Add LFS_READYONLY define, to allow smaller builds providing read-only mode

lfs.c

@@ -118,28 +118,25 @@ static int lfs_bd_cmp(lfs_t *lfs,
         lfs_block_t block, lfs_off_t off,
         const void *buffer, lfs_size_t size) {
     const uint8_t *data = buffer;
-    lfs_size_t diff = 0;
 
-    for (lfs_off_t i = 0; i < size; i += diff) {
-        uint8_t dat[8];
-
-        diff = lfs_min(size-i, sizeof(dat));
-        int res = lfs_bd_read(lfs,
+    for (lfs_off_t i = 0; i < size; i++) {
+        uint8_t dat;
+        int err = lfs_bd_read(lfs,
                 pcache, rcache, hint-i,
-                block, off+i, &dat, diff);
-        if (res) {
-            return res;
+                block, off+i, &dat, 1);
+        if (err) {
+            return err;
         }
 
-        res = memcmp(dat, data + i, diff);
-        if (res) {
-            return res < 0 ? LFS_CMP_LT : LFS_CMP_GT;
+        if (dat != data[i]) {
+            return (dat < data[i]) ? LFS_CMP_LT : LFS_CMP_GT;
         }
     }
 
     return LFS_CMP_EQ;
 }
 
+#ifndef LFS_READONLY
 static int lfs_bd_flush(lfs_t *lfs,
         lfs_cache_t *pcache, lfs_cache_t *rcache, bool validate) {
     if (pcache->block != LFS_BLOCK_NULL && pcache->block != LFS_BLOCK_INLINE) {
@@ -172,7 +169,9 @@ static int lfs_bd_flush(lfs_t *lfs,
 
     return 0;
 }
+#endif
 
+#ifndef LFS_READONLY
 static int lfs_bd_sync(lfs_t *lfs,
         lfs_cache_t *pcache, lfs_cache_t *rcache, bool validate) {
     lfs_cache_drop(lfs, rcache);
@@ -186,7 +185,9 @@ static int lfs_bd_sync(lfs_t *lfs,
     LFS_ASSERT(err <= 0);
     return err;
 }
+#endif
 
+#ifndef LFS_READONLY
 static int lfs_bd_prog(lfs_t *lfs,
         lfs_cache_t *pcache, lfs_cache_t *rcache, bool validate,
         lfs_block_t block, lfs_off_t off,
@@ -232,13 +233,16 @@ static int lfs_bd_prog(lfs_t *lfs,
 
     return 0;
 }
+#endif
 
+#ifndef LFS_READONLY
 static int lfs_bd_erase(lfs_t *lfs, lfs_block_t block) {
     LFS_ASSERT(block < lfs->cfg->block_count);
     int err = lfs->cfg->erase(lfs->cfg, block);
     LFS_ASSERT(err <= 0);
     return err;
 }
+#endif
 
 
 /// Small type-level utilities ///
@@ -392,10 +396,12 @@ static void lfs_ctz_fromle32(struct lfs_ctz *ctz) {
     ctz->size = lfs_fromle32(ctz->size);
 }
 
+#ifndef LFS_READONLY
 static void lfs_ctz_tole32(struct lfs_ctz *ctz) {
     ctz->head = lfs_tole32(ctz->head);
     ctz->size = lfs_tole32(ctz->size);
 }
+#endif
 
 static inline void lfs_superblock_fromle32(lfs_superblock_t *superblock) {
     superblock->version     = lfs_fromle32(superblock->version);
@@ -415,33 +421,9 @@ static inline void lfs_superblock_tole32(lfs_superblock_t *superblock) {
     superblock->attr_max    = lfs_tole32(superblock->attr_max);
 }
 
-static inline bool lfs_mlist_isopen(struct lfs_mlist *head,
-        struct lfs_mlist *node) {
-    for (struct lfs_mlist **p = &head; *p; p = &(*p)->next) {
-        if (*p == (struct lfs_mlist*)node) {
-            return true;
-        }
-    }
-
-    return false;
-}
-
-static inline void lfs_mlist_remove(lfs_t *lfs, struct lfs_mlist *mlist) {
-    for (struct lfs_mlist **p = &lfs->mlist; *p; p = &(*p)->next) {
-        if (*p == mlist) {
-            *p = (*p)->next;
-            break;
-        }
-    }
-}
-
-static inline void lfs_mlist_append(lfs_t *lfs, struct lfs_mlist *mlist) {
-    mlist->next = lfs->mlist;
-    lfs->mlist = mlist;
-}
-
 
