[i], j, &word, 4);
+            int err = lfs_read(lfs, tpair[i], j, &word, 4);
             if (err) {
                 return err;
             }
@@ -349,14 +363,14 @@ static int lfs_dir_commit(lfs_t *lfs, lfs_dir_t *dir,
     dir->d.rev += 1;
     lfs_pairswap(dir->pair);
 
-    int err = lfs_bd_erase(lfs, dir->pair[0]);
+    int err = lfs_erase(lfs, dir->pair[0]);
     if (err) {
         return err;
     }
 
     uint32_t crc = 0xffffffff;
     crc = lfs_crc(crc, &dir->d, sizeof(dir->d));
-    err = lfs_bd_prog(lfs, dir->pair[0], 0, &dir->d, sizeof(dir->d));
+    err = lfs_prog(lfs, dir->pair[0], 0, &dir->d, sizeof(dir->d));
     if (err) {
         return err;
     }
@@ -366,7 +380,7 @@ static int lfs_dir_commit(lfs_t *lfs, lfs_dir_t *dir,
     while (off < size) {
         if (entry && off == entry->off) {
             crc = lfs_crc(crc, &entry->d, sizeof(entry->d));
-            int err = lfs_bd_prog(lfs, dir->pair[0],
+            int err = lfs_prog(lfs, dir->pair[0],
                     off, &entry->d, sizeof(entry->d));
             if (err) {
                 return err;
@@ -375,7 +389,7 @@ static int lfs_dir_commit(lfs_t *lfs, lfs_dir_t *dir,
 
             if (data) {
                 crc = lfs_crc(crc, data, entry->d.len - sizeof(entry->d));
-                int err = lfs_bd_prog(lfs, dir->pair[0],
+                int err = lfs_prog(lfs, dir->pair[0],
                         off, data, entry->d.len - sizeof(entry->d));
                 if (err) {
                     return err;
@@ -384,13 +398,13 @@ static int lfs_dir_commit(lfs_t *lfs, lfs_dir_t *dir,
             }
         } else {
             uint8_t data;
-            int err = lfs_bd_read(lfs, dir->pair[1], off, &data, 1);
+            int err = lfs_read(lfs, dir->pair[1], off, &data, 1);
             if (err) {
                 return err;
             }
 
             crc = lfs_crc(crc, &data, 1);
-            err = lfs_bd_prog(lfs, dir->pair[0], off, &data, 1);
+            err = lfs_prog(lfs, dir->pair[0], off, &data, 1);
             if (err) {
                 return err;
             }
@@ -402,7 +416,7 @@ static int lfs_dir_commit(lfs_t *lfs, lfs_dir_t *dir,
     while (off < lfs->cfg->block_size-4) {
         uint8_t data = 0xff;
         crc = lfs_crc(crc, &data, 1);
-        err = lfs_bd_prog(lfs, dir->pair[0], off, &data, 1);
+        err = lfs_prog(lfs, dir->pair[0], off, &data, 1);
         if (err) {
             return err;
         }
@@ -410,12 +424,12 @@ static int lfs_dir_commit(lfs_t *lfs, lfs_dir_t *dir,
         off += 1;
     }
 
-    err = lfs_bd_prog(lfs, dir->pair[0], lfs->cfg->block_size-4, &crc, 4);
+    err = lfs_prog(lfs, dir->pair[0], lfs->cfg->block_size-4, &crc, 4);
     if (err) {
         return err;
     }
 
-    return lfs_bd_sync(lfs);
+    return lfs_sync(lfs);
 }
 
 static int lfs_dir_shift(lfs_t *lfs, lfs_dir_t *dir, lfs_entry_t *entry) {
@@ -423,14 +437,14 @@ static int lfs_dir_shift(lfs_t *lfs, lfs_dir_t *dir, lfs_entry_t *entry) {
     dir->d.size -= entry->d.len;
     lfs_pairswap(dir->pair);
 
