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Diffstat (limited to 'usr.bin/window/README')
| -rw-r--r-- | usr.bin/window/README | 199 |
1 files changed, 199 insertions, 0 deletions
diff --git a/usr.bin/window/README b/usr.bin/window/README new file mode 100644 index 0000000..42d45b3 --- /dev/null +++ b/usr.bin/window/README @@ -0,0 +1,199 @@ +/*- + * Copyright (c) 1990, 1993 + * The Regents of the University of California. All rights reserved. + * + * This code is derived from software contributed to Berkeley by + * Edward Wang at The University of California, Berkeley. + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions + * are met: + * 1. Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * 2. Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in the + * documentation and/or other materials provided with the distribution. + * 3. All advertising materials mentioning features or use of this software + * must display the following acknowledgement: + * This product includes software developed by the University of + * California, Berkeley and its contributors. + * 4. Neither the name of the University nor the names of its contributors + * may be used to endorse or promote products derived from this software + * without specific prior written permission. + * + * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND + * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE + * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE + * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE + * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL + * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS + * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) + * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT + * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY + * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF + * SUCH DAMAGE. + * + * @(#)README 8.1 (Berkeley) 6/6/93 + */ + +Compilation notes: + + Compiler options: + + BYTE_ORDER (used only in ww.h) + It should already be defined in machine/endian.h. + The code knows about BIG_ENDIAN, LITTLE_ENDIAN, and PDP_ENDIAN. + It only cares about byte order in words, so PDP_ENDIAN + is the same as LITTLE_ENDIAN. + OLD_TTY + If you don't have Posix termios, then define this. + VMIN_BUG + Even if you have Posix termios, define this if the MIN and TIME + feature in noncanonical mode doesn't work correctly. + + Ok, there's another one, STR_DEBUG. It turns on consistency checks + in the string allocator. It's been left on since performace doesn't + seem to suffer. There's an abort() somewhere when an inconsistency + is found. It hasn't happened in years. + + The file local.h contains locally tunable constants. + + The makefile used to be updated with mkmf; it has been changed +at various times to use cpp -M and, currently, mkdep. The only library +it needs is termcap. + + Window, as is, only runs on 4.3 (or later) machines. + + On 4.2 machines, at least these modifications must be done: + + delete uses of window size ioctls: TIOCGWINSZ, TIOCSWINSZ, + struct winsize + add to ww.h + typedef int fd_set; + #define FD_ZERO(s) (*(s) = 0) + #define FD_SET(b, s) (*(s) |= 1 << (b)) + #define FD_ISSET(b, s) (*(s) & 1 << (b)) + add to ww.h + #define sigmask(s) (1 << (s) - 1) + + +A few notes about the internals: + + The window package. Windows are opened by calling wwopen(). +Wwwrite() is the primitive for writing to windows. Wwputc(), wwputs(), +and wwprintf() are also supported. Some of the outputs to windows are +delayed. Wwupdate() updates the terminal to match the internal screen +buffer. Wwspawn() spawns a child process on the other end of a window, +with its environment tailored to the window. Visible windows are +doubly linked in the order of their overlap. Wwadd() inserts a window +into the list at a given place. Wwdelete() deletes it. Windows not in +the list are not visible, though wwwrite() still works. Window was +written before the days of X and Sunview, so some of the terminology +is not standard. + + Most functions return -1 on error. Wwopen() returns the null +pointer. An error number is saved in wwerrno. Wwerror() returns an +error string based on wwerrno suitable for printing. + + The terminal drivers perform all output to the physical terminal, +including special functions like character and line insertion and +deletion. The window package keeps a list of known terminals. At +initialization time, the terminal type is matched against the list to +find the right terminal driver to use. The last driver, the generic +driver, matches all terminals and uses the termcap database. The +interface between the window package the terminal driver is the `tt' +structure. It contains pointers to functions to perform special +functions and terminal output, as well as flags about the +characteristics of the terminal. Most of these ideas