xref: /openbsd-src/lib/libc/termios/tcsetattr.3 (revision 73be947e61bb3531e84a5f9836a6c50da1c8011d)

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.Dd $Mdocdate: January 12 2023 $
.Dt TCSETATTR 3
.Os
.Sh NAME
.Nm cfgetispeed ,
.Nm cfsetispeed ,
.Nm cfgetospeed ,
.Nm cfsetospeed ,
.Nm cfsetspeed ,
.Nm cfmakeraw ,
.Nm tcgetattr ,
.Nm tcsetattr
.Nd manipulating the termios structure
.Sh SYNOPSIS
.In termios.h
.Ft speed_t
.Fn cfgetispeed "const struct termios *tp"
.Ft int
.Fn cfsetispeed "struct termios *tp" "speed_t speed"
.Ft speed_t
.Fn cfgetospeed "const struct termios *tp"
.Ft int
.Fn cfsetospeed "struct termios *tp" "speed_t speed"
.Ft int
.Fn cfsetspeed "struct termios *tp" "speed_t speed"
.Ft void
.Fn cfmakeraw "struct termios *tp"
.Ft int
.Fn tcgetattr "int fd" "struct termios *tp"
.Ft int
.Fn tcsetattr "int fd" "int action" "const struct termios *tp"
.Sh DESCRIPTION
The
.Fn cfmakeraw ,
.Fn tcgetattr ,
and
.Fn tcsetattr
functions are provided for getting and setting the
.Vt termios
structure.
.Pp
The
.Fn cfgetispeed ,
.Fn cfsetispeed ,
.Fn cfgetospeed ,
.Fn cfsetospeed ,
and
.Fn cfsetspeed
functions are provided for getting and setting the baud rate values in
the
.Vt termios
structure.
The effects of the functions on the terminal as described below
do not become effective, nor are all errors detected, until the
.Fn tcsetattr
function is called.
Certain values for baud rates set in the
.Vt termios
structure and passed to
.Fn tcsetattr
have special meanings.
These are discussed in the portion of the manual page that describes the
.Fn tcsetattr
function.
.Sh GETTING AND SETTING THE BAUD RATE
The input and output baud rates are found in the
.Vt termios
structure.
The unsigned integer
.Vt speed_t
is typedef'd in the include file
.In termios.h .
On
.Ox ,
the value of the integer corresponds directly to the baud rate being
represented.
However, this is not true of all systems and new code should use the
symbolic value for maximum portability.
.Bd -literal -offset indent
#define B0	0
#define B50	50
#define B75	75
#define B110	110
#define B134	134
#define B150	150
#define B200	200
#define B300	300
#define B600	600
#define B1200	1200
#define	B1800	1800
#define B2400	2400
#define B4800	4800
#define B9600	9600
#define B19200	19200
#define B38400	38400
#ifndef _POSIX_SOURCE
#define EXTA	19200
#define EXTB	38400
#endif  /*_POSIX_SOURCE */
.Ed
.Pp
The
.Fn cfgetispeed
function returns the input baud rate in the
.Vt termios
structure referenced by
.Fa tp .
.Pp
The
.Fn cfsetispeed
function sets the input baud rate in the
.Vt termios
structure referenced by
.Fa tp
to
.Fa speed .
.Pp
The
.Fn cfgetospeed
function returns the output baud rate in the
.Vt termios
structure referenced by
.Fa tp .
.Pp
The
.Fn cfsetospeed
function sets the output baud rate in the
.Vt termios
structure referenced by
.Fa tp
to
.Fa speed .
.Pp
The
.Fn cfsetspeed
function sets both the input and output baud rate in the
.Vt termios
structure referenced by
.Fa tp
to
.Fa speed .
.Pp
Upon successful completion, the functions
.Fn cfsetispeed ,
.Fn cfsetospeed ,
and
.Fn cfsetspeed
return a value of 0.
Otherwise, a value of \-1 is returned and the global variable
.Va errno
is set to indicate the error.
.Sh GETTING AND SETTING THE TERMIOS STATE
This section describes the functions that are used to control the general
terminal interface.
Unless otherwise noted for a specific command, these functions are restricted
from use by background processes.
Attempts to perform these operations shall cause the process group to be sent
a
.Dv SIGTTOU
signal.