-    int err = lfs_bd_erase(lfs, dir->pair[0]);
+    int err = lfs_erase(lfs, dir->pair[0]);
     if (err) {
         return err;
     }
 
     uint32_t crc = 0xffffffff;
     crc = lfs_crc(crc, &dir->d, sizeof(dir->d));
-    err = lfs_bd_prog(lfs, dir->pair[0], 0, &dir->d, sizeof(dir->d));
+    err = lfs_prog(lfs, dir->pair[0], 0, &dir->d, sizeof(dir->d));
     if (err) {
         return err;
     }
@@ -443,13 +457,13 @@ static int lfs_dir_shift(lfs_t *lfs, lfs_dir_t *dir, lfs_entry_t *entry) {
             roff += entry->d.len;
         } else {
             uint8_t data;
-            int err = lfs_bd_read(lfs, dir->pair[1], roff, &data, 1);
+            int err = lfs_read(lfs, dir->pair[1], roff, &data, 1);
             if (err) {
                 return err;
             }
 
             crc = lfs_crc(crc, &data, 1);
-            err = lfs_bd_prog(lfs, dir->pair[0], woff, &data, 1);
+            err = lfs_prog(lfs, dir->pair[0], woff, &data, 1);
             if (err) {
                 return err;
             }
@@ -462,7 +476,7 @@ static int lfs_dir_shift(lfs_t *lfs, lfs_dir_t *dir, lfs_entry_t *entry) {
     while (woff < lfs->cfg->block_size-4) {
         uint8_t data = 0xff;
         crc = lfs_crc(crc, &data, 1);
-        err = lfs_bd_prog(lfs, dir->pair[0], woff, &data, 1);
+        err = lfs_prog(lfs, dir->pair[0], woff, &data, 1);
         if (err) {
             return err;
         }
@@ -471,12 +485,12 @@ static int lfs_dir_shift(lfs_t *lfs, lfs_dir_t *dir, lfs_entry_t *entry) {
         woff += 1;
     }
 
-    err = lfs_bd_prog(lfs, dir->pair[0], lfs->cfg->block_size-4, &crc, 4);
+    err = lfs_prog(lfs, dir->pair[0], lfs->cfg->block_size-4, &crc, 4);
     if (err) {
         return err;
     }
 
-    return lfs_bd_sync(lfs);
+    return lfs_sync(lfs);
 }
 
 static int lfs_dir_append(lfs_t *lfs, lfs_dir_t *dir,
@@ -572,7 +586,7 @@ static int lfs_dir_next(lfs_t *lfs, lfs_dir_t *dir, lfs_entry_t *entry) {
             continue;
         }
 
-        int err = lfs_bd_read(lfs, dir->pair[0], dir->off,
+        int err = lfs_read(lfs, dir->pair[0], dir->off,
                 &entry->d, sizeof(entry->d));
         if (err) {
             return err;
@@ -641,7 +655,7 @@ static int lfs_dir_find(lfs_t *lfs, lfs_dir_t *dir,
                 continue;
             }
 
-            int ret = lfs_bd_cmp(lfs, dir->pair[0],
+            int ret = lfs_cmp(lfs, dir->pair[0],
                     entry->off + sizeof(entry->d), pathlen, pathname);
             if (ret < 0) {
                 return ret;
@@ -788,7 +802,7 @@ int lfs_dir_read(lfs_t *lfs, lfs_dir_t *dir, struct lfs_info *info) {
         info->size = entry.d.u.file.size;
     }
 
-    err = lfs_bd_read(lfs, dir->pair[0], entry.off + sizeof(entry.d),
+    err = lfs_read(lfs, dir->pair[0], entry.off + sizeof(entry.d),
             info->name, entry.d.len - sizeof(entry.d));
     if (err) {
         return err;
@@ -840,7 +854,7 @@ int lfs_dir_rewind(lfs_t *lfs, lfs_dir_t *dir) {
 }
 
