Introduced the LFS_O_SNAPSHOT flag

LFS_O_SNAPSHOT brings back some of littlefs's idiosyncratic behavior
removed in the changes to open file syncing in a form that may be more
useful for users.

LFS_O_SNAPSHOT allows you to open a "snapshot" of a file. This is a cheap,
local copy of a file who's changes are not reflected on disk.

Internally, snapshot files use the same mechanism as pending writes. A
separate, copy-on-write CTZ skip-list is created, with read-only
references to the existing data blocks until a write occurs. The
difference is that snapshot files are not enrolled in the mlist, meaning
they won't get updates from open file syncs, and during close their
contents are simply discarded.

As an extra benefit, LFS_O_CREAT | LFS_O_SNAPSHOT is equivalent to
Linux's O_TMPFILE, making it easy to create temporary, unnamed files.

This may be useful for embedded development, where unnamed flash-backed
buffers may provide a slower, but larger, alternative to RAM-backed
buffers.

lfs.c

@@ -24,6 +24,14 @@ static inline void lfs_cache_zero(lfs_t *lfs, lfs_cache_t *pcache) {
     pcache->block = LFS_BLOCK_NULL;
 }
 
+static inline void lfs_cache_copy(lfs_t *lfs,
+        lfs_cache_t *dcache, const lfs_cache_t *scache) {
+    memcpy(dcache->buffer, scache->buffer, lfs->cfg->cache_size);
+    dcache->block = scache->block;
+    dcache->off   = scache->off;
+    dcache->size  = scache->size;
+}
+
 static int lfs_bd_read(lfs_t *lfs,
         const lfs_cache_t *pcache, lfs_cache_t *rcache, lfs_size_t hint,
         lfs_block_t block, lfs_off_t off,
@@ -630,8 +638,6 @@ static lfs_stag_t lfs_dir_getslice(lfs_t *lfs, const lfs_mdir_t *dir,
                 return err;
             }
 
-            memset((uint8_t*)gbuffer + diff, 0, gsize - diff);
-
             return tag + gdiff;
         }
     }
@@ -815,8 +821,12 @@ static int lfs_dir_traverse(lfs_t *lfs,
                 return err;
             }
         } else if (lfs_tag_type3(tag) == LFS_FROM_USERATTRS) {
+            const struct lfs_attr *a = buffer;
             for (unsigned i = 0; i < lfs_tag_size(tag); i++) {
-                const struct lfs_attr *a = buffer;
+                if (a[i].size > lfs->attr_max) {
+                    return LFS_ERR_NOSPC;
+                }
+
                 int err = cb(data, LFS_MKTAG(LFS_TYPE_USERATTR + a[i].type,
                         lfs_tag_id(tag) + diff, a[i].size), a[i].buffer);
                 if (err) {
@@ -1080,7 +1090,7 @@ static int lfs_dir_fetch(lfs_t *lfs,
 
 static int lfs_dir_getgstate(lfs_t *lfs, const lfs_mdir_t *dir,
         lfs_gstate_t *gstate) {
-    lfs_gstate_t temp;
+    lfs_gstate_t temp = {0};
     lfs_stag_t res = lfs_dir_get(lfs, dir, LFS_MKTAG(0x7ff, 0, 0),
             LFS_MKTAG(LFS_TYPE_MOVESTATE, 0, sizeof(temp)), &temp);
     if (res < 0 && res != LFS_ERR_NOENT) {
@@ -1106,10 +1116,11 @@ static int lfs_dir_getinfo(lfs_t *lfs, lfs_mdir_t *dir,
     }
 
     lfs_stag_t tag = lfs_dir_get(lfs, dir, LFS_MKTAG(0x780, 0x3ff, 0),
-            LFS_MKTAG(LFS_TYPE_NAME, id, lfs->name_max+1), info->name);
+            LFS_MKTAG(LFS_TYPE_NAME, id, lfs->name_max), info->name);
     if (tag < 0) {
         return (int)tag;
     }
+    info->name[lfs_tag_size(tag)] = '\0';
 
     info->type = lfs_tag_type3(tag);
 
@@ -1173,6 +1184,11 @@ static lfs_stag_t lfs_dir_find(lfs_t *lfs, lfs_mdir_t *dir,
     dir->tail[0] = lfs->root[0];
     dir->tail[1] = lfs->root[1];
 
+    // NULL path == root
+    if (!name) {
+        return tag;
+    }
+
     while (true) {
 nextname:
         // skip slashes
@@ -1821,7 +1837,7 @@ relocate:
 #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
+    // check for any open inline files that aren't RAM backed and
     // forcefully evict them, needed for filesystem consistency
     for (lfs_file_t *f = (lfs_file_t*)lfs->mlist; f; f = f->next) {
         if (dir != &f->m && lfs_pair_cmp(f->m.pair, dir->pair) == 0 &&
@@ -2013,6 +2029,7 @@ compact:
 #ifndef LFS_READONLY
 static int lfs_rawmkdir(lfs_t *lfs, const char *path) {
     // deorphan if we haven't yet, needed at most once after poweron
+    LFS_ASSERT(path);
     int err = lfs_fs_forceconsistency(lfs);
     if (err) {
         return err;
@@ -2450,14 +2467,14 @@ static int lfs_file_rawopencfg(lfs_t *lfs, lfs_file_t *file,
         const struct lfs_file_config *cfg) {
 #ifndef LFS_READONLY
     // deorphan if we haven't yet, needed at most once after poweron
-    if ((flags & LFS_O_WRONLY) == LFS_O_WRONLY) {
+    if (flags & LFS_O_WRONLY) {
         int err = lfs_fs_forceconsistency(lfs);
         if (err) {
             return err;
         }
     }
 #else
-    LFS_ASSERT((flags & LFS_O_RDONLY) == LFS_O_RDONLY);
+    LFS_ASSERT(flags & LFS_O_RDONLY);
 #endif
 
     // setup simple file details
@@ -2468,7 +2485,7 @@ static int lfs_file_rawopencfg(lfs_t *lfs, lfs_file_t *file,
     file->off = 0;
     file->cache.buffer = NULL;
 
-    // allocate entry for file if it doesn't exist
+    // find path
     lfs_stag_t tag = lfs_dir_find(lfs, &file->m, &path, &file->id);
     if (tag < 0 && !(tag == LFS_ERR_NOENT && file->id != 0x3ff)) {
         err = tag;
@@ -2476,19 +2493,22 @@ static int lfs_file_rawopencfg(lfs_t *lfs, lfs_file_t *file,
     }
 
     // get id, add to list of mdirs to catch update changes
-    file->type = LFS_TYPE_REG;
+    if (!(flags & LFS_O_SNAPSHOT)) {
-    lfs_mlist_append(lfs, (struct lfs_mlist *)file);
+        file->type = LFS_TYPE_REG;
+        lfs_mlist_append(lfs, (struct lfs_mlist *)file);
+    }
 
-#ifdef LFS_READONLY
+#ifndef LFS_READONLY
-    if (tag == LFS_ERR_NOENT) {
+    if ((flags & LFS_O_CREAT) && (flags & LFS_O_SNAPSHOT) &&
-        err = LFS_ERR_NOENT;
+            (tag == LFS_ERR_NOENT || lfs_tag_type3(tag) != LFS_TYPE_REG)) {
+        // special case for "temporary" files
+        tag = LFS_MKTAG(LFS_TYPE_INLINESTRUCT, 0, 0);
+    } else if ((flags & LFS_O_EXCL) && tag != LFS_ERR_NOENT) {
+        err = LFS_ERR_EXIST;
         goto cleanup;
-#else
+    } else if ((flags & LFS_O_CREAT) && tag == LFS_ERR_NOENT) {
-    if (tag == LFS_ERR_NOENT) {
+        // allocate entry for file if it doesn't exist
-        if (!(flags & LFS_O_CREAT)) {
+        LFS_ASSERT(path);
-            err = LFS_ERR_NOENT;
-            goto cleanup;
-        }
 
         // check that name fits
         lfs_size_t nlen = strlen(path);
@@ -2501,63 +2521,57 @@ static int lfs_file_rawopencfg(lfs_t *lfs, lfs_file_t *file,
         err = lfs_dir_commit(lfs, &file->m, LFS_MKATTRS(
                 {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), NULL}));
+                {LFS_MKTAG(LFS_TYPE_INLINESTRUCT, file->id, 0), NULL},
+                {LFS_MKTAG(LFS_FROM_USERATTRS, file->id,
+                    file->cfg->attr_count), file->cfg->attrs}));
         if (err) {
-            err = LFS_ERR_NAMETOOLONG;
             goto cleanup;
         }
 
