termios.4

早期freebsd实现

process group for which the terminal is the controlling
terminal.  If
.Dv ISIG
is set, the
.Dv INTR
character is
discarded when processed.
.It Dv QUIT
Special character on input and is recognized if the
.Dv ISIG
flag is enabled.  Generates a
.Dv SIGQUIT
signal which is
sent to all processes in the foreground process group
for which the terminal is the controlling terminal.  If
.Dv ISIG
is set, the
.Dv QUIT
character is discarded when
processed.
.It Dv ERASE
Special character on input and is recognized if the
.Dv ICANON
flag is set.  Erases the last character in the
current line; see
.Sx "Canonical Mode Input Processing" .
It does not erase beyond
the start of a line, as delimited by an
.Dv NL ,
.Dv EOF ,
or
.Dv EOL
character.  If
.Dv ICANON
is set, the
.Dv ERASE
character is
discarded when processed.
.It Dv KILL
Special character on input and is recognized if the
.Dv ICANON
flag is set.  Deletes the entire line, as
delimited by a
.Dv NL ,
.Dv EOF ,
or
.Dv EOL
character.  If
.Dv ICANON
is set, the
.Dv KILL
character is discarded when processed.
.It Dv EOF
Special character on input and is recognized if the
.Dv ICANON
flag is set.  When received, all the bytes
waiting to be read are immediately passed to the
process, without waiting for a newline, and the
.Dv EOF
is discarded.  Thus, if there are no bytes waiting (that
is, the
.Dv EOF
occurred at the beginning of a line), a byte
count of zero is returned from the read(),
representing an end-of-file indication.  If
.Dv ICANON
is
set, the
.Dv EOF
character is discarded when processed.
.Dv NL
Special character on input and is recognized if the
.Dv ICANON
flag is set.  It is the line delimiter
.Ql \&\en .
.It Dv EOL
Special character on input and is recognized if the
.Dv ICANON
flag is set.  Is an additional line delimiter,
like
.Dv NL .
.It Dv SUSP
If the
.Dv ISIG
flag is enabled, receipt of the
.Dv SUSP
character causes a
.Dv SIGTSTP
signal to be sent to all processes in the
foreground process group for which the terminal is the
controlling terminal, and the
.Dv SUSP
character is
discarded when processed.
.It Dv STOP
Special character on both input and output and is
recognized if the
.Dv IXON
(output control) or
.Dv IXOFF
(input
control) flag is set.  Can be used to temporarily
suspend output.  It is useful with fast terminals to
prevent output from disappearing before it can be read.
If
.Dv IXON
is set, the
.Dv STOP
character is discarded when
processed.
.It Dv START
Special character on both input and output and is
recognized if the
.Dv IXON
(output control) or
.Dv IXOFF
(input
control) flag is set.  Can be used to resume output that
has been suspended by a
.Dv STOP
character.  If
.Dv IXON
is set, the
.Dv START
character is discarded when processed.
.Dv CR
Special character on input and is recognized if the
.Dv ICANON
flag is set; it is the
.Ql \&\er ,
as denoted in the
.Tn \&C
Standard {2}.  When
.Dv ICANON
and
.Dv ICRNL
are set and
.Dv IGNCR
is not set, this character is translated into a
.Dv NL ,
and
has the same effect as a
.Dv NL
character.
.El
.Pp
The following special characters are extensions defined by this
system and are not a part of 1003.1 termios.
.Bl -tag -width indent
.It Dv EOL2
Secondary
.Dv EOL
character.  Same function as
.Dv EOL.
.It Dv WERASE
Special character on input and is recognized if the
.Dv ICANON
flag is set.  Erases the last word in the current
line according to one of two algorithms.  If the
.Dv ALTWERASE
flag is not set, first any preceding whitespace is
erased, and then the maximal sequence of non-whitespace
characters.  If
.Dv ALTWERASE
is set, first any preceding
whitespace is erased, and then the maximal sequence
of alphabetic/underscores or non alphabetic/underscores.
