summaryrefslogtreecommitdiffstats
path: root/unix/tclUnixPipe.c
blob: 238801e87b052de5c618c908f0540156a4418e0b (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
/* 
 * tclUnixPipe.c --
 *
 *	This file implements the UNIX-specific exec pipeline functions,
 *	the "pipe" channel driver, and the "pid" Tcl command.
 *
 * Copyright (c) 1991-1994 The Regents of the University of California.
 * Copyright (c) 1994-1997 Sun Microsystems, Inc.
 *
 * See the file "license.terms" for information on usage and redistribution
 * of this file, and for a DISCLAIMER OF ALL WARRANTIES.
 *
 * RCS: @(#) $Id: tclUnixPipe.c,v 1.5 1999/11/30 08:37:15 hobbs Exp $
 */

#include "tclInt.h"
#include "tclPort.h"

/*
 * The following macros convert between TclFile's and fd's.  The conversion
 * simple involves shifting fd's up by one to ensure that no valid fd is ever
 * the same as NULL.
 */

#define MakeFile(fd) ((TclFile)(((int)fd)+1))
#define GetFd(file) (((int)file)-1)

/*
 * This structure describes per-instance state of a pipe based channel.
 */

typedef struct PipeState {
    Tcl_Channel channel;/* Channel associated with this file. */
    TclFile inFile;	/* Output from pipe. */
    TclFile outFile;	/* Input to pipe. */
    TclFile errorFile;	/* Error output from pipe. */
    int numPids;	/* How many processes are attached to this pipe? */
    Tcl_Pid *pidPtr;	/* The process IDs themselves. Allocated by
                         * the creator of the pipe. */
    int isNonBlocking;	/* Nonzero when the pipe is in nonblocking mode.
                         * Used to decide whether to wait for the children
                         * at close time. */
} PipeState;

/*
 * Declarations for local procedures defined in this file:
 */

static int	PipeBlockModeProc _ANSI_ARGS_((ClientData instanceData,
		    int mode));
static int	PipeCloseProc _ANSI_ARGS_((ClientData instanceData,
		    Tcl_Interp *interp));
static int	PipeGetHandleProc _ANSI_ARGS_((ClientData instanceData,
		    int direction, ClientData *handlePtr));
static int	PipeInputProc _ANSI_ARGS_((ClientData instanceData,
		    char *buf, int toRead, int *errorCode));
static int	PipeOutputProc _ANSI_ARGS_((
		    ClientData instanceData, char *buf, int toWrite,
		    int *errorCode));
static void	PipeWatchProc _ANSI_ARGS_((ClientData instanceData, int mask));
static void	RestoreSignals _ANSI_ARGS_((void));
static int	SetupStdFile _ANSI_ARGS_((TclFile file, int type));

/*
 * This structure describes the channel type structure for command pipe
 * based IO:
 */

static Tcl_ChannelType pipeChannelType = {
    "pipe",				/* Type name. */
    PipeBlockModeProc,			/* Set blocking/nonblocking mode.*/
    PipeCloseProc,			/* Close proc. */
    PipeInputProc,			/* Input proc. */
    PipeOutputProc,			/* Output proc. */
    NULL,				/* Seek proc. */
    NULL,				/* Set option proc. */
    NULL,				/* Get option proc. */
    PipeWatchProc,			/* Initialize notifier. */
    PipeGetHandleProc,			/* Get OS handles out of channel. */
};

/*
 *----------------------------------------------------------------------
 *
 * TclpMakeFile --
 *
 *	Make a TclFile from a channel.
 *
 * Results:
 *	Returns a new TclFile or NULL on failure.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

TclFile
TclpMakeFile(channel, direction)
    Tcl_Channel channel;	/* Channel to get file from. */
    int direction;		/* Either TCL_READABLE or TCL_WRITABLE. */
{
    ClientData data;

    if (Tcl_GetChannelHandle(channel, direction, (ClientData *) &data)
	    == TCL_OK) {
	return MakeFile((int)data);
    } else {
	return (TclFile) NULL;
    }
}

/*
 *----------------------------------------------------------------------
 *
 * TclpOpenFile --
 *
 *	Open a file for use in a pipeline.  
 *
 * Results:
 *	Returns a new TclFile handle or NULL on failure.
 *
 * Side effects:
 *	May cause a file to be created on the file system.
 *
 *----------------------------------------------------------------------
 */

