Cleaned up config usage in file logic

The main change here was to drop the in-place twiddling of custom
attributes to match the internal attribute structures. The original
thought was that this could allow the compiler to garbage collect more
of the custom attribute logic when not used, but since this occurs in
the common lfs_file_opencfg function, gc can't really happen.

Not twiddling the user's structure is the polite thing to do, opens up
the ability to store the lfs_attr structure in ROM, and avoids surprising
the user if they attempt to use the structure for their own purposes.

This means we can make the lfs_attr structure const and rely on the list
in the lfs_file_config structure, similar to how we rely on the global
lfs_config structure.

Some other tweaks:
- Dropped the global file_buffer, replaced entirely by per-file buffers.
- Updated LFS_INLINE_MAX and LFS_ATTR_MAX to correct values
- Added workaround for compiler bug related to zero initializer:
  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53119

lfs.c

@@ -759,7 +759,7 @@ static int lfs_dir_alloc(lfs_t *lfs, lfs_mdir_t *dir,
     dir->tail[1] = tail[1];
     dir->erased = false;
     dir->split = split;
-    dir->locals = (lfs_globals_t){0};
+    dir->locals = (lfs_globals_t){{{0}}};
 
     // don't write out yet, let caller take care of that
     return 0;
@@ -775,7 +775,7 @@ static int lfs_dir_compact(lfs_t *lfs,
     // There's nothing special about our global delta, so feed it back
     // into the global global delta
     lfs_globalsxor(&lfs->diff, &dir->locals);
-    dir->locals = (lfs_globals_t){0};
+    dir->locals = (lfs_globals_t){{{0}}};
 
     // increment revision count
     dir->rev += 1;
@@ -929,7 +929,7 @@ relocate:
     if (!relocated) {
         // successful commit, update globals
         lfs_globalsxor(&dir->locals, &lfs->diff);
-        lfs->diff = (lfs_globals_t){0};
+        lfs->diff = (lfs_globals_t){{{0}}};
     } else {
         // update references if we relocated
         LFS_DEBUG("Relocating %d %d to %d %d",
@@ -1070,7 +1070,7 @@ compact:
         dir->etag = commit.ptag;
         // successful commit, update globals
         lfs_globalsxor(&dir->locals, &lfs->diff);
-        lfs->diff = (lfs_globals_t){0};
+        lfs->diff = (lfs_globals_t){{{0}}};
     }
 
     // update globals that are affected
@@ -1142,7 +1142,7 @@ static int32_t lfs_dir_find(lfs_t *lfs,
         uint16_t tempcount = 0;
         lfs_block_t temptail[2] = {0xffffffff, 0xffffffff};
         bool tempsplit = false;
-        lfs_globals_t templocals = (lfs_globals_t){0};
+        lfs_globals_t templocals = (lfs_globals_t){{{0}}};
 
         while (true) {
             // extract next tag
@@ -1882,37 +1882,30 @@ int lfs_file_opencfg(lfs_t *lfs, lfs_file_t *file,
     file->id = lfs_tagid(tag);
     file->flags = flags;
     file->pos = 0;
-    file->attrs = NULL;
-
-    if (cfg && cfg->attrs) {
-        // fetch attrs
-        for (const struct lfs_attr *a = cfg->attrs; a; a = a->next) {
-            if ((file->flags & 3) != LFS_O_WRONLY) {
-                int32_t res = lfs_dir_get(lfs, &cwd, 0x7ffff000,
-                        LFS_MKTAG(0x100 | a->type, file->id, a->size), a->buffer);
-                if (res < 0 && res != LFS_ERR_NOENT) {
-                    return res;
-                }
-            }
-
-            if ((file->flags & 3) != LFS_O_RDONLY) {
-                if (a->size > lfs->attr_size) {
-                    return LFS_ERR_NOSPC;
-                }
 
-                file->flags |= LFS_F_DIRTY;
+    // fetch attrs
+    for (const struct lfs_attr *a = file->cfg->attrs; a; a = a->next) {
+        if ((file->flags & 3) != LFS_O_WRONLY) {
+            int32_t res = lfs_dir_get(lfs, &cwd, 0x7ffff000,
+                    LFS_MKTAG(0x100 | a->type, file->id, a->size), a->buffer);
+            if (res < 0 && res != LFS_ERR_NOENT) {
+                return res;
             }
         }
 
-        file->attrs = cfg->attrs;
+        if ((file->flags & 3) != LFS_O_RDONLY) {
+            if (a->size > lfs->attr_size) {
+                return LFS_ERR_NOSPC;
+            }
+
+            file->flags |= LFS_F_DIRTY;
+        }
     }
 
