fork/exec clobbers write. I need ideas why... Post: 302119220

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Top Forums Programming fork/exec clobbers write. I need ideas why... Post 302119220 by frequency8 on Tuesday 29th of May 2007 12:20:12 AM

05-29-2007

Registered User

neither one worked.

Below is a crude, but working example of what I mean. Please be gentle on the coding errors.

Code:

/*I wrote the original base code. I only know of one person that has taken this code and improved upon it.
*/
#include <sys/types.h>
#include <sys/wait.h>


#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <string.h>

#define PATH "/home/cda/input"
#define COUNT 20
#define MAXLINE 1024

enum
  {
    /*NINSULTS = sizeof(insults) / sizeof(insults[0]),*/
    PAUSE = 3,
    TIMES = 24
  };


void init(void) 
{
  /*system("mesg -ye -r -xw");*/
  system("mesg n");
}

 static void
 tel(char *user, char *what)
{
  pid_t   pid;
  /*int     status;*/

  pid = fork();
  if (pid < 0) {
    perror("fork failed");
    exit(EXIT_FAILURE);
  }
  if (pid == 0) {
    execlp("tel", "tel", user, what, (char *)0);
    perror("execlp tel failed");
    exit(EXIT_FAILURE);
  }
  /*status = 0;
  wait(&status);
  if (status != 0) {
    fprintf(stderr, "tel failed, bailing.\n");
    exit(EXIT_FAILURE);
    }*/
}


int main(int argc, char *argv[])
{
  char    **users;
  int     i, j, k;
  char **strarray = NULL;
  int strcount = 0;
  char line[MAXLINE];
  FILE *fp;
  char *new;

  int status;

  if (argc < 2) {
    fprintf(stderr, "Usage: telflood user[s].\n");
    return(EXIT_FAILURE);
  }

  /*i need to get around to fixing this*/
  init();

  for(j=0; j < COUNT; j++) {
    if ((fp = fopen(PATH,"r")) == NULL){
      exit(1);
    }

    while((fgets(line, MAXLINE, fp)) != NULL) {
      strarray = (char **)realloc(strarray, (strcount + 1) * sizeof(char *));
      strarray[strcount++] = strdup(line);
    }

  }

  /*char *new = malloc(5*strlen(strarray[0]) + (strlen(strarray[0])+1) );*/

  new=malloc(85*strlen(strarray[0]) + (strlen(strarray[0]) + 1) );

  for(k=0; k<80; k++){
    strcat(new, strarray[0]);
  }



  for (i = 1, j = -1; i < TIMES; i++) {
    for (users = argv + 1; *users; users++) {
      /*tel(*users, insults[j = ((j + 1) % NINSULTS)]);*/
      tel(*users, new);
      sleep(PAUSE);

      status = 0;
      wait(&status);
      if (status != 0) {
        fprintf(stderr, "tel failed, bailing.\n");
        exit(EXIT_FAILURE);
      }

      /*sleep(PAUSE);*/
    }
  }



  for(i = 0; i < COUNT; i++)
    free((void *)strarray[i]);
  free((void *)strarray);
  free(new);


  fclose(fp);
  return(EXIT_SUCCESS);
}

[cda@localhost ~]$ more input
la

[cda@localhost ~]$ ./flood cdalten
cda logged on more than once
Telegram to pts/5...Telegram from cda on pts/5 at 21:12 PDT ...
la
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SENT
EOF (cda)

frequency8

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explain_setpgrp

explain_setpgrp(3)					     Library Functions Manual						explain_setpgrp(3)

NAME

       explain_setpgrp - explain setpgrp(2) errors

SYNOPSIS

       #include <libexplain/setpgrp.h>
       const char *explain_setpgrp(pid_t pid, pid_t pgid);
       const char *explain_errno_setpgrp(int errnum, pid_t pid, pid_t pgid);
       void explain_message_setpgrp(char *message, int message_size, pid_t pid, pid_t pgid);
       void explain_message_errno_setpgrp(char *message, int message_size, int errnum, pid_t pid, pid_t pgid);

DESCRIPTION

       These functions may be used to obtain explanations for errors returned by the setpgrp(2) system call.

       Note:  the  setpgrp(2)  function  has two implementations.  The System V version has no arguments, while the BSD version has two arguments.
       For simplicity of implementation, the argument list seen here includes the pid and pgid arguments.

       The System V getpgid() semantics can be obtained by calling setpgrp(0, 0) on systems with the BSD version, and this is the API  for  libex-
       plain, even on systems that do not use the BSD API.

   explain_setpgrp
       const char *explain_setpgrp(pid_t pid, pid_t pgid);

       The  explain_setpgrp  function  is  used to obtain an explanation of an error returned by the setpgrp(2) system call. The least the message
       will contain is the value of strerror(errno), but usually it will do much better, and indicate the underlying cause in more detail.

