Changed callbacks to take user-provided context directly

This is a style change to make littlefs's callbacks consistent with most
callback declarations found in C. That is, taking in a user-provided
`void*`.

Previously, these callbacks took a pointer to the config struct itself,
which indirectly contained a user provided context, and this gets the
job done, but taking in a callback with a `void*` is arguably more
expected, has a better chance of integrating with C++/OS-specific code,
and is more likely to be optimized out by a clever compiler.

---

As a part of these changes, the geometry for the test bds needed to be
moved into bd specific configuration objects. This is a good change as
it also allows for testing situations where littlefs's geometry does not
match the underlying bd.

bd/lfs_testbd.h

@@ -13,8 +13,7 @@
 #include "bd/lfs_filebd.h"
 
 #ifdef __cplusplus
-extern "C"
-{
+extern "C" {
 #endif
 
 
@@ -45,6 +44,20 @@ typedef int32_t  lfs_testbd_swear_t;
 
 // testbd config, this is required for testing
 struct lfs_testbd_cfg {
+    // Minimum size of block read. All read operations must be a
+    // multiple of this value.
+    lfs_size_t read_size;
+
+    // Minimum size of block program. All program operations must be a
+    // multiple of this value.
+    lfs_size_t prog_size;
+
+    // Size of an erasable block.
+    lfs_size_t erase_size;
+
+    // Number of erasable blocks on the device.
+    lfs_size_t erase_count;
+
     // 8-bit erase value to use for simulating erases. -1 does not simulate
     // erases, which can speed up testing by avoiding all the extra block-device
     // operations to store the erase value.
@@ -71,21 +84,15 @@ struct lfs_testbd_cfg {
 // testbd state
 typedef struct lfs_testbd {
     union {
-        struct {
-            lfs_filebd_t bd;
-            struct lfs_filebd_cfg cfg;
-        } file;
-        struct {
-            lfs_rambd_t bd;
-            struct lfs_rambd_cfg cfg;
-        } ram;
-    } u;
+        lfs_filebd_t filebd;
+        lfs_rambd_t rambd;
+    } impl;
 
     bool persist;
     uint32_t power_cycles;
     lfs_testbd_wear_t *wear;
 
-    const struct lfs_testbd_cfg *cfg;
+    struct lfs_testbd_cfg cfg;
 } lfs_testbd_t;
 
 
@@ -95,46 +102,45 @@ typedef struct lfs_testbd {
 //
 // Note that filebd is used if a path is provided, if path is NULL
 // testbd will use rambd which can be much faster.
-int lfs_testbd_create(const struct lfs_cfg *cfg, const char *path);
-int lfs_testbd_createcfg(const struct lfs_cfg *cfg, const char *path,
-        const struct lfs_testbd_cfg *bdcfg);
+int lfs_testbd_createcfg(lfs_testbd_t *bd, const char *path,
+        const struct lfs_testbd_cfg *cfg);
 
 // Clean up memory associated with block device
-int lfs_testbd_destroy(const struct lfs_cfg *cfg);
+int lfs_testbd_destroy(lfs_testbd_t *bd);
 
 // Read a block
-int lfs_testbd_read(const struct lfs_cfg *cfg, lfs_block_t block,
+int lfs_testbd_read(lfs_testbd_t *bd, lfs_block_t block,
         lfs_off_t off, void *buffer, lfs_size_t size);
 
 // Program a block
 //
 // The block must have previously been erased.
-int lfs_testbd_prog(const struct lfs_cfg *cfg, lfs_block_t block,
+int lfs_testbd_prog(lfs_testbd_t *bd, lfs_block_t block,
         lfs_off_t off, const void *buffer, lfs_size_t size);
 
 // Erase a block
 //
 // A block must be erased before being programmed. The
 // state of an erased block is undefined.
-int lfs_testbd_erase(const struct lfs_cfg *cfg, lfs_block_t block);
+int lfs_testbd_erase(lfs_testbd_t *bd, lfs_block_t block);
 
 // Sync the block device
-int lfs_testbd_sync(const struct lfs_cfg *cfg);
+int lfs_testbd_sync(lfs_testbd_t *bd);
 
 
 /// Additional extended API for driving test features ///
 
 // Get simulated wear on a given block
-lfs_testbd_swear_t lfs_testbd_getwear(const struct lfs_cfg *cfg,
+lfs_testbd_swear_t lfs_testbd_getwear(lfs_testbd_t *bd,
         lfs_block_t block);
 
 // Manually set simulated wear on a given block
-int lfs_testbd_setwear(const struct lfs_cfg *cfg,
+int lfs_testbd_setwear(lfs_testbd_t *bd,
         lfs_block_t block, lfs_testbd_wear_t wear);
 
 
 #ifdef __cplusplus
-} /* extern "C" */
+}
 #endif
 
 #endif