What's wrong in this code?? This code is about Limiting the maximum size of file the process can create

Question

Code to write data in to file example.txt.. which is working fine

// basic file operations
#include <iostream>
#include <fstream>
using namespace std;

int main () {
  ofstream myfile;
  myfile.open ("example.txt");
  myfile << "Writing this to a file.\n";
  myfile << "Writing this to a file.\n";
  myfile << "Writing this to a file.\n";
  myfile << "Writing this to a file.\n";
  myfile << "Writing this to a file.\n";
  myfile << "Writing this to a file.\n";
  myfile.close();
  return 0;
}

File : filelimit.c below which takes input as the compiled binary of above code
In this code i am setting the file size limit of process to 10 bytes and the above code is trying to write more than 10 bytes. According to below code if a process is trying to write more than 10 bytes to file it should send the signal SIGXFSZ (see more about this here)

It is not sending here... Why??

#include <stdio.h>
#include <signal.h>
#include <unistd.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>

void handler(int sig)
{
    if(sig == SIGXFSZ)
        printf("Inside handler with correct signal\n");
    else
        printf("Inside handler with wrong signal\n");
}


int main(int argc, char const *argv[])
{
    pid_t pid;
    pid = fork();

    if(pid == 0)
    {
        signal(SIGXFSZ, handler);

        char command[256];
        scanf("%s", command);

        int ret;

        struct rlimit rl;
        rl.rlim_cur = 10;
        rl.rlim_max = 10;
        setrlimit (RLIMIT_FSIZE, &rl);

        char *envp[] = { NULL };
        char *argv[] = { command , NULL };
        ret = execve(command, argv, envp);

        while(1);
    }
    else
    {
        printf("%d - %d\n", getpid(), pid);
        signal(SIGXFSZ, handler);
        while(1);
    }
    return 0;
}

Comments

I tried to test the code and saw that the file example.txt is created with 10 bytes only i.e "Writing th" which is expected, can u please explain what u are expecting.

---

Now I got ur question, so I tried the following program
I tried with the following program -

    int main()
    {
            char command[]="./b"; // b is my binary name from previous file
            struct rlimit rl;
    
            signal(SIGXFSZ, handler);
            rl.rlim_cur = 10;
            rl.rlim_max = 10;
            setrlimit (RLIMIT_FSIZE, &rl);
    
            char *envp[] = { NULL };
            char *argv[] = { command , NULL };
    
            execve(command, argv, envp);
            while(1);
    
            return 0;
    }

Output

    File size limit exceeded

So now the conclusion is it is something to do with the fork and signal handling, which is in WIP, but nice question...

---

@Salil Yes, i'm asking for catching the file limit exceeded signal

---

@Raghu that's what I tried without forking and it worked.

---

But i want with fork. Please let me know if you find the answer with fork

---

Not sure if serves your purpose, changed the behaviour of child and parent process and in parent process it worked I mean signal raised and cought properly.

Done few experiment and tried to send the signal explicitly to child process which was working properly

So the summary is it is still not solved and my take is setrlimit is working properly but does not raise a signal if it is called from child process this could be because of some (additional) setting required or a bug :(