Implementing symlinks in a virtual file system

Question

I'm working on a virtual file system which isn't disk based, kind of like /proc. Now I want to create a symlink within it to a target on a ext3 file system. I haven't found any standard documentation on ways to achieve this. What I've guessed so far is that I have to write a function to put in for symlink in struct inode_operations. But frankly I'm at a loss even with the function parameters.

If it matters, I started off with this tutorial on LWN: http://lwn.net/Articles/13325/

EDIT: I'm working with libfs, not FUSE at the moment

Answer 1

Presumably you're using fuse, if you're not, do :)

All you have to do is implement the getattr function to tell the kernel that the object is a symlink, then implement the readlink function and return the path that the link should link to; the kernel will do the rest.

Answer 2

I was able to accomplish it finally. Here is what I did (some details may differ depending on what the filesystem wants to achieve):

1. Create inode of the symlink with the S_IFLNK mode and add the target to the i_private field.

2. Implement follow_link because generic_readlink requires it to be present

static void *sample_follow_link (struct dentry *dentry, struct nameidata *nd)
{
    nd->depth = 0;
    nd_set_link(nd, (char *)dentry->d_inode->i_private);
    return NULL;
}

static struct inode_operations sample_inode_ops = {
    .readlink = generic_readlink,
    .follow_link = sample_follow_link,
};

.....
//in the function for the dentry and inode creation 
inode->i_op = sample_inode_ops