         tag = LFS_MKTAG(LFS_TYPE_INLINESTRUCT, 0, 0);
-    } else if (flags & LFS_O_EXCL) {
+    } else /**/
-        err = LFS_ERR_EXIST;
+#endif     /**/
+    /*********/
+    /**/ if (tag == LFS_ERR_NOENT) {
+        err = LFS_ERR_NOENT;
         goto cleanup;
-#endif
     } else if (lfs_tag_type3(tag) != LFS_TYPE_REG) {
         err = LFS_ERR_ISDIR;
         goto cleanup;
-#ifndef LFS_READONLY
-    } else if (flags & LFS_O_TRUNC) {
-        // truncate if requested
-        tag = LFS_MKTAG(LFS_TYPE_INLINESTRUCT, file->id, 0);
-        file->flags |= LFS_F_DIRTY;
-#endif
     } else {
-        // try to load what's on disk, if it's inlined we'll fix it later
-        tag = lfs_dir_get(lfs, &file->m, LFS_MKTAG(0x700, 0x3ff, 0),
-                LFS_MKTAG(LFS_TYPE_STRUCT, file->id, 8), &file->ctz);
-        if (tag < 0) {
-            err = tag;
-            goto cleanup;
-        }
-        lfs_ctz_fromle32(&file->ctz);
-    }
-
-    // fetch attrs
-    for (unsigned i = 0; i < file->cfg->attr_count; i++) {
-        // if opened for read / read-write operations
-        if ((file->flags & LFS_O_RDONLY) == LFS_O_RDONLY) {
-            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,
-                        file->id, file->cfg->attrs[i].size),
-                        file->cfg->attrs[i].buffer);
-            if (res < 0 && res != LFS_ERR_NOENT) {
-                err = res;
-                goto cleanup;
-            }
-        }
-
 #ifndef LFS_READONLY
-        // if opened for write / read-write operations
+        if (flags & LFS_O_TRUNC) {
-        if ((file->flags & LFS_O_WRONLY) == LFS_O_WRONLY) {
+            // truncate if requested
-            if (file->cfg->attrs[i].size > lfs->attr_max) {
+            // always mark dirty in case we have custom attributes
-                err = LFS_ERR_NOSPC;
+            tag = LFS_MKTAG(LFS_TYPE_INLINESTRUCT, 0, 0);
+            file->flags |= LFS_F_DIRTY;
+        } else /**/
+#endif  /*********/
+        /**/ {
+            // try to load what's on disk, if it's inlined we'll fix it later
+            tag = lfs_dir_get(lfs, &file->m, LFS_MKTAG(0x700, 0x3ff, 0),
+                    LFS_MKTAG(LFS_TYPE_STRUCT, file->id, 8), &file->ctz);
+            if (tag < 0) {
+                err = tag;
                 goto cleanup;
             }
-
+            lfs_ctz_fromle32(&file->ctz);
-            file->flags |= LFS_F_DIRTY;
+        }
+
+        // fetch attrs if opened for read / read-write operations
+        if (flags & LFS_O_RDONLY) {
+            for (lfs_size_t i = 0; i < file->cfg->attr_count; i++) {
+                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,
+                            file->id, file->cfg->attrs[i].size),
+                            file->cfg->attrs[i].buffer);
+                if (res < 0 && res != LFS_ERR_NOENT) {
+                    err = res;
+                    goto cleanup;
+                }
+            }
         }
-#endif
     }
 
     // allocate buffer if needed
@@ -2602,7 +2616,7 @@ static int lfs_file_rawopencfg(lfs_t *lfs, lfs_file_t *file,
 cleanup:
     // clean up lingering resources
 #ifndef LFS_READONLY
-    file->flags |= LFS_F_ERRED;
+    file->flags |= LFS_F_ZOMBIE;
 #endif
     lfs_file_rawclose(lfs, file);
     return err;
@@ -2616,10 +2630,9 @@ static int lfs_file_rawopen(lfs_t *lfs, lfs_file_t *file,
 }
 
 static int lfs_file_rawclose(lfs_t *lfs, lfs_file_t *file) {
-#ifndef LFS_READONLY
-    int err = lfs_file_rawsync(lfs, file);
-#else
     int err = 0;
+#ifndef LFS_READONLY
+    err = lfs_file_rawsync(lfs, file);
 #endif
 
     // remove from list of mdirs
@@ -2801,17 +2814,21 @@ relocate:
 
 #ifndef LFS_READONLY
 static int lfs_file_rawsync(lfs_t *lfs, lfs_file_t *file) {
-    if (file->flags & LFS_F_ERRED) {
+    if (file->flags & LFS_F_ZOMBIE) {
         // it's not safe to do anything if our file errored
         return 0;
     }
 
     int err = lfs_file_flush(lfs, file);
     if (err) {
-        file->flags |= LFS_F_ERRED;
+        file->flags |= LFS_F_ZOMBIE;
         return err;
     }
 
+    if (file->flags & LFS_O_SNAPSHOT) {
+        // we do flush snapshot files, but we don't commit, so stop here
+        return 0;
+    }
 
     if ((file->flags & LFS_F_DIRTY) &&
             !lfs_pair_isnull(file->m.pair)) {
@@ -2841,10 +2858,41 @@ static int lfs_file_rawsync(lfs_t *lfs, lfs_file_t *file) {
                 {LFS_MKTAG(LFS_FROM_USERATTRS, file->id,
                     file->cfg->attr_count), file->cfg->attrs}));
         if (err) {
-            file->flags |= LFS_F_ERRED;
+            file->flags |= LFS_F_ZOMBIE;
             return err;
         }
 
+        // update readable handles referencing this file device-side
+        for (lfs_file_t *f = (lfs_file_t*)lfs->mlist; f; f = f->next) {
+            if (f != file &&
+                    f->type == LFS_TYPE_REG &&
+                    lfs_pair_cmp(f->m.pair, file->m.pair) == 0 &&
+                    f->id == file->id &&
+                    // only readable handles because wronly files
+                    // may reference attributes in ROM
+                    (f->flags & LFS_O_RDONLY)) {
+                // sync disk structure
+                f->ctz = file->ctz;
+                // copying the cache is required for inline files
+                lfs_cache_copy(lfs, &f->cache, &file->cache);
+
+                // sync attrs
+                for (lfs_size_t i = 0; i < f->cfg->attr_count; i++) {
+                    for (lfs_size_t j = 0; j < file->cfg->attr_count; j++) {
+                        if (f->cfg->attrs[i].type == file->cfg->attrs[i].type) {
+                            memcpy(f->cfg->attrs[i].buffer,
+                                    file->cfg->attrs[i].buffer,
+                                    lfs_min(
+                                        f->cfg->attrs[i].size,
+                                        file->cfg->attrs[i].size));
+                        }
+                    }
+                }
+
+                f->flags &= ~(LFS_F_DIRTY | LFS_F_WRITING | LFS_F_READING);
+            }
+        }
+
         file->flags &= ~LFS_F_DIRTY;
     }
 
@@ -2854,7 +2902,7 @@ static int lfs_file_rawsync(lfs_t *lfs, lfs_file_t *file) {
 
 static lfs_ssize_t lfs_file_rawread(lfs_t *lfs, lfs_file_t *file,
         void *buffer, lfs_size_t size) {
-    LFS_ASSERT((file->flags & LFS_O_RDONLY) == LFS_O_RDONLY);
+    LFS_ASSERT(file->flags & LFS_O_RDONLY);
 
     uint8_t *data = buffer;
     lfs_size_t nsize = size;
@@ -2928,7 +2976,7 @@ static lfs_ssize_t lfs_file_rawread(lfs_t *lfs, lfs_file_t *file,
 #ifndef LFS_READONLY
 static lfs_ssize_t lfs_file_rawwrite(lfs_t *lfs, lfs_file_t *file,
         const void *buffer, lfs_size_t size) {
-    LFS_ASSERT((file->flags & LFS_O_WRONLY) == LFS_O_WRONLY);
+    LFS_ASSERT(file->flags & LFS_O_WRONLY);
 
     const uint8_t *data = buffer;
     lfs_size_t nsize = size;
@@ -2970,7 +3018,7 @@ static lfs_ssize_t lfs_file_rawwrite(lfs_t *lfs, lfs_file_t *file,
         // inline file doesn't fit anymore
         int err = lfs_file_outline(lfs, file);
         if (err) {
-            file->flags |= LFS_F_ERRED;
+            file->flags |= LFS_F_ZOMBIE;
             return err;
         }
     }
@@ -2986,7 +3034,7 @@ static lfs_ssize_t lfs_file_rawwrite(lfs_t *lfs, lfs_file_t *file,
                             file->ctz.head, file->ctz.size,
                             file->pos-1, &file->block, &file->off);
                     if (err) {
-                        file->flags |= LFS_F_ERRED;
+                        file->flags |= LFS_F_ZOMBIE;
                         return err;
                     }
 
@@ -3000,7 +3048,7 @@ static lfs_ssize_t lfs_file_rawwrite(lfs_t *lfs, lfs_file_t *file,
                         file->block, file->pos,
                         &file->block, &file->off);
                 if (err) {
-                    file->flags |= LFS_F_ERRED;
+                    file->flags |= LFS_F_ZOMBIE;
                     return err;
                 }
             } else {
@@ -3020,7 +3068,7 @@ static lfs_ssize_t lfs_file_rawwrite(lfs_t *lfs, lfs_file_t *file,
                 if (err == LFS_ERR_CORRUPT) {
                     goto relocate;
                 }
-                file->flags |= LFS_F_ERRED;
+                file->flags |= LFS_F_ZOMBIE;
                 return err;
             }
 
@@ -3028,7 +3076,7 @@ static lfs_ssize_t lfs_file_rawwrite(lfs_t *lfs, lfs_file_t *file,
 relocate:
             err = lfs_file_relocate(lfs, file);
             if (err) {
-                file->flags |= LFS_F_ERRED;
+                file->flags |= LFS_F_ZOMBIE;
                 return err;
             }
         }
@@ -3041,7 +3089,7 @@ relocate:
         lfs_alloc_ack(lfs);
     }
 
-    file->flags &= ~LFS_F_ERRED;
+    file->flags &= ~LFS_F_ZOMBIE;
     return size;
 }
 #endif
@@ -3078,7 +3126,7 @@ static lfs_soff_t lfs_file_rawseek(lfs_t *lfs, lfs_file_t *file,
 
 #ifndef LFS_READONLY
 static int lfs_file_rawtruncate(lfs_t *lfs, lfs_file_t *file, lfs_off_t size) {
-    LFS_ASSERT((file->flags & LFS_O_WRONLY) == LFS_O_WRONLY);
+    LFS_ASSERT(file->flags & LFS_O_WRONLY);
 
     if (size > LFS_FILE_MAX) {
         return LFS_ERR_INVAL;
@@ -3424,8 +3472,34 @@ static int lfs_commitattr(lfs_t *lfs, const char *path,
         }
     }
 
-    return lfs_dir_commit(lfs, &cwd, LFS_MKATTRS(
+    int err = lfs_dir_commit(lfs, &cwd, LFS_MKATTRS(
             {LFS_MKTAG(LFS_TYPE_USERATTR + type, id, size), buffer}));
+    if (err) {
+        return err;
+    }
+
+    if (lfs_tag_type3(tag) == LFS_TYPE_REG && size != 0x3ff) {
+        // sync attrs with any files open for reading, this follows
+        // the behavior of lfs_file_sync with attributes
+        for (lfs_file_t *f = (lfs_file_t*)lfs->mlist; f; f = f->next) {
+            if (f->type == LFS_TYPE_REG &&
+                    lfs_pair_cmp(f->m.pair, cwd.pair) == 0 &&
+                    f->id == id &&
+                    // only readable handles because wronly files
+                    // may reference attributes in ROM
+                    (f->flags & LFS_O_RDONLY)) {
+                // sync attrs
+                for (lfs_size_t i = 0; i < f->cfg->attr_count; i++) {
+                    if (f->cfg->attrs[i].type == type) {
+                        memcpy(f->cfg->attrs[i].buffer, buffer,
+                                lfs_min(f->cfg->attrs[i].size, size));
+                    }
+                }
+            }
+        }
+    }
+
+    return 0;
 }
 #endif
 
