netdev - Re: [PATCH bpf-next v10 2/4] bpf: new helper to obtain namespace data from current task New bpf helper bpf_get_current_pidns

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Date:   Fri, 6 Sep 2019 17:00:20 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Carlos Neira <cneirabustos@...il.com>
Cc:     netdev@...r.kernel.org, yhs@...com, ebiederm@...ssion.com,
        brouer@...hat.com, bpf@...r.kernel.org
Subject: Re: [PATCH bpf-next v10 2/4] bpf: new helper to obtain namespace
 data from  current task New bpf helper bpf_get_current_pidns_info.

On Fri, Sep 06, 2019 at 04:46:47PM +0100, Al Viro wrote:

> > Where do I begin?
> > 	* getname_kernel() is there for purpose
> > 	* so's kern_path(), damnit
> 
> Oh, and filename_lookup() *CAN* sleep, obviously.  So that
> GFP_ATOMIC above is completely pointless.
> 
> > > +
> > > +	inode = d_backing_inode(kp.dentry);
> > > +	pidns_info->dev = (u32)inode->i_rdev;

In the original variant of patchset it used to be ->i_sb->s_dev,
which is also bloody strange - you are not asking filename_lookup()
to follow symlinks, so you'd get that of whatever filesystem
/proc/self/ns resides on.

->i_rdev use makes no sense whatsoever - it's a symlink and
neither it nor its target are device nodes; ->i_rdev will be
left zero for both.

What data are you really trying to get there?