 
-/// Index list operations ///
+/// File index list operations ///
 static int lfs_index(lfs_t *lfs, lfs_off_t *off) {
     lfs_off_t i = 0;
 
@@ -853,7 +867,9 @@ static int lfs_index(lfs_t *lfs, lfs_off_t *off) {
     return i;
 }
 
-static int lfs_index_find(lfs_t *lfs, lfs_block_t head, lfs_size_t size,
+static int lfs_index_find(lfs_t *lfs,
+        lfs_cache_t *rcache, const lfs_cache_t *pcache,
+        lfs_block_t head, lfs_size_t size,
         lfs_size_t pos, lfs_block_t *block, lfs_off_t *off) {
     if (size == 0) {
         *block = 0;
@@ -869,7 +885,7 @@ static int lfs_index_find(lfs_t *lfs, lfs_block_t head, lfs_size_t size,
                 lfs_npw2(current-target+1) - 1,
                 lfs_min(lfs_ctz(current)+1, lfs->words-1) - 1);
 
-        int err = lfs_bd_read(lfs, head, 4*skip, &head, 4);
+        int err = lfs_cache_read(lfs, rcache, pcache, head, 4*skip, &head, 4);
         if (err) {
             return err;
         }
@@ -883,6 +899,7 @@ static int lfs_index_find(lfs_t *lfs, lfs_block_t head, lfs_size_t size,
 }
 
 static int lfs_index_extend(lfs_t *lfs,
+        lfs_cache_t *rcache, lfs_cache_t *pcache,
         lfs_block_t head, lfs_size_t size,
         lfs_off_t *block, lfs_block_t *off) {
     // go ahead and grab a block
@@ -891,7 +908,7 @@ static int lfs_index_extend(lfs_t *lfs,
         return err;
     }
 
-    err = lfs_bd_erase(lfs, *block);
+    err = lfs_erase(lfs, *block);
     if (err) {
         return err;
     }
@@ -909,12 +926,12 @@ static int lfs_index_extend(lfs_t *lfs,
     if (size != lfs->cfg->block_size) {
         for (lfs_off_t i = 0; i < size; i++) {
             uint8_t data;
-            int err = lfs_bd_read(lfs, head, i, &data, 1);
+            int err = lfs_cache_read(lfs, rcache, NULL, head, i, &data, 1);
             if (err) {
                 return err;
             }
 
-            err = lfs_bd_prog(lfs, *block, i, &data, 1);
+            err = lfs_cache_prog(lfs, pcache, *block, i, &data, 1);
             if (err) {
                 return err;
             }
@@ -929,13 +946,13 @@ static int lfs_index_extend(lfs_t *lfs,
     lfs_size_t skips = lfs_min(lfs_ctz(index)+1, lfs->words-1);
 
     for (lfs_off_t i = 0; i < skips; i++) {
-        int err = lfs_bd_prog(lfs, *block, 4*i, &head, 4);
+        int err = lfs_cache_prog(lfs, pcache, *block, 4*i, &head, 4);
         if (err) {
             return err;
         }
 
         if (i != skips-1) {
-            err = lfs_bd_read(lfs, head, 4*i, &head, 4);
+            err = lfs_cache_read(lfs, rcache, NULL, head, 4*i, &head, 4);
             if (err) {
                 return err;
             }
@@ -947,6 +964,7 @@ static int lfs_index_extend(lfs_t *lfs,
 }
 
 static int lfs_index_traverse(lfs_t *lfs,
+        lfs_cache_t *rcache, const lfs_cache_t *pcache,
         lfs_block_t head, lfs_size_t size,
         int (*cb)(void*, lfs_block_t), void *data) {
     if (size == 0) {
@@ -965,7 +983,7 @@ static int lfs_index_traverse(lfs_t *lfs,
             return 0;
         }
 