@@ -5084,7 +5158,8 @@ int lfs_file_close(lfs_t *lfs, lfs_file_t *file) {
         return err;
     }
     LFS_TRACE("lfs_file_close(%p, %p)", (void*)lfs, (void*)file);
-    LFS_ASSERT(lfs_mlist_isopen(lfs->mlist, (struct lfs_mlist*)file));
+    LFS_ASSERT((file->flags & LFS_O_SNAPSHOT) ||
+            lfs_mlist_isopen(lfs->mlist, (struct lfs_mlist*)file));
 
     err = lfs_file_rawclose(lfs, file);
 
@@ -5100,7 +5175,8 @@ int lfs_file_sync(lfs_t *lfs, lfs_file_t *file) {
         return err;
     }
     LFS_TRACE("lfs_file_sync(%p, %p)", (void*)lfs, (void*)file);
-    LFS_ASSERT(lfs_mlist_isopen(lfs->mlist, (struct lfs_mlist*)file));
+    LFS_ASSERT((file->flags & LFS_O_SNAPSHOT) ||
+            lfs_mlist_isopen(lfs->mlist, (struct lfs_mlist*)file));
 
     err = lfs_file_rawsync(lfs, file);
 
@@ -5118,7 +5194,8 @@ 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(lfs_mlist_isopen(lfs->mlist, (struct lfs_mlist*)file));
+    LFS_ASSERT((file->flags & LFS_O_SNAPSHOT) ||
+            lfs_mlist_isopen(lfs->mlist, (struct lfs_mlist*)file));
 
     lfs_ssize_t res = lfs_file_rawread(lfs, file, buffer, size);
 
@@ -5136,7 +5213,8 @@ 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(lfs_mlist_isopen(lfs->mlist, (struct lfs_mlist*)file));
+    LFS_ASSERT((file->flags & LFS_O_SNAPSHOT) ||
+            lfs_mlist_isopen(lfs->mlist, (struct lfs_mlist*)file));
 
     lfs_ssize_t res = lfs_file_rawwrite(lfs, file, buffer, size);
 
@@ -5154,7 +5232,8 @@ lfs_soff_t lfs_file_seek(lfs_t *lfs, lfs_file_t *file,
     }
     LFS_TRACE("lfs_file_seek(%p, %p, %"PRId32", %d)",
             (void*)lfs, (void*)file, off, whence);
-    LFS_ASSERT(lfs_mlist_isopen(lfs->mlist, (struct lfs_mlist*)file));
+    LFS_ASSERT((file->flags & LFS_O_SNAPSHOT) ||
+            lfs_mlist_isopen(lfs->mlist, (struct lfs_mlist*)file));
 
     lfs_soff_t res = lfs_file_rawseek(lfs, file, off, whence);
 
@@ -5171,7 +5250,8 @@ 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(lfs_mlist_isopen(lfs->mlist, (struct lfs_mlist*)file));
+    LFS_ASSERT((file->flags & LFS_O_SNAPSHOT) ||
+            lfs_mlist_isopen(lfs->mlist, (struct lfs_mlist*)file));
 
     err = lfs_file_rawtruncate(lfs, file, size);
 
@@ -5187,7 +5267,8 @@ lfs_soff_t lfs_file_tell(lfs_t *lfs, lfs_file_t *file) {
         return err;
     }
     LFS_TRACE("lfs_file_tell(%p, %p)", (void*)lfs, (void*)file);
-    LFS_ASSERT(lfs_mlist_isopen(lfs->mlist, (struct lfs_mlist*)file));
+    LFS_ASSERT((file->flags & LFS_O_SNAPSHOT) ||
+            lfs_mlist_isopen(lfs->mlist, (struct lfs_mlist*)file));
 
     lfs_soff_t res = lfs_file_rawtell(lfs, file);
 
@@ -5216,7 +5297,8 @@ lfs_soff_t lfs_file_size(lfs_t *lfs, lfs_file_t *file) {
         return err;
     }
     LFS_TRACE("lfs_file_size(%p, %p)", (void*)lfs, (void*)file);
-    LFS_ASSERT(lfs_mlist_isopen(lfs->mlist, (struct lfs_mlist*)file));
+    LFS_ASSERT((file->flags & LFS_O_SNAPSHOT) ||
+            lfs_mlist_isopen(lfs->mlist, (struct lfs_mlist*)file));
 
     lfs_soff_t res = lfs_file_rawsize(lfs, file);
 

lfs.h

@@ -123,26 +123,30 @@ enum lfs_type {
 // File open flags
 enum lfs_open_flags {
     // open flags
-    LFS_O_RDONLY = 1,         // Open a file as read only
+    LFS_O_RDONLY    = 1,        // Open a file as read only
 #ifndef LFS_READONLY
-    LFS_O_WRONLY = 2,         // Open a file as write only
+    LFS_O_WRONLY    = 2,        // Open a file as write only
-    LFS_O_RDWR   = 3,         // Open a file as read and write
+    LFS_O_RDWR      = 3,        // Open a file as read and write
-    LFS_O_CREAT  = 0x0100,    // Create a file if it does not exist
+#endif
-    LFS_O_EXCL   = 0x0200,    // Fail if a file already exists
+
-    LFS_O_TRUNC  = 0x0400,    // Truncate the existing file to zero size
+#ifndef LFS_READONLY
-    LFS_O_APPEND = 0x0800,    // Move to end of file on every write
+    LFS_O_CREAT     = 0x0100,   // Create a file if it does not exist
+    LFS_O_EXCL      = 0x0200,   // Fail if a file already exists
+    LFS_O_TRUNC     = 0x0400,   // Truncate the existing file to zero size
+    LFS_O_APPEND    = 0x0800,   // Move to end of file on every write
+    LFS_O_SNAPSHOT  = 0x1000,   // Open a temporary snapshot, ignore changes
 #endif
 
     // internally used flags
 #ifndef LFS_READONLY
-    LFS_F_DIRTY   = 0x010000, // File does not match storage
+    LFS_F_DIRTY     = 0x010000, // File does not match storage
-    LFS_F_WRITING = 0x020000, // File has been written since last flush
 #endif
-    LFS_F_READING = 0x040000, // File has been read since last flush
+    LFS_F_READING   = 0x020000, // File has been read since last flush
 #ifndef LFS_READONLY
-    LFS_F_ERRED   = 0x080000, // An error occurred during write
+    LFS_F_WRITING   = 0x040000, // File has been written since last flush
+    LFS_F_ZOMBIE    = 0x080000, // An error occurred during write
 #endif
-    LFS_F_INLINE  = 0x100000, // Currently inlined in directory entry
+    LFS_F_INLINE    = 0x100000, // Currently inlined in directory entry
 };
 
 // File seek flags
@@ -294,16 +298,15 @@ struct lfs_file_config {
     void *buffer;
 
     // Optional list of custom attributes related to the file. If the file
-    // is opened with read access, these attributes will be read from disk
+    // is opened for reading, these attributes will be read from disk during
-    // during the open call. If the file is opened with write access, the
+    // open. If the file is open for writing, these attribute will be atomically
-    // attributes will be written to disk every file sync or close. This
+    // written to disk when the file is written to disk. Note that these
-    // write occurs atomically with update to the file's contents.
+    // attributes are not written unless the file is modified.
     //
     // Custom attributes are uniquely identified by an 8-bit type and limited
-    // to LFS_ATTR_MAX bytes. When read, if the stored attribute is smaller
+    // to LFS_ATTR_MAX bytes. If the stored attribute is larger than the
-    // than the buffer, it will be padded with zeros. If the stored attribute
+    // provided buffer, it will be silently truncated. If no attribute is
-    // is larger, then it will be silently truncated. If the attribute is not
+    // found, and the file is open for writing, it will be created implicitly.
-    // found, it will be created implicitly.
     struct lfs_attr *attrs;
 
     // Number of custom attributes in the list
@@ -471,10 +474,9 @@ int lfs_stat(lfs_t *lfs, const char *path, struct lfs_info *info);
 // Get a custom attribute
 //
 // Custom attributes are uniquely identified by an 8-bit type and limited
-// to LFS_ATTR_MAX bytes. When read, if the stored attribute is smaller than
+// to LFS_ATTR_MAX bytes. If the stored attribute is larger than the
-// the buffer, it will be padded with zeros. If the stored attribute is larger,
+// provided buffer, it will be silently truncated. If no attribute is found,
-// then it will be silently truncated. If no attribute is found, the error
+// the error LFS_ERR_NOATTR is returned and the buffer is filled with zeros.
-// LFS_ERR_NOATTR is returned and the buffer is filled with zeros.
 //
 // Returns the size of the attribute, or a negative error code on failure.
 // Note, the returned size is the size of the attribute on disk, irrespective

tests/test_attrs.toml

@@ -16,41 +16,39 @@ code = '''
     lfs_getattr(&lfs, "hello", 'A', buffer,    4) => 4;
     lfs_getattr(&lfs, "hello", 'B', buffer+4,  6) => 6;
     lfs_getattr(&lfs, "hello", 'C', buffer+10, 5) => 5;
-    memcmp(buffer,    "aaaa",   4) => 0;
+    assert(memcmp(buffer,    "aaaa",   4) == 0);
-    memcmp(buffer+4,  "bbbbbb", 6) => 0;
+    assert(memcmp(buffer+4,  "bbbbbb", 6) == 0);
-    memcmp(buffer+10, "ccccc",  5) => 0;
+    assert(memcmp(buffer+10, "ccccc",  5) == 0);
 