TclFile
TclpOpenFile(fname, mode)
    CONST char *fname;		/* The name of the file to open. */
    int mode;			/* In what mode to open the file? */
{
    int fd;
    char *native;
    Tcl_DString ds;

    native = Tcl_UtfToExternalDString(NULL, fname, -1, &ds);
    fd = open(native, mode, 0666);			/* INTL: Native. */
    Tcl_DStringFree(&ds);
    if (fd != -1) {
        fcntl(fd, F_SETFD, FD_CLOEXEC);

	/*
	 * If the file is being opened for writing, seek to the end
	 * so we can append to any data already in the file.
	 */

	if (mode & O_WRONLY) {
	    lseek(fd, 0, SEEK_END);
	}

	/*
	 * Increment the fd so it can't be 0, which would conflict with
	 * the NULL return for errors.
	 */

	return MakeFile(fd);
    }
    return NULL;
}

/*
 *----------------------------------------------------------------------
 *
 * TclpCreateTempFile --
 *
 *	This function creates a temporary file initialized with an
 *	optional string, and returns a file handle with the file pointer
 *	at the beginning of the file.
 *
 * Results:
 *	A handle to a file.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

TclFile
TclpCreateTempFile(contents)
    CONST char *contents;	/* String to write into temp file, or NULL. */
{
    char fileName[L_tmpnam];
    int fd;

    tmpnam(fileName);					/* INTL: Native. */
    fd = open(fileName, O_RDWR|O_CREAT|O_TRUNC, 0666);	/* INTL: Native. */
    if (fd == -1) {
	return NULL;
    }
    fcntl(fd, F_SETFD, FD_CLOEXEC);
    unlink(fileName);					/* INTL: Native. */

    if (contents != NULL) {
	if (write(fd, contents, strlen(contents)) == -1) {
	    close(fd);
	    return NULL;
	}
	lseek(fd, 0, SEEK_SET);
    }
    return MakeFile(fd);
}

/*
 *----------------------------------------------------------------------
 *
 * TclpCreatePipe --
 *
 *      Creates a pipe - simply calls the pipe() function.
 *
 * Results:
 *      Returns 1 on success, 0 on failure. 
 *
 * Side effects:
 *      Creates a pipe.
 *
 *----------------------------------------------------------------------
 */

int
TclpCreatePipe(readPipe, writePipe)
    TclFile *readPipe;		/* Location to store file handle for
				 * read side of pipe. */
    TclFile *writePipe;		/* Location to store file handle for
				 * write side of pipe. */
{
    int pipeIds[2];

    if (pipe(pipeIds) != 0) {
	return 0;
    }

    fcntl(pipeIds[0], F_SETFD, FD_CLOEXEC);
    fcntl(pipeIds[1], F_SETFD, FD_CLOEXEC);

    *readPipe = MakeFile(pipeIds[0]);
    *writePipe = MakeFile(pipeIds[1]);
    return 1;
}

/*
 *----------------------------------------------------------------------
 *
 * TclpCloseFile --
 *
 *	Implements a mechanism to close a UNIX file.
 *
 * Results:
 *	Returns 0 on success, or -1 on error, setting errno.
 *
 * Side effects:
 *	The file is closed.
 *
 *----------------------------------------------------------------------
 */

int
TclpCloseFile(file)
    TclFile file;	/* The file to close. */
{
    int fd = GetFd(file);

    /*
     * Refuse to close the fds for stdin, stdout and stderr.
     */
    
    if ((fd == 0) || (fd == 1) || (fd == 2)) {
        return 0;
    }
    
    Tcl_DeleteFileHandler(fd);
    return close(fd);
}

/*
 *---------------------------------------------------------------------------
 *
 * TclpCreateProcess --
 *
 *	Create a child process that has the specified files as its 
 *	standard input, output, and error.  The child process runs
 *	asynchronously and runs with the same environment variables
 *	as the creating process.
 *
 *	The path is searched to find the specified executable.  
 *
 * Results:
 *	The return value is TCL_ERROR and an error message is left in
 *	the interp's result if there was a problem creating the child 
 *	process.  Otherwise, the return value is TCL_OK and *pidPtr is
 *	filled with the process id of the child process.
 * 
 * Side effects:
 *	A process is created.
 *	
 *---------------------------------------------------------------------------
 */

