Commit | Line | Data |
---|---|---|
e08c6f11 KM |
1 | .\" @(#)mpx.2 4.1 (Berkeley) %G% |
2 | .\" | |
3 | .TH MPX 2 | |
4 | .AT 3 | |
5 | .SH NAME | |
6 | mpx \- create and manipulate multiplexed files | |
7 | .SH SYNOPSIS | |
8 | .nf | |
9 | .B mpx(name, access) | |
10 | .B char *name; | |
11 | .PP | |
12 | .B join(fd, xd) | |
13 | .PP | |
14 | .B chan(xd) | |
15 | .PP | |
16 | .B extract(i, xd) | |
17 | .PP | |
18 | .B attach(i, xd) | |
19 | .PP | |
20 | .B detach(i, xd) | |
21 | .PP | |
22 | .B connect(fd, cd, end) | |
23 | .PP | |
24 | .B npgrp(i, xd, pgrp) | |
25 | .PP | |
26 | .B ckill(i, xd, signal) | |
27 | .PP | |
28 | .B #include <sys/mx.h> | |
29 | .B mpxcall(cmd, vec) | |
30 | .B int *vec; | |
31 | .fi | |
32 | .SH DESCRIPTION | |
33 | .PP | |
34 | .B mpxcall(cmd, vec) | |
35 | is the system call shared by the | |
36 | library routines described below. | |
37 | .I Cmd | |
38 | selects a command using values | |
39 | defined in | |
40 | .IR <sys/mx.h> . | |
41 | .I Vec | |
42 | is the address of a | |
43 | structure containing the arguments | |
44 | for the command. | |
45 | .PP | |
46 | .B mpx(name, access) | |
47 | .PP | |
48 | .I Mpx | |
49 | creates and opens the file | |
50 | .I name | |
51 | with access permission | |
52 | .I access | |
53 | (see | |
54 | .IR creat (2)) | |
55 | and returns a file descriptor available for | |
56 | reading and writing. | |
57 | A \-1 is returned if the file cannot be created, | |
58 | if | |
59 | .I name | |
60 | already exists, or | |
61 | if the file table or other operating system | |
62 | data structures are full. | |
63 | The file descriptor is required for use | |
64 | with other routines. | |
65 | .PP | |
66 | If | |
67 | .I name | |
68 | is 0, | |
69 | a file descriptor is returned as described | |
70 | but no entry is created in the file system. | |
71 | .PP | |
72 | Once created an mpx file may be opened | |
73 | (see | |
74 | .IR open (2)) | |
75 | by any process. | |
76 | This provides a form of interprocess communication | |
77 | whereby a process B can `call' process A | |
78 | by opening an mpx file | |
79 | created by A. | |
80 | To B, the file is ordinary with one exception: | |
81 | the | |
82 | .I connect | |
83 | primitive could be applied to it. | |
84 | Otherwise the functions | |
85 | described below are used only in process A | |
86 | and descendants that inherit the open mpx file. | |
87 | .PP | |
88 | When a process opens an mpx file, the owner of the | |
89 | file receives a control message when the file is next read. | |
90 | The method for `answering' | |
91 | this kind of call involves | |
92 | using | |
93 | .I attach | |
94 | and | |
95 | .I detach | |
96 | as described in more detail below. | |
97 | .PP | |
98 | Once B has opened A's mpx file | |
99 | it is said to have a | |
100 | .I channel | |
101 | to A. | |
102 | A channel is a pair of data streams: | |
103 | in this case, one from B to A and the | |
104 | other from A to B. | |
105 | Several processes may open the same mpx file | |
106 | yielding multiple channels within the one mpx file. | |
107 | By accessing the appropriate channel, | |
108 | A can communicate with B and any others. | |
109 | When A reads (see | |
110 | .IR read (2)) | |
111 | from the mpx file | |
112 | data written to A by the other processes appears | |
113 | in A's buffer using a record format | |
114 | described in | |
115 | .IR mpxio (5). | |
116 | When A writes (see | |
117 | .IR write (2)) | |
118 | on its mpx file the data must be formatted in a similar way. | |
119 | .PP | |
120 | The following commands | |
121 | are used to manipulate mpx files and channels. | |
122 | .IP | |
123 | .IR join \- | |
124 | adds a new channel on an mpx file to an open file F. | |
125 | I/O on the new channel is I/O on F. | |
126 | .br | |
127 | .IR chan \- | |
128 | creates a new channel. | |
129 | .br | |
130 | .IR extract \- | |
