Cygwin: pipe: do short writes only once in nonblocking case too

[newlib-cygwin.git] / winsup / cygwin / fhandler / pipe.cc

/* fhandler_pipe.cc: pipes for Cygwin.

This file is part of Cygwin.

This software is a copyrighted work licensed under the terms of the
Cygwin license.  Please consult the file "CYGWIN_LICENSE" for
details. */

#include "winsup.h"
#include <stdlib.h>
#include <sys/socket.h>
#include "cygerrno.h"
#include "security.h"
#include "path.h"
#include "fhandler.h"
#include "select.h"
#include "dtable.h"
#include "cygheap.h"
#include "pinfo.h"
#include "shared_info.h"
#include "tls_pbuf.h"
#include "sigproc.h"
#include <assert.h>

/* This is only to be used for writing.  When reading,
STATUS_PIPE_EMPTY simply means there's no data to be read. */
#define STATUS_PIPE_IS_CLOSED(status)   \
                ({ NTSTATUS _s = (status); \
                   _s == STATUS_PIPE_CLOSING \
                   || _s == STATUS_PIPE_BROKEN \
                   || _s == STATUS_PIPE_EMPTY; })

fhandler_pipe_fifo::fhandler_pipe_fifo ()
  : fhandler_base (), pipe_buf_size (DEFAULT_PIPEBUFSIZE)
{
}


fhandler_pipe::fhandler_pipe ()
  : fhandler_pipe_fifo (), popen_pid (0)
{
  need_fork_fixup (true);
}

/* The following function is intended for fhandler_pipe objects
   created by the second version of fhandler_pipe::create below.  See
   the comment preceding the latter.

   In addition to setting the blocking mode of the pipe handle, it
   also sets the pipe's read mode to byte_stream unconditionally. */
void
fhandler_pipe::set_pipe_non_blocking (bool nonblocking)
{
  NTSTATUS status;
  IO_STATUS_BLOCK io;
  FILE_PIPE_INFORMATION fpi;

  fpi.ReadMode = FILE_PIPE_BYTE_STREAM_MODE;
  fpi.CompletionMode = nonblocking ? FILE_PIPE_COMPLETE_OPERATION
    : FILE_PIPE_QUEUE_OPERATION;
  status = NtSetInformationFile (get_handle (), &io, &fpi, sizeof fpi,
                                 FilePipeInformation);
  if (!NT_SUCCESS (status))
    debug_printf ("NtSetInformationFile(FilePipeInformation): %y", status);
}

int
fhandler_pipe::init (HANDLE f, DWORD a, mode_t mode, int64_t uniq_id)
{
  /* FIXME: Have to clean this up someday
     FIXME: Do we have to check for both !get_win32_name() and
     !*get_win32_name()? */
  if ((!get_win32_name () || !*get_win32_name ()) && get_name ())
    {
      char *d;
      const char *s;
      char *hold_normalized_name = (char *) alloca (strlen (get_name ()) + 1);
      for (s = get_name (), d = hold_normalized_name; *s; s++, d++)
        if (*s == '/')
          *d = '\\';
        else
          *d = *s;
      *d = '\0';
      set_name (hold_normalized_name);
    }

  bool opened_properly = a & FILE_CREATE_PIPE_INSTANCE;
  a &= ~FILE_CREATE_PIPE_INSTANCE;
  fhandler_base::init (f, a, mode);
  close_on_exec (mode & O_CLOEXEC);
  set_ino (uniq_id);
  set_unique_id (uniq_id | !!(mode & GENERIC_WRITE));
  if (opened_properly)
    /* Set read pipe always nonblocking to allow signal handling
       even with FILE_SYNCHRONOUS_IO_NONALERT. */
    set_pipe_non_blocking (get_device () == FH_PIPER ?
                           true : is_nonblocking ());

  /* Store pipe name to path_conv pc for query_hdl check */
  if (get_dev () == FH_PIPEW)
    {
      UNICODE_STRING name;
      WCHAR pipename_buf[MAX_PATH];
      __small_swprintf (pipename_buf, L"%S%S-%u-pipe-nt-%p",
                        &ro_u_npfs, &cygheap->installation_key,
                        GetCurrentProcessId (), unique_id >> 32);
      name.Length = wcslen (pipename_buf) * sizeof (WCHAR);
      name.MaximumLength = sizeof (pipename_buf);
      name.Buffer = pipename_buf;
      pc.set_nt_native_path (&name);
    }

  return 1;
}

extern "C" int sscanf (const char *, const char *, ...);

int
fhandler_pipe::open (int flags, mode_t mode)
{
  HANDLE proc, nio_hdl = NULL;
  int64_t uniq_id;
  fhandler_pipe *fh = NULL, *fhr = NULL, *fhw = NULL;
  size_t size;
  int pid, rwflags = (flags & O_ACCMODE);
  bool inh;
  bool got_one = false;

  if (sscanf (get_name (), "/proc/%d/fd/pipe:[%llu]",
              &pid, (long long *) &uniq_id) < 2)
    {
      set_errno (ENOENT);
      return 0;
    }
  if (pid == myself->pid)
    {
      cygheap_fdenum cfd (true);
      while (cfd.next () >= 0)
        {
          /* Windows doesn't allow to copy a pipe HANDLE with another access
             mode.  So we check for read and write side of pipe and try to
             find the one matching the requested access mode. */
          if (cfd->get_unique_id () == uniq_id)
            got_one = true;
          else if (cfd->get_unique_id () == uniq_id + 1)
            got_one = true;
          else
            continue;
          if ((rwflags == O_RDONLY && !(cfd->get_access () & GENERIC_READ))
              || (rwflags == O_WRONLY && !(cfd->get_access () & GENERIC_WRITE)))
            continue;
          copy_from (cfd);
          set_handle (NULL);
          pc.close_conv_handle ();
          if (!cfd->dup (this, flags))
            return 1;
          return 0;
        }
      /* Found the pipe but access mode didn't match? EACCES.
         Otherwise ENOENT */
      set_errno (got_one ? EACCES : ENOENT);
      return 0;
    }