    /* ARGSUSED */
int
TclpCreateProcess(interp, argc, argv, inputFile, outputFile, errorFile, 
	pidPtr)
    Tcl_Interp *interp;		/* Interpreter in which to leave errors that
				 * occurred when creating the child process.
				 * Error messages from the child process
				 * itself are sent to errorFile. */
    int argc;			/* Number of arguments in following array. */
    char **argv;		/* Array of argument strings in UTF-8.
				 * argv[0] contains the name of the executable
				 * translated using Tcl_TranslateFileName
				 * call).  Additional arguments have not been
				 * converted. */
    TclFile inputFile;		/* If non-NULL, gives the file to use as
				 * input for the child process.  If inputFile
				 * file is not readable or is NULL, the child
				 * will receive no standard input. */
    TclFile outputFile;		/* If non-NULL, gives the file that
				 * receives output from the child process.  If
				 * outputFile file is not writeable or is
				 * NULL, output from the child will be
				 * discarded. */
    TclFile errorFile;		/* If non-NULL, gives the file that
				 * receives errors from the child process.  If
				 * errorFile file is not writeable or is NULL,
				 * errors from the child will be discarded.
				 * errorFile may be the same as outputFile. */
    Tcl_Pid *pidPtr;		/* If this procedure is successful, pidPtr
				 * is filled with the process id of the child
				 * process. */
{
    TclFile errPipeIn, errPipeOut;
    int joinThisError, count, status, fd;
    char errSpace[200 + TCL_INTEGER_SPACE];
    Tcl_DString *dsArray;
    char **newArgv;
    int pid, i;
    
    errPipeIn = NULL;
    errPipeOut = NULL;
    pid = -1;

    /*
     * Create a pipe that the child can use to return error
     * information if anything goes wrong.
     */

    if (TclpCreatePipe(&errPipeIn, &errPipeOut) == 0) {
	Tcl_AppendResult(interp, "couldn't create pipe: ",
		Tcl_PosixError(interp), (char *) NULL);
	goto error;
    }

    /*
     * We need to allocate and convert this before the (v)fork
     * so it is properly deallocated later
     */
    dsArray = (Tcl_DString *) ckalloc(argc * sizeof(Tcl_DString));
    newArgv = (char **) ckalloc((argc+1) * sizeof(char *));
    newArgv[argc] = NULL;
    for (i = 0; i < argc; i++) {
	newArgv[i] = Tcl_UtfToExternalDString(NULL, argv[i], -1, &dsArray[i]);
    }

    joinThisError = (errorFile == outputFile);
    pid = vfork();
    if (pid == 0) {
	fd = GetFd(errPipeOut);

	/*
	 * Set up stdio file handles for the child process.
	 */

	if (!SetupStdFile(inputFile, TCL_STDIN)
		|| !SetupStdFile(outputFile, TCL_STDOUT)
		|| (!joinThisError && !SetupStdFile(errorFile, TCL_STDERR))
		|| (joinThisError &&
			((dup2(1,2) == -1) ||
			 (fcntl(2, F_SETFD, 0) != 0)))) {
	    sprintf(errSpace,
		    "%dforked process couldn't set up input/output: ", errno);
	    write(fd, errSpace, (size_t) strlen(errSpace));
	    _exit(1);
	}

	/*
	 * Close the input side of the error pipe.
	 */

	RestoreSignals();
	execvp(newArgv[0], newArgv);			/* INTL: Native. */
	sprintf(errSpace, "%dcouldn't execute \"%.150s\": ", errno, argv[0]);
	write(fd, errSpace, (size_t) strlen(errSpace));
	_exit(1);
    }
    
    /*
     * Free the mem we used for the fork
     */
    for (i = 0; i < argc; i++) {
	Tcl_DStringFree(&dsArray[i]);
    }
    ckfree((char *) dsArray);
    ckfree((char *) newArgv);

    if (pid == -1) {
	Tcl_AppendResult(interp, "couldn't fork child process: ",
		Tcl_PosixError(interp), (char *) NULL);
	goto error;
    }

    /*
     * Read back from the error pipe to see if the child started
     * up OK.  The info in the pipe (if any) consists of a decimal
     * errno value followed by an error message.
     */

