find a set of opened files / files currently in use by a process in linux

lsof.c

/**
 * Find current files in use for a specific process
 *
 * @Author: Devendra Naga ([email protected])
 *
 * License MIT
 */
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <dirent.h>
#include <sys/types.h>
#include <sys/stat.h>

int get_open_files(pid_t pid)
{
    DIR *d;
    struct dirent *dirp;
    char dirpath[100];

    snprintf(dirpath, sizeof(dirpath), "/proc/%d/fd", pid);

    // open /proc/pid/fd
    d = opendir(dirpath);
    if (!d) {
        return -1;
    }

    while ((dirp = readdir(d)) != NULL) {
        if (!strcmp(dirp->d_name, ".") ||
                !strcmp(dirp->d_name, "..")) {
            continue;
        }

        char file[512];
        char realpath[512];
        ssize_t res;

        memset(file, 0, sizeof(file));
        memset(realpath, 0, sizeof(realpath));

        // get the real file name that's in /proc/pid/fd/
        snprintf(file, sizeof(file), "%s/%s", dirpath, dirp->d_name);

        // validate if its not a directory .. we are looking for only files
        struct stat file_type;
        int ret;
        ret = stat(file, &file_type);
        if ((ret != -1) && (!S_ISDIR(file_type.st_mode))) {
            res = readlink(file, realpath, sizeof(realpath));
            if (res != -1) { // here's the rael name of the file
                printf("file %s\n", realpath);
            }
        }
    }

    closedir(d);
    return 0;
}

int main()
{
    FILE *fp;

    // testing
    fp = fopen("./lsof.txt", "w");

    get_open_files(getpid());
}