How to open and read file from `struct inode *` in Linux kernel

Question

I want to check the content of a file from Linux Kernel v3.0.8 knowing only struct inode *. I only need to read the beginning of a file pointed by this inode, then close and return. I don't care about additional information like filename/mountpoint etc.. In fact, the file may not have the name (like deleted but still open). Is it possible?

Answer 1

I finally did it like this:

1. This is needed.

struct path root;
struct file *filerd;

2. Get the init task fs root.

task_lock(&init_task);
get_fs_root(init_task.fs, &root);
task_unlock(&init_task);

3. Change dentry to this file:

root.dentry = d_find_alias(inode);

4. Open file:

filerd = file_open_root(root.dentry->d_parent, root.mnt,
                        root.dentry->d_name.name, O_RDONLY);

It worked for every process I tested and for different mount points, which surprised me.