* select.cc (pipe_data_available): New function - uses NtQueryInformationFile
to return information about pipes. (peek_pipe): Rewrite to use pipe_data_available for both read and write tests.
This commit is contained in:
Christopher Faylor
parent
2ec2d00e1b
commit
a7a1247770
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@ -1,3 +1,10 @@
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2011-05-31 Christopher Faylor <me.cygwin2011@cgf.cx>
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* select.cc (pipe_data_available): New function - uses
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NtQueryInformationFile to return information about pipes.
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(peek_pipe): Rewrite to use pipe_data_available for both read and write
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tests.
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2011-05-30 Christopher Faylor <me.cygwin2011@cgf.cx>
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* dtable.cc (dtable::select_write): Add missing argument to
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@ -473,26 +473,71 @@ no_verify (select_record *, fd_set *, fd_set *, fd_set *)
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return 0;
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}
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static int
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pipe_data_available (int fd, fhandler_base *fh, HANDLE h, bool writing)
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{
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IO_STATUS_BLOCK iosb = {0};
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FILE_PIPE_LOCAL_INFORMATION fpli = {0};
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bool res = false;
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if (NtQueryInformationFile (h,
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&iosb,
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&fpli,
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sizeof (fpli),
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FilePipeLocalInformation))
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{
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/* If NtQueryInformationFile fails, optimistically assume the
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pipe is writable. This could happen if we somehow
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inherit a pipe that doesn't permit FILE_READ_ATTRIBUTES
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access on the write end. */
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select_printf ("fd %d, %s, NtQueryInformationFile failed",
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fd, fh->get_name ());
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res = writing ? true : -1;
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}
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else if (!writing)
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{
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res = !!fpli.ReadDataAvailable;
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select_printf ("fd %d, %s, read avail %u", fd, fh->get_name (), fpli.ReadDataAvailable);
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}
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else
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{
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/* If there is anything available in the pipe buffer then signal
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that. This means that a pipe could still block since you could
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be trying to write more to the pipe than is available in the
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buffer but that is the hazard of select(). */
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if ((fpli.WriteQuotaAvailable = (fpli.OutboundQuota - fpli.ReadDataAvailable)))
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{
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select_printf ("fd %d, %s, write: size %lu, avail %lu", fd,
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fh->get_name (), fpli.OutboundQuota,
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fpli.WriteQuotaAvailable);
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res = true;
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}
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/* If we somehow inherit a tiny pipe (size < PIPE_BUF), then consider
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the pipe writable only if it is completely empty, to minimize the
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probability that a subsequent write will block. */
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else if (fpli.OutboundQuota < PIPE_BUF &&
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fpli.WriteQuotaAvailable == fpli.OutboundQuota)
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{
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select_printf ("fd, %s, write tiny pipe: size %lu, avail %lu",
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fd, fh->get_name (), fpli.OutboundQuota,
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fpli.WriteQuotaAvailable);
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res = true;
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}
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}
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return res;
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}
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static int
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peek_pipe (select_record *s, bool from_select)
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{
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HANDLE h;
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set_handle_or_return_if_not_open (h, s);
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int n = 0;
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int gotone = 0;
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fhandler_base *fh = (fhandler_base *) s->fh;
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/* Don't check if this is a non-blocking fd and I/O is still active.
