termio.4

来自「<B>Digital的Unix操作系统VAX 4.2源码</B>」· 4 代码 · 共 729 行 · 第 1/2 页

.TH termio 4
.SH Name
termio \- System V terminal interface
.SH Description
.PP
This section specificly describes the System V terminal
interface.
A general description of the available terminal interfaces
is provided in
.MS tty 4 .
.PP
When a terminal file is opened,
it normally causes
the process to wait until a connection is established.
In practice, users' programs seldom open these
files; they are opened by
.PN getty
and become a user's
standard input, output, and error files.
The very first terminal file opened
by the process group leader of a terminal
file not already associated with a process group
becomes the
.I control terminal
for that process group.
The control terminal plays a special
role in handling quit and interrupt signals, as discussed
later.
The control terminal is inherited by a child process during a
.MS fork 2 .
A process can break this association by changing its
process group using
.MS setpgrp 2 .
.PP
A terminal associated with one of these files ordinarily
operates in full-duplex mode.
Characters can be typed at any time,
even while output is occurring.  They are only lost when the
system's character input buffers become completely
full, which is rare,
or when the user has accumulated the maximum allowed number of
input characters that have not yet been read by some program.
Currently, this limit is (MAX_INPUT) characters,
as defined in
.PN <limits.h> .
When the input limit is reached, all the
saved characters are thrown away without notice.
.PP
Normally, terminal input is processed in units of lines.
A line is delimited by a newline (ASCII LF)
character, an end-of-file (ASCII EOT) character,
or an end-of-line character.
This means that a program attempting
to read is suspended until an entire line has been
typed.
No matter how many characters are requested
in the read call, at most one line will be returned.
It is not, however, necessary to read a whole line at
once; any number of characters can be
requested in a read, even one, without losing information.
.PP
Some characters have special meaning when input.
For example, during input
.I erase
and
.I kill,
processing is normally done.  
The erase character erases the last character typed, except that it will
not erase beyond the beginning of a line.  Typically the 
erase character is the number sign (#).
The kill character kills (deletes) the entire input line, and optionally
outputs a newline character.
The default kill character is the at sign (@).  Both characters operate on a
key-stroke basis, independently of any backspacing or tabbing.
Both the erase and kill characters
can be entered literally by preceding them with
the escape character
.RB ( \e ).
In this case the escape character is not read.
The erase and kill characters can be changed.
.PP
Certain characters have special functions on input.
These functions and their default character values
are summarized as follows:
.TP "\w'START\ \ \ 'u"
.PN INTR
(Rubout or ASCII DEL)
generates an
.I interrupt
signal that is sent to all processes
with the associated control terminal.
Normally, each such process is forced to terminate,
but arrangements can be made either to
ignore the signal or to receive a
trap to an agreed-upon location;
see
.MS signal 3 .
.TP
.PN QUIT
(CTRL/| or ASCII FS)
generates a
.I quit
signal.
Its treatment is identical to the interrupt signal
except that, unless a receiving process has
made other arrangements, it is not only terminated
but a core image file
(called
.BR core )
is created in the current working directory.
.TP
.PN ERASE
The number sign (#) erases the preceding character.
It will not erase beyond the start of a line,
as delimited by an NL, EOF, or EOL character.
.TP
.PN KILL
The at sign (@) deletes the entire line,
as delimited by an NL, EOF, or EOL character.
.TP
.PN EOF
(CTRL/D or ASCII EOT) can
be used to generate an end-of-file
from a terminal.
When received, all the characters
waiting to be read are immediately passed to
the program, without waiting for a newline,
and the EOF is discarded.
Thus, if there are no characters waiting, which
is to say the EOF
occurred at the beginning of a line,
zero characters are passed back,
which is the standard end-of-file indication.
.TP
.PN NL
(ASCII LF) is the normal line delimiter.
It can not be changed or escaped.
.TP
.PN EOL
(ASCII NUL) is an additional line delimiter, like NL.
It is not normally used.
.TP
.PN STOP
(CTRL/S or ASCII DC3)
can be used to temporarily suspend output.
It is useful with CRT
terminals to prevent output from
disappearing before it can be read.
While output is suspended, STOP
characters are ignored and not read.
.TP
.PN START
(CTRL/Q or ASCII DC1)
is used to resume output that has been suspended by a STOP
character.
While output is not suspended, START
characters are ignored and not read.
The START/STOP characters
can not be changed or escaped.
.TP
.PN MIN
Used to control terminal I/O when the ICANON flag is not set in the c_lflag.
Input processing behaves as described in the 
.B "MIN/TIME Interaction"
section that follows.
.TP
.PN TIME
Used to control terminal I/O when the ICANON flag is not set in the c_lflag.
Input processing behaves as described in the 
.B "MIN/TIME Interaction"
section that follows.
.PP
The character values for INTR, QUIT, ERASE, KILL, EOF, MIN, TIME, and
EOL can be changed to suit individual tastes.  The ERASE, KILL, and EOF
characters can be escaped by a preceding backslash (\\) character, in
which case no special function is performed.
.PP
When one or more
characters are written, they are transmitted
to the terminal as soon as previously-written characters
have finished typing.
Input characters are echoed by putting them in the output queue
as they arrive.
If a process produces characters more rapidly than they can be typed,
it is suspended when its output queue exceeds some limit.