     lfs_setattr(&lfs, "hello", 'B', "", 0) => 0;
     lfs_getattr(&lfs, "hello", 'A', buffer,    4) => 4;
     lfs_getattr(&lfs, "hello", 'B', buffer+4,  6) => 0;
     lfs_getattr(&lfs, "hello", 'C', buffer+10, 5) => 5;
-    memcmp(buffer,    "aaaa",         4) => 0;
+    assert(memcmp(buffer,    "aaaa",         4) == 0);
-    memcmp(buffer+4,  "\0\0\0\0\0\0", 6) => 0;
+    assert(memcmp(buffer+10, "ccccc",        5) == 0);
-    memcmp(buffer+10, "ccccc",        5) => 0;
 
     lfs_removeattr(&lfs, "hello", 'B') => 0;
     lfs_getattr(&lfs, "hello", 'A', buffer,    4) => 4;
     lfs_getattr(&lfs, "hello", 'B', buffer+4,  6) => LFS_ERR_NOATTR;
     lfs_getattr(&lfs, "hello", 'C', buffer+10, 5) => 5;
-    memcmp(buffer,    "aaaa",         4) => 0;
+    assert(memcmp(buffer,    "aaaa",         4) == 0);
-    memcmp(buffer+4,  "\0\0\0\0\0\0", 6) => 0;
+    assert(memcmp(buffer+10, "ccccc",        5) == 0);
-    memcmp(buffer+10, "ccccc",        5) => 0;
 
     lfs_setattr(&lfs, "hello", 'B', "dddddd", 6) => 0;
     lfs_getattr(&lfs, "hello", 'A', buffer,    4) => 4;
     lfs_getattr(&lfs, "hello", 'B', buffer+4,  6) => 6;
     lfs_getattr(&lfs, "hello", 'C', buffer+10, 5) => 5;
-    memcmp(buffer,    "aaaa",   4) => 0;
+    assert(memcmp(buffer,    "aaaa",   4) == 0);
-    memcmp(buffer+4,  "dddddd", 6) => 0;
+    assert(memcmp(buffer+4,  "dddddd", 6) == 0);
-    memcmp(buffer+10, "ccccc",  5) => 0;
+    assert(memcmp(buffer+10, "ccccc",  5) == 0);
 
     lfs_setattr(&lfs, "hello", 'B', "eee", 3) => 0;
     lfs_getattr(&lfs, "hello", 'A', buffer,    4) => 4;
     lfs_getattr(&lfs, "hello", 'B', buffer+4,  6) => 3;
     lfs_getattr(&lfs, "hello", 'C', buffer+10, 5) => 5;
-    memcmp(buffer,    "aaaa",      4) => 0;
+    assert(memcmp(buffer,    "aaaa",  4) == 0);
-    memcmp(buffer+4,  "eee\0\0\0", 6) => 0;
+    assert(memcmp(buffer+4,  "eee",   3) == 0);
-    memcmp(buffer+10, "ccccc",     5) => 0;
+    assert(memcmp(buffer+10, "ccccc", 5) == 0);
 
     lfs_setattr(&lfs, "hello", 'A', buffer, LFS_ATTR_MAX+1) => LFS_ERR_NOSPC;
     lfs_setattr(&lfs, "hello", 'B', "fffffffff", 9) => 0;
@@ -65,13 +63,13 @@ code = '''
     lfs_getattr(&lfs, "hello", 'A', buffer,    4) => 4;
     lfs_getattr(&lfs, "hello", 'B', buffer+4,  9) => 9;
     lfs_getattr(&lfs, "hello", 'C', buffer+13, 5) => 5;
-    memcmp(buffer,    "aaaa",      4) => 0;
+    assert(memcmp(buffer,    "aaaa",      4) == 0);
-    memcmp(buffer+4,  "fffffffff", 9) => 0;
+    assert(memcmp(buffer+4,  "fffffffff", 9) == 0);
-    memcmp(buffer+13, "ccccc",     5) => 0;
+    assert(memcmp(buffer+13, "ccccc",     5) == 0);
 
     lfs_file_open(&lfs, &file, "hello/hello", LFS_O_RDONLY) => 0;
     lfs_file_read(&lfs, &file, buffer, sizeof(buffer)) => strlen("hello");
-    memcmp(buffer, "hello", strlen("hello")) => 0;
+    assert(memcmp(buffer, "hello", strlen("hello")) == 0);
     lfs_file_close(&lfs, &file);
     lfs_unmount(&lfs) => 0;
 '''
@@ -94,41 +92,39 @@ code = '''
     lfs_getattr(&lfs, "/", 'A', buffer,    4) => 4;
     lfs_getattr(&lfs, "/", 'B', buffer+4,  6) => 6;
     lfs_getattr(&lfs, "/", 'C', buffer+10, 5) => 5;
-    memcmp(buffer,    "aaaa",   4) => 0;
+    assert(memcmp(buffer,    "aaaa",   4) == 0);
-    memcmp(buffer+4,  "bbbbbb", 6) => 0;
+    assert(memcmp(buffer+4,  "bbbbbb", 6) == 0);
-    memcmp(buffer+10, "ccccc",  5) => 0;
+    assert(memcmp(buffer+10, "ccccc",  5) == 0);
 
     lfs_setattr(&lfs, "/", 'B', "", 0) => 0;
     lfs_getattr(&lfs, "/", 'A', buffer,    4) => 4;
     lfs_getattr(&lfs, "/", 'B', buffer+4,  6) => 0;
     lfs_getattr(&lfs, "/", 'C', buffer+10, 5) => 5;
-    memcmp(buffer,    "aaaa",         4) => 0;
+    assert(memcmp(buffer,    "aaaa",  4) == 0);
-    memcmp(buffer+4,  "\0\0\0\0\0\0", 6) => 0;
+    assert(memcmp(buffer+10, "ccccc", 5) == 0);
-    memcmp(buffer+10, "ccccc",        5) => 0;
 
     lfs_removeattr(&lfs, "/", 'B') => 0;
     lfs_getattr(&lfs, "/", 'A', buffer,    4) => 4;
     lfs_getattr(&lfs, "/", 'B', buffer+4,  6) => LFS_ERR_NOATTR;
     lfs_getattr(&lfs, "/", 'C', buffer+10, 5) => 5;
-    memcmp(buffer,    "aaaa",         4) => 0;
+    assert(memcmp(buffer,    "aaaa",  4) == 0);
-    memcmp(buffer+4,  "\0\0\0\0\0\0", 6) => 0;
+    assert(memcmp(buffer+10, "ccccc", 5) == 0);
-    memcmp(buffer+10, "ccccc",        5) => 0;
 
     lfs_setattr(&lfs, "/", 'B', "dddddd", 6) => 0;
     lfs_getattr(&lfs, "/", 'A', buffer,    4) => 4;
     lfs_getattr(&lfs, "/", 'B', buffer+4,  6) => 6;
     lfs_getattr(&lfs, "/", 'C', buffer+10, 5) => 5;
-    memcmp(buffer,    "aaaa",   4) => 0;
+    assert(memcmp(buffer,    "aaaa",   4) == 0);
-    memcmp(buffer+4,  "dddddd", 6) => 0;
+    assert(memcmp(buffer+4,  "dddddd", 6) == 0);
-    memcmp(buffer+10, "ccccc",  5) => 0;
+    assert(memcmp(buffer+10, "ccccc",  5) == 0);
 
     lfs_setattr(&lfs, "/", 'B', "eee", 3) => 0;
     lfs_getattr(&lfs, "/", 'A', buffer,    4) => 4;
     lfs_getattr(&lfs, "/", 'B', buffer+4,  6) => 3;
     lfs_getattr(&lfs, "/", 'C', buffer+10, 5) => 5;
-    memcmp(buffer,    "aaaa",      4) => 0;
+    assert(memcmp(buffer,    "aaaa",  4) == 0);
-    memcmp(buffer+4,  "eee\0\0\0", 6) => 0;
+    assert(memcmp(buffer+4,  "eee",   3) == 0);
-    memcmp(buffer+10, "ccccc",     5) => 0;
+    assert(memcmp(buffer+10, "ccccc", 5) == 0);
 
     lfs_setattr(&lfs, "/", 'A', buffer, LFS_ATTR_MAX+1) => LFS_ERR_NOSPC;
     lfs_setattr(&lfs, "/", 'B', "fffffffff", 9) => 0;
@@ -142,13 +138,13 @@ code = '''
     lfs_getattr(&lfs, "/", 'A', buffer,    4) => 4;
     lfs_getattr(&lfs, "/", 'B', buffer+4,  9) => 9;
     lfs_getattr(&lfs, "/", 'C', buffer+13, 5) => 5;
-    memcmp(buffer,    "aaaa",      4) => 0;
+    assert(memcmp(buffer,    "aaaa",      4) == 0);
-    memcmp(buffer+4,  "fffffffff", 9) => 0;
+    assert(memcmp(buffer+4,  "fffffffff", 9) == 0);
-    memcmp(buffer+13, "ccccc",     5) => 0;
+    assert(memcmp(buffer+13, "ccccc",     5) == 0);
 
     lfs_file_open(&lfs, &file, "hello/hello", LFS_O_RDONLY) => 0;
     lfs_file_read(&lfs, &file, buffer, sizeof(buffer)) => strlen("hello");
-    memcmp(buffer, "hello", strlen("hello")) => 0;
+    assert(memcmp(buffer, "hello", strlen("hello")) == 0);
     lfs_file_close(&lfs, &file);
     lfs_unmount(&lfs) => 0;
 '''
@@ -176,52 +172,55 @@ code = '''
     memcpy(buffer,    "aaaa",   4);
     memcpy(buffer+4,  "bbbbbb", 6);
     memcpy(buffer+10, "ccccc",  5);
+    lfs_file_write(&lfs, &file, "hi", 2) => 2;
     lfs_file_close(&lfs, &file) => 0;
     memset(buffer, 0, 15);
     lfs_file_opencfg(&lfs, &file, "hello/hello", LFS_O_RDONLY, &cfg1) => 0;
     lfs_file_close(&lfs, &file) => 0;
-    memcmp(buffer,    "aaaa",   4) => 0;
+    assert(memcmp(buffer,    "aaaa",   4) == 0);
-    memcmp(buffer+4,  "bbbbbb", 6) => 0;
+    assert(memcmp(buffer+4,  "bbbbbb", 6) == 0);
-    memcmp(buffer+10, "ccccc",  5) => 0;
+    assert(memcmp(buffer+10, "ccccc",  5) == 0);
 