  pinfo p (pid);
  if (!p)
    {
      set_errno (ESRCH);
      return 0;
    }
  if (!(proc = OpenProcess (PROCESS_DUP_HANDLE, false, p->dwProcessId)))
    {
      __seterrno ();
      return 0;
    }
  fhr = p->pipe_fhandler (uniq_id, size);
  if (fhr && rwflags == O_RDONLY)
    fh = fhr;
  else
    {
      fhw = p->pipe_fhandler (uniq_id + 1, size);
      if (fhw && rwflags == O_WRONLY)
        fh = fhw;
    }
  if (!fh)
    {
      /* Too bad, but Windows only allows the same access mode when dup'ing
         the pipe. */
      set_errno (fhr || fhw ? EACCES : ENOENT);
      goto out;
    }
  inh = !(flags & O_CLOEXEC);
  if (!DuplicateHandle (proc, fh->get_handle (), GetCurrentProcess (),
                        &nio_hdl, 0, inh, DUPLICATE_SAME_ACCESS))
    {
      __seterrno ();
      goto out;
    }
  init (nio_hdl, fh->get_access (), mode & O_TEXT ?: O_BINARY,
        fh->get_plain_ino ());
  cfree (fh);
  CloseHandle (proc);
  return 1;
out:
  if (nio_hdl)
    CloseHandle (nio_hdl);
  if (fh)
    free (fh);
  if (proc)
    CloseHandle (proc);
  return 0;
}

bool
fhandler_pipe::open_setup (int flags)
{
  bool read_mtx_created = false;

  if (!fhandler_base::open_setup (flags))
    goto err;
  if (get_dev () == FH_PIPER && !read_mtx)
    {
      SECURITY_ATTRIBUTES *sa = sec_none_cloexec (flags);
      read_mtx = CreateMutex (sa, FALSE, NULL);
      if (read_mtx)
        read_mtx_created = true;
      else
        {
          debug_printf ("CreateMutex read_mtx failed: %E");
          goto err;
        }
    }
  if (!hdl_cnt_mtx)
    {
      SECURITY_ATTRIBUTES *sa = sec_none_cloexec (flags);
      hdl_cnt_mtx = CreateMutex (sa, FALSE, NULL);
      if (!hdl_cnt_mtx)
        {
          debug_printf ("CreateMutex hdl_cnt_mtx failed: %E");
          goto err_close_read_mtx;
        }
    }
  return true;

err_close_read_mtx:
  if (read_mtx_created)
    CloseHandle (read_mtx);
err:
  return false;
}

off_t
fhandler_pipe::lseek (off_t offset, int whence)
{
  debug_printf ("(%D, %d)", offset, whence);
  set_errno (ESPIPE);
  return -1;
}

int
fhandler_pipe::fadvise (off_t offset, off_t length, int advice)
{
  return ESPIPE;
}

int
fhandler_pipe::fallocate (int mode, off_t offset, off_t length)
{
  return (mode & __FALLOC_FL_TRUNCATE) ? EINVAL : ESPIPE;
}

char *
fhandler_pipe::get_proc_fd_name (char *buf)
{
  __small_sprintf (buf, "pipe:[%U]", get_plain_ino ());
  return buf;
}

void
fhandler_pipe::release_select_sem (const char *from)
{
  LONG n_release;
  if (get_dev () == FH_PIPER) /* Number of select() and writer */
    n_release = get_obj_handle_count (select_sem)
      - get_obj_handle_count (read_mtx);
  else /* Number of select() call and reader */
    n_release = get_obj_handle_count (select_sem)
      - get_obj_handle_count (get_handle ());
  debug_printf("%s(%s) release %d", from,
               get_dev () == FH_PIPER ? "PIPER" : "PIPEW", n_release);
  if (n_release)
    ReleaseSemaphore (select_sem, n_release, NULL);
}

void
fhandler_pipe::raw_read (void *ptr, size_t& len)
{
  size_t nbytes = 0;
  NTSTATUS status = STATUS_SUCCESS;
  IO_STATUS_BLOCK io;
  ULONGLONG t0 = GetTickCount64 (); /* Init timer */
  const ULONGLONG t0_threshold = 20;

  if (!len)
    return;

  DWORD timeout = is_nonblocking () ? 0 : INFINITE;
  DWORD waitret = cygwait (read_mtx, timeout);
  switch (waitret)
    {
    case WAIT_OBJECT_0:
      break;
    case WAIT_TIMEOUT:
      set_errno (EAGAIN);
      len = (size_t) -1;
      return;
    case WAIT_SIGNALED:
      set_errno (EINTR);
      len = (size_t) -1;
      return;
    case WAIT_CANCELED:
      pthread::static_cancel_self ();
      /* NOTREACHED */
    default:
      /* Should not reach here. */
      __seterrno ();
      len = (size_t) -1;
      return;
    }
  while (nbytes < len)
    {
      ULONG_PTR nbytes_now = 0;
      ULONG len1 = (ULONG) (len - nbytes);
      DWORD select_sem_timeout = 0;

      FILE_PIPE_LOCAL_INFORMATION fpli;
      status = NtQueryInformationFile (get_handle (), &io,
                                       &fpli, sizeof (fpli),
                                       FilePipeLocalInformation);
      if (NT_SUCCESS (status))
        {
          if (fpli.ReadDataAvailable == 0 && nbytes != 0)
            break;
        }
      else if (nbytes != 0)
        break;
      status = NtReadFile (get_handle (), NULL, NULL, NULL, &io, ptr,
                           len1, NULL, NULL);
      if (isclosed ())  /* A signal handler might have closed the fd. */
        {
          set_errno (EBADF);
          nbytes = (size_t) -1;
        }
      else if (NT_SUCCESS (status) || status == STATUS_BUFFER_OVERFLOW)
        {
          nbytes_now = io.Information;
          ptr = ((char *) ptr) + nbytes_now;
          nbytes += nbytes_now;
          if (select_sem && nbytes_now > 0)
            release_select_sem ("raw_read");
        }
      else
        {
          /* Some errors are not really errors.  Detect such cases here.  */
          switch (status)
            {
            case STATUS_END_OF_FILE:
            case STATUS_PIPE_BROKEN:
              /* This is really EOF.  */
              break;
            case STATUS_PIPE_LISTENING:
            case STATUS_PIPE_EMPTY:
              if (nbytes != 0)
                break;
              if (is_nonblocking ())
                {
                  set_errno (EAGAIN);
                  nbytes = (size_t) -1;
                  break;
                }
              /* If the pipe is a non-cygwin pipe, select_sem trick
                 does not work. As a result, the following cygwait()
                 will return only after timeout occurs. This causes
                 performance degradation. However, setting timeout
                 to zero causes high CPU load. So, set timeout to
                 non-zero only when select_sem is valid or pipe is
                 not ready to read for more than t0_threshold.
                 This prevents both the performance degradation and
                 the high CPU load. */
              if (select_sem || GetTickCount64 () - t0 > t0_threshold)
                select_sem_timeout = 1;
              waitret = cygwait (select_sem, select_sem_timeout);
              if (waitret == WAIT_CANCELED)
                pthread::static_cancel_self ();
              else if (waitret == WAIT_SIGNALED)
                {
                  set_errno (EINTR);
                  nbytes = (size_t) -1;
                  break;
                }
              continue;
            default:
              __seterrno_from_nt_status (status);
              nbytes = (size_t) -1;
              break;
            }
        }