When the queue has drained down to some threshold,
the program is resumed.
.PP
When the carrier signal from the data-set drops, a
.I hang-up
signal, SIGHUP, is sent to all processes
that have this terminal
as the control terminal.
Unless other arrangements have been made,
this signal causes the processes to terminate.
If the hang-up signal is ignored, any subsequent read
returns with an end-of-file indication.
Thus, programs that read a terminal and test for
end-of-file can terminate appropriately when
hung up on.
.PP
Several
.MS ioctl 2
system calls apply to terminal files.
The primary calls use the following structure,
defined in 
.PN <termio.h> :
.PP
.ta .6i 1.3i 1.8i 2.6i
.nf
struct	termio {
	unsigned	short	c_iflag;	/\(** input modes \(**/
	unsigned	short	c_oflag;	/\(** output modes \(**/
	unsigned	short	c_cflag;	/\(** control modes \(**/
	unsigned	short	c_lflag;	/\(** local modes \(**/
	char		c_line;		/\(** line discipline \(**/
	unsigned	char	c_cc[\s-1NCC\s+1];	/\(** control chars \(**/
};
.fi
.PP
The special control characters are defined by the array
.IR c_cc .
The initial values
for each function are as follows:
.ta 13n
.nf
VINTR	DEL
VQUIT	FS
VERASE	#
VKILL	@
VEOF	EOT
VEOL	NUL
VMIN	6
VTIME	1
.fi
.PP
The
.I c_iflag
field describes the basic terminal input control:
.PP
.ta 13n
.nf
IGNBRK	Ignore break condition.
BRKINT	Signal interrupt on break.
IGNPAR	Ignore characters with parity errors.
PARMRK	Mark parity errors.
INPCK	Enable input parity check.
ISTRIP	Strip character.
INLCR	Map NL to CR on input.
IGNCR	Ignore CR.
ICRNL	Map CR to NL on input.
IUCLC	Map uppercase to lowercase on input.
IXON	Enable start/stop output control.
IXANY	Enable any character to restart output.
IXOFF	Enable start/stop input control.
.fi
.PP
If IGNBRK is set, the break condition
(a character framing error, with data all zeros)
is ignored, that is, not put on the input queue
and therefore not read by any process.
Otherwise, if BRKINT is set,
the break condition generates an interrupt signal
and flushes both the input and output queues.
If IGNPAR is set,
characters with other framing and parity errors are ignored.
.PP
If PARMRK is set, a character with
a framing or parity error that is not ignored
is read as the three-character sequence:
0377, 0, X,
where X is the data of the character received in error.
To avoid ambiguity in this case,
if ISTRIP is not set,
a valid character of 0377 is read as 0377, 0377.
If PARMRK is not set,
a framing or parity error that is not ignored
is read as the character NUL (0).
.PP
If INPCK is set,
input parity checking is enabled.
If INPCK is not set,
input parity checking is disabled.
This allows output parity generation, without
input parity errors.
.PP
If ISTRIP is set,
valid input characters are first stripped to seven bits.
Otherwise, all eight bits are processed.
.PP
If INLCR is set, a received NL character is translated into a CR character.
If IGNCR is set, a received CR character is ignored (not read).
Otherwise, if ICRNL is set, a received CR character is translated into a
NL character.
.PP
If IUCLC is set,
a received uppercase letter is translated
into the corresponding lowercase letter.
.PP
If IXON is set, start/stop output control is enabled.  A received STOP
character suspends output and a received START
character restarts output.
All start/stop characters are ignored and not read.
If IXANY is set, any input character restarts output
that has been suspended.
.PP
If IXOFF is set, the system transmits START/STOP
characters when the input queue is
nearly empty/full.
.PP
The initial input control value is
all-bits-clear.
.PP
The
.I c_oflag
field specifies the system treatment of output:
.PP
.ta 13n
.nf
OPOST	Postprocess output.
OLCUC	Map lower case to upper on output.
ONLCR	Map NL to CR-NL on output.
OCRNL	Map CR to NL on output.
ONOCR	No CR output at column 0.
ONLRET	NL performs CR function.
OFILL	Use fill characters for delay.
OFDEL	Fill is DEL or else NUL.
.sp
NLDLY	Select newline delays:
NL0	Newline delay type 0. 
NL1	Newline delay type 1.
.sp
CRDLY	Select carriage-return delays:
CR0	Carriage-return delay type 0. 
CR1	Carriage-return delay type 1.
CR2	Carriage-return delay type 2.
CR3	Carriage-return delay type 3.
.sp
TABDLY	Select horizontal-tab delays:
TAB0	Horizontal-tab delay type 0.
TAB1	Horizontal-tab delay type 1.
TAB2	Horizontal-tab delay type 2.
TAB3	Expand tabs to spaces.
.sp
BSDLY	Select backspace delays:
BS0	Backspace delay type 0.
BS1	Backspace delay type 1.
.sp
VTDLY	Select vertical-tab delays:
VT0	Vertical-tab delay type 0.
VT1	Vertical-tab delay type 1.
.sp
FFDLY	Select form-feed delays:
FF0	Form-feed delay type 0.
FF1	Form-feed delay type 1.
.DT
.fi
.PP
If OPOST is set,
output characters are post-processed
as indicated by the remaining flags,
otherwise characters are transmitted without change.
.PP
If OLCUC is set,
a lowercase letter is transmitted as