tools: Add guest trace agent as a user tool

This patch adds a user tool, "trace agent" for sending trace data of a guest to
a Host in low overhead. This agent has the following functions:
 - splice a page of ring-buffer to read_pipe without memory copying
 - splice the page from write_pipe to virtio-console without memory copying
 - write trace data to stdout by using -o option
 - controlled by start/stop orders from a Host

Changes in v2:
 - Cleanup (change fprintf() to pr_err() and an include guard)

Signed-off-by: Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@hitachi.com>
Acked-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

tools/virtio/virtio-trace/Makefile

@@ -0,0 +1,14 @@
+CC = gcc
+CFLAGS = -O2 -Wall
+LFLAG = -lpthread
+
+all: trace-agent
+
+.c.o:
+	$(CC) $(CFLAGS) $(LFLAG) -c $^ -o $@
+
+trace-agent: trace-agent.o trace-agent-ctl.o trace-agent-rw.o
+	$(CC) $(CFLAGS) $(LFLAG) -o $@ $^
+
+clean:
+	rm -f *.o trace-agent

tools/virtio/virtio-trace/README

@@ -0,0 +1,118 @@
+Trace Agent for virtio-trace
+============================
+
+Trace agent is a user tool for sending trace data of a guest to a Host in low
+overhead. Trace agent has the following functions:
+ - splice a page of ring-buffer to read_pipe without memory copying
+ - splice the page from write_pipe to virtio-console without memory copying
+ - write trace data to stdout by using -o option
+ - controlled by start/stop orders from a Host
+
+The trace agent operates as follows:
+ 1) Initialize all structures.
+ 2) Create a read/write thread per CPU. Each thread is bound to a CPU.
+    The read/write threads hold it.
+ 3) A controller thread does poll() for a start order of a host.
+ 4) After the controller of the trace agent receives a start order from a host,
+    the controller wake read/write threads.
+ 5) The read/write threads start to read trace data from ring-buffers and
+    write the data to virtio-serial.
+ 6) If the controller receives a stop order from a host, the read/write threads
+    stop to read trace data.
+
+
+Files
+=====
+
+README: this file
+Makefile: Makefile of trace agent for virtio-trace
+trace-agent.c: includes main function, sets up for operating trace agent
+trace-agent.h: includes all structures and some macros
+trace-agent-ctl.c: includes controller function for read/write threads
+trace-agent-rw.c: includes read/write threads function
+
+
+Setup
+=====
+
+To use this trace agent for virtio-trace, we need to prepare some virtio-serial
+I/Fs.
+
+1) Make FIFO in a host
+ virtio-trace uses virtio-serial pipe as trace data paths as to the number
+of CPUs and a control path, so FIFO (named pipe) should be created as follows:
+	# mkdir /tmp/virtio-trace/
+	# mkfifo /tmp/virtio-trace/trace-path-cpu{0,1,2,...,X}.{in,out}
+	# mkfifo /tmp/virtio-trace/agent-ctl-path.{in,out}
+
+For example, if a guest use three CPUs, the names are
+	trace-path-cpu{0,1,2}.{in.out}
+and
+	agent-ctl-path.{in,out}.
+
+2) Set up of virtio-serial pipe in a host
+ Add qemu option to use virtio-serial pipe.
+
+ ##virtio-serial device##
+     -device virtio-serial-pci,id=virtio-serial0\
+ ##control path##
+     -chardev pipe,id=charchannel0,path=/tmp/virtio-trace/agent-ctl-path\
+     -device virtserialport,bus=virtio-serial0.0,nr=1,chardev=charchannel0,\
+      id=channel0,name=agent-ctl-path\
+ ##data path##
+     -chardev pipe,id=charchannel1,path=/tmp/virtio-trace/trace-path-cpu0\
+     -device virtserialport,bus=virtio-serial0.0,nr=2,chardev=charchannel0,\
+      id=channel1,name=trace-path-cpu0\
+      ...
+
+If you manage guests with libvirt, add the following tags to domain XML files.
+Then, libvirt passes the same command option to qemu.
+
+	<channel type='pipe'>
+	   <source path='/tmp/virtio-trace/agent-ctl-path'/>
+	   <target type='virtio' name='agent-ctl-path'/>
+	   <address type='virtio-serial' controller='0' bus='0' port='0'/>
+	</channel>
+	<channel type='pipe'>
+	   <source path='/tmp/virtio-trace/trace-path-cpu0'/>
+	   <target type='virtio' name='trace-path-cpu0'/>
+	   <address type='virtio-serial' controller='0' bus='0' port='1'/>
+	</channel>
+	...
+Here, chardev names are restricted to trace-path-cpuX and agent-ctl-path. For
+example, if a guest use three CPUs, chardev names should be trace-path-cpu0,
+trace-path-cpu1, trace-path-cpu2, and agent-ctl-path.
+
+3) Boot the guest
+ You can find some chardev in /dev/virtio-ports/ in the guest.
+
+
+Run
+===
+
+0) Build trace agent in a guest
+	$ make
+
+1) Enable ftrace in the guest
+ <Example>
+	# echo 1 > /sys/kernel/debug/tracing/events/sched/enable
+
+2) Run trace agent in the guest
+ This agent must be operated as root.
+	# ./trace-agent
+read/write threads in the agent wait for start order from host. If you add -o
+option, trace data are output via stdout in the guest.
+
+3) Open FIFO in a host
+	# cat /tmp/virtio-trace/trace-path-cpu0.out
+If a host does not open these, trace data get stuck in buffers of virtio. Then,
+the guest will stop by specification of chardev in QEMU. This blocking mode may
+be solved in the future.
+
+4) Start to read trace data by ordering from a host
+ A host injects read start order to the guest via virtio-serial.
+	# echo 1 > /tmp/virtio-trace/agent-ctl-path.in
+
+5) Stop to read trace data by ordering from a host
+ A host injects read stop order to the guest via virtio-serial.
+	# echo 0 > /tmp/virtio-trace/agent-ctl-path.in

