Changed lfs_dir_alloc to maximize block cycles for new metadata pairs

Previously we only bumped the revision count if an eviction would occur
immediately (and possibly corrupt littlefs). This works, but does risk
an unoptimal superblock size if an almost-exhausted superblock was
allocated during lfs_format.

As pointed out by tim-nordell-nimbelink, we can align the revision count
to maximize the number of block cycles without breaking the existing
requirements of increasing revision counts.

As an added benefit, littlefs's wear-leveling should behave more
consistently after this change.

Makefile

@@ -26,8 +26,6 @@ endif
 override CFLAGS += -I.
 override CFLAGS += -std=c99 -Wall -pedantic
 override CFLAGS += -Wextra -Wshadow -Wjump-misses-init -Wundef
-# Remove missing-field-initializers because of GCC bug
-override CFLAGS += -Wno-missing-field-initializers
 
 ifdef VERBOSE
 override TFLAGS += -v

lfs.c

@@ -1375,8 +1375,12 @@ static int lfs_dir_alloc(lfs_t *lfs, lfs_mdir_t *dir) {
         return err;
     }
 
-    // make sure we don't immediately evict
+    // to make sure we don't immediately evict, align the new revision count
-    dir->rev += dir->rev & 1;
+    // to our block_cycles modulus, see lfs_dir_compact for why our modulus
+    // is tweaked this way
+    if (lfs->cfg->block_cycles > 0) {
+        dir->rev = lfs_alignup(dir->rev, ((lfs->cfg->block_cycles+1)|1));
+    }
 
     // set defaults
     dir->off = sizeof(dir->rev);
@@ -2432,9 +2436,9 @@ int lfs_file_opencfg(lfs_t *lfs, lfs_file_t *file,
 
         // get next slot and create entry to remember name
         err = lfs_dir_commit(lfs, &file->m, LFS_MKATTRS(
-                {LFS_MKTAG(LFS_TYPE_CREATE, file->id, 0)},
+                {LFS_MKTAG(LFS_TYPE_CREATE, file->id, 0), NULL},
                 {LFS_MKTAG(LFS_TYPE_REG, file->id, nlen), path},
-                {LFS_MKTAG(LFS_TYPE_INLINESTRUCT, file->id, 0)}));
+                {LFS_MKTAG(LFS_TYPE_INLINESTRUCT, file->id, 0), NULL}));
         if (err) {
             err = LFS_ERR_NAMETOOLONG;
             goto cleanup;
@@ -3200,7 +3204,7 @@ int lfs_remove(lfs_t *lfs, const char *path) {
 
     // delete the entry
     err = lfs_dir_commit(lfs, &cwd, LFS_MKATTRS(
-            {LFS_MKTAG(LFS_TYPE_DELETE, lfs_tag_id(tag), 0)}));
+            {LFS_MKTAG(LFS_TYPE_DELETE, lfs_tag_id(tag), 0), NULL}));
     if (err) {
         lfs->mlist = dir.next;
         LFS_TRACE("lfs_remove -> %d", err);
@@ -3326,12 +3330,12 @@ int lfs_rename(lfs_t *lfs, const char *oldpath, const char *newpath) {
     // move over all attributes
     err = lfs_dir_commit(lfs, &newcwd, LFS_MKATTRS(
             {LFS_MKTAG_IF(prevtag != LFS_ERR_NOENT,
-                LFS_TYPE_DELETE, newid, 0)},
+                LFS_TYPE_DELETE, newid, 0), NULL},
-            {LFS_MKTAG(LFS_TYPE_CREATE, newid, 0)},
+            {LFS_MKTAG(LFS_TYPE_CREATE, newid, 0), NULL},
             {LFS_MKTAG(lfs_tag_type3(oldtag), newid, strlen(newpath)), newpath},
             {LFS_MKTAG(LFS_FROM_MOVE, newid, lfs_tag_id(oldtag)), &oldcwd},
             {LFS_MKTAG_IF(samepair,
-                LFS_TYPE_DELETE, newoldid, 0)}));
+                LFS_TYPE_DELETE, newoldid, 0), NULL}));
     if (err) {
         lfs->mlist = prevdir.next;
         LFS_TRACE("lfs_rename -> %d", err);
@@ -3344,7 +3348,7 @@ int lfs_rename(lfs_t *lfs, const char *oldpath, const char *newpath) {
         // prep gstate and delete move id
         lfs_fs_prepmove(lfs, 0x3ff, NULL);
         err = lfs_dir_commit(lfs, &oldcwd, LFS_MKATTRS(
-                {LFS_MKTAG(LFS_TYPE_DELETE, lfs_tag_id(oldtag), 0)}));
+                {LFS_MKTAG(LFS_TYPE_DELETE, lfs_tag_id(oldtag), 0), NULL}));
         if (err) {
             lfs->mlist = prevdir.next;
             LFS_TRACE("lfs_rename -> %d", err);
@@ -3636,7 +3640,7 @@ int lfs_format(lfs_t *lfs, const struct lfs_config *cfg) {
 
         lfs_superblock_tole32(&superblock);
         err = lfs_dir_commit(lfs, &root, LFS_MKATTRS(
-                {LFS_MKTAG(LFS_TYPE_CREATE, 0, 0)},
+                {LFS_MKTAG(LFS_TYPE_CREATE, 0, 0), NULL},
                 {LFS_MKTAG(LFS_TYPE_SUPERBLOCK, 0, 8), "littlefs"},
                 {LFS_MKTAG(LFS_TYPE_INLINESTRUCT, 0, sizeof(superblock)),
                     &superblock}));
@@ -4050,7 +4054,7 @@ static int lfs_fs_relocate(lfs_t *lfs,
         lfs_pair_tole32(newpair);
         int err = lfs_dir_commit(lfs, &parent, LFS_MKATTRS(
                 {LFS_MKTAG_IF(moveid != 0x3ff,
-                    LFS_TYPE_DELETE, moveid, 0)},
+                    LFS_TYPE_DELETE, moveid, 0), NULL},
                 {tag, newpair}));
         lfs_pair_fromle32(newpair);
         if (err) {
@@ -4084,7 +4088,7 @@ static int lfs_fs_relocate(lfs_t *lfs,
         lfs_pair_tole32(newpair);
         err = lfs_dir_commit(lfs, &parent, LFS_MKATTRS(
                 {LFS_MKTAG_IF(moveid != 0x3ff,
-                    LFS_TYPE_DELETE, moveid, 0)},
+                    LFS_TYPE_DELETE, moveid, 0), NULL},
                 {LFS_MKTAG(LFS_TYPE_TAIL + parent.split, 0x3ff, 8), newpair}));
         lfs_pair_fromle32(newpair);
         if (err) {
@@ -4132,7 +4136,7 @@ static int lfs_fs_demove(lfs_t *lfs) {
     uint16_t moveid = lfs_tag_id(lfs->gdisk.tag);
     lfs_fs_prepmove(lfs, 0x3ff, NULL);
     err = lfs_dir_commit(lfs, &movedir, LFS_MKATTRS(
-            {LFS_MKTAG(LFS_TYPE_DELETE, moveid, 0)}));
+            {LFS_MKTAG(LFS_TYPE_DELETE, moveid, 0), NULL}));
     if (err) {
         return err;
     }