Is there a way to find the file names of files mapped to the virtual memory area of a process in the linux kernel?

Question

Been working on a project for a few weeks now and I've hit a pretty significant roadblock and I was hoping somebody here might be able to offer some guidance.

All I need to do is write a system call that reports statistics of a process’s virtual address space when called. Those statistics, according to the assignment criteria, need to include the size of the process’s virtual address space, each virtual memory area’s access permissions, and the names of files mapped to these virtual memory areas.

The first two I have working, the last appears to not be possible, at least from what my research and attempts so far have turned up. I've isolated it down to accessing the vm_file struct within the vm_area_struct of the process and using that to get to the f_path, but past that I'm still stuck on how to get from there to a format that can actually be put into a printk statement, and everything I've tried hasn't output anything when I finally get the kernel recompiled.

Here's where the code sits at the moment. Am I even on the right track?

#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/mm_types.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/path.h>
#include <linux/dcache.h>

asmlinkage int sys_project3a1(unsigned int processID)
{
    struct task_struct *task;
    for_each_process(task)
    {    
     if (task->pid == processID)
     {
         unsigned long  virtualAddressSpace = 0;
         struct vm_area_struct *vmlist;

         printk("Process ID: %d", task->pid);

         for (vmlist = task->mm->mmap; vmlist!=NULL; vmlist=vmlist->vm_next)
         {
             unsigned long space = vmlist->vm_end - vmlist->vm_start;
             char *tmp;
             char *pathname;
             struct file *file;
             struct path *path;
             printk("Process Access Permissions: %lu", (unsigned long)(vmlist->vm_page_prot.pgprot));

             file = vmlist->vm_file;

             path = &file->f_path;
             path_get(path);

             tmp = (char *)__get_free_page(GFP_TEMPORARY);

             pathname = d_path(path, tmp, PAGE_SIZE);    

             printk("Path Name: %s", pathname);
             free_page((unsigned long)tmp);
             virtualAddressSpace += space;
         }
         printk("Process Virtual Address Space: %lu", virtualAddressSpace);

     }
    }    
    return 1;
}

Answer 1

struct vm_area_struct *vas;

vas->vm_file->f_path.dentry->d_name.name

Answer 2

I was in a similar situation and had to find this on my own. Hope others who come here benefit from my answer.

So I am assuming you want the values corresponding to "Mapping" column of a pmap command ouput. The following works for me(tried on v4.6.4):

char filename[50];
if(vmlist->vm_file){ 
    strcpy(filename, vmlist->vm_file->f_path.dentry->d_iname);
}
else{ // implies an anonymous mapping i.e. not file backup'ed
    strcpy(filename, "[ anon ]");
}

After getting to the path, follow it's dentry field and then d_iname which is the mapped file's name. Doesn't look quite pretty, but does the job.