     // allocate buffer if needed
     file->cache.block = 0xffffffff;
-    if (file->cfg && file->cfg->buffer) {
+    if (file->cfg->buffer) {
         file->cache.buffer = file->cfg->buffer;
-    } else if (lfs->cfg->file_buffer) {
-        file->cache.buffer = lfs->cfg->file_buffer;
     } else if ((file->flags & 3) == LFS_O_RDONLY) {
         file->cache.buffer = lfs_malloc(lfs->cfg->read_size);
         if (!file->cache.buffer) {
@@ -1954,7 +1947,8 @@ int lfs_file_opencfg(lfs_t *lfs, lfs_file_t *file,
 
 int lfs_file_open(lfs_t *lfs, lfs_file_t *file,
         const char *path, int flags) {
-    return lfs_file_opencfg(lfs, file, path, flags, NULL);
+    static const struct lfs_file_config defaults = {0};
+    return lfs_file_opencfg(lfs, file, path, flags, &defaults);
 }
 
 int lfs_file_close(lfs_t *lfs, lfs_file_t *file) {
@@ -1969,7 +1963,7 @@ int lfs_file_close(lfs_t *lfs, lfs_file_t *file) {
     }
 
     // clean up memory
-    if (!(file->cfg && file->cfg->buffer) && !lfs->cfg->file_buffer) {
+    if (file->cfg->buffer) {
         lfs_free(file->cache.buffer);
     }
 
@@ -2119,7 +2113,7 @@ int lfs_file_sync(lfs_t *lfs, lfs_file_t *file) {
             int err = lfs_dir_commit(lfs, &cwd,
                     LFS_MKATTR(LFS_TYPE_CTZSTRUCT, file->id,
                         &file->ctz.head, sizeof(file->ctz),
-                    LFS_MKATTR(LFS_FROM_ATTRS, file->id, file->attrs, 0,
+                    LFS_MKATTR(LFS_FROM_ATTRS, file->id, file->cfg->attrs, 0,
                     NULL)));
             if (err) {
                 return err;
@@ -2128,7 +2122,7 @@ int lfs_file_sync(lfs_t *lfs, lfs_file_t *file) {
             int err = lfs_dir_commit(lfs, &cwd,
                     LFS_MKATTR(LFS_TYPE_INLINESTRUCT, file->id,
                             file->cache.buffer, file->ctz.size,
-                    LFS_MKATTR(LFS_FROM_ATTRS, file->id, file->attrs, 0,
+                    LFS_MKATTR(LFS_FROM_ATTRS, file->id, file->cfg->attrs, 0,
                     NULL)));
             if (err) {
                 return err;
@@ -2237,7 +2231,7 @@ lfs_ssize_t lfs_file_write(lfs_t *lfs, lfs_file_t *file,
     }
 
     if ((file->flags & LFS_F_INLINE) &&
-            file->pos + nsize >= lfs->cfg->inline_size) {
+            file->pos + nsize >= lfs->inline_size) {
         // inline file doesn't fit anymore
         file->block = 0xfffffffe;
         file->off = file->pos;
@@ -3365,7 +3359,7 @@ int lfs_scan(lfs_t *lfs) {
     }
 
     lfs_mdir_t dir = {.tail = {0, 1}};
-    lfs->diff = (lfs_globals_t){0};
+    lfs->diff = (lfs_globals_t){{{0}}};
 
     // iterate over all directory directory entries
     while (!lfs_pairisnull(dir.tail)) {
@@ -3382,7 +3376,7 @@ int lfs_scan(lfs_t *lfs) {
     // TODO does this only run once?
     // TODO Should we inline this into init??
     lfs_globalsxor(&lfs->globals, &lfs->diff);
-    lfs->diff = (lfs_globals_t){0};
+    lfs->diff = (lfs_globals_t){{{0}}};
     if (!lfs_pairisnull(lfs->globals.move.pair)) {
         LFS_DEBUG("Found move %d %d %d",
                 lfs->globals.move.pair[0],

lfs.h

@@ -54,16 +54,18 @@ typedef uint32_t lfs_block_t;
 // read and prog cache, but if a file can be inline it does not need its own
 // data block. LFS_ATTR_MAX + LFS_INLINE_MAX must be <= 0xffff. Stored in
 // superblock and must be respected by other littlefs drivers.
+// TODO doc
 #ifndef LFS_INLINE_MAX
-#define LFS_INLINE_MAX 0x3ff
+#define LFS_INLINE_MAX 0xfff
 #endif
 
 // Maximum size of all attributes per file in bytes, may be redefined but a
 // a smaller LFS_ATTR_MAX has no benefit. LFS_ATTR_MAX + LFS_INLINE_MAX
 // must be <= 0xffff. Stored in superblock and must be respected by other
 // littlefs drivers.
+// TODO doc
 #ifndef LFS_ATTR_MAX
-#define LFS_ATTR_MAX 0x3f
+#define LFS_ATTR_MAX 0xfff
 #endif
 
 // Max name size in bytes, may be redefined to reduce the size of the
@@ -211,10 +213,6 @@ struct lfs_config {
     // 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;
-
     // Optional upper limit on inlined files in bytes. Large inline files
     // require a larger read and prog cache, but if a file can be inlined it
     // does not need its own data block. Must be smaller than the read size
@@ -317,7 +315,6 @@ typedef struct lfs_file {
     } ctz;
 
     const struct lfs_file_config *cfg;
-    const struct lfs_attr *attrs;
     uint32_t flags;
     lfs_off_t pos;
     lfs_block_t block;