path: root/Utilities/cmlibuv/src/unix/os390.c

/* Copyright libuv project contributors. All rights reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to
 * deal in the Software without restriction, including without limitation the
 * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
 * sell copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 */

#include "internal.h"
#include <sys/ioctl.h>
#include <net/if.h>
#include <utmpx.h>
#include <unistd.h>
#include <sys/ps.h>
#include <builtins.h>
#include <termios.h>
#include <sys/msg.h>
#if defined(__clang__)
#include "csrsic.h"
#else
#include "//'SYS1.SAMPLIB(CSRSIC)'"
#endif

#define CVT_PTR           0x10
#define PSA_PTR           0x00
#define CSD_OFFSET        0x294

/*
    Long-term average CPU service used by this logical partition,
    in millions of service units per hour. If this value is above
    the partition's defined capacity, the partition will be capped.
    It is calculated using the physical CPU adjustment factor
    (RCTPCPUA) so it may not match other measures of service which
    are based on the logical CPU adjustment factor. It is available
    if the hardware supports LPAR cluster.
*/
#define RCTLACS_OFFSET    0xC4

/* 32-bit count of alive CPUs. This includes both CPs and IFAs */
#define CSD_NUMBER_ONLINE_CPUS        0xD4

/* Address of system resources manager (SRM) control table */
#define CVTOPCTP_OFFSET   0x25C

/* Address of the RCT table */
#define RMCTRCT_OFFSET    0xE4

/* Address of the rsm control and enumeration area. */
#define CVTRCEP_OFFSET    0x490

/*
    Number of frames currently available to system.
    Excluded are frames backing perm storage, frames offline, and bad frames.
*/
#define RCEPOOL_OFFSET    0x004

/* Total number of frames currently on all available frame queues. */
#define RCEAFC_OFFSET     0x088

/* CPC model length from the CSRSI Service. */
#define CPCMODEL_LENGTH   16

/* Pointer to the home (current) ASCB. */
#define PSAAOLD           0x224

/* Pointer to rsm address space block extension. */
#define ASCBRSME          0x16C

/*
    NUMBER OF FRAMES CURRENTLY IN USE BY THIS ADDRESS SPACE.
    It does not include 2G frames.
*/
#define RAXFMCT           0x2C

/* Thread Entry constants */
#define PGTH_CURRENT  1
#define PGTH_LEN      26
#define PGTHAPATH     0x20
#pragma linkage(BPX4GTH, OS)
#pragma linkage(BPX1GTH, OS)

/* TOD Clock resolution in nanoseconds */
#define TOD_RES 4.096

typedef unsigned data_area_ptr_assign_type;

typedef union {
  struct {
#if defined(_LP64)
    data_area_ptr_assign_type lower;
#endif
    data_area_ptr_assign_type assign;
  };
  char* deref;
} data_area_ptr;


void uv_loadavg(double avg[3]) {
  /* TODO: implement the following */
  avg[0] = 0;
  avg[1] = 0;
  avg[2] = 0;
}


int uv__platform_loop_init(uv_loop_t* loop) {
  uv__os390_epoll* ep;

  ep = epoll_create1(0);
  loop->ep = ep;
  if (ep == NULL)
    return UV__ERR(errno);

  return 0;
}


void uv__platform_loop_delete(uv_loop_t* loop) {
  if (loop->ep != NULL) {
    epoll_queue_close(loop->ep);
    loop->ep = NULL;
  }
}


uint64_t uv__hrtime(uv_clocktype_t type) {
  unsigned long long timestamp;
  __stckf(&timestamp);
  /* Convert to nanoseconds */
  return timestamp / TOD_RES;
}


/*
    Get the exe path using the thread entry information
    in the address space.
*/
static int getexe(const int pid, char* buf, size_t len) {
  struct {
    int pid;
    int thid[2];
    char accesspid;
    char accessthid;
    char asid[2];
    char loginname[8];
    char flag;
    char len;
  } Input_data;

  union {
    struct {
      char gthb[4];
      int pid;
      int thid[2];
      char accesspid;
      char accessthid[3];
      int lenused;
      int offsetProcess;
      int offsetConTTY;
      int offsetPath;
      int offsetCommand;
      int offsetFileData;
      int offsetThread;
    } Output_data;
    char buf[2048];
  } Output_buf;

  struct Output_path_type {
    char gthe[4];
    short int len;
    char path[1024];
  };

  int Input_length;
  int Output_length;
  void* Input_address;
  void* Output_address;
  struct Output_path_type* Output_path;
  int rv;
  int rc;
  int rsn;