 /// Internal operations predeclared here ///
+#ifndef LFS_READONLY
 static int lfs_dir_commit(lfs_t *lfs, lfs_mdir_t *dir,
         const struct lfs_mattr *attrs, int attrcount);
 static int lfs_dir_compact(lfs_t *lfs,
@@ -458,10 +440,13 @@ static lfs_stag_t lfs_fs_parent(lfs_t *lfs, const lfs_block_t dir[2],
         lfs_mdir_t *parent);
 static int lfs_fs_relocate(lfs_t *lfs,
         const lfs_block_t oldpair[2], lfs_block_t newpair[2]);
+#endif
 int lfs_fs_traverseraw(lfs_t *lfs,
         int (*cb)(void *data, lfs_block_t block), void *data,
         bool includeorphans);
+#ifndef LFS_READONLY
 static int lfs_fs_forceconsistency(lfs_t *lfs);
+#endif
 static int lfs_deinit(lfs_t *lfs);
 #ifdef LFS_MIGRATE
 static int lfs1_traverse(lfs_t *lfs,
@@ -469,6 +454,7 @@ static int lfs1_traverse(lfs_t *lfs,
 #endif
 
 /// Block allocator ///
+#ifndef LFS_READONLY
 static int lfs_alloc_lookahead(void *p, lfs_block_t block) {
     lfs_t *lfs = (lfs_t*)p;
     lfs_block_t off = ((block - lfs->free.off)
@@ -480,22 +466,22 @@ static int lfs_alloc_lookahead(void *p, lfs_block_t block) {
 
     return 0;
 }
+#endif
 
-// indicate allocated blocks have been committed into the filesystem, this
-// is to prevent blocks from being garbage collected in the middle of a
-// commit operation
 static void lfs_alloc_ack(lfs_t *lfs) {
     lfs->free.ack = lfs->cfg->block_count;
 }
 
-// drop the lookahead buffer, this is done during mounting and failed
-// traversals in order to avoid invalid lookahead state
-static void lfs_alloc_drop(lfs_t *lfs) {
+// Invalidate the lookahead buffer. This is done during mounting and
+// failed traversals
+static void lfs_alloc_reset(lfs_t *lfs) {
+    lfs->free.off = lfs->seed % lfs->cfg->block_size;
     lfs->free.size = 0;
     lfs->free.i = 0;
     lfs_alloc_ack(lfs);
 }
 
+#ifndef LFS_READONLY
 static int lfs_alloc(lfs_t *lfs, lfs_block_t *block) {
     while (true) {
         while (lfs->free.i != lfs->free.size) {
@@ -536,11 +522,12 @@ static int lfs_alloc(lfs_t *lfs, lfs_block_t *block) {
         memset(lfs->free.buffer, 0, lfs->cfg->lookahead_size);
         int err = lfs_fs_traverseraw(lfs, lfs_alloc_lookahead, lfs, true);
         if (err) {
-            lfs_alloc_drop(lfs);
+            lfs_alloc_reset(lfs);
             return err;
         }
     }
 }
+#endif
 
 /// Metadata pair and directory operations ///
 static lfs_stag_t lfs_dir_getslice(lfs_t *lfs, const lfs_mdir_t *dir,
@@ -673,6 +660,7 @@ static int lfs_dir_getread(lfs_t *lfs, const lfs_mdir_t *dir,
     return 0;
 }
 
+#ifndef LFS_READONLY
 static int lfs_dir_traverse_filter(void *p,
         lfs_tag_t tag, const void *buffer) {
     lfs_tag_t *filtertag = p;
@@ -700,7 +688,9 @@ static int lfs_dir_traverse_filter(void *p,
 
     return false;
 }
+#endif
 
+#ifndef LFS_READONLY
 static int lfs_dir_traverse(lfs_t *lfs,
         const lfs_mdir_t *dir, lfs_off_t off, lfs_tag_t ptag,
         const struct lfs_mattr *attrs, int attrcount,
@@ -794,6 +784,7 @@ static int lfs_dir_traverse(lfs_t *lfs,
         }
     }
 }
+#endif
 
 static lfs_stag_t lfs_dir_fetchmatch(lfs_t *lfs,
         lfs_mdir_t *dir, const lfs_block_t pair[2],
@@ -901,10 +892,8 @@ static lfs_stag_t lfs_dir_fetchmatch(lfs_t *lfs,
                 ptag ^= (lfs_tag_t)(lfs_tag_chunk(tag) & 1U) << 31;
 
                 // toss our crc into the filesystem seed for
-                // pseudorandom numbers, note we use another crc here
-                // as a collection function because it is sufficiently
-                // random and convenient
-                lfs->seed = lfs_crc(lfs->seed, &crc, sizeof(crc));
+                // pseudorandom numbers
+                lfs->seed ^= crc;
 
                 // update with what's found so far
                 besttag = tempbesttag;
@@ -1233,6 +1222,7 @@ struct lfs_commit {
     lfs_off_t end;
 };
 
+#ifndef LFS_READONLY
 static int lfs_dir_commitprog(lfs_t *lfs, struct lfs_commit *commit,
         const void *buffer, lfs_size_t size) {
     int err = lfs_bd_prog(lfs,
@@ -1247,7 +1237,9 @@ static int lfs_dir_commitprog(lfs_t *lfs, struct lfs_commit *commit,
     commit->off += size;
     return 0;
 }
+#endif
 
