Re: [RFC][PATCH 03/13] ovl: lookup redirect by file handle

[Vivek Goyal <vgoyal@redhat.com>]

On Mon, Apr 17, 2017 at 02:59:33AM +0300, Amir Goldstein wrote:

[..]
> @@ -272,6 +385,33 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
>  			goto out_put_upper;
>  	}
>  
> +	/* Try to lookup lower layers by file handle (at root) */
> +	d.by_path = false;
> +	for (i = 0; !d.stop && d.fh && i < roe->numlower; i++) {
> +		struct path lowerpath = roe->lowerstack[i];
> +
> +		d.last = i == roe->numlower - 1;
> +		err = ovl_lookup_layer_fh(&lowerpath, &d, &this);
> +		if (err)
> +			goto out_put;
> +
> +		if (!this)
> +			continue;
> +
> +		stack[ctr].dentry = this;
> +		stack[ctr].mnt = lowerpath.mnt;
> +		ctr++;
> +	}
> +
> +	/* Fallback to lookup lower layers by name (at parent) */
> +	if (ctr) {
> +		d.stop = true;

Hi Amir,

Got a very basic question. So say I two lower layers and a directory is
in present in both, say lower1/dir1 and lower2/dir1. Now this directory
gets copied up to upper/dir1. Assume lower1/dir1 is being copied up. So
upper/dir1 will save file handle of lower1/dir1 right? This file handle
does not represent lower2/dir1?

IOW, later when I am doing lookup, then using file handle I will find
dentry of lower1/dir1 but not lower2/dir1. And looks like we will not
path based lookup as ctr will be non-zero (as we found one dentry in
one path).

What am I missing.

(This ovl_lookup() logic has become really twisted now. I wished it was
 little easier to read.)

Vivek