How to find a dentry from an inode/pathname?

问题

I am working on a module to read a files xattributes on open. I have hooked the sys_open and due to this I need to get the dentry of the file without opening the file. In brief I have the inode and the absolute path but having trouble to figure out; how to get a dentry from these. All comments are very much appreciated.

回答1:

As per my understating you are trying to get the dentry path from your driver module during the open callback function . If so; then before putting down the way I am adding the structure list which are required to access the the dentry information.

include/linux/fs.h

Struct file{
struct path             f_path;
};

include/linux/path.h

struct path {
           struct vfsmount *mnt;
           struct dentry *dentry;
  };

include/linux/dcache.h

struct dentry {
};

So you can do like this.

 static int sample_open(struct inode *inode, struct file *file)
    { 
    char *path, *dentry,*par_dentry;
    char buff[256];
    dentry = file->f_path.dentry->d_iname;
    pr_info("dentry :%s\n",dentry);
    par_dentry = file->f_path.dentry->d_parent->d_iname;
    pr_info("parent dentry :%s\n",par_dentry);
    path=dentry_path_raw(file->f_path.dentry,buff,256);
    pr_info("Dentry path %s\n",path);
    }

回答2:

The question is wrong. Extended attributes are stored in the inode, thus as long as you have the inode you can just access them.

I have hooked the sys_open and due to this I need to get the dentry of the file without opening the file.

This is wrong on 2 accounts.

sys_open is not the only place which can open a file.
even if you hooked into all places, the additional lookup you perform can find a different file than the one which got opened (consider a joker doing cp file1 toopen; cp fil2 toopen in a loop)

What you want to is use the LSM framework (Linux Security Modules). In particular see security_file_open.

However, given the quality of the question I have to ask what is this about. Is this a college project? I would argue you are not prepared to work on it and would suggest changing to a non-kernel one if possible.

来源：https://stackoverflow.com/questions/43235313/how-to-find-a-dentry-from-an-inode-pathname

标签

Linux

linux-kernel

inode