+#ifndef LFS_READONLY
 static int lfs_dir_commitattr(lfs_t *lfs, struct lfs_commit *commit,
         lfs_tag_t tag, const void *buffer) {
     // check if we fit
@@ -1292,15 +1284,16 @@ static int lfs_dir_commitattr(lfs_t *lfs, struct lfs_commit *commit,
     commit->ptag = tag & 0x7fffffff;
     return 0;
 }
+#endif
 
+#ifndef LFS_READONLY
 static int lfs_dir_commitcrc(lfs_t *lfs, struct lfs_commit *commit) {
+    const lfs_off_t off1 = commit->off;
+    const uint32_t crc1 = commit->crc;
     // align to program units
-    const lfs_off_t end = lfs_alignup(commit->off + 2*sizeof(uint32_t),
+    const lfs_off_t end = lfs_alignup(off1 + 2*sizeof(uint32_t),
             lfs->cfg->prog_size);
 
-    lfs_off_t off1 = 0;
-    uint32_t crc1 = 0;
-
     // create crc tags to fill up remainder of commit, note that
     // padding is not crced, which lets fetches skip padding but
     // makes committing a bit more complicated
@@ -1336,12 +1329,6 @@ static int lfs_dir_commitcrc(lfs_t *lfs, struct lfs_commit *commit) {
             return err;
         }
 
-        // keep track of non-padding checksum to verify
-        if (off1 == 0) {
-            off1 = commit->off + sizeof(uint32_t);
-            crc1 = commit->crc;
-        }
-
         commit->off += sizeof(tag)+lfs_tag_size(tag);
         commit->ptag = tag ^ ((lfs_tag_t)reset << 31);
         commit->crc = 0xffffffff; // reset crc for next "commit"
@@ -1355,7 +1342,7 @@ static int lfs_dir_commitcrc(lfs_t *lfs, struct lfs_commit *commit) {
 
     // successful commit, check checksums to make sure
     lfs_off_t off = commit->begin;
-    lfs_off_t noff = off1;
+    lfs_off_t noff = off1 + sizeof(uint32_t);
     while (off < end) {
         uint32_t crc = 0xffffffff;
         for (lfs_off_t i = off; i < noff+sizeof(uint32_t); i++) {
@@ -1392,7 +1379,9 @@ static int lfs_dir_commitcrc(lfs_t *lfs, struct lfs_commit *commit) {
 
     return 0;
 }
+#endif
 
+#ifndef LFS_READONLY
 static int lfs_dir_alloc(lfs_t *lfs, lfs_mdir_t *dir) {
     // allocate pair of dir blocks (backwards, so we write block 1 first)
     for (int i = 0; i < 2; i++) {
@@ -1430,7 +1419,9 @@ static int lfs_dir_alloc(lfs_t *lfs, lfs_mdir_t *dir) {
     // don't write out yet, let caller take care of that
     return 0;
 }
+#endif
 
+#ifndef LFS_READONLY
 static int lfs_dir_drop(lfs_t *lfs, lfs_mdir_t *dir, lfs_mdir_t *tail) {
     // steal state
     int err = lfs_dir_getgstate(lfs, tail, &lfs->gdelta);
@@ -1449,7 +1440,9 @@ static int lfs_dir_drop(lfs_t *lfs, lfs_mdir_t *dir, lfs_mdir_t *tail) {
 
     return 0;
 }
+#endif
 
+#ifndef LFS_READONLY
 static int lfs_dir_split(lfs_t *lfs,
         lfs_mdir_t *dir, const struct lfs_mattr *attrs, int attrcount,
         lfs_mdir_t *source, uint16_t split, uint16_t end) {
@@ -1482,7 +1475,9 @@ static int lfs_dir_split(lfs_t *lfs,
 
     return 0;
 }
+#endif
 
+#ifndef LFS_READONLY
 static int lfs_dir_commit_size(void *p, lfs_tag_t tag, const void *buffer) {
     lfs_size_t *size = p;
     (void)buffer;
@@ -1490,17 +1485,23 @@ static int lfs_dir_commit_size(void *p, lfs_tag_t tag, const void *buffer) {
     *size += lfs_tag_dsize(tag);
     return 0;
 }
+#endif
 
+#ifndef LFS_READONLY
 struct lfs_dir_commit_commit {
     lfs_t *lfs;
     struct lfs_commit *commit;
 };
+#endif
 
+#ifndef LFS_READONLY
 static int lfs_dir_commit_commit(void *p, lfs_tag_t tag, const void *buffer) {
     struct lfs_dir_commit_commit *commit = p;
     return lfs_dir_commitattr(commit->lfs, commit->commit, tag, buffer);
 }
+#endif
 