  Input_length = PGTH_LEN;
  Output_length = sizeof(Output_buf);
  Output_address = &Output_buf;
  Input_address = &Input_data;
  memset(&Input_data, 0, sizeof Input_data);
  Input_data.flag |= PGTHAPATH;
  Input_data.pid = pid;
  Input_data.accesspid = PGTH_CURRENT;

#ifdef _LP64
  BPX4GTH(&Input_length,
          &Input_address,
          &Output_length,
          &Output_address,
          &rv,
          &rc,
          &rsn);
#else
  BPX1GTH(&Input_length,
          &Input_address,
          &Output_length,
          &Output_address,
          &rv,
          &rc,
          &rsn);
#endif

  if (rv == -1) {
    errno = rc;
    return -1;
  }

  /* Check highest byte to ensure data availability */
  assert(((Output_buf.Output_data.offsetPath >>24) & 0xFF) == 'A');

  /* Get the offset from the lowest 3 bytes */
  Output_path = (struct Output_path_type*) ((char*) (&Output_buf) +
      (Output_buf.Output_data.offsetPath & 0x00FFFFFF));

  if (Output_path->len >= len) {
    errno = ENOBUFS;
    return -1;
  }

  uv__strscpy(buf, Output_path->path, len);

  return 0;
}


/*
 * We could use a static buffer for the path manipulations that we need outside
 * of the function, but this function could be called by multiple consumers and
 * we don't want to potentially create a race condition in the use of snprintf.
 * There is no direct way of getting the exe path in zOS - either through /procfs
 * or through some libc APIs. The below approach is to parse the argv[0]'s pattern
 * and use it in conjunction with PATH environment variable to craft one.
 */
int uv_exepath(char* buffer, size_t* size) {
  int res;
  char args[PATH_MAX];
  int pid;

  if (buffer == NULL || size == NULL || *size == 0)
    return UV_EINVAL;

  pid = getpid();
  res = getexe(pid, args, sizeof(args));
  if (res < 0)
    return UV_EINVAL;

  return uv__search_path(args, buffer, size);
}


uint64_t uv_get_free_memory(void) {
  uint64_t freeram;

  data_area_ptr cvt = {0};
  data_area_ptr rcep = {0};
  cvt.assign = *(data_area_ptr_assign_type*)(CVT_PTR);
  rcep.assign = *(data_area_ptr_assign_type*)(cvt.deref + CVTRCEP_OFFSET);
  freeram = *((uint64_t*)(rcep.deref + RCEAFC_OFFSET)) * 4;
  return freeram;
}


uint64_t uv_get_total_memory(void) {
  uint64_t totalram;

  data_area_ptr cvt = {0};
  data_area_ptr rcep = {0};
  cvt.assign = *(data_area_ptr_assign_type*)(CVT_PTR);
  rcep.assign = *(data_area_ptr_assign_type*)(cvt.deref + CVTRCEP_OFFSET);
  totalram = *((uint64_t*)(rcep.deref + RCEPOOL_OFFSET)) * 4;
  return totalram;
}


uint64_t uv_get_constrained_memory(void) {
  return 0;  /* Memory constraints are unknown. */
}


int uv_resident_set_memory(size_t* rss) {
  char* ascb;
  char* rax;
  size_t nframes;

  ascb  = *(char* __ptr32 *)(PSA_PTR + PSAAOLD);
  rax = *(char* __ptr32 *)(ascb + ASCBRSME);
  nframes = *(unsigned int*)(rax + RAXFMCT);