-        err = lfs_bd_read(lfs, head, 0, &head, 4);
+        err = lfs_cache_read(lfs, rcache, pcache, head, 0, &head, 4);
         if (err) {
             return err;
         }
@@ -1016,19 +1034,34 @@ int lfs_file_open(lfs_t *lfs, lfs_file_t *file,
     // setup file struct
     file->pair[0] = cwd.pair[0];
     file->pair[1] = cwd.pair[1];
-    file->off = entry.off;
+    file->poff = entry.off;
     file->head = entry.d.u.file.head;
     file->size = entry.d.u.file.size;
     file->flags = flags;
     file->pos = 0;
-    file->wblock = 0;
-    file->rblock = 0;
+    file->block = 0;
 
     if (flags & LFS_O_TRUNC) {
         file->head = 0;
         file->size = 0;
     }
 
+    // allocate buffer if needed
+    file->cache.off = -1;
+    if (lfs->cfg->file_buffer) {
+        file->cache.buffer = lfs->cfg->file_buffer;
+    } else if ((file->flags & 3) == LFS_O_RDONLY) {
+        file->cache.buffer = malloc(lfs->cfg->read_size);
+        if (!file->cache.buffer) {
+            return LFS_ERR_NOMEM;
+        }
+    } else {
+        file->cache.buffer = malloc(lfs->cfg->prog_size);
+        if (!file->cache.buffer) {
+            return LFS_ERR_NOMEM;
+        }
+    }
+
     // add to list of files
     file->next = lfs->files;
     lfs->files = file;
@@ -1047,16 +1080,22 @@ int lfs_file_close(lfs_t *lfs, lfs_file_t *file) {
         }
     }
 
+    // clean up memory
+    if (!lfs->cfg->file_buffer) {
+        free(file->cache.buffer);
+    }
+
     return err;
 }
 
 static int lfs_file_flush(lfs_t *lfs, lfs_file_t *file) {
-    if (file->rblock) {
-        // just drop read block
-        file->rblock = 0;
+    if (file->flags & LFS_F_READING) {
+        // just drop read cache
+        file->cache.off = -1;
+        file->flags &= ~LFS_F_READING;
     }
 
-    if (file->wblock) {
+    if (file->flags & LFS_F_WRITING) {
         lfs_off_t pos = file->pos;
 
         // copy over anything after current branch
@@ -1065,10 +1104,13 @@ static int lfs_file_flush(lfs_t *lfs, lfs_file_t *file) {
             .size = file->size,
             .flags = LFS_O_RDONLY,
             .pos = file->pos,
-            .rblock = 0,
+            .cache = lfs->rcache,
         };
+        lfs->rcache.off = -1;
 
         while (file->pos < file->size) {
+            // copy over a byte at a time, leave it up to caching
+            // to make this efficient
             uint8_t data;
             lfs_ssize_t res = lfs_file_read(lfs, &orig, &data, 1);
             if (res < 0) {
@@ -1079,13 +1121,25 @@ static int lfs_file_flush(lfs_t *lfs, lfs_file_t *file) {
             if (res < 0) {
                 return res;
             }
+
+            // keep our reference to the rcache in sync
+            if (lfs->rcache.off != -1) {
+                orig.cache.off = -1;
+                lfs->rcache.off = -1;
+            }
+        }
+
+        // write out what we have
+        int err = lfs_cache_flush(lfs, &file->cache);
+        if (err) {
+            return err;
         }
 
         // actual file updates
-        file->head = file->wblock;
+        file->head = file->block;
         file->size = file->pos;
-        file->wblock = 0;
-        file->flags |= LFS_O_DIRTY;
+        file->flags &= ~LFS_F_WRITING;
+        file->flags |= LFS_F_DIRTY;
 
         file->pos = pos;
     }
@@ -1099,7 +1153,7 @@ int lfs_file_sync(lfs_t *lfs, lfs_file_t *file) {
         return err;
     }
 