       The errno global variable will be used to obtain the error value to be decoded.

       pid     The original pid, exactly as passed to the setpgrp(2) system call.

       pgid    The original pgid, exactly as passed to the setpgrp(2) system call.

       Returns:
	       The message explaining the error. This message buffer is shared by all libexplain functions which do not supply a buffer  in  their
	       argument  list.	 This  will  be  overwritten by the next call to any libexplain function which shares this buffer, including other
	       threads.

       Note: This function is not thread safe, because it shares a return buffer across all threads, and many other functions in this library.

       Example: This function is intended to be used in a fashion similar to the following example:
	      if (setpgrp(pid, pgid) < 0)
	      {
		  fprintf(stderr, "%s
", explain_setpgrp(pid, pgid));
		  exit(EXIT_FAILURE);
	      }

       The above code example is available pre-packaged as the explain_setpgrp_or_die(3) function.

   explain_errno_setpgrp
       const char *explain_errno_setpgrp(int errnum, pid_t pid, pid_t pgid);

       The explain_errno_setpgrp function is used to obtain an explanation of an error returned by the setpgrp(2) system call. The least the  mes-
       sage will contain is the value of strerror(errno), but usually it will do much better, and indicate the underlying cause in more detail.

       errnum  The  error value to be decoded, usually obtained from the errno global variable just before this function is called. This is neces-
	       sary if you need to call any code between the system call to be explained and this function, because many libc functions will alter
	       the value of errno.

       pid     The original pid, exactly as passed to the setpgrp(2) system call.

       pgid    The original pgid, exactly as passed to the setpgrp(2) system call.

       Returns:
	       The  message  explaining the error. This message buffer is shared by all libexplain functions which do not supply a buffer in their
	       argument list.  This will be overwritten by the next call to any libexplain function which  shares  this  buffer,  including  other
	       threads.

       Note: This function is not thread safe, because it shares a return buffer across all threads, and many other functions in this library.

       Example: This function is intended to be used in a fashion similar to the following example:
	      if (setpgrp(pid, pgid) < 0)
	      {
		  int err = errno;
		  fprintf(stderr, "%s
", explain_errno_setpgrp(err, pid, pgid));
		  exit(EXIT_FAILURE);
	      }

       The above code example is available pre-packaged as the explain_setpgrp_or_die(3) function.

   explain_message_setpgrp
       void explain_message_setpgrp(char *message, int message_size, pid_t pid, pid_t pgid);

       The  explain_message_setpgrp  function  is  used to obtain an explanation of an error returned by the setpgrp(2) system call. The least the
       message will contain is the value of strerror(errno), but usually it will do much better, and indicate the underlying cause in more detail.

       The errno global variable will be used to obtain the error value to be decoded.

       message The location in which to store the returned message. If a suitable message return buffer is supplied, this function is thread safe.

       message_size
	       The size in bytes of the location in which to store the returned message.

       pid     The original pid, exactly as passed to the setpgrp(2) system call.

       pgid    The original pgid, exactly as passed to the setpgrp(2) system call.

       Example: This function is intended to be used in a fashion similar to the following example:
	      if (setpgrp(pid, pgid) < 0)
	      {
		  char message[3000];
		  explain_message_setpgrp(message, sizeof(message), pid, pgid);
		  fprintf(stderr, "%s
", message);
		  exit(EXIT_FAILURE);
	      }

       The above code example is available pre-packaged as the explain_setpgrp_or_die(3) function.

   explain_message_errno_setpgrp
       void explain_message_errno_setpgrp(char *message, int message_size, int errnum, pid_t pid, pid_t pgid);

       The explain_message_errno_setpgrp function is used to obtain an explanation of an error returned by the setpgrp(2) system call.	The  least
       the  message  will  contain  is the value of strerror(errno), but usually it will do much better, and indicate the underlying cause in more
       detail.

       message The location in which to store the returned message. If a suitable message return buffer is supplied, this function is thread safe.

       message_size
	       The size in bytes of the location in which to store the returned message.

       errnum  The error value to be decoded, usually obtained from the errno global variable just before this function is called. This is  neces-
	       sary if you need to call any code between the system call to be explained and this function, because many libc functions will alter
	       the value of errno.

       pid     The original pid, exactly as passed to the setpgrp(2) system call.

       pgid    The original pgid, exactly as passed to the setpgrp(2) system call.

       Example: This function is intended to be used in a fashion similar to the following example:
	      if (setpgrp(pid, pgid) < 0)
	      {
		  int err = errno;
		  char message[3000];
		  explain_message_errno_setpgrp(message, sizeof(message), err, pid, pgid);
		  fprintf(stderr, "%s
", message);
		  exit(EXIT_FAILURE);
	      }

       The above code example is available pre-packaged as the explain_setpgrp_or_die(3) function.

SEE ALSO

       setpgrp(2)
	       set process group

       explain_setpgrp_or_die(3)
	       set process group and report errors

COPYRIGHT

       libexplain version 0.52
       Copyright (C) 2011 Peter Miller

																explain_setpgrp(3)

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