How to create a folder inside proc/pid

AsmV · 10-09-2018, 04:50 PM

Hi ,

I am writing a character device with a Linux Kernel Module and the kernel version is : 4.14.74..
Basically, a user space process with a given tgid can interact with my device through ioctl.

I need to make a new directory inside /proc/pid (where pid is the tgid of the processes that have interacted with my device) so that I can create inside this new directory some files with some logs.

Is it possible to create a new directory inside /proc/pid without re-compiling the linux kernel?

In particular, I have tried to use :

Quote:

struct proc_dir_entry *proc_create(const char *name, umode_t mode,
struct proc_dir_entry *parent,
const struct file_operations *proc_fops)

but I am not able to get the struct proc_dir_entry * of the pid folder I want to write in because I am not able to include fs/proc/internal.h where PDE is defined.
Is it possible somehow to include PDE or replicate its behavior in my kernel module ?

Quote:

struct file *fp = filp_open("/proc/1",....);
struct proc_dir_entry *parent ;
parent = PDE(fp->f_dentry->d_inode);

Since
Any solution ?

smallpond · 10-10-2018, 12:29 PM

Why are you not able to include internal.h?

AsmV · 10-10-2018, 03:05 PM

Quote:

Originally Posted by smallpond

Why are you not able to include internal.h?

Because it is not accessible from the kernel module :

Quote:

fatal error: fs/proc/internal.h: No such file or directory
#include <fs/proc/internal.h>

Anyway even if I could use PDE, I think it does not work (return NULL) because pid entry are different.
I should modify on the fly the tgid_base_stuff[] defined in fs/proc/base.c to add a new pid entry

frankbell · 10-10-2018, 08:22 PM

/proc is not an actual directory/file system. From man proc:

Quote:

The proc filesystem is a pseudo-filesystem which provides an interface to kernel data structures. It is commonly mounted at /proc. Most of it is read-only, but some files allow kernel variables to be changed.

See the man page for more.