  *rss = nframes * sysconf(_SC_PAGESIZE);
  return 0;
}


int uv_uptime(double* uptime) {
  struct utmpx u ;
  struct utmpx *v;
  time64_t t;

  u.ut_type = BOOT_TIME;
  v = getutxid(&u);
  if (v == NULL)
    return -1;
  *uptime = difftime64(time64(&t), v->ut_tv.tv_sec);
  return 0;
}


int uv_cpu_info(uv_cpu_info_t** cpu_infos, int* count) {
  uv_cpu_info_t* cpu_info;
  int idx;
  siv1v2 info;
  data_area_ptr cvt = {0};
  data_area_ptr csd = {0};
  data_area_ptr rmctrct = {0};
  data_area_ptr cvtopctp = {0};
  int cpu_usage_avg;

  cvt.assign = *(data_area_ptr_assign_type*)(CVT_PTR);

  csd.assign = *((data_area_ptr_assign_type *) (cvt.deref + CSD_OFFSET));
  cvtopctp.assign = *((data_area_ptr_assign_type *) (cvt.deref + CVTOPCTP_OFFSET));
  rmctrct.assign = *((data_area_ptr_assign_type *) (cvtopctp.deref + RMCTRCT_OFFSET));

  *count = *((int*) (csd.deref + CSD_NUMBER_ONLINE_CPUS));
  cpu_usage_avg = *((unsigned short int*) (rmctrct.deref + RCTLACS_OFFSET));

  *cpu_infos = uv__malloc(*count * sizeof(uv_cpu_info_t));
  if (!*cpu_infos)
    return UV_ENOMEM;

  cpu_info = *cpu_infos;
  idx = 0;
  while (idx < *count) {
    cpu_info->speed = *(int*)(info.siv1v2si22v1.si22v1cpucapability);
    cpu_info->model = uv__malloc(CPCMODEL_LENGTH + 1);
    memset(cpu_info->model, '\0', CPCMODEL_LENGTH + 1);
    memcpy(cpu_info->model, info.siv1v2si11v1.si11v1cpcmodel, CPCMODEL_LENGTH);
    cpu_info->cpu_times.user = cpu_usage_avg;
    /* TODO: implement the following */
    cpu_info->cpu_times.sys = 0;
    cpu_info->cpu_times.idle = 0;
    cpu_info->cpu_times.irq = 0;
    cpu_info->cpu_times.nice = 0;
    ++cpu_info;
    ++idx;
  }

  return 0;
}


static int uv__interface_addresses_v6(uv_interface_address_t** addresses,
                                      int* count) {
  uv_interface_address_t* address;
  int sockfd;
  int maxsize;
  __net_ifconf6header_t ifc;
  __net_ifconf6entry_t* ifr;
  __net_ifconf6entry_t* p;
  __net_ifconf6entry_t flg;

  *count = 0;
  /* Assume maximum buffer size allowable */
  maxsize = 16384;

  if (0 > (sockfd = socket(AF_INET, SOCK_DGRAM, IPPROTO_IP)))
    return UV__ERR(errno);

  ifc.__nif6h_version = 1;
  ifc.__nif6h_buflen = maxsize;
  ifc.__nif6h_buffer = uv__calloc(1, maxsize);;

  if (ioctl(sockfd, SIOCGIFCONF6, &ifc) == -1) {
    uv__close(sockfd);
    return UV__ERR(errno);
  }


  *count = 0;
  ifr = (__net_ifconf6entry_t*)(ifc.__nif6h_buffer);
  while ((char*)ifr < (char*)ifc.__nif6h_buffer + ifc.__nif6h_buflen) {
    p = ifr;
    ifr = (__net_ifconf6entry_t*)((char*)ifr + ifc.__nif6h_entrylen);

    if (!(p->__nif6e_addr.sin6_family == AF_INET6 ||
          p->__nif6e_addr.sin6_family == AF_INET))
      continue;

    if (!(p->__nif6e_flags & _NIF6E_FLAGS_ON_LINK_ACTIVE))
      continue;

