Merge pull request #233 from ARMmbed/discourage-no-wear-leveling

Change block_cycles disable from 0 to -1

.travis.yml

@@ -123,7 +123,7 @@ jobs:
       if: branch !~ -prefix$
       install:
         - sudo apt-get install libfuse-dev
-        - git clone --depth 1 https://github.com/geky/littlefs-fuse -b v2-alpha
+        - git clone --depth 1 https://github.com/geky/littlefs-fuse -b v2
         - fusermount -V
         - gcc --version
       before_script:
@@ -158,7 +158,7 @@ jobs:
       if: branch !~ -prefix$
       install:
         - sudo apt-get install libfuse-dev
-        - git clone --depth 1 https://github.com/geky/littlefs-fuse -b v2-alpha v2
+        - git clone --depth 1 https://github.com/geky/littlefs-fuse -b v2 v2
         - git clone --depth 1 https://github.com/geky/littlefs-fuse -b v1 v1
         - fusermount -V
         - gcc --version

lfs.c

@@ -1468,7 +1468,7 @@ static int lfs_dir_compact(lfs_t *lfs,
 
     // increment revision count
     dir->rev += 1;
-    if (lfs->cfg->block_cycles &&
+    if (lfs->cfg->block_cycles > 0 &&
             (dir->rev % (lfs->cfg->block_cycles+1) == 0)) {
         if (lfs_pair_cmp(dir->pair, (const lfs_block_t[2]){0, 1}) == 0) {
             // oh no! we're writing too much to the superblock,
@@ -3226,8 +3226,14 @@ static int lfs_init(lfs_t *lfs, const struct lfs_config *cfg) {
     LFS_ASSERT(4*lfs_npw2(0xffffffff / (lfs->cfg->block_size-2*4))
             <= lfs->cfg->block_size);
 
-    // we don't support some corner cases
-    LFS_ASSERT(lfs->cfg->block_cycles < 0xffffffff);
+    // block_cycles = 0 is no longer supported.
+    //
+    // block_cycles is the number of erase cycles before littlefs evicts
+    // metadata logs as a part of wear leveling. Suggested values are in the
+    // range of 100-1000, or set block_cycles to -1 to disable block-level
+    // wear-leveling.
+    LFS_ASSERT(lfs->cfg->block_cycles != 0);
+
 
     // setup read cache
     if (lfs->cfg->read_buffer) {

lfs.h

@@ -191,9 +191,13 @@ struct lfs_config {
     // Number of erasable blocks on the device.
     lfs_size_t block_count;
 
-    // Number of erase cycles before we should move data to another block.
-    // May be zero, in which case no block-level wear-leveling is performed.
-    uint32_t block_cycles;
+    // Number of erase cycles before littlefs evicts metadata logs and moves 
+    // the metadata to another block. Suggested values are in the
+    // range 100-1000, with large values having better performance at the cost
+    // of less consistent wear distribution.
+    //
+    // Set to -1 to disable block-level wear-leveling.
+    int32_t block_cycles;
 
     // Size of block caches. Each cache buffers a portion of a block in RAM.
     // The littlefs needs a read cache, a program cache, and one additional