If the calling process is blocking or ignoring
.Dv SIGTTOU
signals, the process
is allowed to perform the operation and the
.Dv SIGTTOU
signal is not sent.
.Pp
In all the functions, although
.Fa fd
is an open file descriptor, the functions affect the underlying terminal
file, not just the open file description associated with the particular
file descriptor.
.Pp
The
.Fn cfmakeraw
function sets the flags stored in the
.Vt termios
structure to a state disabling
all input and output processing, giving a
.Dq raw I/O path .
It should be noted that there is no function to reverse this effect.
This is because there are a variety of processing options that could be
re-enabled and the correct method is for an application to snapshot the
current terminal state using the function
.Fn tcgetattr ,
setting raw mode with
.Fn cfmakeraw
and the subsequent
.Fn tcsetattr ,
and then using another
.Fn tcsetattr
with the saved state to revert to the previous terminal state.
.Pp
The
.Fn tcgetattr
function copies the parameters associated with the terminal referenced
by
.Fa fd
in the
.Vt termios
structure referenced by
.Fa tp .
This function is allowed from a background process, although the terminal
attributes may be subsequently changed by a foreground process.
.Pp
The
.Fn tcsetattr
function sets the parameters associated with the terminal from the
.Vt termios
structure referenced by
.Fa tp .
The
.Fa action
field is created by
.Tn OR Ns 'ing
the following values, as specified in the include file
.In termios.h .
.Bl -tag -width "TCSADRAIN"
.It Dv TCSANOW
The change occurs immediately.
.It Dv TCSADRAIN
The change occurs after all output written to
.Fa fd
has been transmitted to the terminal.
This value of
.Fa action
should be used when changing parameters that affect output.
.It Dv TCSAFLUSH
The change occurs after all output written to
.Fa fd
has been transmitted to the terminal.
Additionally, any input that has been received but not read is discarded.
.It Dv TCSASOFT
If this value is
.Tn OR Ns 'ed
into the
.Fa action
value, the values of the
.Fa c_cflag ,
.Fa c_ispeed ,
and
.Fa c_ospeed
fields are ignored.
.El
.Pp
The 0 baud rate is used to terminate the connection.
If 0 is specified as the output speed to the function
.Fn tcsetattr ,
modem control will no longer be asserted on the terminal, disconnecting
the terminal.
.Pp
If zero is specified as the input speed to the function
.Fn tcsetattr ,
the input baud rate will be set to the same value as that specified by
the output baud rate.
.Sh RETURN VALUES
If
.Fn tcsetattr
is unable to make any of the requested changes, it returns \-1 and
sets
.Va errno .
Otherwise, it makes all of the requested changes it can.
If the specified input and output baud rates differ and are a combination
that is not supported, neither baud rate is changed.
.Sh ERRORS
Upon successful completion, the functions
.Fn tcgetattr
and
.Fn tcsetattr
return a value of 0.
Otherwise, they
return \-1 and the global variable
.Va errno
is set to indicate the error, as follows:
.Bl -tag -width Er
.It Bq Er EBADF
The
.Fa fd
argument to
.Fn tcgetattr
or
.Fn tcsetattr
was not a valid file descriptor.
.It Bq Er EINTR
The
.Fn tcsetattr
function was interrupted by a signal.
.It Bq Er EINVAL
The
.Fa action
argument to the
.Fn tcsetattr
function was not valid, or an attempt was made to change an attribute
represented in the
.Vt termios
structure to an unsupported value.
.It Bq Er ENOTTY
The file associated with the
.Fa fd
argument to
.Fn tcgetattr
or
.Fn tcsetattr
is not a terminal.
.El
.Sh SEE ALSO
.Xr tcsendbreak 3 ,
.Xr termios 4
.Sh STANDARDS
The
.Fn cfgetispeed ,
.Fn cfsetispeed ,
.Fn cfgetospeed ,
.Fn cfsetospeed ,
.Fn tcgetattr ,
and
.Fn tcsetattr
functions are compliant with the
.St -p1003.1-88
specification.
The
.Fn cfmakeraw
and
.Fn cfsetspeed
functions,
as well as the
.Dv TCSASOFT
option to the
.Fn tcsetattr
function are extensions to the
.St -p1003.1-88
specification.