    ++(*count);
  }

  /* Alloc the return interface structs */
  *addresses = uv__malloc(*count * sizeof(uv_interface_address_t));
  if (!(*addresses)) {
    uv__close(sockfd);
    return UV_ENOMEM;
  }
  address = *addresses;

  ifr = (__net_ifconf6entry_t*)(ifc.__nif6h_buffer);
  while ((char*)ifr < (char*)ifc.__nif6h_buffer + ifc.__nif6h_buflen) {
    p = ifr;
    ifr = (__net_ifconf6entry_t*)((char*)ifr + ifc.__nif6h_entrylen);

    if (!(p->__nif6e_addr.sin6_family == AF_INET6 ||
          p->__nif6e_addr.sin6_family == AF_INET))
      continue;

    if (!(p->__nif6e_flags & _NIF6E_FLAGS_ON_LINK_ACTIVE))
      continue;

    /* All conditions above must match count loop */

    address->name = uv__strdup(p->__nif6e_name);

    if (p->__nif6e_addr.sin6_family == AF_INET6)
      address->address.address6 = *((struct sockaddr_in6*) &p->__nif6e_addr);
    else
      address->address.address4 = *((struct sockaddr_in*) &p->__nif6e_addr);

    /* TODO: Retrieve netmask using SIOCGIFNETMASK ioctl */

    address->is_internal = flg.__nif6e_flags & _NIF6E_FLAGS_LOOPBACK ? 1 : 0;
    memset(address->phys_addr, 0, sizeof(address->phys_addr));
    address++;
  }

  uv__close(sockfd);
  return 0;
}


int uv_interface_addresses(uv_interface_address_t** addresses, int* count) {
  uv_interface_address_t* address;
  int sockfd;
  int maxsize;
  struct ifconf ifc;
  struct ifreq flg;
  struct ifreq* ifr;
  struct ifreq* p;
  int count_v6;

  *count = 0;
  *addresses = NULL;

  /* get the ipv6 addresses first */
  uv_interface_address_t* addresses_v6;
  uv__interface_addresses_v6(&addresses_v6, &count_v6);

  /* now get the ipv4 addresses */

  /* Assume maximum buffer size allowable */
  maxsize = 16384;

  sockfd = socket(AF_INET, SOCK_DGRAM, IPPROTO_IP);
  if (0 > sockfd)
    return UV__ERR(errno);

  ifc.ifc_req = uv__calloc(1, maxsize);
  ifc.ifc_len = maxsize;
  if (ioctl(sockfd, SIOCGIFCONF, &ifc) == -1) {
    uv__close(sockfd);
    return UV__ERR(errno);
  }

#define MAX(a,b) (((a)>(b))?(a):(b))
#define ADDR_SIZE(p) MAX((p).sa_len, sizeof(p))

  /* Count all up and running ipv4/ipv6 addresses */
  ifr = ifc.ifc_req;
  while ((char*)ifr < (char*)ifc.ifc_req + ifc.ifc_len) {
    p = ifr;
    ifr = (struct ifreq*)
      ((char*)ifr + sizeof(ifr->ifr_name) + ADDR_SIZE(ifr->ifr_addr));

    if (!(p->ifr_addr.sa_family == AF_INET6 ||
          p->ifr_addr.sa_family == AF_INET))
      continue;

    memcpy(flg.ifr_name, p->ifr_name, sizeof(flg.ifr_name));
    if (ioctl(sockfd, SIOCGIFFLAGS, &flg) == -1) {
      uv__close(sockfd);
      return UV__ERR(errno);
    }

    if (!(flg.ifr_flags & IFF_UP && flg.ifr_flags & IFF_RUNNING))
      continue;

    (*count)++;
  }

  if (*count == 0) {
    uv__close(sockfd);
    return 0;
  }

  /* Alloc the return interface structs */
  *addresses = uv__malloc((*count + count_v6) *
                          sizeof(uv_interface_address_t));

  if (!(*addresses)) {
    uv__close(sockfd);
    return UV_ENOMEM;
  }
  address = *addresses;