+#ifndef LFS_READONLY
 static int lfs_dir_compact(lfs_t *lfs,
         lfs_mdir_t *dir, const struct lfs_mattr *attrs, int attrcount,
         lfs_mdir_t *source, uint16_t begin, uint16_t end) {
@@ -1755,7 +1756,9 @@ relocate:
 
     return 0;
 }
+#endif
 
+#ifndef LFS_READONLY
 static int lfs_dir_commit(lfs_t *lfs, lfs_mdir_t *dir,
         const struct lfs_mattr *attrs, int attrcount) {
     // check for any inline files that aren't RAM backed and
@@ -1943,10 +1946,14 @@ compact:
 
     return 0;
 }
+#endif
 
 
 /// Top level directory operations ///
 int lfs_mkdir(lfs_t *lfs, const char *path) {
+#ifdef LFS_READONLY
+    return LFS_ERR_NOSYS;
+#else
     LFS_TRACE("lfs_mkdir(%p, \"%s\")", (void*)lfs, path);
     // deorphan if we haven't yet, needed at most once after poweron
     int err = lfs_fs_forceconsistency(lfs);
@@ -2043,12 +2050,11 @@ int lfs_mkdir(lfs_t *lfs, const char *path) {
 
     LFS_TRACE("lfs_mkdir -> %d", 0);
     return 0;
+#endif
 }
 
 int lfs_dir_open(lfs_t *lfs, lfs_dir_t *dir, const char *path) {
     LFS_TRACE("lfs_dir_open(%p, %p, \"%s\")", (void*)lfs, (void*)dir, path);
-    LFS_ASSERT(!lfs_mlist_isopen(lfs->mlist, (struct lfs_mlist*)dir));
-
     lfs_stag_t tag = lfs_dir_find(lfs, &dir->m, &path, NULL);
     if (tag < 0) {
         LFS_TRACE("lfs_dir_open -> %"PRId32, tag);
@@ -2091,7 +2097,8 @@ int lfs_dir_open(lfs_t *lfs, lfs_dir_t *dir, const char *path) {
 
     // add to list of mdirs
     dir->type = LFS_TYPE_DIR;
-    lfs_mlist_append(lfs, (struct lfs_mlist *)dir);
+    dir->next = (lfs_dir_t*)lfs->mlist;
+    lfs->mlist = (struct lfs_mlist*)dir;
 
     LFS_TRACE("lfs_dir_open -> %d", 0);
     return 0;
@@ -2100,7 +2107,12 @@ int lfs_dir_open(lfs_t *lfs, lfs_dir_t *dir, const char *path) {
 int lfs_dir_close(lfs_t *lfs, lfs_dir_t *dir) {
     LFS_TRACE("lfs_dir_close(%p, %p)", (void*)lfs, (void*)dir);
     // remove from list of mdirs
-    lfs_mlist_remove(lfs, (struct lfs_mlist *)dir);
+    for (struct lfs_mlist **p = &lfs->mlist; *p; p = &(*p)->next) {
+        if (*p == (struct lfs_mlist*)dir) {
+            *p = (*p)->next;
+            break;
+        }
+    }
 
     LFS_TRACE("lfs_dir_close -> %d", 0);
     return 0;
@@ -2273,6 +2285,7 @@ static int lfs_ctz_find(lfs_t *lfs,
     return 0;
 }
 
+#ifndef LFS_READONLY
 static int lfs_ctz_extend(lfs_t *lfs,
         lfs_cache_t *pcache, lfs_cache_t *rcache,
         lfs_block_t head, lfs_size_t size,
@@ -2370,6 +2383,7 @@ relocate:
         lfs_cache_drop(lfs, pcache);
     }
 }
+#endif
 
 static int lfs_ctz_traverse(lfs_t *lfs,
         const lfs_cache_t *pcache, lfs_cache_t *rcache,
@@ -2423,15 +2437,18 @@ int lfs_file_opencfg(lfs_t *lfs, lfs_file_t *file,
                  ".buffer=%p, .attrs=%p, .attr_count=%"PRIu32"})",
             (void*)lfs, (void*)file, path, flags,
             (void*)cfg, cfg->buffer, (void*)cfg->attrs, cfg->attr_count);
-    LFS_ASSERT(!lfs_mlist_isopen(lfs->mlist, (struct lfs_mlist*)file));
 
     // deorphan if we haven't yet, needed at most once after poweron
-    if ((flags & LFS_O_RDWR) != LFS_O_RDONLY) {
+    if ((flags & 3) != LFS_O_RDONLY) {
+#ifdef LFS_READONLY
+        return LFS_ERR_INVAL;
+#else
         int err = lfs_fs_forceconsistency(lfs);
         if (err) {
             LFS_TRACE("lfs_file_opencfg -> %d", err);
             return err;
         }
+#endif
     }
 
     // setup simple file details
@@ -2451,9 +2468,14 @@ int lfs_file_opencfg(lfs_t *lfs, lfs_file_t *file,
 