      if ((nbytes_now == 0 && !NT_SUCCESS (status))
          || status == STATUS_BUFFER_OVERFLOW)
        break;
    }
  ReleaseMutex (read_mtx);
  len = nbytes;
}

bool
fhandler_pipe::reader_closed ()
{
  if (!query_hdl)
    return false;
  WaitForSingleObject (hdl_cnt_mtx, INFINITE);
  int n_reader = get_obj_handle_count (query_hdl);
  int n_writer = get_obj_handle_count (get_handle ());
  ReleaseMutex (hdl_cnt_mtx);
  return n_reader == n_writer;
}

ssize_t
fhandler_pipe_fifo::raw_write (const void *ptr, size_t len)
{
  size_t nbytes = 0;
  ULONG chunk;
  NTSTATUS status = STATUS_SUCCESS;
  IO_STATUS_BLOCK io;
  HANDLE evt;
  bool short_write_once = false;

  if (!len)
    return 0;

  if (reader_closed ())
    {
      set_errno (EPIPE);
      raise (SIGPIPE);
      return -1;
    }

  if (len <= pipe_buf_size || pipe_buf_size == 0)
    chunk = len;
  else if (is_nonblocking ())
    chunk = len = pipe_buf_size;
  else
    chunk = pipe_buf_size;

  if (!(evt = CreateEvent (NULL, false, false, NULL)))
    {
      __seterrno ();
      return -1;
    }

  /* Write in chunks, accumulating a total.  If there's an error, just
     return the accumulated total unless the first write fails, in
     which case return -1. */
  while (nbytes < len)
    {
      ULONG_PTR nbytes_now = 0;
      size_t left = len - nbytes;
      ULONG len1;
      DWORD waitret = WAIT_OBJECT_0;

      if (left > chunk)
        len1 = chunk;
      else
        len1 = (ULONG) left;

      /* NtWriteFile returns success with # of bytes written == 0 if writing
         on a non-blocking pipe fails because the pipe buffer doesn't have
         sufficient space.

         POSIX requires
         - A write request for {PIPE_BUF} or fewer bytes shall have the
           following effect: if there is sufficient space available in the
           pipe, write() shall transfer all the data and return the number
           of bytes requested. Otherwise, write() shall transfer no data and
           return -1 with errno set to [EAGAIN].

         - A write request for more than {PIPE_BUF} bytes shall cause one
           of the following:

          - When at least one byte can be written, transfer what it can and
            return the number of bytes written. When all data previously
            written to the pipe is read, it shall transfer at least {PIPE_BUF}
            bytes.

          - When no data can be written, transfer no data, and return -1 with
            errno set to [EAGAIN]. */
      while (len1 > 0)
        {
          status = NtWriteFile (get_handle (), evt, NULL, NULL, &io,
                                (PVOID) ptr, len1, NULL, NULL);
          if (status == STATUS_PENDING)
            {
              do
                {
                  /* To allow constant reader_closed() checking even if the
                     signal has been set up with SA_RESTART, we're handling
                     the signal here --> cw_sig_eintr. */
                  waitret = cygwait (evt, (DWORD) 0, cw_cancel | cw_sig_eintr);
                  /* Break out if no SA_RESTART. */
                  if (waitret == WAIT_SIGNALED
                      && !_my_tls.call_signal_handler ())
                    break;
                  if (reader_closed ())
                    {
                      CancelIo (get_handle ());
                      set_errno (EPIPE);
                      raise (SIGPIPE);
                      goto out;
                    }
                  else
                    cygwait (select_sem, 10, cw_cancel);
                  /* If we got a timeout in the blocking case, and we already
                     did a short write, we got a signal in the previous loop. */
                  if (waitret == WAIT_TIMEOUT && short_write_once)
                    {
                      waitret = WAIT_SIGNALED;
                      break;
                    }
                }
              /* Loop in case of blocking write or SA_RESTART */
              while (waitret == WAIT_TIMEOUT || waitret == WAIT_SIGNALED);
              /* If io.Status is STATUS_CANCELLED after CancelIo, IO has
                 actually been cancelled and io.Information contains the
                 number of bytes processed so far.
                 Otherwise IO has been finished regulary and io.Status
                 contains valid success or error information. */
              CancelIo (get_handle ());
              if (waitret == WAIT_SIGNALED && io.Status != STATUS_CANCELLED)
                waitret = WAIT_OBJECT_0;

