tcflow - suspend or restart the transmission or reception of data
int tcflow(int fildes, int action);
The tcflow() function shall suspend or restart transmission or reception of data on the object referred to by fildes, depending on the value of action. The fildes argument is an open file descriptor associated with a terminal.
If action is TCOOFF, output shall be suspended.
If action is TCOON, suspended output shall be restarted.
If action is TCIOFF and fildes refers to a terminal device, the system shall transmit a STOP character, which is intended to cause the terminal device to stop transmitting data to the system. If fildes is associated with a pseudo-terminal, the STOP character need not be transmitted.
If action is TCION and fildes refers to a terminal device, the system shall transmit a START character, which is intended to cause the terminal device to start transmitting data to the system. If fildes is associated with a pseudo-terminal, the START character need not be transmitted.
The default on the opening of a terminal file is that neither its input nor its output are suspended.
Attempts to use tcflow() 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.
Upon successful completion, 0 shall be returned. Otherwise, -1 shall be returned and errno set to indicate the error.
The tcflow() function shall fail if:
- The fildes argument is not a valid file descriptor.
- The action argument is not a supported value.
- The process group of the writing process is orphaned, the calling thread is not blocking SIGTTOU, and the process is not ignoring SIGTTOU.
- The file associated with fildes is not a terminal.
XBD General Terminal Interface, <termios.h>
First released in Issue 3. Included for alignment with the POSIX.1-1988 standard.
The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:
The [EIO] error is added.
SD5-XSH-ERN-190 is applied, clarifying in the DESCRIPTION the transmission of START and STOP characters.
POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0642 , XSH/TC1-2008/0643 , and XSH/TC1-2008/0644  are applied.
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