    TclpCloseFile(errPipeOut);
    errPipeOut = NULL;

    fd = GetFd(errPipeIn);
    count = read(fd, errSpace, (size_t) (sizeof(errSpace) - 1));
    if (count > 0) {
	char *end;
	errSpace[count] = 0;
	errno = strtol(errSpace, &end, 10);
	Tcl_AppendResult(interp, end, Tcl_PosixError(interp),
		(char *) NULL);
	goto error;
    }
    
    TclpCloseFile(errPipeIn);
    *pidPtr = (Tcl_Pid) pid;
    return TCL_OK;

    error:
    if (pid != -1) {
	/*
	 * Reap the child process now if an error occurred during its
	 * startup.
	 */

	Tcl_WaitPid((Tcl_Pid) pid, &status, WNOHANG);
    }
    
    if (errPipeIn) {
	TclpCloseFile(errPipeIn);
    }
    if (errPipeOut) {
	TclpCloseFile(errPipeOut);
    }
    return TCL_ERROR;
}

/*
 *----------------------------------------------------------------------
 *
 * RestoreSignals --
 *
 *      This procedure is invoked in a forked child process just before
 *      exec-ing a new program to restore all signals to their default
 *      settings.
 *
 * Results:
 *      None.
 *
 * Side effects:
 *      Signal settings get changed.
 *
 *----------------------------------------------------------------------
 */
 
static void
RestoreSignals()
{
#ifdef SIGABRT
    signal(SIGABRT, SIG_DFL);
#endif
#ifdef SIGALRM
    signal(SIGALRM, SIG_DFL);
#endif
#ifdef SIGFPE
    signal(SIGFPE, SIG_DFL);
#endif
#ifdef SIGHUP
    signal(SIGHUP, SIG_DFL);
#endif
#ifdef SIGILL
    signal(SIGILL, SIG_DFL);
#endif
#ifdef SIGINT
    signal(SIGINT, SIG_DFL);
#endif
#ifdef SIGPIPE
    signal(SIGPIPE, SIG_DFL);
#endif
#ifdef SIGQUIT
    signal(SIGQUIT, SIG_DFL);
#endif
#ifdef SIGSEGV
    signal(SIGSEGV, SIG_DFL);
#endif
#ifdef SIGTERM
    signal(SIGTERM, SIG_DFL);
#endif
#ifdef SIGUSR1
    signal(SIGUSR1, SIG_DFL);
#endif
#ifdef SIGUSR2
    signal(SIGUSR2, SIG_DFL);
#endif
#ifdef SIGCHLD
    signal(SIGCHLD, SIG_DFL);
#endif
#ifdef SIGCONT
    signal(SIGCONT, SIG_DFL);
#endif
#ifdef SIGTSTP
    signal(SIGTSTP, SIG_DFL);
#endif
#ifdef SIGTTIN
    signal(SIGTTIN, SIG_DFL);
#endif
#ifdef SIGTTOU
    signal(SIGTTOU, SIG_DFL);
#endif
}

/*
 *----------------------------------------------------------------------
 *
 * SetupStdFile --
 *
 *	Set up stdio file handles for the child process, using the
 *	current standard channels if no other files are specified.
 *	If no standard channel is defined, or if no file is associated
 *	with the channel, then the corresponding standard fd is closed.
 *
 * Results:
 *	Returns 1 on success, or 0 on failure.
 *
 * Side effects:
 *	Replaces stdio fds.
 *
 *----------------------------------------------------------------------
 */

static int
SetupStdFile(file, type)
    TclFile file;		/* File to dup, or NULL. */
    int type;			/* One of TCL_STDIN, TCL_STDOUT, TCL_STDERR */
{
    Tcl_Channel channel;
    int fd;
    int targetFd = 0;		/* Initializations here needed only to */
    int direction = 0;		/* prevent warnings about using uninitialized
				 * variables. */

    switch (type) {
	case TCL_STDIN:
	    targetFd = 0;
	    direction = TCL_READABLE;
	    break;
	case TCL_STDOUT:
	    targetFd = 1;
	    direction = TCL_WRITABLE;
	    break;
	case TCL_STDERR:
	    targetFd = 2;
	    direction = TCL_WRITABLE;
	    break;
    }

    if (!file) {
	channel = Tcl_GetStdChannel(type);
	if (channel) {
	    file = TclpMakeFile(channel, direction);
	}
    }
    if (file) {
	fd = GetFd(file);
	if (fd != targetFd) {
	    if (dup2(fd, targetFd) == -1) {
		return 0;
	    }