     attrs1[1].size = 0;
     lfs_file_opencfg(&lfs, &file, "hello/hello", LFS_O_WRONLY, &cfg1) => 0;
+    lfs_file_write(&lfs, &file, "hi", 2) => 2;
     lfs_file_close(&lfs, &file) => 0;
     memset(buffer, 0, 15);
     attrs1[1].size = 6;
     lfs_file_opencfg(&lfs, &file, "hello/hello", LFS_O_RDONLY, &cfg1) => 0;
     lfs_file_close(&lfs, &file) => 0;
-    memcmp(buffer,    "aaaa",         4) => 0;
+    assert(memcmp(buffer,    "aaaa",  4) == 0);
-    memcmp(buffer+4,  "\0\0\0\0\0\0", 6) => 0;
+    assert(memcmp(buffer+10, "ccccc", 5) == 0);
-    memcmp(buffer+10, "ccccc",        5) => 0;
 
     attrs1[1].size = 6;
     lfs_file_opencfg(&lfs, &file, "hello/hello", LFS_O_WRONLY, &cfg1) => 0;
     memcpy(buffer+4,  "dddddd", 6);
+    lfs_file_write(&lfs, &file, "hi", 2) => 2;
     lfs_file_close(&lfs, &file) => 0;
     memset(buffer, 0, 15);
     attrs1[1].size = 6;
     lfs_file_opencfg(&lfs, &file, "hello/hello", LFS_O_RDONLY, &cfg1) => 0;
     lfs_file_close(&lfs, &file) => 0;
-    memcmp(buffer,    "aaaa",   4) => 0;
+    assert(memcmp(buffer,    "aaaa",   4) == 0);
-    memcmp(buffer+4,  "dddddd", 6) => 0;
+    assert(memcmp(buffer+4,  "dddddd", 6) == 0);
-    memcmp(buffer+10, "ccccc",  5) => 0;
+    assert(memcmp(buffer+10, "ccccc",  5) == 0);
 
     attrs1[1].size = 3;
     lfs_file_opencfg(&lfs, &file, "hello/hello", LFS_O_WRONLY, &cfg1) => 0;
     memcpy(buffer+4,  "eee", 3);
+    lfs_file_write(&lfs, &file, "hi", 2) => 2;
     lfs_file_close(&lfs, &file) => 0;
     memset(buffer, 0, 15);
     attrs1[1].size = 6;
     lfs_file_opencfg(&lfs, &file, "hello/hello", LFS_O_RDONLY, &cfg1) => 0;
     lfs_file_close(&lfs, &file) => 0;
-    memcmp(buffer,    "aaaa",      4) => 0;
+    assert(memcmp(buffer,    "aaaa",  4) == 0);
-    memcmp(buffer+4,  "eee\0\0\0", 6) => 0;
+    assert(memcmp(buffer+4,  "eee",   3) == 0);
-    memcmp(buffer+10, "ccccc",     5) => 0;
+    assert(memcmp(buffer+10, "ccccc", 5) == 0);
 
     attrs1[0].size = LFS_ATTR_MAX+1;
-    lfs_file_opencfg(&lfs, &file, "hello/hello", LFS_O_WRONLY, &cfg1)
+    lfs_file_opencfg(&lfs, &file, "hello/hello2",
-        => LFS_ERR_NOSPC;
+            LFS_O_WRONLY | LFS_O_CREAT, &cfg1) => LFS_ERR_NOSPC;
 
     struct lfs_attr attrs2[] = {
         {'A', buffer,    4},
@@ -231,6 +230,7 @@ code = '''
     struct lfs_file_config cfg2 = {.attrs=attrs2, .attr_count=3};
     lfs_file_opencfg(&lfs, &file, "hello/hello", LFS_O_RDWR, &cfg2) => 0;
     memcpy(buffer+4,  "fffffffff", 9);
+    lfs_file_write(&lfs, &file, "hi", 2) => 2;
     lfs_file_close(&lfs, &file) => 0;
     attrs1[0].size = 4;
     lfs_file_opencfg(&lfs, &file, "hello/hello", LFS_O_RDONLY, &cfg1) => 0;
@@ -249,13 +249,13 @@ code = '''
 
     lfs_file_opencfg(&lfs, &file, "hello/hello", LFS_O_RDONLY, &cfg3) => 0;
     lfs_file_close(&lfs, &file) => 0;
-    memcmp(buffer,    "aaaa",      4) => 0;
+    assert(memcmp(buffer,    "aaaa",      4) == 0);
-    memcmp(buffer+4,  "fffffffff", 9) => 0;
+    assert(memcmp(buffer+4,  "fffffffff", 9) == 0);
-    memcmp(buffer+13, "ccccc",     5) => 0;
+    assert(memcmp(buffer+13, "ccccc",     5) == 0);
 
     lfs_file_open(&lfs, &file, "hello/hello", LFS_O_RDONLY) => 0;
     lfs_file_read(&lfs, &file, buffer, sizeof(buffer)) => strlen("hello");
-    memcmp(buffer, "hello", strlen("hello")) => 0;
+    assert(memcmp(buffer, "hillo", strlen("hello")) == 0);
     lfs_file_close(&lfs, &file);
     lfs_unmount(&lfs) => 0;
 '''
@@ -287,17 +287,16 @@ code = '''
     lfs_getattr(&lfs, "hello/hello", 'B', buffer,    9) => 9;
     lfs_getattr(&lfs, "hello/hello", 'C', buffer+9,  9) => 5;
     lfs_getattr(&lfs, "hello/hello", 'D', buffer+18, 9) => LFS_ERR_NOATTR;
-    memcmp(buffer,    "fffffffff",          9) => 0;
+    assert(memcmp(buffer,    "fffffffff", 9) == 0);
-    memcmp(buffer+9,  "ccccc\0\0\0\0",      9) => 0;
+    assert(memcmp(buffer+9,  "ccccc",     5) == 0);
-    memcmp(buffer+18, "\0\0\0\0\0\0\0\0\0", 9) => 0;
 
+    lfs_file_write(&lfs, &file, "hi", 2) => 2;
     lfs_file_sync(&lfs, &file) => 0;
     lfs_getattr(&lfs, "hello/hello", 'B', buffer,    9) => 4;
     lfs_getattr(&lfs, "hello/hello", 'C', buffer+9,  9) => 0;
     lfs_getattr(&lfs, "hello/hello", 'D', buffer+18, 9) => 4;
-    memcmp(buffer,    "gggg\0\0\0\0\0",     9) => 0;
+    assert(memcmp(buffer,    "gggg", 4) == 0);
-    memcmp(buffer+9,  "\0\0\0\0\0\0\0\0\0", 9) => 0;
+    assert(memcmp(buffer+18, "hhhh", 4) == 0);
-    memcmp(buffer+18, "hhhh\0\0\0\0\0",     9) => 0;
 
     lfs_file_close(&lfs, &file) => 0;
     lfs_unmount(&lfs) => 0;

tests/test_interspersed.toml

@@ -242,3 +242,695 @@ code = '''
 