              if (waitret == WAIT_CANCELED)
                status = STATUS_THREAD_CANCELED;
              else if (waitret == WAIT_SIGNALED)
                status = STATUS_THREAD_SIGNALED;
              else if (waitret == WAIT_TIMEOUT && io.Status == STATUS_CANCELLED)
                status = STATUS_SUCCESS;
              else
                status = io.Status;
            }
          if (status != STATUS_THREAD_SIGNALED && !NT_SUCCESS (status))
            break;
          if (io.Information > 0 || len <= PIPE_BUF || short_write_once)
            break;
          /* Independent of being blocking or non-blocking, if we're here,
             the pipe has less space than requested.  If the pipe is a
             non-Cygwin pipe, just try the old strategy of trying a half
             write.  If the pipe has at
             least PIPE_BUF bytes available, try to write all matching
             PIPE_BUF sized blocks.  If it's less than PIPE_BUF,  try
             the next less power of 2 bytes.  This is not really the Linux
             strategy because Linux is filling the pages of a pipe buffer
             in a very implementation-defined way we can't emulate, but it
             resembles it closely enough to get useful results. */
          ssize_t avail = pipe_data_available (-1, this, get_handle (),
                                               PDA_WRITE);
          if (avail < 1)        /* error or pipe closed */
            break;
          if (avail > len1)     /* somebody read from the pipe */
            avail = len1;
          if (avail == 1)       /* 1 byte left or non-Cygwin pipe */
            len1 >>= 1;
          else if (avail >= PIPE_BUF)
            len1 = avail & ~(PIPE_BUF - 1);
          else
            len1 = 1 << (31 - __builtin_clzl (avail));
          short_write_once = true;
        }
      if (isclosed ())  /* A signal handler might have closed the fd. */
        {
          if (waitret == WAIT_OBJECT_0)
            set_errno (EBADF);
          else
            __seterrno ();
        }
      else if (NT_SUCCESS (status)
               || status == STATUS_THREAD_CANCELED
               || status == STATUS_THREAD_SIGNALED)
        {
          nbytes_now = io.Information;
          ptr = ((char *) ptr) + nbytes_now;
          nbytes += nbytes_now;
          if (select_sem && nbytes_now > 0)
            release_select_sem ("raw_write");
          /* 0 bytes returned?  EAGAIN.  See above. */
          if (NT_SUCCESS (status) && nbytes == 0)
            set_errno (EAGAIN);
        }
      else if (STATUS_PIPE_IS_CLOSED (status))
        {
          set_errno (EPIPE);
          raise (SIGPIPE);
        }
      else
        __seterrno_from_nt_status (status);

      if (nbytes_now == 0 || short_write_once)
        break;
    }
out:
  CloseHandle (evt);
  if (status == STATUS_THREAD_SIGNALED && nbytes == 0)
    set_errno (EINTR);
  else if (status == STATUS_THREAD_CANCELED)
    pthread::static_cancel_self ();
  return nbytes ?: -1;
}

void
fhandler_pipe::set_close_on_exec (bool val)
{
  fhandler_base::set_close_on_exec (val);
  if (read_mtx)
    set_no_inheritance (read_mtx, val);
  if (select_sem)
    set_no_inheritance (select_sem, val);
  if (query_hdl)
    set_no_inheritance (query_hdl, val);
  set_no_inheritance (hdl_cnt_mtx, val);
}

void
fhandler_pipe::fixup_after_fork (HANDLE parent)
{
  fork_fixup (parent, hdl_cnt_mtx, "hdl_cnt_mtx");
  WaitForSingleObject (hdl_cnt_mtx, INFINITE);
  if (read_mtx)
    fork_fixup (parent, read_mtx, "read_mtx");
  if (select_sem)
    fork_fixup (parent, select_sem, "select_sem");
  if (query_hdl)
    fork_fixup (parent, query_hdl, "query_hdl");
  if (query_hdl_close_req_evt)
    fork_fixup (parent, query_hdl_close_req_evt, "query_hdl_close_req_evt");

  fhandler_base::fixup_after_fork (parent);
  ReleaseMutex (hdl_cnt_mtx);
}

void
fhandler_pipe::fixup_after_exec ()
{
  /* Set read pipe itself always non-blocking for cygwin process.
     Blocking/non-blocking is simulated in raw_read(). For write
     pipe, follow is_nonblocking(). */
  bool mode = get_device () == FH_PIPEW ? is_nonblocking () : true;
  set_pipe_non_blocking (mode);
  fhandler_base::fixup_after_exec ();
}

int
fhandler_pipe::dup (fhandler_base *child, int flags)
{
  fhandler_pipe *ftp = (fhandler_pipe *) child;
  ftp->set_popen_pid (0);

  int res = 0;
  WaitForSingleObject (hdl_cnt_mtx, INFINITE);
  if (fhandler_base::dup (child, flags))
    res = -1;
  else if (read_mtx &&
           !DuplicateHandle (GetCurrentProcess (), read_mtx,
                             GetCurrentProcess (), &ftp->read_mtx,
                             0, !(flags & O_CLOEXEC), DUPLICATE_SAME_ACCESS))
    {
      __seterrno ();
      ftp->close ();
      res = -1;
    }
  else if (select_sem &&
           !DuplicateHandle (GetCurrentProcess (), select_sem,
                             GetCurrentProcess (), &ftp->select_sem,
                             0, !(flags & O_CLOEXEC), DUPLICATE_SAME_ACCESS))
    {
      __seterrno ();
      ftp->close ();
      res = -1;
    }
  else if (query_hdl &&
           !DuplicateHandle (GetCurrentProcess (), query_hdl,
                             GetCurrentProcess (), &ftp->query_hdl,
                             0, !(flags & O_CLOEXEC), DUPLICATE_SAME_ACCESS))
    {
      __seterrno ();
      ftp->close ();
      res = -1;
    }
  else if (!DuplicateHandle (GetCurrentProcess (), hdl_cnt_mtx,
                             GetCurrentProcess (), &ftp->hdl_cnt_mtx,
                             0, !(flags & O_CLOEXEC), DUPLICATE_SAME_ACCESS))
    {
      __seterrno ();
      ftp->close ();
      res = -1;
    }
  else if (query_hdl_close_req_evt &&
           !DuplicateHandle (GetCurrentProcess (), query_hdl_close_req_evt,
                             GetCurrentProcess (),
                             &ftp->query_hdl_close_req_evt,
                             0, !(flags & O_CLOEXEC), DUPLICATE_SAME_ACCESS))
    {
      __seterrno ();
      ftp->close ();
      res = -1;
    }
  ReleaseMutex (hdl_cnt_mtx);

  debug_printf ("res %d", res);
  return res;
}

int
fhandler_pipe::close ()
{
  if (select_sem)
    {
      release_select_sem ("close");
      CloseHandle (select_sem);
    }
  if (read_mtx)
    CloseHandle (read_mtx);
  WaitForSingleObject (hdl_cnt_mtx, INFINITE);
  if (query_hdl)
    CloseHandle (query_hdl);
  if (query_hdl_close_req_evt)
    CloseHandle (query_hdl_close_req_evt);
  int ret = fhandler_base::close ();
  ReleaseMutex (hdl_cnt_mtx);
  CloseHandle (hdl_cnt_mtx);
  if (query_hdl_proc)
    CloseHandle (query_hdl_proc);
  return ret;
}