  /* copy over the ipv6 addresses */
  memcpy(address, addresses_v6, count_v6 * sizeof(uv_interface_address_t));
  address += count_v6;
  *count += count_v6;
  uv__free(addresses_v6);

  ifr = ifc.ifc_req;
  while ((char*)ifr < (char*)ifc.ifc_req + ifc.ifc_len) {
    p = ifr;
    ifr = (struct ifreq*)
      ((char*)ifr + sizeof(ifr->ifr_name) + ADDR_SIZE(ifr->ifr_addr));

    if (!(p->ifr_addr.sa_family == AF_INET6 ||
          p->ifr_addr.sa_family == AF_INET))
      continue;

    memcpy(flg.ifr_name, p->ifr_name, sizeof(flg.ifr_name));
    if (ioctl(sockfd, SIOCGIFFLAGS, &flg) == -1) {
      uv__close(sockfd);
      return UV_ENOSYS;
    }

    if (!(flg.ifr_flags & IFF_UP && flg.ifr_flags & IFF_RUNNING))
      continue;

    /* All conditions above must match count loop */

    address->name = uv__strdup(p->ifr_name);

    if (p->ifr_addr.sa_family == AF_INET6) {
      address->address.address6 = *((struct sockaddr_in6*) &p->ifr_addr);
    } else {
      address->address.address4 = *((struct sockaddr_in*) &p->ifr_addr);
    }

    address->is_internal = flg.ifr_flags & IFF_LOOPBACK ? 1 : 0;
    memset(address->phys_addr, 0, sizeof(address->phys_addr));
    address++;
  }

#undef ADDR_SIZE
#undef MAX

  uv__close(sockfd);
  return 0;
}


void uv_free_interface_addresses(uv_interface_address_t* addresses,
                                 int count) {
  int i;
  for (i = 0; i < count; ++i)
    uv__free(addresses[i].name);
  uv__free(addresses);
}


void uv__platform_invalidate_fd(uv_loop_t* loop, int fd) {
  struct epoll_event* events;
  struct epoll_event dummy;
  uintptr_t i;
  uintptr_t nfds;

  assert(loop->watchers != NULL);
  assert(fd >= 0);

  events = (struct epoll_event*) loop->watchers[loop->nwatchers];
  nfds = (uintptr_t) loop->watchers[loop->nwatchers + 1];
  if (events != NULL)
    /* Invalidate events with same file descriptor */
    for (i = 0; i < nfds; i++)
      if ((int) events[i].fd == fd)
        events[i].fd = -1;

  /* Remove the file descriptor from the epoll. */
  if (loop->ep != NULL)
    epoll_ctl(loop->ep, EPOLL_CTL_DEL, fd, &dummy);
}


int uv__io_check_fd(uv_loop_t* loop, int fd) {
  struct pollfd p[1];
  int rv;

  p[0].fd = fd;
  p[0].events = POLLIN;

  do
    rv = poll(p, 1, 0);
  while (rv == -1 && errno == EINTR);

  if (rv == -1)
    abort();

  if (p[0].revents & POLLNVAL)
    return -1;

  return 0;
}


void uv__fs_event_close(uv_fs_event_t* handle) {
  uv_fs_event_stop(handle);
}


int uv_fs_event_init(uv_loop_t* loop, uv_fs_event_t* handle) {
  uv__handle_init(loop, (uv_handle_t*)handle, UV_FS_EVENT);
  return 0;
}


int uv_fs_event_start(uv_fs_event_t* handle, uv_fs_event_cb cb,
                      const char* filename, unsigned int flags) {
  uv__os390_epoll* ep;
  _RFIS reg_struct;
  char* path;
  int rc;

  if (uv__is_active(handle))
    return UV_EINVAL;

  ep = handle->loop->ep;
  assert(ep->msg_queue != -1);

  reg_struct.__rfis_cmd  = _RFIS_REG;
  reg_struct.__rfis_qid  = ep->msg_queue;
  reg_struct.__rfis_type = 1;
  memcpy(reg_struct.__rfis_utok, &handle, sizeof(handle));

  path = uv__strdup(filename);
  if (path == NULL)
    return UV_ENOMEM;

  rc = __w_pioctl(path, _IOCC_REGFILEINT, sizeof(reg_struct), &reg_struct);
  if (rc != 0)
    return UV__ERR(errno);

  uv__handle_start(handle);
  handle->path = path;
  handle->cb = cb;
  memcpy(handle->rfis_rftok, reg_struct.__rfis_rftok,
         sizeof(handle->rfis_rftok));

  return 0;
}


int uv_fs_event_stop(uv_fs_event_t* handle) {
  uv__os390_epoll* ep;
  _RFIS reg_struct;
  int rc;

  if (!uv__is_active(handle))
    return 0;

  ep = handle->loop->ep;
  assert(ep->msg_queue != -1);

  reg_struct.__rfis_cmd  = _RFIS_UNREG;
  reg_struct.__rfis_qid  = ep->msg_queue;
  reg_struct.__rfis_type = 1;
  memcpy(reg_struct.__rfis_rftok, handle->rfis_rftok,
         sizeof(handle->rfis_rftok));