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That could give a false-positive with peek_pipe and friends. */
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if (fh->has_ongoing_io ())
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return 0;
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/* Don't perform complicated tests if we don't need to. */
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if (!s->read_selected && !s->except_selected)
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goto out;
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if (s->read_selected)
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DWORD dev = fh->get_device ();
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if (s->read_selected && dev != FH_PIPEW)
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{
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if (s->read_ready)
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{
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@ -524,106 +569,37 @@ peek_pipe (select_record *s, bool from_select)
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gotone = s->read_ready = true;
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goto out;
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}
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}
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int n = pipe_data_available (s->fd, fh, h, false);
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if (fh->get_device () == FH_PIPEW)
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select_printf ("%s, select for read/except on write end of pipe",
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fh->get_name ());
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else if (!PeekNamedPipe (h, NULL, 0, NULL, (DWORD *) &n, NULL))
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switch (GetLastError ())
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{
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case ERROR_BAD_PIPE:
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case ERROR_PIPE_BUSY:
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case ERROR_NO_DATA:
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case ERROR_PIPE_NOT_CONNECTED:
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n = 0;
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break;
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default:
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select_printf ("%s, PeekNamedPipe failed, %E", fh->get_name ());
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n = -1;
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break;
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}
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if (n < 0)
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{
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select_printf ("%s, n %d", fh->get_name (), n);
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if (s->except_selected)
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gotone += s->except_ready = true;
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if (s->read_selected)
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gotone += s->read_ready = true;
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}
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if (n > 0 && s->read_selected)
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{
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select_printf ("%s, ready for read: avail %d", fh->get_name (), n);
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gotone += s->read_ready = true;
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}
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if (!gotone && s->fh->hit_eof ())
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{
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select_printf ("%s, saw EOF", fh->get_name ());
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if (s->except_selected)
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gotone += s->except_ready = true;
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if (s->read_selected)
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gotone += s->read_ready = true;
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if (n < 0)
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{
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select_printf ("read: %s, n %d", fh->get_name (), n);
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if (s->except_selected)
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gotone += s->except_ready = true;
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if (s->read_selected)
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gotone += s->read_ready = true;
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}
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else if (n > 0)
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{
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select_printf ("read: %s, ready for read: avail %d", fh->get_name (), n);
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gotone += s->read_ready = true;
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}
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if (!gotone && s->fh->hit_eof ())
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{
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select_printf ("read: %s, saw EOF", fh->get_name ());
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if (s->except_selected)
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gotone += s->except_ready = true;
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if (s->read_selected)
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gotone += s->read_ready = true;
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}
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}
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out:
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if (s->write_selected)
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if (s->write_selected && dev != FH_PIPER)
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{
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if (s->write_ready)
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{
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select_printf ("%s, already ready for write", fh->get_name ());
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gotone++;
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}
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/* Do we need to do anything about SIGTTOU here? */
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else if (fh->get_device () == FH_PIPER)
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select_printf ("%s, select for write on read end of pipe",
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fh->get_name ());
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else
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{
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IO_STATUS_BLOCK iosb = {0};
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FILE_PIPE_LOCAL_INFORMATION fpli = {0};
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if (NtQueryInformationFile (h,
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&iosb,
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&fpli,
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sizeof (fpli),
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FilePipeLocalInformation))
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{
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/* If NtQueryInformationFile fails, optimistically assume the
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pipe is writable. This could happen if we somehow
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inherit a pipe that doesn't permit FILE_READ_ATTRIBUTES
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access on the write end. */
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select_printf ("%s, NtQueryInformationFile failed",
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fh->get_name ());
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gotone += s->write_ready = true;
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}
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/* If there is anything available in the pipe buffer then signal
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that. This means that a pipe could still block since you could
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be trying to write more to the pipe than is available in the
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buffer but that is the hazard of select(). */
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else if ((fpli.WriteQuotaAvailable = (fpli.OutboundQuota - fpli.ReadDataAvailable)))
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{
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select_printf ("%s, ready for write: size %lu, avail %lu",
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fh->get_name (),
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fpli.OutboundQuota,
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fpli.WriteQuotaAvailable);
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gotone += s->write_ready = true;
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}
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/* If we somehow inherit a tiny pipe (size < PIPE_BUF), then consider
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the pipe writable only if it is completely empty, to minimize the
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probability that a subsequent write will block. */
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else if (fpli.OutboundQuota < PIPE_BUF &&
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fpli.WriteQuotaAvailable == fpli.OutboundQuota)
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{
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select_printf ("%s, tiny pipe: size %lu, avail %lu",
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fh->get_name (),
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fpli.OutboundQuota,
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fpli.WriteQuotaAvailable);
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gotone += s->write_ready = true;
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}
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}
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gotone += s->write_ready = pipe_data_available (s->fd, fh, h, true);
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select_printf ("write: %s, gotone %d", fh->get_name (), gotone);
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}
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return gotone;
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}
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