As a special case in this second algorithm, the first previous
non-whitespace character is skipped in determining
whether the preceding word is a sequence of
alphabetic/undercores.  This sounds confusing but turns
out to be quite practical.
.It Dv REPRINT
Special character on input and is recognized if the
.Dv ICANON
flag is set.  Causes the current input edit line
to be retyped.
.It Dv DSUSP
Has similar actions to the
.Dv SUSP
character, except that
the
.Dv SIGTSTP
signal is delivered when one of the processes
in the foreground process group issues a read() to the
controlling terminal.
.It Dv LNEXT
Special character on input and is recognized if the
.Dv IEXTEN
flag is set.  Receipt of this character causes the next
character to be taken literally.
.It Dv DISCARD
Special character on input and is recognized if the
.Dv IEXTEN
flag is set.  Receipt of this character toggles the flushing
of terminal output.
.It Dv STATUS
Special character on input and is recognized if the
.Dv ICANON
flag is set.  Receipt of this character causes a
.Dv SIGINFO
signal to be sent to the foreground process group of the
terminal.  Also, if the
.Dv NOKERNINFO
flag is not set, it
causes the kernel to write a status message to the terminal
that displays the current load average, the name of the
command in the foreground, its process ID, the symbolic
wait channel, the number of user and system seconds used,
the percentage of cpu the process is getting, and the resident
set size of the process.
.El
.Pp
The
.Dv NL
and
.Dv CR
characters cannot be changed.
The values for all the remaining characters can be set and are
described later in the document under
Special Control Characters.
.Pp
Special
character functions associated with changeable special control characters
can be disabled individually by setting their value to
.Dv {_POSIX_VDISABLE};
see
.Sx "Special Control Characters" .
.Pp
If two or more special characters have the same value, the function
performed when that character is received is undefined.
.Ss Modem Disconnect
If a modem disconnect is detected by the terminal interface for a
controlling terminal, and if
.Dv CLOCAL
is not set in the
.Fa c_cflag
field for
the terminal, the
.Dv SIGHUP
signal is sent to the controlling
process associated with the terminal.  Unless other arrangements have
been made, this causes the controlling process to terminate.
Any subsequent call to the read() function returns the value zero,
indicating end of file.  Thus, processes that read a terminal
file and test for end-of-file can terminate appropriately after a
disconnect.
.\" If the
.\" .Er EIO
.\" condition specified in 6.1.1.4 that applies
.\" when the implementation supports job control also exists, it is
.\" unspecified whether the
.\" .Dv EOF
.\" condition or the
.\" .Pf [ Dv EIO
.\" ] is returned.
Any
subsequent write() to the terminal device returns -1, with
.Va errno
set to
.Er EIO ,
until the device is closed.
.Sh General Terminal Interface
.Pp
.Ss Closing a Terminal Device File
The last process to close a terminal device file causes any output
to be sent to the device and any input to be discarded.  Then, if
.Dv HUPCL
is set in the control modes, and the communications port supports a
disconnect function, the terminal device performs a disconnect.
.Ss Parameters That Can Be Set
Routines that need to control certain terminal
.Tn I/O
characteristics
do so by using the termios structure as defined in the header
.Aq Pa termios.h .
This structure contains minimally four scalar elements of bit flags
and one array of special characters.  The scalar flag elements are
named:
.Fa c_iflag ,
.Fa c_oflag ,
.Fa c_cflag ,
and
.Fa c_lflag .
The character array is named
.Fa c_cc ,
and its maximum index is
.Dv NCCS .
