github.com/rohankumardubey/syslog-redirector-golang@v0.0.0-20140320174030-4859f03d829a/src/lib9/rfork.c (about)

     1  // +build !windows
     2  
     3  /*
     4  Plan 9 from User Space src/lib9/rfork.c
     5  http://code.swtch.com/plan9port/src/tip/src/lib9/rfork.c
     6  
     7  Copyright 2001-2007 Russ Cox.  All Rights Reserved.
     8  
     9  Permission is hereby granted, free of charge, to any person obtaining a copy
    10  of this software and associated documentation files (the "Software"), to deal
    11  in the Software without restriction, including without limitation the rights
    12  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
    13  copies of the Software, and to permit persons to whom the Software is
    14  furnished to do so, subject to the following conditions:
    15  
    16  The above copyright notice and this permission notice shall be included in
    17  all copies or substantial portions of the Software.
    18  
    19  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    20  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    21  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
    22  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    23  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    24  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
    25  THE SOFTWARE.
    26  */
    27  
    28  #include <u.h>
    29  #include <sys/wait.h>
    30  #include <signal.h>
    31  #include <libc.h>
    32  #undef rfork
    33  
    34  static void
    35  nop(int x)
    36  {
    37  	USED(x);
    38  }
    39  
    40  int
    41  p9rfork(int flags)
    42  {
    43  	int pid, status;
    44  	int p[2];
    45  	int n;
    46  	char buf[128], *q;
    47  	extern char **environ;
    48  
    49  	if((flags&(RFPROC|RFFDG|RFMEM)) == (RFPROC|RFFDG)){
    50  		/* check other flags before we commit */
    51  		flags &= ~(RFPROC|RFFDG|RFENVG);
    52  		n = (flags & ~(RFNOTEG|RFNAMEG|RFNOWAIT|RFCENVG));
    53  		if(n){
    54  			werrstr("unknown flags %08ux in rfork", n);
    55  			return -1;
    56  		}
    57  		if(flags&RFNOWAIT){
    58  			/*
    59  			 * BUG - should put the signal handler back after we
    60  			 * finish, but I just don't care.  If a program calls with
    61  			 * NOWAIT once, they're not likely to want child notes
    62  			 * after that.
    63  			 */
    64  			signal(SIGCHLD, nop);
    65  			if(pipe(p) < 0)
    66  				return -1;
    67  		}
    68  		pid = fork();
    69  		if(pid == -1)
    70  			return -1;
    71  		if(flags&RFNOWAIT){
    72  			flags &= ~RFNOWAIT;
    73  			if(pid){
    74  				/*
    75  				 * Parent - wait for child to fork wait-free child.
    76  				 * Then read pid from pipe.  Assume pipe buffer can absorb the write.
    77  				 */
    78  				close(p[1]);
    79  				status = 0;
    80  				if(wait4(pid, &status, 0, 0) < 0){
    81  					werrstr("pipe dance - wait4 - %r");
    82  					close(p[0]);
    83  					return -1;
    84  				}
    85  				n = (int)readn(p[0], buf, sizeof buf-1);
    86  				close(p[0]);
    87  				if(!WIFEXITED(status) || WEXITSTATUS(status)!=0 || n <= 0){
    88  					if(!WIFEXITED(status))
    89  						werrstr("pipe dance - !exited 0x%ux", status);
    90  					else if(WEXITSTATUS(status) != 0)
    91  						werrstr("pipe dance - non-zero status 0x%ux", status);
    92  					else if(n < 0)
    93  						werrstr("pipe dance - pipe read error - %r");
    94  					else if(n == 0)
    95  						werrstr("pipe dance - pipe read eof");
    96  					else
    97  						werrstr("pipe dance - unknown failure");
    98  					return -1;
    99  				}
   100  				buf[n] = 0;
   101  				if(buf[0] == 'x'){
   102  					werrstr("%s", buf+2);
   103  					return -1;
   104  				}
   105  				pid = (int)strtol(buf, &q, 0);
   106  			}else{
   107  				/*
   108  				 * Child - fork a new child whose wait message can't
   109  				 * get back to the parent because we're going to exit!
   110  				 */
   111  				signal(SIGCHLD, SIG_IGN);
   112  				close(p[0]);
   113  				pid = fork();
   114  				if(pid){
   115  					/* Child parent - send status over pipe and exit. */
   116  					if(pid > 0)
   117  						fprint(p[1], "%d", pid);
   118  					else
   119  						fprint(p[1], "x %r");
   120  					close(p[1]);
   121  					_exit(0);
   122  				}else{
   123  					/* Child child - close pipe. */
   124  					close(p[1]);
   125  				}
   126  			}
   127  		}
   128  		if(pid != 0)
   129  			return pid;
   130  		if(flags&RFCENVG)
   131  			if(environ)
   132  				*environ = nil;
   133  	}
   134  	if(flags&RFPROC){
   135  		werrstr("cannot use rfork for shared memory -- use libthread");
   136  		return -1;
   137  	}
   138  	if(flags&RFNAMEG){
   139  		/* XXX set $NAMESPACE to a new directory */
   140  		flags &= ~RFNAMEG;
   141  	}
   142  	if(flags&RFNOTEG){
   143  		setpgid(0, getpid());
   144  		flags &= ~RFNOTEG;
   145  	}
   146  	if(flags&RFNOWAIT){
   147  		werrstr("cannot use RFNOWAIT without RFPROC");
   148  		return -1;
   149  	}
   150  	if(flags){
   151  		werrstr("unknown flags %08ux in rfork", flags);
   152  		return -1;
   153  	}
   154  	return 0;
   155  }