#define PIPE_INTRO "\\\\.\\pipe\\cygwin-"

/* Create a pipe, and return handles to the read and write ends,
   just like CreatePipe, but ensure that the write end permits
   FILE_READ_ATTRIBUTES access, on later versions of win32 where
   this is supported.  This access is needed by NtQueryInformationFile,
   which is used to implement select and nonblocking writes.
   Note that the return value is either 0 or GetLastError,
   unlike CreatePipe, which returns a bool for success or failure.  */
DWORD
fhandler_pipe::create (LPSECURITY_ATTRIBUTES sa_ptr, PHANDLE r, PHANDLE w,
                       DWORD psize, const char *name, DWORD open_mode,
                       int64_t *unique_id)
{
  /* Default to error. */
  if (r)
    *r = NULL;
  if (w)
    *w = NULL;

  /* Ensure that there is enough pipe buffer space for atomic writes.  */
  if (!psize)
    psize = DEFAULT_PIPEBUFSIZE;

  char pipename[MAX_PATH];
  size_t len = __small_sprintf (pipename, PIPE_INTRO "%S-",
                                      &cygheap->installation_key);
  DWORD pipe_mode = PIPE_READMODE_BYTE | PIPE_REJECT_REMOTE_CLIENTS;
  if (!name)
    pipe_mode |= pipe_byte ? PIPE_TYPE_BYTE : PIPE_TYPE_MESSAGE;
  else
    pipe_mode |= PIPE_TYPE_MESSAGE;

  if (!name || (open_mode & PIPE_ADD_PID))
    {
      len += __small_sprintf (pipename + len, "%u-", GetCurrentProcessId ());
      open_mode &= ~PIPE_ADD_PID;
    }

  if (name)
    len += __small_sprintf (pipename + len, "%s", name);

  open_mode |= PIPE_ACCESS_INBOUND | FILE_FLAG_FIRST_PIPE_INSTANCE;

  /* Retry CreateNamedPipe as long as the pipe name is in use.
     Retrying will probably never be necessary, but we want
     to be as robust as possible.  */
  DWORD err = 0;
  while (r && !*r)
    {
      static volatile ULONG pipe_unique_id;
      if (!name)
        {
          LONG id = InterlockedIncrement ((LONG *) &pipe_unique_id);
          __small_sprintf (pipename + len, "pipe-%p", id);
          if (unique_id)
            *unique_id = ((int64_t) id << 32 | GetCurrentProcessId ());
        }

      debug_printf ("name %s, size %u, mode %s", pipename, psize,
                    (pipe_mode & PIPE_TYPE_MESSAGE)
                    ? "PIPE_TYPE_MESSAGE" : "PIPE_TYPE_BYTE");

      /* Use CreateNamedPipe instead of CreatePipe, because the latter
         returns a write handle that does not permit FILE_READ_ATTRIBUTES
         access, on versions of win32 earlier than WinXP SP2.
         CreatePipe also stupidly creates a full duplex pipe, which is
         a waste, since only a single direction is actually used.
         It's important to only allow a single instance, to ensure that
         the pipe was not created earlier by some other process, even if
         the pid has been reused.

         Note that the write side of the pipe is opened as PIPE_TYPE_MESSAGE.
         This *seems* to more closely mimic Linux pipe behavior and is
         definitely required for pty handling since fhandler_pty_master
         writes to the pipe in chunks, terminated by newline when CANON mode
         is specified.  */
      *r = CreateNamedPipe (pipename, open_mode, pipe_mode, 1, psize,
                           psize, NMPWAIT_USE_DEFAULT_WAIT, sa_ptr);

      if (*r != INVALID_HANDLE_VALUE)
        {
          debug_printf ("pipe read handle %p", *r);
          err = 0;
          break;
        }

      err = GetLastError ();
      switch (err)
        {
        case ERROR_PIPE_BUSY:
          /* The pipe is already open with compatible parameters.
             Pick a new name and retry.  */
          debug_printf ("pipe busy", !name ? ", retrying" : "");
          if (!name)
            *r = NULL;
          break;
        case ERROR_ACCESS_DENIED:
          /* The pipe is already open with incompatible parameters.
             Pick a new name and retry.  */
          debug_printf ("pipe access denied%s", !name ? ", retrying" : "");
          if (!name)
            *r = NULL;
          break;
        default:
          {
            err = GetLastError ();
            debug_printf ("failed, %E");
          }
        }
    }

  if (err)
    {
      *r = NULL;
      return err;
    }

  if (!w)
    debug_printf ("pipe write handle NULL");
  else
    {
      debug_printf ("CreateFile: name %s", pipename);

      /* Open the named pipe for writing.
         Be sure to permit FILE_READ_ATTRIBUTES access.  */
      DWORD access = GENERIC_WRITE | FILE_READ_ATTRIBUTES;
      if ((open_mode & PIPE_ACCESS_DUPLEX) == PIPE_ACCESS_DUPLEX)
        access |= GENERIC_READ | FILE_WRITE_ATTRIBUTES;
      *w = CreateFile (pipename, access, 0, sa_ptr, OPEN_EXISTING,
                      open_mode & FILE_FLAG_OVERLAPPED, 0);

      if (!*w || *w == INVALID_HANDLE_VALUE)
        {
          /* Failure. */
          DWORD err = GetLastError ();
          debug_printf ("CreateFile failed, r %p, %E", r);
          if (r)
            CloseHandle (*r);
          *w = NULL;
          return err;
        }

      debug_printf ("pipe write handle %p", *w);
    }

  /* Success. */
  return 0;
}

inline static bool
is_running_as_service (void)
{
  return check_token_membership (well_known_service_sid)
    || cygheap->user.saved_sid () == well_known_system_sid;
}

/* The next version of fhandler_pipe::create used to call the previous
   version.  But the read handle created by the latter doesn't have
   FILE_WRITE_ATTRIBUTES access unless the pipe is created with
   PIPE_ACCESS_DUPLEX, and it doesn't seem possible to add that access
   right.  This causes set_pipe_non_blocking to fail.

