How to give filenames to a parent procces using FIFO(in C)? - c

Question

I have 2 processes, one reads from the input a filename, this filename is then given to the child process.The child process determinates in which directories the given file exits and the child procces gives all the directory names back to the parent who then prints these directory names.I need to do this using FIFO(named pipes).I got stuck at the part where the child prcess gives the parent the directory names.Could someone please help?
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
#include <sys/wait.h>
#include <errno.h>
#include <dirent.h>
extern int errno;
#define FIFO "/tmp/fifo0002.1"
//searches for the direrctories
void listdir( const char *dir, const char *filename)
{
DIR *dp;
struct dirent *entry;
struct stat statbuf;
char *subdir;
if((dp = opendir(dir)) == NULL)
{
fprintf(stderr,"cannot open directory: %s\n", dir);
return;
}
while((entry = readdir(dp)) != NULL)
{
if(lstat(entry->d_name, &statbuf) == 0)
{
if(statbuf.st_mode & S_IFDIR)
{
/* Found a directory, but ignore . and .. */
if(strcmp(".", entry->d_name) == 0 || strcmp("..", entry->d_name) == 0)
continue;
// allocate space for parent directory, "/", subdir, plus NULL terminator
subdir = malloc(strlen(dir) + strlen(entry->d_name) + 2);
// Concatenate directory name
strcpy(subdir, dir);
strcat(subdir, "/");
strcat(subdir, entry->d_name);
/* Recurse at a new indent level */
listdir(subdir,filename);
free(subdir);
}
else
{
if(statbuf.st_mode & S_IFREG ){
if (strcmp(entry->d_name,filename)==0){
printf("%s\n",dir);}}
}
}
}
closedir(dp);
}
int main (void)
{ int r_fifo, w_fifo, r1_fifo, w1_fifo;
char filename[100];
printf("enter filename:");
scanf("%s",filename);
char buf[100];
char buf2[100];
pid_t pid;
if ((mkfifo (FIFO, S_IRUSR | S_IWUSR)) == -1) {
/* FIFO exists */
if(errno == EEXIST)
perror ("mkfifo()");
else {
perror("mkfifo()");
exit (EXIT_FAILURE);
} }
pid = fork ();
if (pid == -1)
{ perror ("fork()");
exit (EXIT_FAILURE);
}
else if (pid > 0) {
/*parent procces */
if ((r_fifo = open (FIFO, O_RDONLY)) < 0) {
perror ("open()");
exit (EXIT_FAILURE); }
write (w_fifo, filename, strlen (filename));
/*wait for child */
while (wait (NULL) != pid);
/*read from FIFO -> the directory names
read (r_fifo, buf, strlen (filename));
buf2[strlen(buf2)] = '\0';
printf(" directories:\n %s\n",buf2);*/
}
else {
/*child procces */
if ((w_fifo = open (FIFO, O_WRONLY)) < 0) {
perror ("open()");
exit (EXIT_FAILURE); }
/*Read from FIFO filename */
read (r_fifo, buf, strlen (buf));
buf[strlen(filename)] = '\0';
//printf("%s\n",buf);
listdir("/home/folder1",filename);
//close (w_fifo); /* EOF */
exit (EXIT_SUCCESS); }
return EXIT_SUCCESS;}

Answer 1

The parent process opens the pipe for reading and stores the descriptor in r_fifo. Then it immediately tries to write to the pipe, using the uninitialized w_fifo descriptor.
The child process does the opposite, open the pipe for writing (assigning to w_fifo) then attempts to read using the uninitialized r_fifo variable.
The parent process should open the pipe for writing, and the child process should open for reading. And both needs to use the correct and initialized variables.
There are also many other problems, like you using the strlen function on uninitialized arrays, which will not get the size of the arrays. And in the client you read into buf but use strlen(filename) to set the terminator. And you never initialize filename At all and still pass it to the listdir function.
And you really need to check what read and write returns.