     // get id, add to list of mdirs to catch update changes
     file->type = LFS_TYPE_REG;
-    lfs_mlist_append(lfs, (struct lfs_mlist *)file);
+    file->next = (lfs_file_t*)lfs->mlist;
+    lfs->mlist = (struct lfs_mlist*)file;
 
     if (tag == LFS_ERR_NOENT) {
+#ifdef LFS_READONLY
+        err = LFS_ERR_NOENT;
+        goto cleanup;
+#else
         if (!(flags & LFS_O_CREAT)) {
             err = LFS_ERR_NOENT;
             goto cleanup;
@@ -2477,6 +2499,7 @@ int lfs_file_opencfg(lfs_t *lfs, lfs_file_t *file,
         }
 
         tag = LFS_MKTAG(LFS_TYPE_INLINESTRUCT, 0, 0);
+#endif
     } else if (flags & LFS_O_EXCL) {
         err = LFS_ERR_EXIST;
         goto cleanup;
@@ -2500,7 +2523,7 @@ int lfs_file_opencfg(lfs_t *lfs, lfs_file_t *file,
 
     // fetch attrs
     for (unsigned i = 0; i < file->cfg->attr_count; i++) {
-        if ((file->flags & LFS_O_RDWR) != LFS_O_WRONLY) {
+        if ((file->flags & 3) != LFS_O_WRONLY) {
             lfs_stag_t res = lfs_dir_get(lfs, &file->m,
                     LFS_MKTAG(0x7ff, 0x3ff, 0),
                     LFS_MKTAG(LFS_TYPE_USERATTR + file->cfg->attrs[i].type,
@@ -2512,7 +2535,7 @@ int lfs_file_opencfg(lfs_t *lfs, lfs_file_t *file,
             }
         }
 
-        if ((file->flags & LFS_O_RDWR) != LFS_O_RDONLY) {
+        if ((file->flags & 3) != LFS_O_RDONLY) {
             if (file->cfg->attrs[i].size > lfs->attr_max) {
                 err = LFS_ERR_NOSPC;
                 goto cleanup;
@@ -2587,7 +2610,12 @@ int lfs_file_close(lfs_t *lfs, lfs_file_t *file) {
     int err = lfs_file_sync(lfs, file);
 
     // remove from list of mdirs
-    lfs_mlist_remove(lfs, (struct lfs_mlist*)file);
+    for (struct lfs_mlist **p = &lfs->mlist; *p; p = &(*p)->next) {
+        if (*p == (struct lfs_mlist*)file) {
+            *p = (*p)->next;
+            break;
+        }
+    }
 
     // clean up memory
     if (!file->cfg->buffer) {
@@ -2599,6 +2627,8 @@ int lfs_file_close(lfs_t *lfs, lfs_file_t *file) {
     return err;
 }
 
+
+#ifndef LFS_READONLY
 static int lfs_file_relocate(lfs_t *lfs, lfs_file_t *file) {
     LFS_ASSERT(file->flags & LFS_F_OPENED);
 
@@ -2669,7 +2699,9 @@ relocate:
         lfs_cache_drop(lfs, &lfs->pcache);
     }
 }
+#endif
 
+#ifndef LFS_READONLY
 static int lfs_file_outline(lfs_t *lfs, lfs_file_t *file) {
     file->off = file->pos;
     lfs_alloc_ack(lfs);
@@ -2681,6 +2713,7 @@ static int lfs_file_outline(lfs_t *lfs, lfs_file_t *file) {
     file->flags &= ~LFS_F_INLINE;
     return 0;
 }
+#endif
 
 static int lfs_file_flush(lfs_t *lfs, lfs_file_t *file) {
     LFS_ASSERT(file->flags & LFS_F_OPENED);
@@ -2692,6 +2725,7 @@ static int lfs_file_flush(lfs_t *lfs, lfs_file_t *file) {
         file->flags &= ~LFS_F_READING;
     }
 
+#ifndef LFS_READONLY
     if (file->flags & LFS_F_WRITING) {
         lfs_off_t pos = file->pos;
 
@@ -2758,6 +2792,7 @@ relocate:
 
         file->pos = pos;
     }
+#endif
 
     return 0;
 }
@@ -2779,6 +2814,8 @@ int lfs_file_sync(lfs_t *lfs, lfs_file_t *file) {
         return err;
     }
 