   To fix this we will define a helper function 'nt_create' that is
   similar to the above fhandler_pipe::create but uses
   NtCreateNamedPipeFile instead of CreateNamedPipe; this gives more
   flexibility in setting the access rights.  We will use this helper
   function in the version of fhandler_pipe::create below, which
   suffices for all of our uses of set_pipe_non_blocking.  For
   simplicity, nt_create will omit the 'open_mode' and 'name'
   parameters, which aren't needed for our purposes.  */

static int nt_create (LPSECURITY_ATTRIBUTES, HANDLE &, HANDLE &, DWORD,
                      int64_t *);

int
fhandler_pipe::create (fhandler_pipe *fhs[2], unsigned psize, int mode)
{
  HANDLE r, w;
  SECURITY_ATTRIBUTES *sa = sec_none_cloexec (mode);
  int res = -1;
  int64_t unique_id;

  int ret = nt_create (sa, r, w, psize, &unique_id);
  if (ret)
    {
      __seterrno_from_win_error (ret);
      goto out;
    }
  if ((fhs[0] = (fhandler_pipe *) build_fh_dev (*piper_dev)) == NULL)
    goto err_close_rw_handle;
  if ((fhs[1] = (fhandler_pipe *) build_fh_dev (*pipew_dev)) == NULL)
    goto err_delete_fhs0;
  mode |= mode & O_TEXT ?: O_BINARY;
  fhs[0]->init (r, FILE_CREATE_PIPE_INSTANCE | GENERIC_READ, mode, unique_id);
  fhs[1]->init (w, FILE_CREATE_PIPE_INSTANCE | GENERIC_WRITE, mode, unique_id);

  /* For the read side of the pipe, add a mutex.  See raw_read for the
     usage. */
  fhs[0]->read_mtx = CreateMutexW (sa, FALSE, NULL);
  if (!fhs[0]->read_mtx)
    goto err_delete_fhs1;

  fhs[0]->select_sem = CreateSemaphore (sa, 0, INT32_MAX, NULL);
  if (!fhs[0]->select_sem)
    goto err_close_read_mtx;
  if (!DuplicateHandle (GetCurrentProcess (), fhs[0]->select_sem,
                        GetCurrentProcess (), &fhs[1]->select_sem,
                        0, sa->bInheritHandle, DUPLICATE_SAME_ACCESS))
    goto err_close_select_sem0;

  if (is_running_as_service () &&
      !DuplicateHandle (GetCurrentProcess (), r,
                        GetCurrentProcess (), &fhs[1]->query_hdl,
                        FILE_READ_DATA, sa->bInheritHandle, 0))
    goto err_close_select_sem1;

  fhs[0]->hdl_cnt_mtx = CreateMutexW (sa, FALSE, NULL);
  if (!fhs[0]->hdl_cnt_mtx)
    goto err_close_query_hdl;
  if (!DuplicateHandle (GetCurrentProcess (), fhs[0]->hdl_cnt_mtx,
                        GetCurrentProcess (), &fhs[1]->hdl_cnt_mtx,
                        0, sa->bInheritHandle, DUPLICATE_SAME_ACCESS))
    goto err_close_hdl_cnt_mtx0;

  if (fhs[1]->query_hdl)
    {
      fhs[1]->query_hdl_close_req_evt = CreateEvent (sa, TRUE, FALSE, NULL);
      if (!fhs[1]->query_hdl_close_req_evt)
        goto err_close_hdl_cnt_mtx1;
    }

  res = 0;
  goto out;

err_close_hdl_cnt_mtx1:
  CloseHandle (fhs[1]->hdl_cnt_mtx);
err_close_hdl_cnt_mtx0:
  CloseHandle (fhs[0]->hdl_cnt_mtx);
err_close_query_hdl:
  if (fhs[1]->query_hdl)
    CloseHandle (fhs[1]->query_hdl);
err_close_select_sem1:
  CloseHandle (fhs[1]->select_sem);
err_close_select_sem0:
  CloseHandle (fhs[0]->select_sem);
err_close_read_mtx:
  CloseHandle (fhs[0]->read_mtx);
err_delete_fhs1:
  delete fhs[1];
err_delete_fhs0:
  delete fhs[0];
err_close_rw_handle:
  NtClose (r);
  NtClose (w);
out:
  debug_printf ("%R = pipe([%p, %p], %d, %y)",
                res, fhs[0], fhs[1], psize, mode);
  return res;
}

static int
nt_create (LPSECURITY_ATTRIBUTES sa_ptr, HANDLE &r, HANDLE &w,
                DWORD psize, int64_t *unique_id)
{
  NTSTATUS status;
  HANDLE npfsh;
  ACCESS_MASK access;
  OBJECT_ATTRIBUTES attr;
  IO_STATUS_BLOCK io;
  LARGE_INTEGER timeout;

  /* Default to error. */
  r = NULL;
  w = NULL;

  status = fhandler_base::npfs_handle (npfsh);
  if (!NT_SUCCESS (status))
    {
      __seterrno_from_nt_status (status);
      return GetLastError ();
    }

  /* Ensure that there is enough pipe buffer space for atomic writes.  */
  if (!psize)
    psize = DEFAULT_PIPEBUFSIZE;

  UNICODE_STRING pipename;
  WCHAR pipename_buf[MAX_PATH];
  size_t len = __small_swprintf (pipename_buf, L"%S-%u-",
                                 &cygheap->installation_key,
                                 GetCurrentProcessId ());

  access = GENERIC_READ | FILE_WRITE_ATTRIBUTES | SYNCHRONIZE;
  access |= FILE_WRITE_EA; /* Add this right as a marker of cygwin read pipe */

  ULONG pipe_type = pipe_byte ? FILE_PIPE_BYTE_STREAM_TYPE
    : FILE_PIPE_MESSAGE_TYPE;

  /* Retry NtCreateNamedPipeFile as long as the pipe name is in use.
     Retrying will probably never be necessary, but we want
     to be as robust as possible.  */
  DWORD err = 0;
  while (!r)
    {
      static volatile ULONG pipe_unique_id;
      LONG id = InterlockedIncrement ((LONG *) &pipe_unique_id);
      __small_swprintf (pipename_buf + len, L"pipe-nt-%p", id);
      if (unique_id)
        *unique_id = ((int64_t) id << 32 | GetCurrentProcessId ());

      debug_printf ("name %W, size %u, mode %s", pipename_buf, psize,
                    (pipe_type & FILE_PIPE_MESSAGE_TYPE)
                    ? "PIPE_TYPE_MESSAGE" : "PIPE_TYPE_BYTE");

