usertrace-fast/ltt-usertrace-fast.c

   1 /* LTTng user-space "fast" library
   2  *
   3  * This daemon is spawned by each traced thread (to share the mmap).
   4  *
   5  * Its job is to dump periodically this buffer to disk (when it receives a
   6  * SIGUSR1 from its parent).
   7  *
   8  * It uses the control information in the shared memory area (producer/consumer
   9  * count).
  10  *
  11  * When the parent thread dies (yes, those thing may happen) ;) , this daemon
  12  * will flush the last buffer and write it to disk.
  13  *
  14  * Supplement note for streaming : the daemon is responsible for flushing
  15  * periodically the buffer if it is streaming data.
  16  *
  17  *
  18  * Notes :
  19  * shm memory is typically limited to 4096 units (system wide limit SHMMNI in
  20  * /proc/sys/kernel/shmmni). As it requires computation time upon creation, we
  21  * do not use it : we will use a shared mmap() instead which is passed through
  22  * the fork().
  23  * MAP_SHARED mmap segment. Updated when msync or munmap are called.
  24  * MAP_ANONYMOUS.
  25  * Memory  mapped  by  mmap()  is  preserved across fork(2), with the same
  26  *   attributes.
  27  *
  28  * Eventually, there will be two mode :
  29  * * Slow thread spawn : a fork() is done for each new thread. If the process
  30  *   dies, the data is not lost.
  31  * * Fast thread spawn : a pthread_create() is done by the application for each
  32  *   new thread.
  33  *
  34  * We use a timer to check periodically if the parent died. I think it is less
  35  * intrusive than a ptrace() on the parent, which would get every signal. The
  36  * side effect of this is that we won't be notified if the parent does an
  37  * exec(). In this case, we will just sit there until the parent exits.
  38  *
  39  *
  40  * Copyright 2006 Mathieu Desnoyers
  41  *
  42  */
  43
  44 #include <sys/types.h>
  45 #include <sys/wait.h>
  46 #include <unistd.h>
  47 #include <stdlib.h>
  48 #include <stdio.h>
  49 #include <signal.h>
  50 #include <syscall.h>
  51 #include <features.h>
  52 #include <pthread.h>
  53 #include <malloc.h>
  54 #include <string.h>
  55 #include <sys/mman.h>
  56 #include <signal.h>
  57
  58 #include "ltt-usertrace-fast.h"
  59
  60
  61 /* Writer (the traced application) */
  62
  63 __thread struct ltt_trace_info *thread_trace_info = NULL;
  64
  65 void ltt_usertrace_fast_buffer_switch(void)
  66 {
  67         struct ltt_trace_info *tmp = thread_trace_info;
  68         if(tmp)
  69                 kill(tmp->daemon_id, SIGUSR1);
  70 }
  71
  72 static void ltt_usertrace_fast_cleanup(void *arg)
  73 {
  74         struct ltt_trace_info *tmp = thread_trace_info;
  75         if(tmp) {
  76                 thread_trace_info = NULL;
  77                 kill(tmp->daemon_id, SIGUSR2);
  78                 munmap(tmp, sizeof(*tmp));
  79         }
  80 }
  81
  82 /* Reader (the disk dumper daemon) */
  83
  84 static pid_t traced_pid = 0;
  85 static int parent_exited = 0;
  86
  87 /* signal handling */
  88 static void handler_sigusr1(int signo)
  89 {
  90         printf("LTT Signal %d received : parent buffer switch.\n", signo);
  91 }
  92
  93 static void handler_sigusr2(int signo)
  94 {
  95         printf("LTT Signal %d received : parent exited.\n", signo);
  96         parent_exited = 1;
  97 }
  98
  99 static void handler_sigalarm(int signo)
 100 {
 101         printf("LTT Signal %d received\n", signo);
 102
 103         if(getppid() != traced_pid) {
 104                 /* Parent died */
 105                 printf("LTT Parent %lu died, cleaning up\n", traced_pid);
 106                 traced_pid = 0;
 107         }
 108         alarm(3);
 109 }
 110
 111
 112 /* This function is called by ltt_rw_init which has signals blocked */
 113 static void ltt_usertrace_fast_daemon(struct ltt_trace_info *shared_trace_info,
 114                 sigset_t oldset, pid_t l_traced_pid)
 115 {
 116         struct sigaction act;
 117         int ret;
 118
 119         traced_pid = l_traced_pid;
 120
 121         printf("LTT ltt_usertrace_fast_daemon : init is %d, pid is %lu, traced_pid is %lu\n",
