dahdi_tools 分析 (五) dahdi_monitor

# dahdi_monitor -h
Usage: dahdi_monitor <channel num> [-v[v]] [-m] [-o] [-l limit] [-f FILE | -s FILE | -r FILE1 -t FILE2] [-F FILE | -S FILE | -R FILE1 -T FILE2]
Options:
        -v: Visual mode.  Implies -m.
        -vv: Visual/Verbose mode.  Implies -m.
        -l LIMIT: Stop after reading LIMIT bytes
        -m: Separate rx/tx streams.
        -o: Output audio via OSS.  Note: Only 'normal' combined rx/tx streams are output via OSS.
        -f FILE: Save combined rx/tx stream to mono FILE. Cannot be used with -m.
        -r FILE: Save rx stream to FILE. Implies -m.
        -t FILE: Save tx stream to FILE. Implies -m.
        -s FILE: Save stereo rx/tx stream to FILE. Implies -m.
        -F FILE: Save combined pre-echocanceled rx/tx stream to FILE. Cannot be used with -m.
        -R FILE: Save pre-echocanceled rx stream to FILE. Implies -m.
        -T FILE: Save pre-echocanceled tx stream to FILE. Implies -m.
        -S FILE: Save pre-echocanceled stereo rx/tx stream to FILE. Implies -m.
Examples:
Save a stream to a file
        dahdi_monitor 1 -f stream.raw
Visualize an rx/tx stream and save them to separate files.
        dahdi_monitor 1 -v -r streamrx.raw -t streamtx.raw
Play a combined rx/tx stream via OSS and save it to a file
        dahdi_monitor 1 -o -f stream.raw
Save a combined normal rx/tx stream and a combined 'preecho' rx/tx stream to files
        dahdi_monitor 1 -f stream.raw -F streampreecho.raw
Save a normal rx/tx stream and a 'preecho' rx/tx stream to separate files
        dahdi_monitor 1 -m -r streamrx.raw -t streamtx.raw -R streampreechorx.raw -T streampreechotx.raw

代码分析

	case 'r':
			
			if ((ofh[MON_BRX] = fopen(optarg, "w")) == NULL) {    // 打开输出文件
				fprintf(stderr, "Could not open %s for writing: %s\n", optarg, strerror(errno));
				exit(EXIT_FAILURE);
			}
			fprintf(stderr, "Writing receive stream to %s\n", optarg);
			file_is_wav[MON_BRX] = filename_is_wav(optarg);      // 判断输出文件是否是.wav后缀
			if (file_is_wav[MON_BRX]) {
				wavheader_init(&wavheaders[MON_BRX], 1);         // 是wav 的话先写wav文件头，文件头里的长度信息最后改写
				if (fwrite(&wavheaders[MON_BRX], 1, sizeof(struct wavheader), ofh[MON_BRX]) != sizeof(struct wavheader)) {
					fprintf(stderr, "Could not write wav header to %s: %s\n", optarg, strerror(errno));
					exit(EXIT_FAILURE);
				}
			}
			multichannel = 1;
			savefile = 1;
			break;

	/* Open Pseudo device */
	if ((pfd[MON_BRX] = pseudo_open()) < 0)                    //  打开 /dev/dahdi/pseudo 
		exit(1);
	if (multichannel && ((pfd[MON_TX] = pseudo_open()) < 0))
		exit(1);
	if (preecho) {
		if ((pfd[MON_PRE_BRX] = pseudo_open()) < 0)
			exit(1);
		if (multichannel && ((pfd[MON_PRE_TX] = pseudo_open()) < 0))
			exit(1);
	}

	/* Conference them */
	if (multichannel) {
		memset(&zc, 0, sizeof(zc));
		zc.chan = 0;
		zc.confno = chan;
		/* Two pseudo's, one for tx, one for rx */
		zc.confmode = DAHDI_CONF_MONITOR;
		if (ioctl(pfd[MON_BRX], DAHDI_SETCONF, &zc) < 0) {                      //  DAHDI_SETCONF
			fprintf(stderr, "Unable to monitor: %s\n", strerror(errno));
			exit(1);
		}
		memset(&zc, 0, sizeof(zc));
		zc.chan = 0;
		zc.confno = chan;
		zc.confmode = DAHDI_CONF_MONITORTX;
		if (ioctl(pfd[MON_TX], DAHDI_SETCONF, &zc) < 0) {
			fprintf(stderr, "Unable to monitor: %s\n", strerror(errno));
			exit(1);
		}
		if (preecho) {
			memset(&zc, 0, sizeof(zc));
			zc.chan = 0;
			zc.confno = chan;
			/* Two pseudo's, one for tx, one for rx */
			zc.confmode = DAHDI_CONF_MONITOR_RX_PREECHO;
			if (ioctl(pfd[MON_PRE_BRX], DAHDI_SETCONF, &zc) < 0) {
				fprintf(stderr, "Unable to monitor: %s\n", strerror(errno));
				exit(1);
			}
			memset(&zc, 0, sizeof(zc));
			zc.chan = 0;
			zc.confno = chan;
			zc.confmode = DAHDI_CONF_MONITOR_TX_PREECHO;
			if (ioctl(pfd[MON_PRE_TX], DAHDI_SETCONF, &zc) < 0) {
				fprintf(stderr, "Unable to monitor: %s\n", strerror(errno));
				exit(1);
			}
		}
	}

	/* Now, copy from pseudo to audio */
	while (run) {
		res_brx = read(pfd[MON_BRX], buf_brx, sizeof(buf_brx));    // 从 pseudo 中读取数据
		if (res_brx < 1)
			break;
		readcount += res_brx;
		if (ofh[MON_BRX])
			bytes_written[MON_BRX] += fwrite(buf_brx, 1, res_brx, ofh[MON_BRX]); // 将数据写入文件中

		if (multichannel) {
			res_tx = read(pfd[MON_TX], buf_tx, res_brx);                    // 后面的都是类似操作
			if (res_tx < 1)
				break;
			if (ofh[MON_TX])
				bytes_written[MON_TX] += fwrite(buf_tx, 1, res_tx, ofh[MON_TX]);
			
			}
		}

		if (preecho) {
			res_brx = read(pfd[MON_PRE_BRX],