      RtlInitUnicodeString (&pipename, pipename_buf);

      InitializeObjectAttributes (&attr, &pipename,
                                  sa_ptr->bInheritHandle ? OBJ_INHERIT : 0,
                                  npfsh, sa_ptr->lpSecurityDescriptor);

      timeout.QuadPart = -500000;
      /* Set FILE_SYNCHRONOUS_IO_NONALERT flag so that native
         C# programs work with cygwin pipe. */
      status = NtCreateNamedPipeFile (&r, access, &attr, &io,
                                      FILE_SHARE_READ | FILE_SHARE_WRITE,
                                      FILE_CREATE,
                                      FILE_SYNCHRONOUS_IO_NONALERT, pipe_type,
                                      FILE_PIPE_BYTE_STREAM_MODE,
                                      0, 1, psize, psize, &timeout);

      if (NT_SUCCESS (status))
        {
          debug_printf ("pipe read handle %p", r);
          err = 0;
          break;
        }

      switch (status)
        {
        case STATUS_PIPE_BUSY:
        case STATUS_INSTANCE_NOT_AVAILABLE:
        case STATUS_PIPE_NOT_AVAILABLE:
          /* The pipe is already open with compatible parameters.
             Pick a new name and retry.  */
          debug_printf ("pipe busy, retrying");
          r = NULL;
          break;
        case STATUS_ACCESS_DENIED:
          /* The pipe is already open with incompatible parameters.
             Pick a new name and retry.  */
          debug_printf ("pipe access denied, retrying");
          r = NULL;
          break;
        default:
          {
            __seterrno_from_nt_status (status);
            err = GetLastError ();
            debug_printf ("failed, %E");
            r = NULL;
          }
        }
    }

  if (err)
    {
      r = NULL;
      return err;
    }

  debug_printf ("NtOpenFile: name %S", &pipename);

  access = GENERIC_WRITE | FILE_READ_ATTRIBUTES | SYNCHRONIZE;
  status = NtOpenFile (&w, access, &attr, &io, 0, 0);
  if (!NT_SUCCESS (status))
    {
      DWORD err = GetLastError ();
      debug_printf ("NtOpenFile failed, r %p, %E", r);
      if (r)
        NtClose (r);
      w = NULL;
      return err;
    }

  /* Success. */
  return 0;
}

/* Called by dtable::init_std_file_from_handle for stdio handles
   inherited from non-Cygwin processes. */
void
fhandler_pipe::set_pipe_buf_size ()
{
  NTSTATUS status;
  IO_STATUS_BLOCK io;
  FILE_PIPE_LOCAL_INFORMATION fpli;

  status = NtQueryInformationFile (get_handle (), &io, &fpli, sizeof fpli,
                                   FilePipeLocalInformation);
  if (NT_SUCCESS (status))
    pipe_buf_size = fpli.InboundQuota;
}

int
fhandler_pipe::ioctl (unsigned int cmd, void *p)
{
  int n;

  switch (cmd)
    {
    case FIONREAD:
      if (get_device () == FH_PIPEW)
        {
          set_errno (EINVAL);
          return -1;
        }
      if (!PeekNamedPipe (get_handle (), NULL, 0, NULL, (DWORD *) &n, NULL))
        {
          __seterrno ();
          return -1;
        }
      break;
    default:
      return fhandler_base::ioctl (cmd, p);
      break;
    }
  *(int *) p = n;
  return 0;
}

int
fhandler_pipe::fcntl (int cmd, intptr_t arg)
{
  if (cmd != F_SETFL)
    return fhandler_base::fcntl (cmd, arg);

  const bool was_nonblocking = is_nonblocking ();
  int res = fhandler_base::fcntl (cmd, arg);
  const bool now_nonblocking = is_nonblocking ();
  /* Do not set blocking mode for read pipe to allow signal handling
     even with FILE_SYNCHRONOUS_IO_NONALERT. */
  if (now_nonblocking != was_nonblocking && get_device () != FH_PIPER)
    set_pipe_non_blocking (now_nonblocking);
  return res;
}

int
fhandler_pipe::fstat (struct stat *buf)
{
  int ret = fhandler_base::fstat (buf);
  if (!ret)
    {
      buf->st_dev = FH_PIPE;
      if (!(buf->st_ino = get_plain_ino ()))
        sscanf (get_name (), "/proc/%*d/fd/pipe:[%llu]",
                             (long long *) &buf->st_ino);
    }
  return ret;
}

int
fhandler_pipe::fstatvfs (struct statvfs *sfs)
{
  set_errno (EBADF);
  return -1;
}

HANDLE
fhandler_pipe::temporary_query_hdl ()
{
  if (get_dev () != FH_PIPEW)
    return NULL;

  ULONG len;
  NTSTATUS status;
  tmp_pathbuf tp;
  OBJECT_NAME_INFORMATION *ntfn = (OBJECT_NAME_INFORMATION *) tp.w_get ();

  UNICODE_STRING *name = pc.get_nt_native_path (NULL);

  /* Try process handle opened and pipe handle value cached first
     in order to reduce overhead. */
  if (query_hdl_proc && query_hdl_value)
    {
      HANDLE h;
      if (!DuplicateHandle (query_hdl_proc, query_hdl_value,
                           GetCurrentProcess (), &h, FILE_READ_DATA, 0, 0))
        goto cache_err;
      /* Check name */
      status = NtQueryObject (h, ObjectNameInformation, ntfn, 65536, &len);
      if (!NT_SUCCESS (status) || !ntfn->Name.Buffer)
        goto hdl_err;
      if (RtlEqualUnicodeString (name, &ntfn->Name, FALSE))
        return h;
hdl_err:
      CloseHandle (h);
cache_err:
      CloseHandle (query_hdl_proc);
      query_hdl_proc = NULL;
      query_hdl_value = NULL;
    }

  if (name->Length == 0 || name->Buffer == NULL)
    return NULL; /* Non cygwin pipe? */
  return get_query_hdl_per_process (ntfn); /* Since Win8 */
}