-    if (file->flags & LFS_O_DIRTY) {
+    if (file->flags & LFS_F_DIRTY) {
         // update dir entry
         lfs_dir_t cwd;
         int err = lfs_dir_fetch(lfs, &cwd, file->pair);
@@ -1107,8 +1161,8 @@ int lfs_file_sync(lfs_t *lfs, lfs_file_t *file) {
             return err;
         }
 
-        lfs_entry_t entry = {.off = file->off};
-        err = lfs_bd_read(lfs, cwd.pair[0], entry.off,
+        lfs_entry_t entry = {.off = file->poff};
+        err = lfs_read(lfs, cwd.pair[0], entry.off,
                 &entry.d, sizeof(entry.d));
         if (err) {
             return err;
@@ -1127,7 +1181,7 @@ int lfs_file_sync(lfs_t *lfs, lfs_file_t *file) {
             return err;
         }
 
-        file->flags &= ~LFS_O_DIRTY;
+        file->flags &= ~LFS_F_DIRTY;
     }
 
     return 0;
@@ -1142,7 +1196,7 @@ lfs_ssize_t lfs_file_read(lfs_t *lfs, lfs_file_t *file,
         return LFS_ERR_INVAL;
     }
 
-    if (file->wblock) {
+    if (file->flags & LFS_F_WRITING) {
         // flush out any writes
         int err = lfs_file_flush(lfs, file);
         if (err) {
@@ -1155,23 +1209,28 @@ lfs_ssize_t lfs_file_read(lfs_t *lfs, lfs_file_t *file,
 
     while (nsize > 0) {
         // check if we need a new block
-        if (!file->rblock || file->roff == lfs->cfg->block_size) {
-            int err = lfs_index_find(lfs, file->head, file->size,
-                    file->pos, &file->rblock, &file->roff);
+        if (!(file->flags & LFS_F_READING) ||
+                file->off == lfs->cfg->block_size) {
+            int err = lfs_index_find(lfs, &file->cache, NULL,
+                    file->head, file->size,
+                    file->pos, &file->block, &file->off);
             if (err) {
                 return err;
             }
+
+            file->flags |= LFS_F_READING;
         }
 
         // read as much as we can in current block
-        lfs_size_t diff = lfs_min(nsize, lfs->cfg->block_size - file->roff);
-        int err = lfs_bd_read(lfs, file->rblock, file->roff, data, diff);
+        lfs_size_t diff = lfs_min(nsize, lfs->cfg->block_size - file->off);
+        int err = lfs_cache_read(lfs, &file->cache, NULL,
+                file->block, file->off, data, diff);
         if (err) {
             return err;
         }
 
         file->pos += diff;
-        file->roff += diff;
+        file->off += diff;
         data += diff;
         nsize -= diff;
     }
@@ -1188,7 +1247,7 @@ lfs_ssize_t lfs_file_write(lfs_t *lfs, lfs_file_t *file,
         return LFS_ERR_INVAL;
     }
 
-    if (file->rblock) {
+    if (file->flags & LFS_F_READING) {
         // drop any reads
         int err = lfs_file_flush(lfs, file);
         if (err) {
@@ -1202,44 +1261,45 @@ lfs_ssize_t lfs_file_write(lfs_t *lfs, lfs_file_t *file,
 
     while (nsize > 0) {
         // check if we need a new block
-        if (!file->wblock || file->woff == lfs->cfg->block_size) {
-            if (!file->wblock) {
+        if (!(file->flags & LFS_F_WRITING) ||
+                file->off == lfs->cfg->block_size) {
+            if (!(file->flags & LFS_F_WRITING)) {
                 // find out which block we're extending from
-                int err = lfs_index_find(lfs, file->head, file->size,
-                        file->pos, &file->wblock, &file->woff);
+                int err = lfs_index_find(lfs, &file->cache, NULL,
+                        file->head, file->size,
+                        file->pos, &file->block, &file->off);
                 if (err) {
                     return err;
                 }
+
+                // mark cache as dirty since we may have read data into it
+                file->cache.off = -1;
+                file->flags |= LFS_F_WRITING;
             }
 
