/* if run after vrrp_init_state(), it will be able to detect scripts that* have been disabled because of a sync group and will avoid to start them.*/
static void
vrrp_init_script(list l)
{vrrp_script_t *vscript;element e;for (e = LIST_HEAD(l); e; ELEMENT_NEXT(e)) {vscript = ELEMENT_DATA(e);if (vscript->inuse == 0)vscript->result = VRRP_SCRIPT_STATUS_DISABLED;if (vscript->result == VRRP_SCRIPT_STATUS_INIT) {vscript->result = vscript->rise - 1; /* one success is enough */  // 初始化过程中设置result=rise-1 thread_add_event(master, vrrp_script_thread, vscript, vscript->interval);} else if (vscript->result == VRRP_SCRIPT_STATUS_INIT_GOOD) {vscript->result = vscript->rise; /* one failure is enough */   // 初始化成功, 设置result=risethread_add_event(master, vrrp_script_thread, vscript, vscript->interval);}}
}static int
vrrp_script_child_thread(thread_t * thread)
{int wait_status;vrrp_script_t *vscript = THREAD_ARG(thread);if (thread->type == THREAD_CHILD_TIMEOUT) {pid_t pid;pid = THREAD_CHILD_PID(thread);/* The child hasn't responded. Kill it off. */if (vscript->result > vscript->rise) {vscript->result--;} else {if (vscript->result == vscript->rise)log_message(LOG_INFO, "VRRP_Script(%s) timed out", vscript->sname);vscript->result = 0;    // 初始化时, 脚本调用超时, 将result改成0(最小)}kill(pid, SIGTERM);thread_add_child(thread->master, vrrp_script_child_timeout_thread,vscript, pid, 2);return 0;}wait_status = THREAD_CHILD_STATUS(thread);if (WIFEXITED(wait_status)) {int status;status = WEXITSTATUS(wait_status);  // 脚本返回值为0, 表示执行成功, 非0表示失败.if (status == 0) {/* success */if (vscript->result < vscript->rise - 1) {  // result < rise-1, 表示当前还是KO状态vscript->result++;   // KO状态下, 调用成功则result+1.} else { if (vscript->result < vscript->rise)  // result = rise 表示当前是KO状态转变成OK状态log_message(LOG_INFO, "VRRP_Script(%s) succeeded", vscript->sname);vscript->result = vscript->rise + vscript->fall - 1;  // 脚本从failed状态转变到success状态后, 直接把result改成最大.}} else {/* failure */if (vscript->result > vscript->rise) {  // result > rise, 表示当前是OK状态vscript->result--;  //OK状态下, 脚本调用失败的话, result-1.} else {if (vscript->result >= vscript->rise)  // result=rise, 表示当前是OK状态转变成KO状态log_message(LOG_INFO, "VRRP_Script(%s) failed", vscript->sname);vscript->result = 0;  // 脚本从success状态转变到failed状态后, 直接把result改到最小. }}}return 0;
}/* Update VRRP effective priority based on multiple checkers.* This is a thread which is executed every adver_int.*/
static int
vrrp_update_priority(thread_t * thread)
{vrrp_t *vrrp = THREAD_ARG(thread);int prio_offset, new_prio;/* compute prio_offset right here */prio_offset = 0;/* Now we will sum the weights of all interfaces which are tracked. */if ((!vrrp->sync || vrrp->sync->global_tracking) && !LIST_ISEMPTY(vrrp->track_ifp))prio_offset += vrrp_tracked_weight(vrrp->track_ifp);/* Now we will sum the weights of all scripts which are tracked. */if ((!vrrp->sync || vrrp->sync->global_tracking) && !LIST_ISEMPTY(vrrp->track_script))prio_offset += vrrp_script_weight(vrrp->track_script);if (vrrp->base_priority == VRRP_PRIO_OWNER) {/* we will not run a PRIO_OWNER into a non-PRIO_OWNER */vrrp->effective_priority = VRRP_PRIO_OWNER;} else {/* WARNING! we must compute new_prio on a signed int in orderto detect overflows and avoid wrapping. */new_prio = vrrp->base_priority + prio_offset;if (new_prio < 1)new_prio = 1;else if (new_prio > 254)new_prio = 254;vrrp->effective_priority = new_prio;}/* Register next priority update thread */thread_add_timer(master, vrrp_update_priority, vrrp, vrrp->adver_int);return 0;
}

2. keepalived/include/vrrp_track.h

/* VRRP script tracking results.* The result is an integer between 0 and rise-1 to indicate a DOWN state,* or between rise-1 and rise+fall-1 to indicate an UP state. Upon failure,* we decrease result and set it to zero when we pass below rise. Upon* success, we increase result and set it to rise+fall-1 when we pass above* rise-1.*/
#define VRRP_SCRIPT_STATUS_DISABLED  -3
#define VRRP_SCRIPT_STATUS_INIT_GOOD -2
#define VRRP_SCRIPT_STATUS_INIT      -1/* external script we call to track local processes */
typedef struct _vrrp_script {char           *sname;     /* instance name */char         *script;    /* the command to be called */long          interval;   /* interval between script calls */long         timeout;    /* seconds before script timeout */int          weight;     /* weight associated to this script */int           result;     /* result of last call to this script: 0..R-1 = KO, R..R+F-1 = OK */int          inuse;      /* how many users have weight>0 ? */int          rise;       /* R: how many successes before OK */int            fall;       /* F: how many failures before KO */
} vrrp_script_t;/* Tracked script structure definition */
typedef struct _tracked_sc {int         weight;     /* tracking weight when non-zero */vrrp_script_t        *scr;       /* script pointer, cannot be NULL */
} tracked_sc_t;