  /*
   * This call will take "/" as the path argument in case we
   * don't care to supply the correct path. The system will simply
   * ignore it.
   */
  rc = __w_pioctl("/", _IOCC_REGFILEINT, sizeof(reg_struct), &reg_struct);
  if (rc != 0 && errno != EALREADY && errno != ENOENT)
    abort();

  uv__handle_stop(handle);

  return 0;
}


static int os390_message_queue_handler(uv__os390_epoll* ep) {
  uv_fs_event_t* handle;
  int msglen;
  int events;
  _RFIM msg;

  if (ep->msg_queue == -1)
    return 0;

  msglen = msgrcv(ep->msg_queue, &msg, sizeof(msg), 0, IPC_NOWAIT);

  if (msglen == -1 && errno == ENOMSG)
    return 0;

  if (msglen == -1)
    abort();

  events = 0;
  if (msg.__rfim_event == _RFIM_ATTR || msg.__rfim_event == _RFIM_WRITE)
    events = UV_CHANGE;
  else if (msg.__rfim_event == _RFIM_RENAME)
    events = UV_RENAME;
  else
    /* Some event that we are not interested in. */
    return 0;

  handle = *(uv_fs_event_t**)(msg.__rfim_utok);
  handle->cb(handle, uv__basename_r(handle->path), events, 0);
  return 1;
}


void uv__io_poll(uv_loop_t* loop, int timeout) {
  static const int max_safe_timeout = 1789569;
  struct epoll_event events[1024];
  struct epoll_event* pe;
  struct epoll_event e;
  uv__os390_epoll* ep;
  int real_timeout;
  QUEUE* q;
  uv__io_t* w;
  uint64_t base;
  int count;
  int nfds;
  int fd;
  int op;
  int i;
  int user_timeout;
  int reset_timeout;

  if (loop->nfds == 0) {
    assert(QUEUE_EMPTY(&loop->watcher_queue));
    return;
  }

  while (!QUEUE_EMPTY(&loop->watcher_queue)) {
    uv_stream_t* stream;

    q = QUEUE_HEAD(&loop->watcher_queue);
    QUEUE_REMOVE(q);
    QUEUE_INIT(q);
    w = QUEUE_DATA(q, uv__io_t, watcher_queue);

    assert(w->pevents != 0);
    assert(w->fd >= 0);

    stream= container_of(w, uv_stream_t, io_watcher);

    assert(w->fd < (int) loop->nwatchers);

    e.events = w->pevents;
    e.fd = w->fd;

    if (w->events == 0)
      op = EPOLL_CTL_ADD;
    else
      op = EPOLL_CTL_MOD;

    /* XXX Future optimization: do EPOLL_CTL_MOD lazily if we stop watching
     * events, skip the syscall and squelch the events after epoll_wait().
     */
    if (epoll_ctl(loop->ep, op, w->fd, &e)) {
      if (errno != EEXIST)
        abort();

      assert(op == EPOLL_CTL_ADD);

      /* We've reactivated a file descriptor that's been watched before. */
      if (epoll_ctl(loop->ep, EPOLL_CTL_MOD, w->fd, &e))
        abort();
    }

    w->events = w->pevents;
  }

  assert(timeout >= -1);
  base = loop->time;
  count = 48; /* Benchmarks suggest this gives the best throughput. */
  real_timeout = timeout;
  int nevents = 0;

  if (uv__get_internal_fields(loop)->flags & UV_METRICS_IDLE_TIME) {
    reset_timeout = 1;
    user_timeout = timeout;
    timeout = 0;
  } else {
    reset_timeout = 0;
  }

  nfds = 0;
  for (;;) {
    /* Only need to set the provider_entry_time if timeout != 0. The function
     * will return early if the loop isn't configured with UV_METRICS_IDLE_TIME.
     */
    if (timeout != 0)
      uv__metrics_set_provider_entry_time(loop);

    if (sizeof(int32_t) == sizeof(long) && timeout >= max_safe_timeout)
      timeout = max_safe_timeout;

    nfds = epoll_wait(loop->ep, events,
                      ARRAY_SIZE(events), timeout);

