Question

I need to find the open files of the current process in C Linux. So far all I could figure out was current -> task_struct… then there aren’t a log of resources…eventually I’m supposed to get to open_fds? Also, is the endpoint a bitmap file? How would you get the open files from the bitmap structure or some other weird structure?

Answer 1

on the command line lsof

in C, something like this:

Here is the commented code of a program that prints on screen a list of its own open files:

#include <unistd.h>
#include <stdio.h>
#include <dirent.h>

int main() {
    // the directory we are going to open
    DIR           *d;

    // max length of strings
    int maxpathlength=256;

    // the buffer for the full path
    char path[maxpathlength];

    // /proc/PID/fs contains the list of the open file descriptors among the respective filenames
    sprintf(path,"/proc/%i/fd/",getpid() );

    printf("List of %s:\n",path);

    struct dirent *dir;
    d = opendir(path);
    if (d) {
        //loop for each file inside d
        while1 != NULL) {

            //let's check if it is a symbolic link
            if (dir->d_type == DT_LNK) {

                const int maxlength = 256;

                # string returned by readlink()
                char hardfile[maxlength];

                #string length returned by readlink()
                int len;

                # tempath will contain the current filename among the fullpath
                char tempath[maxlength];

                sprintf(tempath,"%s%s",path,dir->d_name);
                if2!=-1) {
                    hardfile[len]='\0';
                        printf("%s -> %s\n", dir->d_name,hardfile);

                } else
                    printf("error when executing readlink() on %s\n",tempath);

            }
        }

        closedir(d);
    }
    return 0;
}

This code is from: http://mydebian.blogdns.org/?p=229 , which is cached here: http://tinyurl.com/6qlv2nj

See:

How to use lsof(List Opened Files) in a C/C++ application?

http://www.linuxquestions.org/questions/linux-security-4/c-library-for-lsof-183332/

you could also use the lsof command via a popen call.