axfer: add an implementation of waiter for poll(2)

This commit adds support of waiter for poll(2) system call.

Below lines are examples to use this option:
$ axfer transfer --waiter-type=poll -M -P -d 2 -D hw:0,3 /dev/urandom -f dat -vvv
$ axfer transfer --waiter-type=poll -M -C -d 2 -D hw:1,0 /dev/null -r 48000 -vvv

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

axfer/Makefile.am

@@ -50,4 +50,5 @@ axfer_SOURCES = \
 	subcmd-transfer.c \
 	xfer-libasound-irq-mmap.c \
 	waiter.h \
-	waiter.c
+	waiter.c \
+	waiter-poll.c

axfer/waiter-poll.c

@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: GPL-2.0
+//
+// waiter-poll.c - Waiter for event notification by poll(2).
+//
+// Copyright (c) 2018 Takashi Sakamoto <o-takashi@sakamocchi.jp>
+//
+// Licensed under the terms of the GNU General Public License, version 2.
+
+#include "waiter.h"
+#include "misc.h"
+
+#include <stdlib.h>
+#include <errno.h>
+#include <poll.h>
+
+static int poll_prepare(struct waiter_context *waiter)
+{
+	// Nothing to do because an instance of waiter has required data.
+	return 0;
+}
+
+static int poll_wait_event(struct waiter_context *waiter, int timeout_msec)
+{
+	int err;
+
+	err = poll(waiter->pfds, waiter->pfd_count, timeout_msec);
+	if (err < 0)
+		return -errno;
+
+	return err;
+}
+
+static void poll_release(struct waiter_context *waiter)
+{
+	// Nothing to do because an instance of waiter has required data.
+	return;
+}
+
+const struct waiter_data waiter_poll = {
+	.ops = {
+		.prepare	= poll_prepare,
+		.wait_event	= poll_wait_event,
+		.release	= poll_release,
+	},
+};

axfer/waiter.c

@@ -16,6 +16,7 @@
 
 static const char *const waiter_type_labels[] = {
 	[WAITER_TYPE_DEFAULT] = "default",
+	[WAITER_TYPE_POLL] = "poll",
 };
 
 enum waiter_type waiter_type_from_label(const char *label)
@@ -42,7 +43,7 @@ int waiter_context_init(struct waiter_context *waiter,
 		enum waiter_type type;
 		const struct waiter_data *waiter;
 	} entries[] = {
-		{WAITER_TYPE_COUNT,	NULL},
+		{WAITER_TYPE_POLL,	&waiter_poll},
 	};
 	int i;
 

axfer/waiter.h

@@ -13,6 +13,7 @@
 
 enum waiter_type {
 	WAITER_TYPE_DEFAULT = 0,
+	WAITER_TYPE_POLL,
 	WAITER_TYPE_COUNT,
 };
 
@@ -51,4 +52,6 @@ struct waiter_data {
 	unsigned int private_size;
 };
 
+extern const struct waiter_data waiter_poll;
+
 #endif