    /* Update loop->time unconditionally. It's tempting to skip the update when
     * timeout == 0 (i.e. non-blocking poll) but there is no guarantee that the
     * operating system didn't reschedule our process while in the syscall.
     */
    base = loop->time;
    SAVE_ERRNO(uv__update_time(loop));
    if (nfds == 0) {
      assert(timeout != -1);

      if (reset_timeout != 0) {
        timeout = user_timeout;
        reset_timeout = 0;
      }

      if (timeout == -1)
        continue;

      if (timeout == 0)
        return;

      /* We may have been inside the system call for longer than |timeout|
       * milliseconds so we need to update the timestamp to avoid drift.
       */
      goto update_timeout;
    }

    if (nfds == -1) {

      if (errno != EINTR)
        abort();

      if (reset_timeout != 0) {
        timeout = user_timeout;
        reset_timeout = 0;
      }

      if (timeout == -1)
        continue;

      if (timeout == 0)
        return;

      /* Interrupted by a signal. Update timeout and poll again. */
      goto update_timeout;
    }


    assert(loop->watchers != NULL);
    loop->watchers[loop->nwatchers] = (void*) events;
    loop->watchers[loop->nwatchers + 1] = (void*) (uintptr_t) nfds;
    for (i = 0; i < nfds; i++) {
      pe = events + i;
      fd = pe->fd;

      /* Skip invalidated events, see uv__platform_invalidate_fd */
      if (fd == -1)
        continue;

      ep = loop->ep;
      if (pe->is_msg) {
        os390_message_queue_handler(ep);
        continue;
      }

      assert(fd >= 0);
      assert((unsigned) fd < loop->nwatchers);

      w = loop->watchers[fd];

      if (w == NULL) {
        /* File descriptor that we've stopped watching, disarm it.
         *
         * Ignore all errors because we may be racing with another thread
         * when the file descriptor is closed.
         */
        epoll_ctl(loop->ep, EPOLL_CTL_DEL, fd, pe);
        continue;
      }

      /* Give users only events they're interested in. Prevents spurious
       * callbacks when previous callback invocation in this loop has stopped
       * the current watcher. Also, filters out events that users has not
       * requested us to watch.
       */
      pe->events &= w->pevents | POLLERR | POLLHUP;

      if (pe->events == POLLERR || pe->events == POLLHUP)
        pe->events |= w->pevents & (POLLIN | POLLOUT);

      if (pe->events != 0) {
        uv__metrics_update_idle_time(loop);
        w->cb(loop, w, pe->events);
        nevents++;
      }
    }
    loop->watchers[loop->nwatchers] = NULL;
    loop->watchers[loop->nwatchers + 1] = NULL;

    if (reset_timeout != 0) {
      timeout = user_timeout;
      reset_timeout = 0;
    }

    if (nevents != 0) {
      if (nfds == ARRAY_SIZE(events) && --count != 0) {
        /* Poll for more events but don't block this time. */
        timeout = 0;
        continue;
      }
      return;
    }

    if (timeout == 0)
      return;

    if (timeout == -1)
      continue;

update_timeout:
    assert(timeout > 0);

    real_timeout -= (loop->time - base);
    if (real_timeout <= 0)
      return;

    timeout = real_timeout;
  }
}

void uv__set_process_title(const char* title) {
  /* do nothing */
}

int uv__io_fork(uv_loop_t* loop) {
  /*
    Nullify the msg queue but don't close it because
    it is still being used by the parent.
  */
  loop->ep = NULL;

  uv__platform_loop_delete(loop);
  return uv__platform_loop_init(loop);
}