            /*
             * Must clear the close-on-exec flag for the target FD, since
             * some systems (e.g. Ultrix) do not clear the CLOEXEC flag on
             * the target FD.
             */
            
            fcntl(targetFd, F_SETFD, 0);
	} else {
	    int result;

	    /*
	     * Since we aren't dup'ing the file, we need to explicitly clear
	     * the close-on-exec flag.
	     */

	    result = fcntl(fd, F_SETFD, 0);
	}
    } else {
	close(targetFd);
    }
    return 1;
}

/*
 *----------------------------------------------------------------------
 *
 * TclpCreateCommandChannel --
 *
 *	This function is called by the generic IO level to perform
 *	the platform specific channel initialization for a command
 *	channel.
 *
 * Results:
 *	Returns a new channel or NULL on failure.
 *
 * Side effects:
 *	Allocates a new channel.
 *
 *----------------------------------------------------------------------
 */

Tcl_Channel
TclpCreateCommandChannel(readFile, writeFile, errorFile, numPids, pidPtr)
    TclFile readFile;		/* If non-null, gives the file for reading. */
    TclFile writeFile;		/* If non-null, gives the file for writing. */
    TclFile errorFile;		/* If non-null, gives the file where errors
				 * can be read. */
    int numPids;		/* The number of pids in the pid array. */
    Tcl_Pid *pidPtr;		/* An array of process identifiers.
                                 * Allocated by the caller, freed when
                                 * the channel is closed or the processes
                                 * are detached (in a background exec). */
{
    char channelName[16 + TCL_INTEGER_SPACE];
    int channelId;
    PipeState *statePtr = (PipeState *) ckalloc((unsigned) sizeof(PipeState));
    int mode;

    statePtr->inFile = readFile;
    statePtr->outFile = writeFile;
    statePtr->errorFile = errorFile;
    statePtr->numPids = numPids;
    statePtr->pidPtr = pidPtr;
    statePtr->isNonBlocking = 0;

    mode = 0;
    if (readFile) {
        mode |= TCL_READABLE;
    }
    if (writeFile) {
        mode |= TCL_WRITABLE;
    }
    
    /*
     * Use one of the fds associated with the channel as the
     * channel id.
     */

    if (readFile) {
	channelId = GetFd(readFile);
    } else if (writeFile) {
	channelId = GetFd(writeFile);
    } else if (errorFile) {
	channelId = GetFd(errorFile);
    } else {
	channelId = 0;
    }

    /*
     * For backward compatibility with previous versions of Tcl, we
     * use "file%d" as the base name for pipes even though it would
     * be more natural to use "pipe%d".
     */

    sprintf(channelName, "file%d", channelId);
    statePtr->channel = Tcl_CreateChannel(&pipeChannelType, channelName,
            (ClientData) statePtr, mode);
    return statePtr->channel;
}

/*
 *----------------------------------------------------------------------
 *
 * TclGetAndDetachPids --
 *
 *	This procedure is invoked in the generic implementation of a
 *	background "exec" (An exec when invoked with a terminating "&")
 *	to store a list of the PIDs for processes in a command pipeline
 *	in the interp's result and to detach the processes.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Modifies the interp's result. Detaches processes.
 *
 *----------------------------------------------------------------------
 */

void
TclGetAndDetachPids(interp, chan)
    Tcl_Interp *interp;
    Tcl_Channel chan;
{
    PipeState *pipePtr;
    Tcl_ChannelType *chanTypePtr;
    int i;
    char buf[TCL_INTEGER_SPACE];

    /*
     * Punt if the channel is not a command channel.
     */

    chanTypePtr = Tcl_GetChannelType(chan);
    if (chanTypePtr != &pipeChannelType) {
        return;
    }

    pipePtr = (PipeState *) Tcl_GetChannelInstanceData(chan);
    for (i = 0; i < pipePtr->numPids; i++) {
        TclFormatInt(buf, (long) TclpGetPid(pipePtr->pidPtr[i]));
        Tcl_AppendElement(interp, buf);
        Tcl_DetachPids(1, &(pipePtr->pidPtr[i]));
    }
    if (pipePtr->numPids > 0) {
        ckfree((char *) pipePtr->pidPtr);
        pipePtr->numPids = 0;
    }
}