are borrowed +from the Maryland window package, which in turn is based on Goslin's +Emacs. + + The IO system is semi-synchronous. Terminal input is signal +driven, and everything else is done synchronously with a single +select(). It is roughly event-driven, though not in a clean way. + + Normally, in both conversation mode and command mode, window +sleeps in a select() in wwiomux() waiting for data from the +pseudo-terminals. At the same time, terminal input causes SIGIO which +is caught by wwrint(). The select() returns when at least one of the +pseudo-terminals becomes ready for reading. + + Wwrint() is the interrupt handler for tty input. It reads input +into a linear buffer accessed through four pointers: + + +-------+--------------+----------------+ + | empty | data | empty | + +-------+--------------+----------------+ + ^ ^ ^ ^ + | | | | + wwib wwibp wwibq wwibe + +Wwrint() appends characters at the end and increments wwibq (*wwibq++ += c), and characters are taken off the buffer at wwibp using the +wwgetc() and wwpeekc() macros. As is the convention in C, wwibq +and wwibe point to one position beyond the end. In addition, +wwrint() will do a longjmp(wwjmpbuf) if wwsetjmp is true. This is +used by wwiomux() to interrupt the select() which would otherwise +resume after the interrupt. (Actually, I hear this is not true, +but the longjmp feature is used to avoid a race condition as well. +Anyway, it means I didn't have to depend on a feature in a +daily-changing kernel, but that's another story.) The macro +wwinterrupt() returns true if the input buffer is non-empty. +Wwupdate(), wwwrite(), and wwiomux() check this condition and will +return at the first convenient opportunity when it becomes true. +In the case of wwwrite(), the flag ww_nointr in the window structure +overrides this. This feature allows the user to interrupt lengthy +outputs safely. The structure of the input buffer is designed to +avoid race conditions without blocking interrupts. + + Actually, wwsetjmp and wwinterrupt() are part of a software +interrupt scheme used by the two interrupt catchers wwrint() and +wwchild(). Asserting the interrupt lets the synchronous parts of +the program know that there's an interesting asynchronous condition +(i.e., got a keyboard character, or a child process died) that they +might want to process before anything else. The synchronous routines +can check for this condition with wwinterrupt() or by arranging +that a longjmp() be done. + + Wwiomux() copies pseudo-terminal output into their corresponding +windows. Without anything to do, it blocks in a select(), waiting for +read ready on pseudo-terminals. Reads are done into per-window buffers +in the window structures. When there is at least one buffer non-empty, +wwiomux() finds the top most of these windows and writes it using +wwwrite(). Then the process is repeated. A non-blocking select() is +done after a wwwrite() to pick up any output that may have come in +during the write, which may take a long time. Specifically, we use +this to stop output or flush buffer when a pseudo-terminal tells us to +(we use pty packet mode). The select() blocks only when all of the +windows' buffers are empty. A wwupdate() is done prior to this, which +is the only time the screen is guaranteed to be completely up to date. +Wwiomux() loops until wwinterrupt() becomes true. + + The top level routine for all this is mloop(). In conversation +mode, it simply calls wwiomux(), which only returns when input is +available. The input buffer is then written to the pseudo-terminal of +the current window. If the escape character is found in the input, +command mode is entered. Otherwise, the process is repeated. In +command mode, control is transferred to docmd() which returns only when +conversation mode is reentered. Docmd() and other command processing +routines typically wait for input in a loop: + + while (wwpeekc() < 0) + wwiomux(); + +When the loop terminates, wwgetc() is used to read the input buffer. + + Output to the physical terminal is handled by the lowest level +routines of the window package, in the files ttoutput.c and tt.h. The +standard IO package is not used, to get better control over buffering +and to use non-blocking reads in wwrint(). The buffer size is set to +approximately one second of output time, based on the baudrate. + + The result of all this complexity is faster response time, +especially in output stopping and flushing. Wwwrite() checks +wwinterrupt() after every line. It also calls wwupdate() for each line +it writes. The output buffer is limited to one second of output time. +Thus, there is usually only a delay of one to two lines plus one second +after a ^C or ^S. Also, commands that produce lengthy output can be +aborted without actually showing all of it on the terminal. (Try the +'?' command followed by escape immediately.) |