     lfs_unmount(&lfs) => 0;
 '''
+
+[[case]] # open same file reading from separate file handles
+define.READERS = 3
+define.SIZE = [10, 100, 1000, 10000]
+define.RDMODE = ['LFS_O_RDONLY', 'LFS_O_RDWR']
+code = '''
+    const char alphas[] = "abcdefghijklmnopqrstuvwxyz";
+    lfs_format(&lfs, &cfg) => 0;
+    lfs_mount(&lfs, &cfg) => 0;
+    lfs_file_open(&lfs, &file, "shared", LFS_O_CREAT | LFS_O_WRONLY) => 0;
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_write(&lfs, &file, &alphas[j % 26], 1) => 1;
+    }
+    lfs_file_close(&lfs, &file) => 0;
+    lfs_unmount(&lfs) => 0;
+
+    // open all files
+    lfs_mount(&lfs, &cfg) => 0;
+    lfs_file_t readers[READERS];
+    for (int i = 0; i < READERS; i++) {
+        lfs_file_open(&lfs, &readers[i], "shared", RDMODE) => 0;
+    }
+
+    // perform operations while all readers are open
+    for (int i = 0; i < READERS; i++) {
+        for (int j = 0; j < SIZE; j++) {
+            lfs_file_read(&lfs, &readers[i], buffer, 1) => 1;
+            assert(buffer[0] == alphas[j % 26]);
+        }
+    }
+
+    for (int i = 0; i < READERS; i++) {
+        lfs_file_close(&lfs, &readers[i]) => 0;
+    }
+    lfs_unmount(&lfs) => 0;
+'''
+
+[[case]] # open same file reading and writing from separate file handles
+define.READERS = 3
+define.SIZE = [10, 100, 1000, 10000]
+define.RDMODE = ['LFS_O_RDONLY', 'LFS_O_RDWR']
+define.WRMODE = ['LFS_O_WRONLY', 'LFS_O_RDWR']
+code = '''
+    const char alphas[] = "abcdefghijklmnopqrstuvwxyz";
+    const char nums[] = "0123456789";
+    lfs_format(&lfs, &cfg) => 0;
+    lfs_mount(&lfs, &cfg) => 0;
+    lfs_file_open(&lfs, &file, "shared", LFS_O_CREAT | LFS_O_WRONLY) => 0;
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_write(&lfs, &file, &alphas[j % 26], 1) => 1;
+    }
+    lfs_file_close(&lfs, &file) => 0;
+    lfs_unmount(&lfs) => 0;
+
+    // open all files
+    lfs_mount(&lfs, &cfg) => 0;
+    lfs_file_t writer;
+    lfs_file_t readers[READERS];
+    lfs_file_open(&lfs, &writer, "shared", WRMODE) => 0;
+    for (int i = 0; i < READERS; i++) {
+        lfs_file_open(&lfs, &readers[i], "shared", RDMODE) => 0;
+    }
+
+    // perform operations while all readers are open
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_write(&lfs, &writer, &nums[j % 10], 1) => 1;
+    }
+
+    for (int i = 0; i < READERS; i++) {
+        for (int j = 0; j < SIZE/2; j++) {
+            lfs_file_read(&lfs, &readers[i], buffer, 1) => 1;
+            assert(buffer[0] == alphas[j % 26]);
+        }
+    }
+
+    // sync, now write should reflect in all open files
+    lfs_file_sync(&lfs, &writer) => 0;
+
+    for (int i = 0; i < READERS; i++) {
+        for (int j = SIZE/2; j < SIZE; j++) {
+            lfs_file_read(&lfs, &readers[i], buffer, 1) => 1;
+            assert(buffer[0] == nums[j % 10]);
+        }
+    }
+
+    // double check our writer reflects its own changes
+    if (WRMODE == LFS_O_RDWR) {
+        lfs_file_rewind(&lfs, &writer) => 0;
+        for (int j = 0; j < SIZE; j++) {
+            lfs_file_read(&lfs, &writer, buffer, 1) => 1;
+            assert(buffer[0] == nums[j % 10]);
+        }
+    }
+
+    for (int i = 0; i < READERS; i++) {
+        lfs_file_close(&lfs, &readers[i]) => 0;
+    }
+    lfs_unmount(&lfs) => 0;
+'''
+
+[[case]] # check that attributes are updated in open files
+define.READERS = 3
+define.SIZE = 10
+define.RDMODE = ['LFS_O_RDONLY', 'LFS_O_RDWR']
+define.WRMODE = ['LFS_O_WRONLY', 'LFS_O_RDWR']
+code = '''
+    const char alphas[] = "abcdefghijklmnopqrstuvwxyz";
+    const char nums[] = "0123456789";
+    lfs_format(&lfs, &cfg) => 0;
+    lfs_mount(&lfs, &cfg) => 0;
+    const struct lfs_file_config filecfg = {
+        .attr_count = 3,
+        .attrs = (struct lfs_attr[]){
+            {'A', "a",   1},
+            {'B', "bb",  2},
+            {'C', "ccc", 3},
+        },
+    };
+    lfs_file_opencfg(&lfs, &file, "shared",
+            LFS_O_CREAT | LFS_O_WRONLY, &filecfg) => 0;
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_write(&lfs, &file, &alphas[j % 26], 1) => 1;
+    }
+    lfs_file_close(&lfs, &file) => 0;
+    lfs_unmount(&lfs) => 0;
+
+    // open all files
+    lfs_mount(&lfs, &cfg) => 0;
+    lfs_file_t writer;
+    const struct lfs_file_config writercfg = {
+        .attr_count = 3,
+        .attrs = (struct lfs_attr[]){
+            {'A', &(uint8_t[1]){0}, 1},
+            {'B', &(uint8_t[2]){0}, 2},
+            {'C', &(uint8_t[3]){0}, 3}}};
+    lfs_file_t readers[READERS];
+    const struct lfs_file_config readercfgs[READERS] = {
+        {   .attr_count = 3,
+            .attrs = (struct lfs_attr[]){
+                {'A', &(uint8_t[1]){0}, 1},
+                {'B', &(uint8_t[2]){0}, 2},
+                {'C', &(uint8_t[3]){0}, 3}}},
+        {   .attr_count = 3,
+            .attrs = (struct lfs_attr[]){
+                {'A', &(uint8_t[1]){0}, 1},
+                {'B', &(uint8_t[2]){0}, 2},
+                {'C', &(uint8_t[3]){0}, 3}}},
+        {   .attr_count = 3,
+            .attrs = (struct lfs_attr[]){
+                {'A', &(uint8_t[1]){0}, 1},
+                {'B', &(uint8_t[2]){0}, 2},
+                {'C', &(uint8_t[3]){0}, 3}}}};
+    lfs_file_opencfg(&lfs, &writer, "shared",
+            WRMODE, &writercfg) => 0;
+    for (int i = 0; i < READERS; i++) {
+        lfs_file_opencfg(&lfs, &readers[i], "shared",
+                RDMODE, &readercfgs[i]) => 0;
+    }
+
+    // perform operations while all readers are open
+    writercfg.attrs[0].size = 1;
+    memcpy(writercfg.attrs[0].buffer, "0", 1);
+    writercfg.attrs[1].size = 2;
+    memcpy(writercfg.attrs[1].buffer, "11", 2);
+    writercfg.attrs[2].size = 3;
+    memcpy(writercfg.attrs[2].buffer, "222", 3);
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_write(&lfs, &writer, &nums[j % 10], 1) => 1;
+    }
+
+    for (int i = 0; i < READERS; i++) {
+        assert(readercfgs[i].attrs[0].size == 1);
+        assert(memcmp(readercfgs[i].attrs[0].buffer, "a", 1) == 0);
+        assert(readercfgs[i].attrs[1].size == 2);
+        assert(memcmp(readercfgs[i].attrs[1].buffer, "bb", 2) == 0);
+        assert(readercfgs[i].attrs[2].size == 3);
+        assert(memcmp(readercfgs[i].attrs[2].buffer, "ccc", 3) == 0);
+        for (int j = 0; j < SIZE; j++) {
+            lfs_file_read(&lfs, &readers[i], buffer, 1) => 1;
+            assert(buffer[0] == alphas[j % 26]);
+        }
+    }
+
+    // sync, now write should reflect in all open files
+    lfs_file_sync(&lfs, &writer) => 0;
+
+    for (int i = 0; i < READERS; i++) {
+        assert(readercfgs[i].attrs[0].size == 1);
+        assert(memcmp(readercfgs[i].attrs[0].buffer, "0", 1) == 0);
+        assert(readercfgs[i].attrs[1].size == 2);
+        assert(memcmp(readercfgs[i].attrs[1].buffer, "11", 2) == 0);
+        assert(readercfgs[i].attrs[2].size == 3);
+        assert(memcmp(readercfgs[i].attrs[2].buffer, "222", 3) == 0);
+        lfs_file_rewind(&lfs, &readers[i]) => 0;
+        for (int j = 0; j < SIZE; j++) {
+            lfs_file_read(&lfs, &readers[i], buffer, 1) => 1;
+            assert(buffer[0] == nums[j % 10]);
+        }
+    }
+
+    // double check our writer reflects its own changes
+    if (WRMODE == LFS_O_RDWR) {
+        assert(writercfg.attrs[0].size == 1);
+        assert(memcmp(writercfg.attrs[0].buffer, "0", 1) == 0);
+        assert(writercfg.attrs[1].size == 2);
+        assert(memcmp(writercfg.attrs[1].buffer, "11", 2) == 0);
+        assert(writercfg.attrs[2].size == 3);
+        assert(memcmp(writercfg.attrs[2].buffer, "222", 3) == 0);
+        lfs_file_rewind(&lfs, &writer) => 0;
+        for (int j = 0; j < SIZE; j++) {
+            lfs_file_read(&lfs, &writer, buffer, 1) => 1;
+            assert(buffer[0] == nums[j % 10]);
+        }
+    }
+
+    // now try explicit lfs_setattr calls, this should still update open files
+    lfs_setattr(&lfs, "shared", 'A', "A",   1) => 0;
+    lfs_setattr(&lfs, "shared", 'B', "BB",  2) => 0;
+    lfs_setattr(&lfs, "shared", 'C', "CCC", 3) => 0;
+
+    for (int i = 0; i < READERS; i++) {
+        assert(readercfgs[i].attrs[0].size == 1);
+        assert(memcmp(readercfgs[i].attrs[0].buffer, "A", 1) == 0);
+        assert(readercfgs[i].attrs[1].size == 2);
+        assert(memcmp(readercfgs[i].attrs[1].buffer, "BB", 2) == 0);
+        assert(readercfgs[i].attrs[2].size == 3);
+        assert(memcmp(readercfgs[i].attrs[2].buffer, "CCC", 3) == 0);
+        lfs_file_rewind(&lfs, &readers[i]) => 0;
+        for (int j = 0; j < SIZE; j++) {
+            lfs_file_read(&lfs, &readers[i], buffer, 1) => 1;
+            assert(buffer[0] == nums[j % 10]);
+        }
+    }
+
+    if (WRMODE == LFS_O_RDWR) {
+        assert(writercfg.attrs[0].size == 1);
+        assert(memcmp(writercfg.attrs[0].buffer, "A", 1) == 0);
+        assert(writercfg.attrs[1].size == 2);
+        assert(memcmp(writercfg.attrs[1].buffer, "BB", 2) == 0);
+        assert(writercfg.attrs[2].size == 3);
+        assert(memcmp(writercfg.attrs[2].buffer, "CCC", 3) == 0);
+        lfs_file_rewind(&lfs, &writer) => 0;
+        for (int j = 0; j < SIZE; j++) {
+            lfs_file_read(&lfs, &writer, buffer, 1) => 1;
+            assert(buffer[0] == nums[j % 10]);
+        }
+    } else if (WRMODE == LFS_O_WRONLY) {
+        // this should NOT update wronly attributes, these may be
+        // stored in read-only memory
+        assert(writercfg.attrs[0].size == 1);
+        assert(memcmp(writercfg.attrs[0].buffer, "0", 1) == 0);
+        assert(writercfg.attrs[1].size == 2);
+        assert(memcmp(writercfg.attrs[1].buffer, "11", 2) == 0);
+        assert(writercfg.attrs[2].size == 3);
+        assert(memcmp(writercfg.attrs[2].buffer, "222", 3) == 0);
+    }
+
+    for (int i = 0; i < READERS; i++) {
+        lfs_file_close(&lfs, &readers[i]) => 0;
+    }
+    lfs_unmount(&lfs) => 0;
+'''
+
+[[case]] # simple snapshot for reading
+define.SIZE = [10, 100, 1000, 10000]
+code = '''
+    const char alphas[] = "abcdefghijklmnopqrstuvwxyz";
+    const char nums[] = "0123456789";
+    lfs_format(&lfs, &cfg) => 0;
+    lfs_mount(&lfs, &cfg) => 0;
+    const struct lfs_file_config filecfg = {
+        .attr_count = 1,
+        .attrs = (struct lfs_attr[]){
+            {'A', "abcd", 4},
+        },
+    };
+    lfs_file_opencfg(&lfs, &file, "open_me",
+            LFS_O_CREAT | LFS_O_WRONLY, &filecfg) => 0;
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_write(&lfs, &file, &alphas[j % 26], 1) => 1;
+    }
+    lfs_file_close(&lfs, &file) => 0;
+    lfs_unmount(&lfs) => 0;
+
+    // open reader/writer/snapshot
+    lfs_mount(&lfs, &cfg) => 0;
+    lfs_file_t reader;
+    const struct lfs_file_config readercfg = {
+        .attr_count = 1,
+        .attrs = (struct lfs_attr[]){
+            {'A', &(uint8_t[4]){0}, 4}
+        },
+    };
+    lfs_file_t writer;
+    const struct lfs_file_config writercfg = {
+        .attr_count = 1,
+        .attrs = (struct lfs_attr[]){
+            {'A', &(uint8_t[4]){0}, 4}
+        },
+    };
+    lfs_file_t snapshot;
+    const struct lfs_file_config snapshotcfg = {
+        .attr_count = 1,
+        .attrs = (struct lfs_attr[]){
+            {'A', &(uint8_t[4]){0}, 4}
+        },
+    };
+    lfs_file_opencfg(&lfs, &reader, "open_me",
+            LFS_O_RDONLY, &readercfg) => 0;
+    lfs_file_opencfg(&lfs, &writer, "open_me",
+            LFS_O_WRONLY, &writercfg) => 0;
+    lfs_file_opencfg(&lfs, &snapshot, "open_me",
+            LFS_O_RDONLY | LFS_O_SNAPSHOT, &snapshotcfg) => 0;
+
+    assert(memcmp(readercfg.attrs[0].buffer, "abcd", 4) == 0);
+    for (int j = 0; j < SIZE/2; j++) {
+        lfs_file_read(&lfs, &reader, buffer, 1) => 1;
+        assert(buffer[0] == alphas[j % 26]);
+    }
+
+    assert(memcmp(snapshotcfg.attrs[0].buffer, "abcd", 4) == 0);
+    for (int j = 0; j < SIZE/2; j++) {
+        lfs_file_read(&lfs, &snapshot, buffer, 1) => 1;
+        assert(buffer[0] == alphas[j % 26]);
+    }
+
+    // write file
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_write(&lfs, &writer, &nums[j % 10], 1) => 1;
+    }
+    memcpy(writercfg.attrs[0].buffer, "0123", 4);
+    lfs_file_sync(&lfs, &writer) => 0;
+
+    // reader should change
+    assert(memcmp(readercfg.attrs[0].buffer, "0123", 4) == 0);
+    for (int j = SIZE/2; j < SIZE; j++) {
+        lfs_file_read(&lfs, &reader, buffer, 1) => 1;