131 | file descriptor maintenance. | |
132 | .br | |
133 | .IR connect \- | |
134 | similar to join except that the open file F is connected | |
135 | to an existing channel. | |
136 | .br | |
137 | .I attach | |
138 | and | |
139 | .IR detach \- | |
140 | used with call protocol. | |
141 | .br | |
142 | .IR npgrp \- | |
143 | manipulates process group numbers so that a channel | |
144 | can act as a control terminal (see | |
145 | .IR tty (4)). | |
146 | .br | |
147 | .IR ckill \- | |
148 | send signal (see | |
149 | .IR signal (2)) | |
150 | to process group through channel. | |
151 | .PP | |
152 | A maximum of 15 channels may be connected to an | |
153 | mpx file. | |
154 | They are numbered 0 through 14. | |
155 | .I Join | |
156 | may be used to make one mpx file appear as a channel | |
157 | on another mpx file. | |
158 | A hierarchy or tree of mpx files may be set up in this way. | |
159 | In this case | |
160 | one of the mpx files must be the root of a tree | |
161 | where the other mpx files are interior nodes. | |
162 | The maximum depth of such a tree | |
163 | is 4. | |
164 | .PP | |
165 | An | |
166 | .I index | |
167 | is a 16-bit value | |
168 | that denotes a location | |
169 | in an mpx tree other than the root: | |
170 | the path through mpx `nodes' from the root | |
171 | to the location is expressed as a sequence of | |
172 | 4-bit nibbles. | |
173 | The branch taken at the root is represented by | |
174 | the low-order 4-bits of an index. | |
175 | Each succeeding branch is specified by the next | |
176 | higher-order nibble. | |
177 | If the length of a path to be expressed | |
178 | is less than 4, | |
179 | then the illegal channel number, 15, | |
180 | must be used to terminate the sequence. | |
181 | This is not strictly necessary for the | |
182 | simple case of a tree consisting of | |
183 | only a root node: its channels | |
184 | can be expressed by the numbers | |
185 | 0 through 14. | |
186 | An index | |
187 | .I i | |
188 | and file descriptor | |
189 | .I xd | |
190 | for the root of an mpx tree are | |
191 | required as arguments to most | |
192 | of the commands described below. | |
193 | Indices also serve as channel identifiers | |
194 | in the record formats given in | |
195 | .IR mpxio (5). | |
196 | Since \-1 is not a valid index, | |
197 | it can be returned as a error indication | |
198 | by subroutines that normally return | |
199 | indices. | |
200 | .PP | |
201 | The operating system informs the process managing an mpx file | |
202 | of changes in the status of channels attached to the file | |
203 | by generating messages that | |
204 | are read along with data from the channels. | |
205 | The form and content of these messages is described | |
206 | in | |
207 | .IR mpxio (5). | |
208 | .PP | |
209 | .B join(fd, xd) | |
210 | establishes a connection (channel) between an mpx file | |
211 | and another object. | |
212 | .I Fd | |
213 | is an open file descriptor for a character device | |
214 | or an mpx file and | |
215 | .I xd | |
216 | is the file descriptor of an | |
217 | mpx file. | |
218 | .I Join | |
219 | returns the index for the new channel | |
220 | if the operation succeeds and \-1 | |
221 | if it does not. | |
222 | .PP | |
223 | Following join, | |
224 | .I fd | |
225 | may still be used in any system call that would | |
226 | have been meaningful before the join operation. | |
227 | Thus | |
228 | a process can read and write directly to | |
229 | .I fd | |
230 | as well as access it via | |
231 | .I xd. | |
232 | If the number of channels | |
233 | required for a tree of mpx files | |
234 | exceeds the number of open files | |
235 | permitted a process by the operating system, | |
236 | some of the file descriptors can be released using | |
237 | the standard | |
238 | .IR close (2) | |
239 | call. | |
240 | Following a close on an active file descriptor for a channel | |
