Make attribute writing be dependant on attr_count upon close/sync and not upon write

lfs.c

@@ -3180,8 +3180,6 @@ static int lfs_file_opencfg_(lfs_t *lfs, lfs_file_t *file,
                 err = LFS_ERR_NOSPC;
                 goto cleanup;
             }
-
-            file->flags |= LFS_F_DIRTY;
         }
 #endif
     }
@@ -3441,7 +3439,9 @@ static int lfs_file_sync_(lfs_t *lfs, lfs_file_t *file) {
     }
 
 
-    if ((file->flags & LFS_F_DIRTY) &&
+    if (((file->flags & LFS_F_DIRTY) ||
+            (/* User request attributes write */(file->cfg->attr_count > 0) && (file->flags & LFS_O_WRONLY)))
+            &&
             !lfs_pair_isnull(file->m.pair)) {
         // before we commit metadata, we need sync the disk to make sure
         // data writes don't complete after metadata writes

lfs.h

@@ -351,9 +351,9 @@ struct lfs_file_config {
     // Optional list of custom attributes related to the file. If the file
     // is opened with read access, these attributes will be read from disk
     // during the open call. If the file is opened with write access, the
-    // attributes will be written to disk every file sync or close. This
-    // write occurs atomically with update to the file's contents.
-    //
+    // attributes will be written to disk every file sync or close according
+    // to the attr_count value and attrs content upon close. This write occurs
+    // atomically with update to the file's contents.
     // 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 the buffer, it will be padded with zeros. If the stored attribute

tests/test_attrs.toml

@@ -267,6 +267,42 @@ code = '''
     memcmp(buffer, "hello", strlen("hello")) => 0;
     lfs_file_close(&lfs, &file);
     lfs_unmount(&lfs) => 0;
+
+    lfs_mount(&lfs, cfg) => 0;
+    struct lfs_attr attrs4[] = {
+        {'A', buffer,    4},
+    };
+    memset(buffer, 'a', sizeof(buffer));
+    struct lfs_file_config cfg4 = {.attrs=attrs4};
+    lfs_file_open(&lfs, &file, "hello/hello2", LFS_O_WRONLY | LFS_O_CREAT) => 0;
+    lfs_file_close(&lfs, &file);
+
+
+    cfg4.attr_count = 1;
+    lfs_file_opencfg(&lfs, &file, "hello/hello2", LFS_O_WRONLY | LFS_O_RDONLY, &cfg4) => 0;
+    lfs_off_t origin_file_metadata_offset = file.m.off;
+    cfg4.attr_count = 0;
+    lfs_file_sync(&lfs, &file); // No write expected, although that upon opening attr_count was 1
+    lfs_getattr(&lfs, "hello/hello2", 'A', buffer,  4) => LFS_ERR_NOATTR;
+    (file.m.off != origin_file_metadata_offset) => 0; // expecten no write to happen
+    cfg4.attr_count = 1;
+    lfs_file_sync(&lfs, &file); // attributes expected to be written because attr_count is 1, although no write happened
+    lfs_getattr(&lfs, "hello/hello2", 'A', buffer,  4) => 4;
+    lfs_file_close(&lfs, &file);
+
+    memset(buffer, 'b', sizeof(buffer));
+    cfg4.attr_count = 1;
+    lfs_file_opencfg(&lfs, &file, "hello/hello3", LFS_O_WRONLY | LFS_O_CREAT, &cfg4) => 0;
+    lfs_file_sync(&lfs, &file);
+    lfs_getattr(&lfs, "hello/hello3", 'A', buffer,  4) => 4;
+    memcmp(buffer,    "bbbb",      4) => 0;
+    memset(buffer, 'c', sizeof(buffer));
+    lfs_file_sync(&lfs, &file); // attributes expected to be re-written because attr_count is still 1, although no write happened
+    lfs_getattr(&lfs, "hello/hello3", 'A', buffer,  4) => 4;
+    memcmp(buffer,    "cccc",      4) => 0;
+    lfs_file_close(&lfs, &file);
+    lfs_unmount(&lfs) => 0;
+
 '''
 
 [cases.test_attrs_deferred_file]