/*
 *----------------------------------------------------------------------
 *
 * PipeBlockModeProc --
 *
 *	Helper procedure to set blocking and nonblocking modes on a
 *	pipe based channel. Invoked by generic IO level code.
 *
 * Results:
 *	0 if successful, errno when failed.
 *
 * Side effects:
 *	Sets the device into blocking or non-blocking mode.
 *
 *----------------------------------------------------------------------
 */

	/* ARGSUSED */
static int
PipeBlockModeProc(instanceData, mode)
    ClientData instanceData;		/* Pipe state. */
    int mode;				/* The mode to set. Can be one of
                                         * TCL_MODE_BLOCKING or
                                         * TCL_MODE_NONBLOCKING. */
{
    PipeState *psPtr = (PipeState *) instanceData;
    int curStatus;
    int fd;

#ifndef	USE_FIONBIO    
    if (psPtr->inFile) {
        fd = GetFd(psPtr->inFile);
        curStatus = fcntl(fd, F_GETFL);
        if (mode == TCL_MODE_BLOCKING) {
            curStatus &= (~(O_NONBLOCK));
        } else {
            curStatus |= O_NONBLOCK;
        }
        if (fcntl(fd, F_SETFL, curStatus) < 0) {
            return errno;
        }
        curStatus = fcntl(fd, F_GETFL);
    }
    if (psPtr->outFile) {
        fd = GetFd(psPtr->outFile);
        curStatus = fcntl(fd, F_GETFL);
        if (mode == TCL_MODE_BLOCKING) {
            curStatus &= (~(O_NONBLOCK));
        } else {
            curStatus |= O_NONBLOCK;
        }
        if (fcntl(fd, F_SETFL, curStatus) < 0) {
            return errno;
        }
    }
#endif	/* !FIONBIO */

#ifdef	USE_FIONBIO
    if (psPtr->inFile) {
        fd = GetFd(psPtr->inFile);
        if (mode == TCL_MODE_BLOCKING) {
            curStatus = 0;
        } else {
            curStatus = 1;
        }
        if (ioctl(fd, (int) FIONBIO, &curStatus) < 0) {
            return errno;
        }
    }
    if (psPtr->outFile != NULL) {
        fd = GetFd(psPtr->outFile);
        if (mode == TCL_MODE_BLOCKING) {
            curStatus = 0;
        } else {
            curStatus = 1;
        }
        if (ioctl(fd, (int) FIONBIO,  &curStatus) < 0) {
            return errno;
        }
    }
#endif	/* USE_FIONBIO */

    psPtr->isNonBlocking = (mode == TCL_MODE_NONBLOCKING);

    return 0;
}

/*
 *----------------------------------------------------------------------
 *
 * PipeCloseProc --
 *
 *	This procedure is invoked by the generic IO level to perform
 *	channel-type-specific cleanup when a command pipeline channel
 *	is closed.
 *
 * Results:
 *	0 on success, errno otherwise.
 *
 * Side effects:
 *	Closes the command pipeline channel.
 *
 *----------------------------------------------------------------------
 */

	/* ARGSUSED */
static int
PipeCloseProc(instanceData, interp)
    ClientData instanceData;	/* The pipe to close. */
    Tcl_Interp *interp;		/* For error reporting. */
{
    PipeState *pipePtr;
    Tcl_Channel errChan;
    int errorCode, result;

    errorCode = 0;
    result = 0;
    pipePtr = (PipeState *) instanceData;
    if (pipePtr->inFile) {
	if (TclpCloseFile(pipePtr->inFile) < 0) {
	    errorCode = errno;
	}
    }
    if (pipePtr->outFile) {
	if ((TclpCloseFile(pipePtr->outFile) < 0) && (errorCode == 0)) {
	    errorCode = errno;
	}
    }

    if (pipePtr->isNonBlocking || TclInExit()) {
    
	/*
         * If the channel is non-blocking or Tcl is being cleaned up, just
         * detach the children PIDs, reap them (important if we are in a
         * dynamic load module), and discard the errorFile.
         */
        