             // extend file with new blocks
-            int err = lfs_index_extend(lfs, file->wblock, file->pos,
-                    &file->wblock, &file->woff);
+            int err = lfs_index_extend(lfs, &lfs->rcache, &file->cache,
+                    file->block, file->pos,
+                    &file->block, &file->off);
             if (err) {
                 return err;
             }
         }
 
         // program as much as we can in current block
-        lfs_size_t diff = lfs_min(nsize, lfs->cfg->block_size - file->woff);
-        int err = lfs_bd_prog(lfs, file->wblock, file->woff, data, diff);
+        lfs_size_t diff = lfs_min(nsize, lfs->cfg->block_size - file->off);
+        int err = lfs_cache_prog(lfs, &file->cache,
+                file->block, file->off, data, diff);
         if (err) {
             return err;
         }
 
         file->pos += diff;
-        file->woff += diff;
+        file->off += diff;
         data += diff;
         nsize -= diff;
     }
 
-    if (file->flags & LFS_O_SYNC) {
-        int err = lfs_file_sync(lfs, file);
-        if (err) {
-            return err;
-        }
-    }
-
     return size;
 }
 
@@ -1303,7 +1363,7 @@ int lfs_stat(lfs_t *lfs, const char *path, struct lfs_info *info) {
         info->size = entry.d.u.file.size;
     }
 
-    err = lfs_bd_read(lfs, cwd.pair[0], entry.off + sizeof(entry.d),
+    err = lfs_read(lfs, cwd.pair[0], entry.off + sizeof(entry.d),
             info->name, entry.d.len - sizeof(entry.d));
     if (err) {
         return err;
@@ -1593,7 +1653,7 @@ int lfs_mount(lfs_t *lfs, const struct lfs_config *cfg) {
     lfs_superblock_t superblock;
     err = lfs_dir_fetch(lfs, &dir, (const lfs_block_t[2]){0, 1});
     if (!err) {
-        err = lfs_bd_read(lfs, dir.pair[0],
+        err = lfs_read(lfs, dir.pair[0],
                 sizeof(dir.d), &superblock.d, sizeof(superblock.d));
 
         lfs->root[0] = superblock.d.root[0];
@@ -1643,7 +1703,7 @@ int lfs_traverse(lfs_t *lfs, int (*cb)(void*, lfs_block_t), void *data) {
 
         // iterate over contents
         while ((0x7fffffff & dir.d.size) >= dir.off + sizeof(entry.d)) {
-            int err = lfs_bd_read(lfs, dir.pair[0], dir.off,
+            int err = lfs_read(lfs, dir.pair[0], dir.off,
                     &entry.d, sizeof(entry.d));
             if (err) {
                 return err;
@@ -1651,7 +1711,7 @@ int lfs_traverse(lfs_t *lfs, int (*cb)(void*, lfs_block_t), void *data) {
 
             dir.off += entry.d.len;
             if ((0xf & entry.d.type) == LFS_TYPE_REG) {
-                int err = lfs_index_traverse(lfs,
+                int err = lfs_index_traverse(lfs, &lfs->rcache, NULL,
                         entry.d.u.file.head, entry.d.u.file.size, cb, data);
                 if (err) {
                     return err;
@@ -1669,15 +1729,17 @@ int lfs_traverse(lfs_t *lfs, int (*cb)(void*, lfs_block_t), void *data) {
 
     // iterate over any open files
     for (lfs_file_t *f = lfs->files; f; f = f->next) {
-        if (f->flags & LFS_O_DIRTY) {
-            int err = lfs_index_traverse(lfs, f->head, f->size, cb, data);
+        if (f->flags & LFS_F_DIRTY) {
+            int err = lfs_index_traverse(lfs, &lfs->rcache, &f->cache,
+                    f->head, f->size, cb, data);
             if (err) {
                 return err;
             }
         }
 