241 | or internal mpx node, | |
242 | that object may still be accessed through the root of the | |
243 | tree. | |
244 | .PP | |
245 | .B chan(xd) | |
246 | allocates a channel and connects | |
247 | one end of it to the mpx file | |
248 | represented by file descriptor | |
249 | .I xd. | |
250 | .I Chan | |
251 | returns the index of the new channel or | |
252 | a \-1 indicating failure. | |
253 | The | |
254 | .I extract | |
255 | primitive can be used to get a non-multiplexed | |
256 | file descriptor for the free end of a channel | |
257 | created by | |
258 | .I chan. | |
259 | .PP | |
260 | Both | |
261 | .I chan | |
262 | and | |
263 | .I join | |
264 | operate on the mpx file specified by | |
265 | .IR xd . | |
266 | File descriptors for interior nodes of an | |
267 | mpx tree must be preserved or reconstructed with | |
268 | .I extract | |
269 | for use with | |
270 | .I join | |
271 | or | |
272 | .IR chan . | |
273 | For the remaining commands described here, | |
274 | .I xd | |
275 | denotes the file descriptor for the | |
276 | root of an mpx tree. | |
277 | .PP | |
278 | .B extract(i, xd) | |
279 | returns a file descriptor for the object with | |
280 | index | |
281 | .I i | |
282 | on the mpx tree with root file descriptor | |
283 | .I xd. | |
284 | A \-1 is returned by extract if a file descriptor is not available | |
285 | or if the arguments do not refer to an existing | |
286 | channel and mpx file. | |
287 | .PP | |
288 | .B attach(i, xd) | |
289 | .br | |
290 | .BR "detach(i, xd)" . | |
291 | If a process A has created an mpx file represented | |
292 | by file descriptor | |
293 | .I xd, | |
294 | then a process B | |
295 | can open (see | |
296 | .IR open (2)) | |
297 | the mpx file. | |
298 | The purpose is to establish a channel between | |
299 | A and B through the mpx file. | |
300 | .I Attach | |
301 | and | |
302 | .I Detach | |
303 | are used by A to respond to | |
304 | such opens. | |
305 | .PP | |
306 | An open request by B fails immediately if a | |
307 | new channel cannot be allocated on the mpx file, | |
308 | if the mpx file does not exist, | |
309 | or if it does exist | |
310 | but there is no process (A) | |
311 | with a multiplexed file descriptor | |
312 | for the mpx file | |
313 | (i.e. | |
314 | .I xd | |
315 | as returned by | |
316 | .IR mpx (2)). | |
317 | Otherwise a channel | |
318 | with index number | |
319 | .I i | |
320 | is allocated. | |
321 | The next time A reads on file descriptor | |
322 | .IR xd , | |
323 | the WATCH control message | |
324 | (see | |
325 | .IR mpxio (5)) | |
326 | will be delivered on channel | |
327 | .I i. | |
328 | A responds to this message with | |
329 | .I attach | |
330 | or | |
331 | .I detach. | |
332 | The former causes the open to complete and | |
333 | return a file descriptor to B. | |
334 | The latter deallocates channel | |
335 | .I i | |
336 | and causes the open to fail. | |
337 | .PP | |
338 | One mpx file may be placed in `listener' mode. | |
339 | This is done by writing | |
340 | .I "ioctl(xd, MXLSTN, 0)" | |
341 | where | |
342 | .I xd | |
343 | is an mpx file descriptor | |
344 | and MXLSTN is defined in | |
345 | .IR /usr/include/sgtty.h . | |
346 | The semantics of listener mode are that | |
347 | all file names discovered by | |
348 | .IR open (2) | |
349 | to have | |
350 | the syntax | |
351 | .I "system!pathname" | |
352 | (see | |
353 | .IR uucp (1)) | |
354 | are treated as opens on the mpx file. | |
355 | The operating system sends the listener process | |
356 | an OPEN message (see | |
357 | .IR mpxio (5)) | |
358 | which includes the file name being opened. | |
359 | .I Attach | |
360 | and | |
361 | .I detach | |
362 | then apply as described above. | |
363 | .PP | |
364 | .I Detach | |
365 | has two other uses: | |
366 | it closes and releases the resources | |
367 | of any active channel it is applied to, | |
368 | and should be used to respond to | |