 122                         shared_trace_info->init, getpid(), traced_pid);
 123
 124         act.sa_handler = handler_sigusr1;
 125         act.sa_flags = 0;
 126         sigemptyset(&(act.sa_mask));
 127         sigaddset(&(act.sa_mask), SIGUSR1);
 128         sigaction(SIGUSR1, &act, NULL);
 129
 130         act.sa_handler = handler_sigusr2;
 131         act.sa_flags = 0;
 132         sigemptyset(&(act.sa_mask));
 133         sigaddset(&(act.sa_mask), SIGUSR2);
 134         sigaction(SIGUSR2, &act, NULL);
 135
 136         act.sa_handler = handler_sigalarm;
 137         act.sa_flags = 0;
 138         sigemptyset(&(act.sa_mask));
 139         sigaddset(&(act.sa_mask), SIGALRM);
 140         sigaction(SIGALRM, &act, NULL);
 141
 142         /* Enable signals */
 143         ret = pthread_sigmask(SIG_SETMASK, &oldset, NULL);
 144         if(ret) {
 145                 printf("LTT Error in pthread_sigmask\n");
 146         }
 147
 148         alarm(3);
 149
 150         while(1) {
 151                 pause();
 152                 if(traced_pid == 0) break; /* parent died */
 153                 if(parent_exited) break;
 154                 printf("LTT Doing a buffer switch read. pid is : %lu\n", getpid());
 155                 //printf("Test parent. pid is : %lu, ppid is %lu\n", getpid(), getppid());
 156         }
 157
 158         /* Buffer force switch (flush) */
 159         //TODO
 160
 161         /* The parent thread is dead and we have finished with the buffer */
 162         munmap(shared_trace_info, sizeof(*shared_trace_info));
 163
 164         exit(0);
 165 }
 166
 167
 168 /* Reader-writer initialization */
 169
 170 static enum ltt_process_role { LTT_ROLE_WRITER, LTT_ROLE_READER }
 171         role = LTT_ROLE_WRITER;
 172
 173
 174 void ltt_rw_init(void)
 175 {
 176         pid_t pid;
 177         struct ltt_trace_info *shared_trace_info;
 178         int ret;
 179         sigset_t set, oldset;
 180         pid_t l_traced_pid = getpid();
 181
 182         /* parent : create the shared memory map */
 183         shared_trace_info = mmap(0, sizeof(*thread_trace_info),
 184                         PROT_READ|PROT_WRITE, MAP_SHARED|MAP_ANONYMOUS, 0, 0);
 185         memset(shared_trace_info, 0, sizeof(*shared_trace_info));
 186         shared_trace_info->init = 1;
 187
 188         /* Disable signals */
 189   ret = sigfillset(&set);
 190   if(ret) {
 191     printf("LTT Error in sigfillset\n");
 192   }
 193
 194
 195   ret = pthread_sigmask(SIG_BLOCK, &set, &oldset);
 196   if(ret) {
 197     printf("LTT Error in pthread_sigmask\n");
 198   }
 199
 200         pid = fork();
 201         if(pid > 0) {
 202                 /* Parent */
 203                 shared_trace_info->daemon_id = pid;
 204                 thread_trace_info = shared_trace_info;
 205
 206                 /* Enable signals */
 207                 ret = pthread_sigmask(SIG_SETMASK, &oldset, NULL);
 208                 if(ret) {
 209                         printf("LTT Error in pthread_sigmask\n");
 210                 }
 211         } else if(pid == 0) {
 212                 /* Child */
 213                 role = LTT_ROLE_READER;
 214                 ltt_usertrace_fast_daemon(shared_trace_info, oldset, l_traced_pid);
 215                 /* Should never return */
 216                 exit(-1);
 217         } else if(pid < 0) {
 218                 /* fork error */
 219                 perror("LTT Error in forking ltt-usertrace-fast");
 220         }
 221 }
 222
 223 static __thread struct _pthread_cleanup_buffer cleanup_buffer;
 224
 225 void ltt_thread_init(void)
 226 {
 227         _pthread_cleanup_push(&cleanup_buffer, ltt_usertrace_fast_cleanup, NULL);
 228         ltt_rw_init();
 229 }
 230
 231 void __attribute__((constructor)) __ltt_usertrace_fast_init(void)
 232 {
 233   printf("LTT usertrace-fast init\n");
 234
 235         ltt_rw_init();
 236 }
 237
 238 void __attribute__((destructor)) __ltt_usertrace_fast_fini(void)
 239 {
 240         if(role == LTT_ROLE_WRITER) {
 241           printf("LTT usertrace-fast fini\n");
 242                 ltt_usertrace_fast_cleanup(NULL);
 243         }
 244 }
 245