+
+#ifndef LFS_READONLY
     if ((file->flags & LFS_F_DIRTY) &&
             !lfs_pair_isnull(file->m.pair)) {
         // update dir entry
@@ -2814,6 +2851,7 @@ int lfs_file_sync(lfs_t *lfs, lfs_file_t *file) {
 
         file->flags &= ~LFS_F_DIRTY;
     }
+#endif
 
     LFS_TRACE("lfs_file_sync -> %d", 0);
     return 0;
@@ -2824,11 +2862,12 @@ lfs_ssize_t lfs_file_read(lfs_t *lfs, lfs_file_t *file,
     LFS_TRACE("lfs_file_read(%p, %p, %p, %"PRIu32")",
             (void*)lfs, (void*)file, buffer, size);
     LFS_ASSERT(file->flags & LFS_F_OPENED);
-    LFS_ASSERT((file->flags & LFS_O_RDWR) != LFS_O_WRONLY);
+    LFS_ASSERT((file->flags & 3) != LFS_O_WRONLY);
 
     uint8_t *data = buffer;
     lfs_size_t nsize = size;
 
+#ifndef LFS_READONLY
     if (file->flags & LFS_F_WRITING) {
         // flush out any writes
         int err = lfs_file_flush(lfs, file);
@@ -2837,6 +2876,7 @@ lfs_ssize_t lfs_file_read(lfs_t *lfs, lfs_file_t *file,
             return err;
         }
     }
+#endif
 
     if (file->pos >= file->ctz.size) {
         // eof if past end
@@ -2904,8 +2944,12 @@ lfs_ssize_t lfs_file_write(lfs_t *lfs, lfs_file_t *file,
     LFS_TRACE("lfs_file_write(%p, %p, %p, %"PRIu32")",
             (void*)lfs, (void*)file, buffer, size);
     LFS_ASSERT(file->flags & LFS_F_OPENED);
-    LFS_ASSERT((file->flags & LFS_O_RDWR) != LFS_O_RDONLY);
+    LFS_ASSERT((file->flags & 3) != LFS_O_RDONLY);
 
+
+#ifdef LFS_READONLY
+    return LFS_ERR_NOSYS;
+#else
     const uint8_t *data = buffer;
     lfs_size_t nsize = size;
 
@@ -3028,6 +3072,7 @@ relocate:
     file->flags &= ~LFS_F_ERRED;
     LFS_TRACE("lfs_file_write -> %"PRId32, size);
     return size;
+#endif
 }
 
 lfs_soff_t lfs_file_seek(lfs_t *lfs, lfs_file_t *file,
@@ -3069,13 +3114,16 @@ int lfs_file_truncate(lfs_t *lfs, lfs_file_t *file, lfs_off_t size) {
     LFS_TRACE("lfs_file_truncate(%p, %p, %"PRIu32")",
             (void*)lfs, (void*)file, size);
     LFS_ASSERT(file->flags & LFS_F_OPENED);
-    LFS_ASSERT((file->flags & LFS_O_RDWR) != LFS_O_RDONLY);
+    LFS_ASSERT((file->flags & 3) != LFS_O_RDONLY);
 
     if (size > LFS_FILE_MAX) {
         LFS_TRACE("lfs_file_truncate -> %d", LFS_ERR_INVAL);
         return LFS_ERR_INVAL;
     }
 
+#ifdef LFS_READONLY
+    return LFS_ERR_NOSYS;
+#else
     lfs_off_t pos = file->pos;
     lfs_off_t oldsize = lfs_file_size(lfs, file);
     if (size < oldsize) {
@@ -3127,6 +3175,7 @@ int lfs_file_truncate(lfs_t *lfs, lfs_file_t *file, lfs_off_t size) {
 
     LFS_TRACE("lfs_file_truncate -> %d", 0);
     return 0;
+#endif
 }
 
 lfs_soff_t lfs_file_tell(lfs_t *lfs, lfs_file_t *file) {
@@ -3153,11 +3202,15 @@ lfs_soff_t lfs_file_size(lfs_t *lfs, lfs_file_t *file) {
     LFS_TRACE("lfs_file_size(%p, %p)", (void*)lfs, (void*)file);
     LFS_ASSERT(file->flags & LFS_F_OPENED);
     (void)lfs;
+
+#ifndef LFS_READONLY
     if (file->flags & LFS_F_WRITING) {
         LFS_TRACE("lfs_file_size -> %"PRId32,
                 lfs_max(file->pos, file->ctz.size));
         return lfs_max(file->pos, file->ctz.size);
-    } else {
+    } else
+#endif
+    {
         LFS_TRACE("lfs_file_size -> %"PRId32, file->ctz.size);
         return file->ctz.size;
     }
@@ -3181,6 +3234,10 @@ int lfs_stat(lfs_t *lfs, const char *path, struct lfs_info *info) {
 
 int lfs_remove(lfs_t *lfs, const char *path) {
     LFS_TRACE("lfs_remove(%p, \"%s\")", (void*)lfs, path);
+
+#ifdef LFS_READONLY
+    return LFS_ERR_NOSYS;
+#else
     // deorphan if we haven't yet, needed at most once after poweron
     int err = lfs_fs_forceconsistency(lfs);
     if (err) {
@@ -3258,11 +3315,15 @@ int lfs_remove(lfs_t *lfs, const char *path) {
 
