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Yoshihiro YUNOMAErustyrussell
Yoshihiro YUNOMAE
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rustyrussell
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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 <[email protected]> Acked-by: Amit Shah <[email protected]> Signed-off-by: Rusty Russell <[email protected]>
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‎tools/virtio/virtio-trace/Makefile‎

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

‎tools/virtio/virtio-trace/README‎

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

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

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

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