-        if (f->wblock) {
-            int err = lfs_index_traverse(lfs, f->wblock, f->pos, cb, data);
+        if (f->flags & LFS_F_WRITING) {
+            int err = lfs_index_traverse(lfs, &lfs->rcache, &f->cache,
+                    f->block, f->pos, cb, data);
             if (err) {
                 return err;
             }

lfs.h

@@ -47,15 +47,19 @@ enum lfs_type {
 };
 
 enum lfs_open_flags {
-    LFS_O_RDONLY = 0,
-    LFS_O_WRONLY = 1,
-    LFS_O_RDWR   = 2,
-    LFS_O_CREAT  = 0x020,
-    LFS_O_EXCL   = 0x040,
-    LFS_O_TRUNC  = 0x080,
-    LFS_O_APPEND = 0x100,
-    LFS_O_SYNC   = 0x200,
-    LFS_O_DIRTY  = 0x10000,
+    // open flags
+    LFS_O_RDONLY = 1,
+    LFS_O_WRONLY = 2,
+    LFS_O_RDWR   = 3,
+    LFS_O_CREAT  = 0x0100,
+    LFS_O_EXCL   = 0x0200,
+    LFS_O_TRUNC  = 0x0400,
+    LFS_O_APPEND = 0x0800,
+
+    // internally used flags
+    LFS_F_DIRTY   = 0x10000,
+    LFS_F_WRITING = 0x20000,
+    LFS_F_READING = 0x40000,
 };
 
 enum lfs_whence_flags {
@@ -112,6 +116,10 @@ struct lfs_config {
     // Optional, statically allocated lookahead buffer.
     // Must be 1 bit per lookahead block.
     void *lookahead_buffer;
+
+    // Optional, statically allocated buffer for files. Must be program sized.
+    // If enabled, only one file may be opened at a time
+    void *file_buffer;
 };
 
 // File info structure
@@ -144,21 +152,25 @@ typedef struct lfs_entry {
     } d;
 } lfs_entry_t;
 
+typedef struct lfs_cache {
+    lfs_block_t block;
+    lfs_off_t off;
+    uint8_t *buffer;
+} lfs_cache_t;
+
 typedef struct lfs_file {
     struct lfs_file *next;
     lfs_block_t pair[2];
-    lfs_off_t off;
+    lfs_off_t poff;
+
     lfs_block_t head;
     lfs_size_t size;
 
     uint32_t flags;
     lfs_off_t pos;
-
-    lfs_block_t wblock;
-    lfs_off_t woff;
-
-    lfs_block_t rblock;
-    lfs_off_t roff;
+    lfs_block_t block;
+    lfs_off_t off;
+    lfs_cache_t cache;
 } lfs_file_t;
 
 typedef struct lfs_dir {
@@ -189,6 +201,12 @@ typedef struct lfs_superblock {
     } d;
 } lfs_superblock_t;
 
+typedef struct lfs_free {
+    lfs_block_t start;
+    lfs_block_t off;
+    uint32_t *lookahead;
+} lfs_free_t;
+
 // littlefs type
 typedef struct lfs {
     const struct lfs_config *cfg;
@@ -198,17 +216,10 @@ typedef struct lfs {
     lfs_dir_t *scratch;
     lfs_file_t *files;
 
-    struct {
-        lfs_block_t block;
-        lfs_off_t off;
-        uint8_t *buffer;
-    } rcache, pcache;
-
-    struct {
-        lfs_block_t start;
-        lfs_block_t off;
-        uint32_t *lookahead;
-    } free;
+    lfs_cache_t rcache;
+    lfs_cache_t pcache;
+
+    lfs_free_t free;
 } lfs_t;