+        assert(buffer[0] == nums[j % 10]);
+    }
+
+    // snapshot should remain unchanged
+    assert(memcmp(snapshotcfg.attrs[0].buffer, "abcd", 4) == 0);
+    for (int j = SIZE/2; j < SIZE; j++) {
+        lfs_file_read(&lfs, &snapshot, buffer, 1) => 1;
+        assert(buffer[0] == alphas[j % 26]);
+    }
+
+    lfs_file_close(&lfs, &reader) => 0;
+    lfs_file_close(&lfs, &writer) => 0;
+    lfs_file_close(&lfs, &snapshot) => 0;
+
+    // disk should change
+    lfs_file_opencfg(&lfs, &reader, "open_me",
+            LFS_O_RDONLY, &readercfg) => 0;
+    assert(memcmp(readercfg.attrs[0].buffer, "0123", 4) == 0);
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_read(&lfs, &reader, buffer, 1) => 1;
+        assert(buffer[0] == nums[j % 10]);
+    }
+    lfs_file_close(&lfs, &reader) => 0;
+    lfs_unmount(&lfs) => 0;
+
+    lfs_mount(&lfs, &cfg) => 0;
+    lfs_file_opencfg(&lfs, &reader, "open_me",
+            LFS_O_RDONLY, &readercfg) => 0;
+    assert(memcmp(readercfg.attrs[0].buffer, "0123", 4) == 0);
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_read(&lfs, &reader, buffer, 1) => 1;
+        assert(buffer[0] == nums[j % 10]);
+    }
+    lfs_file_close(&lfs, &reader) => 0;
+    lfs_unmount(&lfs) => 0;
+'''
+
+[[case]] # simple snapshot for writing
+define.SIZE = [10, 100, 1000, 10000]
+code = '''
+    const char alphas[] = "abcdefghijklmnopqrstuvwxyz";
+    const char nums[] = "0123456789";
+    lfs_format(&lfs, &cfg) => 0;
+    lfs_mount(&lfs, &cfg) => 0;
+    const struct lfs_file_config filecfg = {
+        .attr_count = 1,
+        .attrs = (struct lfs_attr[]){
+            {'A', "abcd", 4},
+        },
+    };
+    lfs_file_opencfg(&lfs, &file, "open_me",
+            LFS_O_CREAT | LFS_O_WRONLY, &filecfg) => 0;
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_write(&lfs, &file, &alphas[j % 26], 1) => 1;
+    }
+    lfs_file_close(&lfs, &file) => 0;
+    lfs_unmount(&lfs) => 0;
+
+    // open reader/snapshot
+    lfs_mount(&lfs, &cfg) => 0;
+    lfs_file_t reader;
+    const struct lfs_file_config readercfg = {
+        .attr_count = 1,
+        .attrs = (struct lfs_attr[]){
+            {'A', &(uint8_t[4]){0}, 4}
+        },
+    };
+    lfs_file_t snapshot;
+    const struct lfs_file_config snapshotcfg = {
+        .attr_count = 1,
+        .attrs = (struct lfs_attr[]){
+            {'A', &(uint8_t[4]){0}, 4}
+        },
+    };
+    lfs_file_opencfg(&lfs, &reader, "open_me",
+            LFS_O_RDONLY, &readercfg) => 0;
+    lfs_file_opencfg(&lfs, &snapshot, "open_me",
+            LFS_O_RDWR | LFS_O_SNAPSHOT, &snapshotcfg) => 0;
+
+    assert(memcmp(readercfg.attrs[0].buffer, "abcd", 4) == 0);
+    for (int j = 0; j < SIZE/2; j++) {
+        lfs_file_read(&lfs, &reader, buffer, 1) => 1;
+        assert(buffer[0] == alphas[j % 26]);
+    }
+
+    assert(memcmp(snapshotcfg.attrs[0].buffer, "abcd", 4) == 0);
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_read(&lfs, &snapshot, buffer, 1) => 1;
+        assert(buffer[0] == alphas[j % 26]);
+    }
+
+    // modify snapshot
+    lfs_file_rewind(&lfs, &snapshot) => 0;
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_write(&lfs, &snapshot, &nums[j % 10], 1) => 1;
+    }
+    memcpy(snapshotcfg.attrs[0].buffer, "0123", 4);
+
+    lfs_file_rewind(&lfs, &snapshot) => 0;
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_read(&lfs, &snapshot, buffer, 1) => 1;
+        assert(buffer[0] == nums[j % 10]);
+    }
+
+    lfs_file_sync(&lfs, &snapshot) => 0;
+
+    // reader should not change
+    assert(memcmp(readercfg.attrs[0].buffer, "abcd", 4) == 0);
+    for (int j = SIZE/2; j < SIZE; j++) {
+        lfs_file_read(&lfs, &reader, buffer, 1) => 1;
+        assert(buffer[0] == alphas[j % 26]);
+    }
+
+    // snapshot should changed
+    assert(memcmp(snapshotcfg.attrs[0].buffer, "0123", 4) == 0);
+    lfs_file_rewind(&lfs, &snapshot) => 0;
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_read(&lfs, &snapshot, buffer, 1) => 1;
+        assert(buffer[0] == nums[j % 10]);
+    }
+
+    lfs_file_close(&lfs, &reader) => 0;
+    lfs_file_close(&lfs, &snapshot) => 0;
+
+    // disk should not change
+    lfs_file_opencfg(&lfs, &reader, "open_me",
+            LFS_O_RDONLY, &readercfg) => 0;
+    assert(memcmp(readercfg.attrs[0].buffer, "abcd", 4) == 0);
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_read(&lfs, &reader, buffer, 1) => 1;
+        assert(buffer[0] == alphas[j % 26]);
+    }
+    lfs_file_close(&lfs, &reader) => 0;
+    lfs_unmount(&lfs) => 0;
+
+    lfs_mount(&lfs, &cfg) => 0;
+    lfs_file_opencfg(&lfs, &reader, "open_me",
+            LFS_O_RDONLY, &readercfg) => 0;
+    assert(memcmp(readercfg.attrs[0].buffer, "abcd", 4) == 0);
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_read(&lfs, &reader, buffer, 1) => 1;
+        assert(buffer[0] == alphas[j % 26]);
+    }
+    lfs_file_close(&lfs, &reader) => 0;
+    lfs_unmount(&lfs) => 0;
+'''
+
+[[case]] # temporary files
+define.SIZE = [10, 100, 1000, 10000]
+define.TMP_PATH = 'range(4)'
+code = '''
+    const char alphas[] = "abcdefghijklmnopqrstuvwxyz";
+    const char nums[] = "0123456789";
+    const char caps[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
+    lfs_format(&lfs, &cfg) => 0;
+    lfs_mount(&lfs, &cfg) => 0;
+    const struct lfs_file_config filecfg = {
+        .attr_count = 1,
+        .attrs = (struct lfs_attr[]){
+            {'A', "abcd", 4},
+        },
+    };
+    lfs_file_opencfg(&lfs, &file, "open_me",
+            LFS_O_CREAT | LFS_O_WRONLY, &filecfg) => 0;
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_write(&lfs, &file, &alphas[j % 26], 1) => 1;
+    }
+    lfs_file_close(&lfs, &file) => 0;
+    lfs_file_opencfg(&lfs, &file, "dont_open_me",
+            LFS_O_CREAT | LFS_O_WRONLY, &filecfg) => 0;
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_write(&lfs, &file, &alphas[j % 26], 1) => 1;
+    }
+    lfs_file_close(&lfs, &file) => 0;
+    lfs_unmount(&lfs) => 0;
+
+    // open reader/writer/temp
+    lfs_mount(&lfs, &cfg) => 0;
+    lfs_file_t reader;
+    const struct lfs_file_config readercfg = {
+        .attr_count = 1,
+        .attrs = (struct lfs_attr[]){
+            {'A', &(uint8_t[4]){0}, 4}
+        },
+    };
+    lfs_file_t writer;
+    const struct lfs_file_config writercfg = {
+        .attr_count = 1,
+        .attrs = (struct lfs_attr[]){
+            {'A', &(uint8_t[4]){0}, 4}
+        },
+    };
+    lfs_file_t tmp;
+    const struct lfs_file_config tmpcfg = {
+        .attr_count = 1,
+        .attrs = (struct lfs_attr[]){
+            {'A', &(uint8_t[4]){0}, 4}
+        },
+    };
+    lfs_file_opencfg(&lfs, &reader, "open_me",
+            LFS_O_RDONLY, &readercfg) => 0;
+    lfs_file_opencfg(&lfs, &writer, "open_me",
+            LFS_O_WRONLY, &writercfg) => 0;
+    const char *tmp_paths[] = {NULL, "/", "/tmp", "/open_me.tmp"};
+    lfs_file_opencfg(&lfs, &tmp, tmp_paths[TMP_PATH],
+            LFS_O_RDWR | LFS_O_CREAT | LFS_O_SNAPSHOT, &tmpcfg) => 0;
+
+    assert(memcmp(readercfg.attrs[0].buffer, "abcd", 4) == 0);
+    for (int j = 0; j < SIZE/3; j++) {
+        lfs_file_read(&lfs, &reader, buffer, 1) => 1;
+        assert(buffer[0] == alphas[j % 26]);
+    }
+
+    assert(memcmp(tmpcfg.attrs[0].buffer, "\0\0\0\0", 4) == 0);
+    assert(lfs_file_size(&lfs, &tmp) == 0);
+
+    // write to tmp
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_write(&lfs, &tmp, &nums[j % 10], 1) => 1;
+    }
+    memcpy(tmpcfg.attrs[0].buffer, "0123", 4);
+
+    lfs_file_rewind(&lfs, &tmp) => 0;
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_read(&lfs, &tmp, buffer, 1) => 1;
+        assert(buffer[0] == nums[j % 10]);
+    }
+
+    lfs_file_sync(&lfs, &tmp) => 0;
+
+    // reader should not change
+    assert(memcmp(readercfg.attrs[0].buffer, "abcd", 4) == 0);
+    for (int j = SIZE/3; j < 2*SIZE/3; j++) {
+        lfs_file_read(&lfs, &reader, buffer, 1) => 1;
+        assert(buffer[0] == alphas[j % 26]);
+    }
+
+    // tmp should change
+    assert(memcmp(tmpcfg.attrs[0].buffer, "0123", 4) == 0);
+    lfs_file_rewind(&lfs, &tmp) => 0;
+    for (int j = 0; j < SIZE/2; j++) {
+        lfs_file_read(&lfs, &tmp, buffer, 1) => 1;
+        assert(buffer[0] == nums[j % 10]);
+    }
+
+    // write to file
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_write(&lfs, &writer, &caps[j % 26], 1) => 1;
+    }
+    memcpy(writercfg.attrs[0].buffer, "ABCD", 4);
+    lfs_file_sync(&lfs, &writer) => 0;
+
+    // reader should change
+    assert(memcmp(readercfg.attrs[0].buffer, "ABCD", 4) == 0);
+    for (int j = 2*SIZE/3; j < SIZE; j++) {
+        lfs_file_read(&lfs, &reader, buffer, 1) => 1;
+        assert(buffer[0] == caps[j % 26]);
+    }
+
+    // tmp should not change
+    assert(memcmp(tmpcfg.attrs[0].buffer, "0123", 4) == 0);
+    for (int j = SIZE/2; j < SIZE; j++) {
+        lfs_file_read(&lfs, &tmp, buffer, 1) => 1;
+        assert(buffer[0] == nums[j % 10]);
+    }
+
+    lfs_file_close(&lfs, &reader) => 0;
+    lfs_file_close(&lfs, &writer) => 0;
+    lfs_file_close(&lfs, &tmp) => 0;
+
+    // tmp should not appear on disk
+    lfs_dir_open(&lfs, &dir, "/") => 0;
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_DIR);
+    assert(strcmp(info.name, ".") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_DIR);
+    assert(strcmp(info.name, "..") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_REG);
+    assert(strcmp(info.name, "dont_open_me") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_REG);
+    assert(strcmp(info.name, "open_me") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 0;
+    lfs_dir_close(&lfs, &dir) => 0;
+    lfs_file_opencfg(&lfs, &reader, "open_me",
+            LFS_O_RDONLY, &readercfg) => 0;
+    assert(memcmp(readercfg.attrs[0].buffer, "ABCD", 4) == 0);
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_read(&lfs, &reader, buffer, 1) => 1;
+        assert(buffer[0] == caps[j % 26]);
+    }
+    lfs_file_close(&lfs, &reader) => 0;
+    lfs_file_opencfg(&lfs, &reader, "dont_open_me",
+            LFS_O_RDONLY, &readercfg) => 0;
+    assert(memcmp(readercfg.attrs[0].buffer, "abcd", 4) == 0);
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_read(&lfs, &reader, buffer, 1) => 1;
+        assert(buffer[0] == alphas[j % 26]);
+    }
+    lfs_file_close(&lfs, &reader) => 0;
+    lfs_unmount(&lfs) => 0;
+
+    lfs_mount(&lfs, &cfg) => 0;
+    lfs_dir_open(&lfs, &dir, "/") => 0;
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_DIR);
+    assert(strcmp(info.name, ".") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_DIR);
+    assert(strcmp(info.name, "..") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_REG);
+    assert(strcmp(info.name, "dont_open_me") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_REG);
+    assert(strcmp(info.name, "open_me") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 0;
+    lfs_dir_close(&lfs, &dir) => 0;
+    lfs_file_opencfg(&lfs, &reader, "open_me",
+            LFS_O_RDONLY, &readercfg) => 0;
+    assert(memcmp(readercfg.attrs[0].buffer, "ABCD", 4) == 0);
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_read(&lfs, &reader, buffer, 1) => 1;
+        assert(buffer[0] == caps[j % 26]);
+    }
+    lfs_file_close(&lfs, &reader) => 0;
+    lfs_file_opencfg(&lfs, &reader, "dont_open_me",
+            LFS_O_RDONLY, &readercfg) => 0;
+    assert(memcmp(readercfg.attrs[0].buffer, "abcd", 4) == 0);
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_read(&lfs, &reader, buffer, 1) => 1;
+        assert(buffer[0] == alphas[j % 26]);
+    }
+    lfs_file_close(&lfs, &reader) => 0;
+    lfs_unmount(&lfs) => 0;
+'''
+
+[[case]] # test snapshot open errors
+code = '''
+    lfs_format(&lfs, &cfg) => 0;
+    lfs_mount(&lfs, &cfg) => 0;
+    lfs_file_open(&lfs, &file, NULL,
+            LFS_O_RDWR | LFS_O_SNAPSHOT) => LFS_ERR_ISDIR;
+    lfs_file_open(&lfs, &file, "/",
+            LFS_O_RDWR | LFS_O_SNAPSHOT) => LFS_ERR_ISDIR;
+    lfs_file_open(&lfs, &file, "/tmp",
+            LFS_O_RDWR | LFS_O_SNAPSHOT) => LFS_ERR_NOENT;
+    lfs_file_open(&lfs, &file, "/tmp/",
+            LFS_O_RDWR | LFS_O_CREAT | LFS_O_SNAPSHOT) => LFS_ERR_NOENT;
+    lfs_file_open(&lfs, &file, "/tmp/tmp",
+            LFS_O_RDWR | LFS_O_CREAT | LFS_O_SNAPSHOT) => LFS_ERR_NOENT;
+    lfs_unmount(&lfs) => 0;
+'''

