From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Howells <dhowells@redhat.com>
Subject: Re: [PATCH 03/25] vfs: Allow fsinfo() to query what's in an fs_context [ver #14]
Date: Wed, 26 Jun 2019 11:02:59 +0100
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To: Christian Brauner <christian@brauner.io>
Cc: dhowells@redhat.com, viro@zeniv.linux.org.uk, raven@themaw.net, mszeredi@redhat.com, linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
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Christian Brauner <christian@brauner.io> wrote:

> > +	ret = mutex_lock_interruptible(&fc->uapi_mutex);
> > +	if (ret == 0) {
> > +		ret = -EIO;
> 
> Why EIO when there's no root dentry?

Because I don't want to use ENODATA/EBADF and preferably not EINVAL and
because the context you're accessing isn't in the correct state for you to be
able to do that.  How about EBADFD ("File descriptor in bad state")?

David