tcdrain

Synopsis

#include <termios.h>

int tcdrain(int fildes);

Status

Partially implemented

Conformance

IEEE Std 1003.1-2017

Description

The tcdrain() function shall block until all output written to the object referred to by fildes is transmitted. The fildes argument is an open file descriptor associated with a terminal.

Any attempts to use tcdrain() from a process which is a member of a background process group on a fildes associated with its controlling terminal, shall cause the process group to be sent a SIGTTOU signal. If the calling thread is blocking SIGTTOU signals or the process is ignoring SIGTTOU signals, the process shall be allowed to perform the operation, and no signal is sent.

Return value

Upon successful completion, 0 shall be returned. Otherwise, -1 shall be returned and errno set to indicate the error.

Errors

The tcdrain() function shall fail if:

  • EBADF - The fildes argument is not a valid file descriptor.

  • EINTR - A signal interrupted tcdrain().

  • EIO - The process group of the writing process is orphaned, the calling thread is not blocking SIGTTOU, and the process is not ignoring SIGTTOU.

  • ENOTTY - The file associated with fildes is not a terminal.

  • EINVAL - The file associated with fildes is not a terminal, and the server handling it reports unsupported requests with EINVAL (see POSIX deviations).

POSIX deviations

If the file associated with fildes is not a terminal, the error reported by tcdrain() depends on the server handling the file. The function is implemented on top of ioctl(), and the kernel forwards every request to the server without checking the type of the file. Servers that do not handle terminal requests report them either with ENOTTY (for example files in jffs2) or with EINVAL (for example pipes and files in dummyfs).