.Ss Input Modes
Values of the
.Fa c_iflag
field describe the basic
terminal input control, and are composed of
following masks:
.Pp
.Bl -tag -width IMAXBEL -offset indent -compact
.It Dv IGNBRK
/* ignore BREAK condition */
.It Dv BRKINT
/* map BREAK to SIGINTR */
.It Dv IGNPAR
/* ignore (discard) parity errors */
.It Dv PARMRK
/* mark parity and framing errors */
.It Dv INPCK
/* enable checking of parity errors */
.It Dv ISTRIP
/* strip 8th bit off chars */
.It Dv INLCR
/* map NL into CR */
.It Dv IGNCR
/* ignore CR */
.It Dv ICRNL
/* map CR to NL (ala CRMOD) */
.It Dv IXON
/* enable output flow control */
.It Dv IXOFF
/* enable input flow control */
.It Dv IXANY
/* any char will restart after stop */
.It Dv IMAXBEL
/* ring bell on input queue full */
.El
.Pp
In the context of asynchronous serial data transmission, a break
condition is defined as a sequence of zero-valued bits that continues for
more than the time to send one byte.  The entire sequence of zero-valued
bits is interpreted as a single break condition, even if it continues for
a time equivalent to more than one byte.  In contexts other than
asynchronous serial data transmission the definition of a break condition
is implementation defined.
.Pp
If
.Dv IGNBRK
is set, a break condition detected on input is ignored, that
is, not put on the input queue and therefore not read by any process.  If
.Dv IGNBRK
is not set and
.Dv BRKINT
is set, the break condition flushes the
input and output queues and if the terminal is the controlling terminal
of a foreground process group, the break condition generates a
single
.Dv SIGINT
signal to that foreground process group.  If neither
.Dv IGNBRK
nor
.Dv BRKINT
is set, a break condition is read as a single
.Ql \&\e0 ,
or if
.Dv PARMRK
is set, as
.Ql \&\e377 ,
.Ql \&\e0 ,
.Ql \&\e0 .
.Pp
If
.Dv IGNPAR
is set, a byte with a framing or parity error (other than
break) is ignored.
.Pp
If
.Dv PARMRK
is set, and
.Dv IGNPAR
is not set, a byte with a framing or parity
error (other than break) is given to the application as the
three-character sequence
.Ql \&\e377 ,
.Ql \&\e0 ,
X, where
.Ql \&\e377 ,
.Ql \&\e0
is a two-character
flag preceding each sequence and X is the data of the character received
in error.  To avoid ambiguity in this case, if
.Dv ISTRIP
is not set, a valid
character of
.Ql \&\e377
is given to the application as
.Ql \&\e377 ,
.Ql \&\e377 .
If
neither
.Dv PARMRK
nor
.Dv IGNPAR
is set, a framing or parity error (other than
break) is given to the application as a single character
.Ql \&\e0 .
.Pp
If
.Dv INPCK
is set, input parity checking is enabled.  If
.Dv INPCK
is not set,
input parity checking is disabled, allowing output parity generation
without input parity errors.  Note that whether input parity checking is
enabled or disabled is independent of whether parity detection is enabled
or disabled (see
.Sx "Control Modes" ) .
If parity detection is enabled but input
parity checking is disabled, the hardware to which the terminal is
connected recognizes the parity bit, but the terminal special file
does not check whether this bit is set correctly or not.
.Pp
If
.Dv ISTRIP
is set, valid input bytes are first stripped to seven bits,
otherwise all eight bits are processed.
.Pp
If
.Dv INLCR
is set, a received
.Dv NL
character is translated into a
.Dv CR
character.  If
.Dv IGNCR
is set, a received
.Dv CR
character is ignored (not
read).  If
.Dv IGNCR
is not set and
.Dv ICRNL
is set, a received
.Dv CR
character is
translated into a
.Dv NL
character.
.Pp
If
.Dv IXON
is set, start/stop output control is enabled.  A received
.Dv STOP
character suspends output and a received
.Dv START
character
restarts output. If
.Dv IXANY
is also set, then any character may
restart output. When
.Dv IXON
is set,
.Dv START
and
.Dv STOP
characters are not
read, but merely perform flow control functions.  When
.Dv IXON
is not set,
the
.Dv START
and
.Dv STOP
characters are read.
.Pp
If
.Dv IXOFF
is set, start/stop input control is enabled.  The system shall
transmit one or more
.Dv STOP
characters, which are intended to cause the
terminal device to stop transmitting data, as needed to prevent the input
queue from overflowing and causing the undefined behavior described in
.Sx "Input Processing and Reading Data" ,
and shall transmit one or more