+ /*
+ * Main extraction routine.
+ *
+ * The extraction backend is provided a list of dentries that have been
+ * prepared for extraction. It is free to extract them in any way that
+ * it chooses. Ideally, it should choose a method that maximizes
+ * performance.
+ *
+ * The target string will be provided in ctx->common.target. This might
+ * be a directory, although extraction backends are free to interpret it
+ * as they wish. TODO: in some cases, the common extraction code also
+ * interprets the target string. This should be completely isolated to
+ * extraction backends.
+ *
+ * The extraction flags will be provided in ctx->common.extract_flags.
+ * Extraction backends should examine them and implement the behaviors
+ * for as many flags as possible. Some flags are already handled by the
+ * common extraction code. TODO: this needs to be better formalized.
+ *
+ * @dentry_list, the list of dentries, will be ordered such that the
+ * ancestor of any dentry always precedes any descendents. Unless
+ * @single_tree_only is set, it's possible that the dentries consist of
+ * multiple disconnected trees.
+ *
+ * 'd_extraction_name' and 'd_extraction_name_nchars' of each dentry
+ * will be set to indicate the actual name with which the dentry should
+ * be extracted. This may or may not be the same as 'file_name'.
+ * TODO: really, the extraction backends should be responsible for
+ * generating 'd_extraction_name'.
+ *
+ * Each dentry will refer to a valid inode in 'd_inode'.
+ * 'd_inode->i_extraction_aliases' will contain a list of just the
+ * dentries of that inode being extracted. This will be a (possibly
+ * nonproper) subset of the 'd_inode->i_dentry' list.
+ *
+ * The streams required to be extracted will already be prepared in
+ * 'apply_ctx'. The extraction backend should call
+ * extract_stream_list() to extract them.
+ *
+ * The will_extract_dentry() utility function, given an arbitrary dentry
+ * in the WIM image (which may not be in the extraction list), can be
+ * used to determine if that dentry is in the extraction list.
+ *
+ * Return 0 if successful; otherwise a positive wimlib error code.
+ */