        Tcl_DetachPids(pipePtr->numPids, pipePtr->pidPtr);
        Tcl_ReapDetachedProcs();

        if (pipePtr->errorFile) {
	    TclpCloseFile(pipePtr->errorFile);
        }
    } else {
        
	/*
         * Wrap the error file into a channel and give it to the cleanup
         * routine.
         */

        if (pipePtr->errorFile) {
	    errChan = Tcl_MakeFileChannel(
		(ClientData) GetFd(pipePtr->errorFile), TCL_READABLE);
        } else {
            errChan = NULL;
        }
        result = TclCleanupChildren(interp, pipePtr->numPids, pipePtr->pidPtr,
                errChan);
    }

    if (pipePtr->numPids != 0) {
        ckfree((char *) pipePtr->pidPtr);
    }
    ckfree((char *) pipePtr);
    if (errorCode == 0) {
        return result;
    }
    return errorCode;
}

/*
 *----------------------------------------------------------------------
 *
 * PipeInputProc --
 *
 *	This procedure is invoked from the generic IO level to read
 *	input from a command pipeline based channel.
 *
 * Results:
 *	The number of bytes read is returned or -1 on error. An output
 *	argument contains a POSIX error code if an error occurs, or zero.
 *
 * Side effects:
 *	Reads input from the input device of the channel.
 *
 *----------------------------------------------------------------------
 */

static int
PipeInputProc(instanceData, buf, toRead, errorCodePtr)
    ClientData instanceData;		/* Pipe state. */
    char *buf;				/* Where to store data read. */
    int toRead;				/* How much space is available
                                         * in the buffer? */
    int *errorCodePtr;			/* Where to store error code. */
{
    PipeState *psPtr = (PipeState *) instanceData;
    int bytesRead;			/* How many bytes were actually
                                         * read from the input device? */

    *errorCodePtr = 0;
    
    /*
     * Assume there is always enough input available. This will block
     * appropriately, and read will unblock as soon as a short read is
     * possible, if the channel is in blocking mode. If the channel is
     * nonblocking, the read will never block.
     */

    bytesRead = read(GetFd(psPtr->inFile), buf, (size_t) toRead);
    if (bytesRead > -1) {
        return bytesRead;
    }
    *errorCodePtr = errno;
    return -1;
}

/*
 *----------------------------------------------------------------------
 *
 * PipeOutputProc--
 *
 *	This procedure is invoked from the generic IO level to write
 *	output to a command pipeline based channel.
 *
 * Results:
 *	The number of bytes written is returned or -1 on error. An
 *	output argument	contains a POSIX error code if an error occurred,
 *	or zero.
 *
 * Side effects:
 *	Writes output on the output device of the channel.
 *
 *----------------------------------------------------------------------
 */

static int
PipeOutputProc(instanceData, buf, toWrite, errorCodePtr)
    ClientData instanceData;		/* Pipe state. */
    char *buf;				/* The data buffer. */
    int toWrite;			/* How many bytes to write? */
    int *errorCodePtr;			/* Where to store error code. */
{
    PipeState *psPtr = (PipeState *) instanceData;
    int written;

    *errorCodePtr = 0;
    written = write(GetFd(psPtr->outFile), buf, (size_t) toWrite);
    if (written > -1) {
        return written;
    }
    *errorCodePtr = errno;
    return -1;
}

/*
 *----------------------------------------------------------------------
 *
 * PipeWatchProc --
 *
 *	Initialize the notifier to watch the fds from this channel.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Sets up the notifier so that a future event on the channel will
 *	be seen by Tcl.
 *
 *----------------------------------------------------------------------
 */

static void
PipeWatchProc(instanceData, mask)
    ClientData instanceData;		/* The pipe state. */
    int mask;				/* Events of interest; an OR-ed
                                         * combination of TCL_READABLE,
                                         * TCL_WRITABEL and TCL_EXCEPTION. */
{
    PipeState *psPtr = (PipeState *) instanceData;
    int newmask;

    if (psPtr->inFile) {
	newmask = mask & (TCL_READABLE | TCL_EXCEPTION);
	if (newmask) {
	    Tcl_CreateFileHandler(GetFd(psPtr->inFile), mask,
		    (Tcl_FileProc *) Tcl_NotifyChannel,
		    (ClientData) psPtr->channel);
	} else {
	    Tcl_DeleteFileHandler(GetFd(psPtr->inFile));
	}
    }
    if (psPtr->outFile) {
	newmask = mask & (TCL_WRITABLE | TCL_EXCEPTION);
	if (newmask) {
	    Tcl_CreateFileHandler(GetFd(psPtr->outFile), mask,
		    (Tcl_FileProc *) Tcl_NotifyChannel,
		    (ClientData) psPtr->channel);
	} else {
	    Tcl_DeleteFileHandler(GetFd(psPtr->outFile));
	}
    }
}

