From 5ff39998bf0ce71bd8fc8d0f002ceb81b711992f Mon Sep 17 00:00:00 2001
From: Andre Noll <maan@tuebingen.mpg.de>
Date: Sun, 28 Jun 2015 16:18:22 +0200
Subject: [PATCH] filter: Make ->open() optional.

There is no need to force each filter to supply this method, so teach
the three callers of ->open() to check for NULL pointers.

The commit also fixes some trivial language issues in the documentation
of ->open() and ->close().
---
 audiod.c |  3 ++-
 filter.c |  3 ++-
 filter.h | 13 +++++++------
 play.c   |  3 ++-
 4 files changed, 13 insertions(+), 9 deletions(-)

diff --git a/audiod.c b/audiod.c
index fedeff7a..285d2762 100644
--- a/audiod.c
+++ b/audiod.c
@@ -596,7 +596,8 @@ static void open_filters(struct slot_info *s)
 			EMBRACE(.name = f->name, .parent = parent,
 				.handler = f->execute, .context = fn));
 
-		f->open(fn);
+		if (f->open)
+			f->open(fn);
 		sprintf(buf, "%s (slot %d)", f->name, (int)(s - slot));
 		fn->task = task_register(&(struct task_info) {
 			.name = buf,
diff --git a/filter.c b/filter.c
index 9378e469..804b5e1e 100644
--- a/filter.c
+++ b/filter.c
@@ -142,7 +142,8 @@ int main(int argc, char *argv[])
 		ti.pre_select = f->pre_select;
 		ti.post_select = f->post_select;
 		ti.context = fn;
-		f->open(fn);
+		if (f->open)
+			f->open(fn);
 		fn->task = task_register(&ti, &s);
 		parent = fn->btrn;
 	}
diff --git a/filter.h b/filter.h
index 937bb42b..0bd54690 100644
--- a/filter.h
+++ b/filter.h
@@ -58,17 +58,18 @@ struct filter {
 	/**
 	 * Open one instance of this filter.
 	 *
-	 * This should allocate the output buffer of the given filter node and do any
-	 * other filter-specific preparations like initializing the private_data member
-	 * of \a fn suitably. The open function is assumed to succeed.
+	 * This should allocate the output buffer of the given filter node and
+	 * do any other filter-specific preparations like initializing the
+	 * private_data member of \a fn suitably. The open function is
+	 * optional, If it is provided, it is assumed to succeed.
 	 */
 	void (*open)(struct filter_node *fn);
 	/**
 	 * Close one instance of this filter.
 	 *
-	 * Free all resources of associated with \a fn that were previously allocated
-	 * by the open() function. It's OK to leave this alone if the filter does not
-	 * need any cleanups.
+	 * Free all resources associated with \a fn that were previously
+	 * allocated by the open() function. It's OK to set this to NULL if the
+	 * filter does not need to perform any cleanup operation.
 	 */
 	void (*close)(struct filter_node *fn);
 	/**
diff --git a/play.c b/play.c
index a7ce563b..d2539ee1 100644
--- a/play.c
+++ b/play.c
@@ -397,7 +397,8 @@ static int load_file(struct play_task *pt)
 	pt->fn.btrn = btr_new_node(&(struct btr_node_description)
 		EMBRACE(.name = decoder->name, .parent = pt->rn.btrn,
 			.handler = decoder->execute, .context = &pt->fn));
-	decoder->open(&pt->fn);
+	if (decoder->open)
+		decoder->open(&pt->fn);
 
 	/* setup default writer */
 	pt->wn.conf = check_writer_arg_or_die(NULL, &pt->wn.writer_num);
-- 
2.39.5