mufs: implement mufs_seek() to seek and tell the position within a file

include/fs/mufs.h

@@ -42,5 +42,6 @@ int mufs_mkdir(struct mufs *fs, const char *path);
 int mufs_create(struct mufs *fs, const char *path);
 struct mufs_file *mufs_open(struct mufs *fs, const char *path, int mode);
 void mufs_close(struct mufs_file *file);
+long mufs_seek(struct mufs_file *file, long offset, int whence);
 size_t mufs_read(struct mufs_file *file, void *data, size_t len);
 size_t mufs_write(struct mufs_file *file, const void *data, size_t len);

source/fs/mufs/file.c

@@ -54,6 +54,26 @@ void mufs_close(struct mufs_file *file)
 	free(file);
 }
 
+long mufs_seek(struct mufs_file *file, long offset, int whence)
+{
+	if (!file)
+		return -1;
+
+	switch (whence) {
+	case SEEK_SET: break;
+	case SEEK_CUR: offset = file->va + offset; break;
+	case SEEK_END: offset = file->tree->file_size; break;
+	default: return -1;
+	}
+
+	if (offset > file->tree->file_size || offset >= UINT32_MAX)
+		return -1;
+
+	file->va = offset;
+
+	return offset;
+}
+
 size_t mufs_read(struct mufs_file *file, void *data, size_t len)
 {
 	size_t ret;