     LFS_TRACE("lfs_remove -> %d", 0);
     return 0;
+#endif
 }
 
 int lfs_rename(lfs_t *lfs, const char *oldpath, const char *newpath) {
     LFS_TRACE("lfs_rename(%p, \"%s\", \"%s\")", (void*)lfs, oldpath, newpath);
 
+#ifdef LFS_READONLY
+    return LFS_ERR_NOSYS;
+#else
     // deorphan if we haven't yet, needed at most once after poweron
     int err = lfs_fs_forceconsistency(lfs);
     if (err) {
@@ -3403,6 +3464,7 @@ int lfs_rename(lfs_t *lfs, const char *oldpath, const char *newpath) {
 
     LFS_TRACE("lfs_rename -> %d", 0);
     return 0;
+#endif
 }
 
 lfs_ssize_t lfs_getattr(lfs_t *lfs, const char *path,
@@ -3446,6 +3508,7 @@ lfs_ssize_t lfs_getattr(lfs_t *lfs, const char *path,
     return size;
 }
 
+#ifndef LFS_READONLY
 static int lfs_commitattr(lfs_t *lfs, const char *path,
         uint8_t type, const void *buffer, lfs_size_t size) {
     lfs_mdir_t cwd;
@@ -3467,11 +3530,15 @@ static int lfs_commitattr(lfs_t *lfs, const char *path,
     return lfs_dir_commit(lfs, &cwd, LFS_MKATTRS(
             {LFS_MKTAG(LFS_TYPE_USERATTR + type, id, size), buffer}));
 }
+#endif
 
 int lfs_setattr(lfs_t *lfs, const char *path,
         uint8_t type, const void *buffer, lfs_size_t size) {
     LFS_TRACE("lfs_setattr(%p, \"%s\", %"PRIu8", %p, %"PRIu32")",
             (void*)lfs, path, type, buffer, size);
+#ifdef LFS_READONLY
+    return LFS_ERR_NOSYS;
+#else
     if (size > lfs->attr_max) {
         LFS_TRACE("lfs_setattr -> %d", LFS_ERR_NOSPC);
         return LFS_ERR_NOSPC;
@@ -3480,13 +3547,18 @@ int lfs_setattr(lfs_t *lfs, const char *path,
     int err = lfs_commitattr(lfs, path, type, buffer, size);
     LFS_TRACE("lfs_setattr -> %d", err);
     return err;
+#endif
 }
 
 int lfs_removeattr(lfs_t *lfs, const char *path, uint8_t type) {
     LFS_TRACE("lfs_removeattr(%p, \"%s\", %"PRIu8")", (void*)lfs, path, type);
+#ifdef LFS_READONLY
+    return LFS_ERR_NOSYS;
+#else
     int err = lfs_commitattr(lfs, path, type, NULL, 0x3ff);
     LFS_TRACE("lfs_removeattr -> %d", err);
     return err;
+#endif
 }
 
 
@@ -3632,6 +3704,10 @@ int lfs_format(lfs_t *lfs, const struct lfs_config *cfg) {
             cfg->block_cycles, cfg->cache_size, cfg->lookahead_size,
             cfg->read_buffer, cfg->prog_buffer, cfg->lookahead_buffer,
             cfg->name_max, cfg->file_max, cfg->attr_max);
+
+#ifdef LFS_READONLY
+    return LFS_ERR_NOSYS;
+#else
     int err = 0;
     {
         err = lfs_init(lfs, cfg);
@@ -3694,6 +3770,8 @@ cleanup:
     lfs_deinit(lfs);
     LFS_TRACE("lfs_format -> %d", err);
     return err;
+
+#endif
 }
 
 int lfs_mount(lfs_t *lfs, const struct lfs_config *cfg) {
@@ -3828,10 +3906,8 @@ int lfs_mount(lfs_t *lfs, const struct lfs_config *cfg) {
     lfs->gstate.tag += !lfs_tag_isvalid(lfs->gstate.tag);
     lfs->gdisk = lfs->gstate;
 
-    // setup free lookahead, to distribute allocations uniformly across
-    // boots, we start the allocator at a random location
-    lfs->free.off = lfs->seed % lfs->cfg->block_count;
-    lfs_alloc_drop(lfs);
+    // setup free lookahead
+    lfs_alloc_reset(lfs);
 
     LFS_TRACE("lfs_mount -> %d", 0);
     return 0;
@@ -3935,6 +4011,7 @@ int lfs_fs_traverseraw(lfs_t *lfs,
             }
         }
 
+#ifndef LFS_READONLY
         if ((f->flags & LFS_F_WRITING) && !(f->flags & LFS_F_INLINE)) {
             int err = lfs_ctz_traverse(lfs, &f->cache, &lfs->rcache,
                     f->block, f->pos, cb, data);
@@ -3942,6 +4019,7 @@ int lfs_fs_traverseraw(lfs_t *lfs,
                 return err;
             }
         }
+#endif
     }
 
     return 0;
@@ -3956,6 +4034,7 @@ int lfs_fs_traverse(lfs_t *lfs,
     return err;
 }
 