HANDLE
fhandler_pipe::get_query_hdl_per_process (OBJECT_NAME_INFORMATION *ntfn)
{
  winpids pids ((DWORD) 0);

  /* In most cases, it is faster to check the processes in reverse order. */
  for (LONG i = (LONG) pids.npids - 1; i >= 0; i--)
    {
      NTSTATUS status;
      ULONG len;

      /* Non-cygwin app may call ReadFile() for empty pipe, which makes
        NtQueryObject() for ObjectNameInformation block. Therefore, do
        not try to get query_hdl for non-cygwin apps. */
      _pinfo *p = pids[i];
      if (!p || ISSTATE (p, PID_NOTCYGWIN))
        continue;

      HANDLE proc = OpenProcess (PROCESS_DUP_HANDLE
                                 | PROCESS_QUERY_INFORMATION,
                                 0, p->dwProcessId);
      if (!proc)
        continue;

      /* Retrieve process handles */
      DWORD n_handle = 256;
      PPROCESS_HANDLE_SNAPSHOT_INFORMATION phi;
      do
        {
          DWORD nbytes = 2 * sizeof (ULONG_PTR) +
            n_handle * sizeof (PROCESS_HANDLE_TABLE_ENTRY_INFO);
          phi = (PPROCESS_HANDLE_SNAPSHOT_INFORMATION)
            HeapAlloc (GetProcessHeap (), 0, nbytes);
          if (!phi)
            goto close_proc;
          /* NtQueryInformationProcess can return STATUS_SUCCESS with
             invalid handle data for certain processes.  See
             https://github.com/processhacker/processhacker/blob/05f5e9fa477dcaa1709d9518170d18e1b3b8330d/phlib/native.c#L5754.
             We need to ensure that NumberOfHandles is zero in this
             case to avoid a crash in the for loop below. */
          phi->NumberOfHandles = 0;
          status = NtQueryInformationProcess (proc, ProcessHandleInformation,
                                              phi, nbytes, &len);
          if (NT_SUCCESS (status))
            break;
          HeapFree (GetProcessHeap (), 0, phi);
          n_handle *= 2;
        }
      while (n_handle < (1L<<20) && status == STATUS_INFO_LENGTH_MISMATCH);
      if (!NT_SUCCESS (status))
        goto close_proc;

      /* Sanity check in case Microsoft changes
         NtQueryInformationProcess and the initialization of
         NumberOfHandles above is no longer sufficient. */
      assert (phi->NumberOfHandles <= n_handle);
      for (ULONG j = 0; j < phi->NumberOfHandles; j++)
        {
          /* Check for the peculiarity of cygwin read pipe */
          const ULONG access = FILE_READ_DATA | FILE_READ_EA
            | FILE_WRITE_EA /* marker */
            | FILE_READ_ATTRIBUTES | FILE_WRITE_ATTRIBUTES
            | READ_CONTROL | SYNCHRONIZE;
          if (phi->Handles[j].GrantedAccess != access)
            continue;

          /* Retrieve handle */
          HANDLE h = (HANDLE)(intptr_t) phi->Handles[j].HandleValue;
          BOOL res = DuplicateHandle (proc, h, GetCurrentProcess (), &h,
                                      FILE_READ_DATA, 0, 0);
          if (!res)
            continue;

          /* Check object name */
          status = NtQueryObject (h, ObjectNameInformation,
                                  ntfn, 65536, &len);
          if (!NT_SUCCESS (status) || !ntfn->Name.Buffer)
            goto close_handle;
          if (RtlEqualUnicodeString (pc.get_nt_native_path (),
                                     &ntfn->Name, FALSE))
            {
              query_hdl_proc = proc;
              query_hdl_value = (HANDLE)(intptr_t) phi->Handles[j].HandleValue;
              HeapFree (GetProcessHeap (), 0, phi);
              return h;
            }
close_handle:
          CloseHandle (h);
        }
      HeapFree (GetProcessHeap (), 0, phi);
close_proc:
      CloseHandle (proc);
    }
  return NULL;
}

void
fhandler_pipe::spawn_worker (int fileno_stdin, int fileno_stdout,
                             int fileno_stderr)
{
  bool need_send_noncygchld_sig = false;

  /* spawn_worker() is called from spawn.cc only when non-cygwin app
     is started. Set pipe mode blocking for the non-cygwin process. */
  int fd;
  cygheap_fdenum cfd (false);
  while ((fd = cfd.next ()) >= 0)
    if (cfd->get_dev () == FH_PIPEW
        && (fd == fileno_stdout || fd == fileno_stderr))
      {
        fhandler_pipe *pipe = (fhandler_pipe *)(fhandler_base *) cfd;
        pipe->set_pipe_non_blocking (false);

        /* Setup for query_ndl stuff. Read the comment below. */
        if (pipe->request_close_query_hdl ())
          need_send_noncygchld_sig = true;
      }
    else if (cfd->get_dev () == FH_PIPER && fd == fileno_stdin)
      {
        fhandler_pipe *pipe = (fhandler_pipe *)(fhandler_base *) cfd;
        pipe->set_pipe_non_blocking (false);
      }

  /* If multiple writers including non-cygwin app exist, the non-cygwin
     app cannot detect pipe closure on the read side when the pipe is
     created by system account or the pipe creator is running as service.
     This is because query_hdl which is held in write side also is a read
     end of the pipe, so the pipe is still alive for the non-cygwin app
     even after the reader is closed.

     To avoid this problem, let all processes in the same process
     group close query_hdl using internal signal __SIGNONCYGCHLD when
     non-cygwin app is started.  */
  if (need_send_noncygchld_sig)
    {
      tty_min dummy_tty;
      dummy_tty.ntty = (fh_devices) myself->ctty;
      dummy_tty.pgid = myself->pgid;
      tty_min *t = cygwin_shared->tty.get_cttyp ();
      if (!t) /* If tty is not allocated, use dummy_tty instead. */
        t = &dummy_tty;
      /* Emit __SIGNONCYGCHLD to let all processes in the
         process group close query_hdl. */
      t->kill_pgrp (__SIGNONCYGCHLD);
    }
}