tests/test_paths.toml

@@ -95,9 +95,9 @@ code = '''
 
     lfs_mkdir(&lfs, "coffee/../milk") => 0;
     lfs_stat(&lfs, "coffee/../milk", &info) => 0;
-    strcmp(info.name, "milk") => 0;
+    assert(strcmp(info.name, "milk") == 0);
     lfs_stat(&lfs, "milk", &info) => 0;
-    strcmp(info.name, "milk") => 0;
+    assert(strcmp(info.name, "milk") == 0);
     lfs_unmount(&lfs) => 0;
 '''
 
@@ -129,9 +129,9 @@ code = '''
     lfs_mount(&lfs, &cfg) => 0;
     lfs_mkdir(&lfs, ".milk") => 0;
     lfs_stat(&lfs, ".milk", &info) => 0;
-    strcmp(info.name, ".milk") => 0;
+    assert(strcmp(info.name, ".milk") == 0);
     lfs_stat(&lfs, "tea/.././.milk", &info) => 0;
-    strcmp(info.name, ".milk") => 0;
+    assert(strcmp(info.name, ".milk") == 0);
     lfs_unmount(&lfs) => 0;
 '''
 
@@ -149,13 +149,13 @@ code = '''
     lfs_mkdir(&lfs, "coffee/coldcoffee") => 0;
 
     lfs_stat(&lfs, "coffee/../../../../../../tea/hottea", &info) => 0;
-    strcmp(info.name, "hottea") => 0;
+    assert(strcmp(info.name, "hottea") == 0);
 
     lfs_mkdir(&lfs, "coffee/../../../../../../milk") => 0;
     lfs_stat(&lfs, "coffee/../../../../../../milk", &info) => 0;
-    strcmp(info.name, "milk") => 0;
+    assert(strcmp(info.name, "milk") == 0);
     lfs_stat(&lfs, "milk", &info) => 0;
-    strcmp(info.name, "milk") => 0;
+    assert(strcmp(info.name, "milk") == 0);
     lfs_unmount(&lfs) => 0;
 '''