+#ifndef LFS_READONLY
 static int lfs_fs_pred(lfs_t *lfs,
         const lfs_block_t pair[2], lfs_mdir_t *pdir) {
     // iterate over all directory directory entries
@@ -3981,12 +4060,16 @@ static int lfs_fs_pred(lfs_t *lfs,
 
     return LFS_ERR_NOENT;
 }
+#endif
 
+#ifndef LFS_READONLY
 struct lfs_fs_parent_match {
     lfs_t *lfs;
     const lfs_block_t pair[2];
 };
+#endif
 
+#ifndef LFS_READONLY
 static int lfs_fs_parent_match(void *data,
         lfs_tag_t tag, const void *buffer) {
     struct lfs_fs_parent_match *find = data;
@@ -4005,7 +4088,9 @@ static int lfs_fs_parent_match(void *data,
     lfs_pair_fromle32(child);
     return (lfs_pair_cmp(child, find->pair) == 0) ? LFS_CMP_EQ : LFS_CMP_LT;
 }
+#endif
 
+#ifndef LFS_READONLY
 static lfs_stag_t lfs_fs_parent(lfs_t *lfs, const lfs_block_t pair[2],
         lfs_mdir_t *parent) {
     // use fetchmatch with callback to find pairs
@@ -4032,7 +4117,9 @@ static lfs_stag_t lfs_fs_parent(lfs_t *lfs, const lfs_block_t pair[2],
 
     return LFS_ERR_NOENT;
 }
+#endif
 
+#ifndef LFS_READONLY
 static int lfs_fs_relocate(lfs_t *lfs,
         const lfs_block_t oldpair[2], lfs_block_t newpair[2]) {
     // update internal root
@@ -4127,14 +4214,18 @@ static int lfs_fs_relocate(lfs_t *lfs,
 
     return 0;
 }
+#endif
 
+#ifndef LFS_READONLY
 static void lfs_fs_preporphans(lfs_t *lfs, int8_t orphans) {
     LFS_ASSERT(lfs_tag_size(lfs->gstate.tag) > 0 || orphans >= 0);
     lfs->gstate.tag += orphans;
     lfs->gstate.tag = ((lfs->gstate.tag & ~LFS_MKTAG(0x800, 0, 0)) |
             ((uint32_t)lfs_gstate_hasorphans(&lfs->gstate) << 31));
 }
+#endif
 
+#ifndef LFS_READONLY
 static void lfs_fs_prepmove(lfs_t *lfs,
         uint16_t id, const lfs_block_t pair[2]) {
     lfs->gstate.tag = ((lfs->gstate.tag & ~LFS_MKTAG(0x7ff, 0x3ff, 0)) |
@@ -4142,7 +4233,9 @@ static void lfs_fs_prepmove(lfs_t *lfs,
     lfs->gstate.pair[0] = (id != 0x3ff) ? pair[0] : 0;
     lfs->gstate.pair[1] = (id != 0x3ff) ? pair[1] : 0;
 }
+#endif
 
+#ifndef LFS_READONLY
 static int lfs_fs_demove(lfs_t *lfs) {
     if (!lfs_gstate_hasmove(&lfs->gdisk)) {
         return 0;
@@ -4172,7 +4265,9 @@ static int lfs_fs_demove(lfs_t *lfs) {
 
     return 0;
 }
+#endif
 
+#ifndef LFS_READONLY
 static int lfs_fs_deorphan(lfs_t *lfs) {
     if (!lfs_gstate_hasorphans(&lfs->gstate)) {
         return 0;
@@ -4246,7 +4341,9 @@ static int lfs_fs_deorphan(lfs_t *lfs) {
     lfs_fs_preporphans(lfs, -lfs_gstate_getorphans(&lfs->gstate));
     return 0;
 }
+#endif
 
+#ifndef LFS_READONLY
 static int lfs_fs_forceconsistency(lfs_t *lfs) {
     int err = lfs_fs_demove(lfs);
     if (err) {
@@ -4260,6 +4357,7 @@ static int lfs_fs_forceconsistency(lfs_t *lfs) {
 
     return 0;
 }
+#endif
 
 static int lfs_fs_size_count(void *p, lfs_block_t block) {
     (void)block;

lfs.h

@@ -76,6 +76,7 @@ enum lfs_error {
     LFS_ERR_EXIST       = -17,  // Entry already exists
     LFS_ERR_NOTDIR      = -20,  // Entry is not a dir
     LFS_ERR_ISDIR       = -21,  // Entry is a dir
+    LFS_ERR_NOSYS       = -38,  // Function not implemened
     LFS_ERR_NOTEMPTY    = -39,  // Dir is not empty
     LFS_ERR_BADF        = -9,   // Bad file number
     LFS_ERR_FBIG        = -27,  // File too large