usertrace fast work

[lttv.git] / usertrace-fast / ltt-usertrace-fast.c

/* LTTng user-space "fast" library
 *
 * This daemon is spawned by each traced thread (to share the mmap).
 *
 * Its job is to dump periodically this buffer to disk (when it receives a
 * SIGUSR1 from its parent).
 *
 * It uses the control information in the shared memory area (producer/consumer
 * count).
 *
 * When the parent thread dies (yes, those thing may happen) ;) , this daemon
 * will flush the last buffer and write it to disk.
 *
 * Supplement note for streaming : the daemon is responsible for flushing
 * periodically the buffer if it is streaming data.
 * 
 *
 * Notes :
 * shm memory is typically limited to 4096 units (system wide limit SHMMNI in
 * /proc/sys/kernel/shmmni). As it requires computation time upon creation, we
 * do not use it : we will use a shared mmap() instead which is passed through
 * the fork().
 * MAP_SHARED mmap segment. Updated when msync or munmap are called.
 * MAP_ANONYMOUS.
 * Memory  mapped  by  mmap()  is  preserved across fork(2), with the same
 *   attributes.
 * 
 * Eventually, there will be two mode :
 * * Slow thread spawn : a fork() is done for each new thread. If the process
 *   dies, the data is not lost.
 * * Fast thread spawn : a pthread_create() is done by the application for each
 *   new thread.
 *
 * We use a timer to check periodically if the parent died. I think it is less
 * intrusive than a ptrace() on the parent, which would get every signal. The
 * side effect of this is that we won't be notified if the parent does an
 * exec(). In this case, we will just sit there until the parent exits.
 * 
 *   
 * Copyright 2006 Mathieu Desnoyers
 *
 */

#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <signal.h>
#include <syscall.h>
#include <features.h>
#include <pthread.h>
#include <malloc.h>
#include <string.h>
#include <sys/mman.h>
#include <signal.h>

#include "ltt-usertrace-fast.h"


/* Writer (the traced application) */

__thread struct ltt_trace_info *thread_trace_info = NULL;

void ltt_usertrace_fast_buffer_switch(void)
{
	struct ltt_trace_info *tmp = thread_trace_info;
	if(tmp)
		kill(tmp->daemon_id, SIGUSR1);
}

static void ltt_usertrace_fast_cleanup(void *arg)
{
	struct ltt_trace_info *tmp = thread_trace_info;
	if(tmp) {
		thread_trace_info = NULL;
		kill(tmp->daemon_id, SIGUSR2);
		munmap(tmp, sizeof(*tmp));
	}
}

/* Reader (the disk dumper daemon) */

static pid_t traced_pid = 0;
static int parent_exited = 0;

/* signal handling */
static void handler_sigusr1(int signo)
{
	printf("LTT Signal %d received : parent buffer switch.\n", signo);
}

static void handler_sigusr2(int signo)
{
	printf("LTT Signal %d received : parent exited.\n", signo);
	parent_exited = 1;
}

static void handler_sigalarm(int signo)
{
	printf("LTT Signal %d received\n", signo);

	if(getppid() != traced_pid) {
		/* Parent died */
		printf("LTT Parent %lu died, cleaning up\n", traced_pid);
		traced_pid = 0;
	}
	alarm(3);
}


/* This function is called by ltt_rw_init which has signals blocked */
static void ltt_usertrace_fast_daemon(struct ltt_trace_info *shared_trace_info,
		sigset_t oldset, pid_t l_traced_pid)
{
	struct sigaction act;
	int ret;

	traced_pid = l_traced_pid;

	printf("LTT ltt_usertrace_fast_daemon : init is %d, pid is %lu, traced_pid is %lu\n",
			shared_trace_info->init, getpid(), traced_pid);

	act.sa_handler = handler_sigusr1;
	act.sa_flags = 0;
	sigemptyset(&(act.sa_mask));
	sigaddset(&(act.sa_mask), SIGUSR1);
	sigaction(SIGUSR1, &act, NULL);

	act.sa_handler = handler_sigusr2;
	act.sa_flags = 0;
	sigemptyset(&(act.sa_mask));
	sigaddset(&(act.sa_mask), SIGUSR2);
	sigaction(SIGUSR2, &act, NULL);

	act.sa_handler = handler_sigalarm;
	act.sa_flags = 0;
	sigemptyset(&(act.sa_mask));
	sigaddset(&(act.sa_mask), SIGALRM);
	sigaction(SIGALRM, &act, NULL);

	/* Enable signals */
	ret = pthread_sigmask(SIG_SETMASK, &oldset, NULL);
	if(ret) {
		printf("LTT Error in pthread_sigmask\n");
	}

	alarm(3);

	while(1) {
		pause();
		if(traced_pid == 0) break; /* parent died */
		if(parent_exited) break;
		printf("LTT Doing a buffer switch read. pid is : %lu\n", getpid());
		//printf("Test parent. pid is : %lu, ppid is %lu\n", getpid(), getppid());
	}

	/* Buffer force switch (flush) */
	//TODO
	
	/* The parent thread is dead and we have finished with the buffer */
	munmap(shared_trace_info, sizeof(*shared_trace_info));
	
	exit(0);
}


/* Reader-writer initialization */

static enum ltt_process_role { LTT_ROLE_WRITER, LTT_ROLE_READER }
	role = LTT_ROLE_WRITER;


void ltt_rw_init(void)
{
	pid_t pid;
	struct ltt_trace_info *shared_trace_info;
	int ret;
	sigset_t set, oldset;
	pid_t l_traced_pid = getpid();

	/* parent : create the shared memory map */
	shared_trace_info = mmap(0, sizeof(*thread_trace_info),
			PROT_READ|PROT_WRITE, MAP_SHARED|MAP_ANONYMOUS, 0, 0);
	memset(shared_trace_info, 0, sizeof(*shared_trace_info));
	shared_trace_info->init = 1;

	/* Disable signals */
  ret = sigfillset(&set);
  if(ret) {
    printf("LTT Error in sigfillset\n");
  } 
	
	
  ret = pthread_sigmask(SIG_BLOCK, &set, &oldset);
  if(ret) {
    printf("LTT Error in pthread_sigmask\n");
  }

	pid = fork();
	if(pid > 0) {
		/* Parent */
		shared_trace_info->daemon_id = pid;
		thread_trace_info = shared_trace_info;

		/* Enable signals */
		ret = pthread_sigmask(SIG_SETMASK, &oldset, NULL);
		if(ret) {
			printf("LTT Error in pthread_sigmask\n");
		}
	} else if(pid == 0) {
		/* Child */
		role = LTT_ROLE_READER;
		ltt_usertrace_fast_daemon(shared_trace_info, oldset, l_traced_pid);
		/* Should never return */
		exit(-1);
	} else if(pid < 0) {
		/* fork error */
		perror("LTT Error in forking ltt-usertrace-fast");
	}
}

static __thread struct _pthread_cleanup_buffer cleanup_buffer;

void ltt_thread_init(void)
{
	_pthread_cleanup_push(&cleanup_buffer, ltt_usertrace_fast_cleanup, NULL);
	ltt_rw_init();
}
	
void __attribute__((constructor)) __ltt_usertrace_fast_init(void)
{
  printf("LTT usertrace-fast init\n");

	ltt_rw_init();
}

void __attribute__((destructor)) __ltt_usertrace_fast_fini(void)
{
	if(role == LTT_ROLE_WRITER) {
	  printf("LTT usertrace-fast fini\n");
		ltt_usertrace_fast_cleanup(NULL);
	}
}