369 | a CLOSE message (see | |
370 | .IR mpxio (5)) | |
371 | on a channel so the channel may be reused. | |
372 | .PP | |
373 | .BR "connect(fd, cd, end)" . | |
374 | .I Fd | |
375 | is a character file descriptor and | |
376 | .I cd | |
377 | is a file descriptor for a channel, | |
378 | such as might be obtained via | |
379 | .I "extract( chan(xd), xd)" | |
380 | or by | |
381 | .IR open (2) | |
382 | followed by | |
383 | .I attach. | |
384 | .I Connect | |
385 | splices the two streams together. | |
386 | If | |
387 | .I end | |
388 | is negative, only | |
389 | the output of | |
390 | .I fd | |
391 | is spliced to the input of | |
392 | .I cd. | |
393 | If | |
394 | .I end | |
395 | is positive, the output of | |
396 | .I cd | |
397 | is spliced to the input of | |
398 | .I fd. | |
399 | If | |
400 | .I end | |
401 | is zero, then both splices are made. | |
402 | .PP | |
403 | .BR "npgrp(i, xd, pgrp)" . | |
404 | If | |
405 | .I xd | |
406 | is negative | |
407 | .I npgrp | |
408 | applies to the process executing it, | |
409 | otherwise | |
410 | .I i | |
411 | and | |
412 | .I xd | |
413 | are interpreted as a channel index and | |
414 | mpx file descriptor | |
415 | and | |
416 | .I npgrp | |
417 | is applied to the process on the | |
418 | non-multiplexed end of the channel. | |
419 | If | |
420 | .I pgrp | |
421 | is zero, the process group number of the indicated process | |
422 | is set to the process number of that process, | |
423 | otherwise the value of | |
424 | .I pgrp | |
425 | is used as the process group number. | |
426 | .PP | |
427 | .I Npgrp | |
428 | normally returns the new process group number. | |
429 | If | |
430 | .I i | |
431 | and | |
432 | .I xd | |
433 | specify a nonexistent channel, | |
434 | .I npgrp | |
435 | returns \-1. | |
436 | .PP | |
437 | .B ckill(i, xd, signal) | |
438 | sends the specified signal (see | |
439 | .IR signal (2)) | |
440 | through the channel specified by | |
441 | .I i | |
442 | and | |
443 | .I xd. | |
444 | If the channel is connected to anything other | |
445 | than a process, | |
446 | .I ckill | |
447 | is a null operation. | |
448 | If there is a process at the other end of the channel, | |
449 | the process group will be interrupted (see | |
450 | .IR signal (2), | |
451 | .IR kill (2)). | |
452 | .I Ckill | |
453 | normally returns | |
454 | .I signal. | |
455 | If | |
456 | .I ch | |
457 | and | |
458 | .I xd | |
459 | specify a nonexistent channel, | |
460 | .I ckill | |
461 | returns \-1. | |
462 | .SH FILES | |
463 | /usr/include/sys/mx.h | |
464 | .br | |
465 | /usr/include/sgtty.h | |
466 | .SH "SEE ALSO" | |
467 | mpxio(5) | |
468 | .SH BUGS | |
469 | .PP | |
470 | Mpx files are an experimental part of the operating | |
471 | system more subject to change and prone to bugs | |
472 | than other parts. | |
473 | .PP | |
474 | Maintenance programs, e.g. | |
475 | .IR icheck (1), | |
476 | diagnose mpx files as an illegal mode. | |
477 | .PP | |
478 | Channels may only be connected to objects in the operating | |
479 | system that are accessible through the line discipline | |
480 | mechanism. | |
481 | .PP | |
482 | Higher performance line disciplines are needed. | |
483 | .PP | |
484 | The maximum tree depth restriction is not really checked. | |
485 | .PP | |
486 | A non-destructive | |
487 | .I disconnect | |
488 | primitive (inverse of | |
489 | .IR connect ) | |
490 | is not provided. | |
491 | .PP | |
492 | A non-blocking flow control strategy | |
493 | based on messages defined in | |
494 | .IR mpxio (5) | |
495 | should not be attempted by novices; | |
496 | the enabling | |
497 | .I ioctl | |
498 | command should be protected. | |
499 | .PP | |
500 | The | |
501 | .I join | |
502 | operation could be subsumed by | |
503 | .I connect. | |
504 | A mechanism is needed for moving a channel from one | |
505 | location in an mpx tree to another. |