-/**
- * the init function of the writer
- *
- * It must fill in all other function pointers of the given
- * writer structure.
- *
- */
-void (*init)(struct writer *w);
-/**
- *
- * open one instance of this writer
- *
- * This function should perform any work necessary to write the incoming
- * stream. If To this aim, it may allocate its private data structure and store
- * a pointer to that structure via the given writer_node paramenter.
- */
-int (*open)(struct writer_node *);
-/**
- *
- * write a chunk of audio data
- *
- * This is called from the driving application whenever a data block of \a
- * chunk_bytes is available. It must return the number of bytes consumed from
- * \a data on success, and negative on errors.
- *
- */
-int (*write)(char *data, size_t nbytes, struct writer_node *);
-void (*pre_select)(struct sched *s, struct task *t);
-void (*post_select)(struct sched *s, struct task *t);
-/**
- * close one instance of the writer
- *
- * This function is assumed to succeed.
- */
-void (*close)(struct writer_node *);
-/**
- * shutdown the writer
- *
- * This is a optional function pointer used for cleaning
- * up.
- */
-void (*shutdown)(struct writer_node *);
-};
-
-/**
- * describes a set of writer nodes that all write the same stream.
- */
-struct writer_node_group {
-/** number of nodes belonging to this group */
-unsigned num_writers;
-/** array of pointers to the corresponding writer nodes */
-struct writer_node *writer_nodes;
-/** keeps track of how many bytes have been written by each node */
-int *written;
-/** the maximum of the chunk_bytes values of the writer nodes in this group */
-size_t max_chunk_bytes;
-/** non-zero if end of file was encountered */
-int *eof;
-char *buf;
-size_t *loaded;
-struct task task;
+ /**
+ * Prepare the fd sets for select.
+ *
+ * This is called from scheduler. It may use the sched pointer to add
+ * any file descriptors or to decrease the select timeout.
+ */
+ void (*pre_select)(struct sched *s, void *context);
+ /**
+ * Write audio data.
+ *
+ * Called from the post_select function of the writer node's task.
+ */
+ int (*post_select)(struct sched *s, void *context);
+ /**
+ * Close one instance of the writer.
+ *
+ * This function is assumed to succeed.
+ */
+ void (*close)(struct writer_node *);
+ /**
+ * The callback handler.
+ *
+ * Each writer may provide an ->execute callback which can be used for
+ * inter-node communication.
+ */
+ btr_command_handler execute;