fatfs: small optimization

kernel-src/fs/fat/fatfs.c

@@ -956,6 +956,7 @@ fatnode_t *fatfs_allocate_node(vfs_t *vfs, int type) {
 	fatnode->cluster = 0;
 	fatnode->parent_dir = NULL;
 	fatnode->dent_disk_offset = 0;
+	fatnode->saved_cluster = 0;
 
 	return fatnode;
 }

kernel-src/fs/fat/fatfs_dir.c

@@ -477,7 +477,6 @@ int fatfs_update_dent(fatfs_t *fatfs, fatnode_t *fatnode) {
 }
 
 static int get_free_dents(fatfs_t *fatfs, fatnode_t *fatnode, size_t dent_count, size_t *dent_offset) {
-	// TODO add a first free search
 	size_t offset = 0;
 	fatfs_dent_t dent;
 	size_t free_count = 0;

kernel-src/fs/fat/fatfs_fat.c

@@ -326,6 +326,7 @@ int fatfs_resize_file(fatfs_t *fatfs, fatnode_t *fatnode, size_t new_size) {
 			return error;
 
 		fatnode->cluster = 0;
+		fatnode->saved_cluster = 0;
 	} else {
 		// truncate a part of the file
 		fatfs_cluster_t cluster;
@@ -335,6 +336,9 @@ int fatfs_resize_file(fatfs_t *fatfs, fatnode_t *fatnode, size_t new_size) {
 
 		__assert(cluster != FATFS_CLUSTER_FREE && fatfs_is_cluster_eof(fatfs, cluster) == false);
 		error = fatfs_cut_chain(fatfs, cluster);
+
+		// no need to update the saved index/cluster as the previour fatfs_get_cluster_from_index call will have
+		// set the index and cluster properly
 	}
 
 	if (error == 0) {

kernel-src/fs/fat/fatfs_rw.c

@@ -1,9 +1,13 @@
 #include <kernel/fatfs.h>
 #include <logging.h>
 
-// TODO optimize this by keeping some metadata in the fatfs node
 int fatfs_get_cluster_from_index(fatfs_t *fs, fatnode_t *node, uintmax_t index, fatfs_cluster_t *cluster) {
-	fatfs_cluster_t iterator = node->cluster;
+	if (node->saved_cluster == 0 || node->saved_index > index) {
+		node->saved_cluster = node->cluster;
+		node->saved_index = 0;
+	}
+
+	fatfs_cluster_t iterator = node->saved_cluster;
 
 	// empty file?
 	if (iterator == 0) {
@@ -42,6 +46,12 @@ int fatfs_get_cluster_from_index(fatfs_t *fs, fatnode_t *node, uintmax_t index,
 		}
 	}
 
+	if (fatfs_is_cluster_eof(fs, iterator) == false) {
+		// update the last found index
+		node->saved_index = index;
+		node->saved_cluster = iterator;
+	}
+
 	*cluster = iterator;
 	return 0;
 }