/*
 *----------------------------------------------------------------------
 *
 * PipeGetHandleProc --
 *
 *	Called from Tcl_GetChannelHandle to retrieve OS handles from
 *	inside a command pipeline based channel.
 *
 * Results:
 *	Returns TCL_OK with the fd in handlePtr, or TCL_ERROR if
 *	there is no handle for the specified direction. 
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

static int
PipeGetHandleProc(instanceData, direction, handlePtr)
    ClientData instanceData;	/* The pipe state. */
    int direction;		/* TCL_READABLE or TCL_WRITABLE */
    ClientData *handlePtr;	/* Where to store the handle.  */
{
    PipeState *psPtr = (PipeState *) instanceData;

    if (direction == TCL_READABLE && psPtr->inFile) {
	*handlePtr = (ClientData) GetFd(psPtr->inFile);
	return TCL_OK;
    }
    if (direction == TCL_WRITABLE && psPtr->outFile) {
	*handlePtr = (ClientData) GetFd(psPtr->outFile);
	return TCL_OK;
    }
    return TCL_ERROR;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_WaitPid --
 *
 *	Implements the waitpid system call on Unix systems.
 *
 * Results:
 *	Result of calling waitpid.
 *
 * Side effects:
 *	Waits for a process to terminate.
 *
 *----------------------------------------------------------------------
 */

Tcl_Pid
Tcl_WaitPid(pid, statPtr, options)
    Tcl_Pid pid;
    int *statPtr;
    int options;
{
    int result;
    pid_t real_pid;

    real_pid = (pid_t) pid;
    while (1) {
	result = (int) waitpid(real_pid, statPtr, options);
	if ((result != -1) || (errno != EINTR)) {
	    return (Tcl_Pid) result;
	}
    }
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_PidObjCmd --
 *
 *	This procedure is invoked to process the "pid" Tcl command.
 *	See the user documentation for details on what it does.
 *
 * Results:
 *	A standard Tcl result.
 *
 * Side effects:
 *	See the user documentation.
 *
 *----------------------------------------------------------------------
 */

	/* ARGSUSED */
int
Tcl_PidObjCmd(dummy, interp, objc, objv)
    ClientData dummy;		/* Not used. */
    Tcl_Interp *interp;		/* Current interpreter. */
    int objc;			/* Number of arguments. */
    Tcl_Obj *CONST *objv;	/* Argument strings. */
{
    Tcl_Channel chan;
    Tcl_ChannelType *chanTypePtr;
    PipeState *pipePtr;
    int i;
    Tcl_Obj *resultPtr, *longObjPtr;

    if (objc > 2) {
	Tcl_WrongNumArgs(interp, 1, objv, "?channelId?");
	return TCL_ERROR;
    }
    if (objc == 1) {
	Tcl_SetLongObj(Tcl_GetObjResult(interp), (long) getpid());
    } else {
        chan = Tcl_GetChannel(interp, Tcl_GetString(objv[1]), NULL);
        if (chan == (Tcl_Channel) NULL) {
	    return TCL_ERROR;
	}
	chanTypePtr = Tcl_GetChannelType(chan);
	if (chanTypePtr != &pipeChannelType) {
	    return TCL_OK;
	}
        pipePtr = (PipeState *) Tcl_GetChannelInstanceData(chan);
	resultPtr = Tcl_GetObjResult(interp);
        for (i = 0; i < pipePtr->numPids; i++) {
	    longObjPtr = Tcl_NewLongObj((long) TclpGetPid(pipePtr->pidPtr[i]));
	    Tcl_ListObjAppendElement(NULL, resultPtr, longObjPtr);
	}
    }
    return TCL_OK;
}