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gaurav
gaurav

Reputation: 891

Getting current working directory within kernel code

I am working on a project in which I need to know the current working directory of the executable which called the system call. I think it would be possible as some system calls like open would make use of that information.

Could you please tell how I can get the current working directory path in a string?

Upvotes: 6

Views: 4751

Answers (3)

garlix
garlix

Reputation: 596

In newer kernels things changed a little bit. You can use this to get the current working directory:

#include <linux/init.h>         // module_{init,exit}()
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/dcache.h>       // dentry_path_raw
#include <linux/fs_struct.h>    // get_fs_pwd

static int __init get_cwd_module_init(void)
{
    struct path abs_path;
    char *buf, *full_path;

    buf = __getname();
    if (!buf)
        return -ENOMEM;

    get_fs_pwd(current->fs, &abs_path);

    full_path = dentry_path_raw(abs_path.dentry, buf, PATH_MAX);
    if (IS_ERR(full_path)) {
        pr_err("dentry_path_raw failed: %li", PTR_ERR(full_path));
    } else {
        pr_info("Full path: '%s'", full_path);
    }
    __putname(buf);
    path_put(&abs_path);
}

static void __exit get_cwd_module_exit(void)
{
    pr_info("exiting...");
}

module_init(get_cwd_module_init)
module_exit(get_cwd_module_exit)

MODULE_AUTHOR("garlix");
MODULE_LICENSE("GPL");

Upvotes: 0

Daimrod
Daimrod

Reputation: 5030

How do you do that in a terminal ? You use pwd which looks at the environment variable named PWD.

#include <stdlib.h>

int main(int ac, char **av) {
    printf("%s\n", getenv("PWD");

    return 0;
}

If you want to know in which directory the executable is located you can combine the information from getenv and from argv[0].

Upvotes: -1

Mat
Mat

Reputation: 206727

You can look at how the getcwd syscall is implemented to see how to do that.

That syscall is in fs/dcache.c and calls:

get_fs_root_and_pwd(current->fs, &root, &pwd);

root and pwd are struct path variables,

That function is defined as an inline function in include/linux/fs_struct.h, which also contains:

static inline void get_fs_pwd(struct fs_struct *fs, struct path *pwd)

and that seems to be what you are after.

Upvotes: 12

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