tools/virtio/virtio-trace/trace-agent-ctl.c

@@ -0,0 +1,137 @@
+/*
+ * Controller of read/write threads for virtio-trace
+ *
+ * Copyright (C) 2012 Hitachi, Ltd.
+ * Created by Yoshihiro Yunomae <yoshihiro.yunomae.ez@hitachi.com>
+ *            Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
+ *
+ * Licensed under GPL version 2 only.
+ *
+ */
+
+#define _GNU_SOURCE
+#include <fcntl.h>
+#include <poll.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include "trace-agent.h"
+
+#define HOST_MSG_SIZE		256
+#define EVENT_WAIT_MSEC		100
+
+static volatile sig_atomic_t global_signal_val;
+bool global_sig_receive;	/* default false */
+bool global_run_operation;	/* default false*/
+
+/* Handle SIGTERM/SIGINT/SIGQUIT to exit */
+static void signal_handler(int sig)
+{
+	global_signal_val = sig;
+}
+
+int rw_ctl_init(const char *ctl_path)
+{
+	int ctl_fd;
+
+	ctl_fd = open(ctl_path, O_RDONLY);
+	if (ctl_fd == -1) {
+		pr_err("Cannot open ctl_fd\n");
+		goto error;
+	}
+
+	return ctl_fd;
+
+error:
+	exit(EXIT_FAILURE);
+}
+
+static int wait_order(int ctl_fd)
+{
+	struct pollfd poll_fd;
+	int ret = 0;
+
+	while (!global_sig_receive) {
+		poll_fd.fd = ctl_fd;
+		poll_fd.events = POLLIN;
+
+		ret = poll(&poll_fd, 1, EVENT_WAIT_MSEC);
+
+		if (global_signal_val) {
+			global_sig_receive = true;
+			pr_info("Receive interrupt %d\n", global_signal_val);
+
+			/* Wakes rw-threads when they are sleeping */
+			if (!global_run_operation)
+				pthread_cond_broadcast(&cond_wakeup);
+
+			ret = -1;
+			break;
+		}
+
+		if (ret < 0) {
+			pr_err("Polling error\n");
+			goto error;
+		}
+
+		if (ret)
+			break;
+	};
+
+	return ret;
+
+error:
+	exit(EXIT_FAILURE);
+}
+
+/*
+ * contol read/write threads by handling global_run_operation
+ */
+void *rw_ctl_loop(int ctl_fd)
+{
+	ssize_t rlen;
+	char buf[HOST_MSG_SIZE];
+	int ret;
+
+	/* Setup signal handlers */
+	signal(SIGTERM, signal_handler);
+	signal(SIGINT, signal_handler);
+	signal(SIGQUIT, signal_handler);
+
+	while (!global_sig_receive) {
+
+		ret = wait_order(ctl_fd);
+		if (ret < 0)
+			break;
+
+		rlen = read(ctl_fd, buf, sizeof(buf));
+		if (rlen < 0) {
+			pr_err("read data error in ctl thread\n");
+			goto error;
+		}
+
+		if (rlen == 2 && buf[0] == '1') {
+			/*
+			 * If host writes '1' to a control path,
+			 * this controller wakes all read/write threads.
+			 */
+			global_run_operation = true;
+			pthread_cond_broadcast(&cond_wakeup);
+			pr_debug("Wake up all read/write threads\n");
+		} else if (rlen == 2 && buf[0] == '0') {
+			/*
+			 * If host writes '0' to a control path, read/write
+			 * threads will wait for notification from Host.
+			 */
+			global_run_operation = false;
+			pr_debug("Stop all read/write threads\n");
+		} else
+			pr_info("Invalid host notification: %s\n", buf);
+	}
+
+	return NULL;
+
+error:
+	exit(EXIT_FAILURE);
+}