Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <162375263398.232295.14755578426619198534.stgit@web.messagingengine.com>
 <162375276735.232295.14056277248741694521.stgit@web.messagingengine.com>
In-Reply-To: <162375276735.232295.14056277248741694521.stgit@web.messagingengine.com>
From:   Miklos Szeredi <miklos@szeredi.hu>
Date:   Wed, 16 Jun 2021 11:11:25 +0200
Message-ID: <CAJfpegtgXvW+vyKQEvQauSXskYiO+GAjViDYo_84sa23eWCjdw@mail.gmail.com>
Subject: Re: [PATCH v7 2/6] kernfs: add a revision to identify directory node changes
To:     Ian Kent <raven@themaw.net>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Tejun Heo <tj@kernel.org>, Eric Sandeen <sandeen@sandeen.net>,
        Fox Chen <foxhlchen@gmail.com>,
        Brice Goglin <brice.goglin@gmail.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Rick Lindsley <ricklind@linux.vnet.ibm.com>,
        David Howells <dhowells@redhat.com>,
        Marcelo Tosatti <mtosatti@redhat.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Carlos Maiolino <cmaiolino@redhat.com>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Kernel Mailing List <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Tue, 15 Jun 2021 at 12:26, Ian Kent <raven@themaw.net> wrote:
>
> Add a revision counter to kernfs directory nodes so it can be used
> to detect if a directory node has changed during negative dentry
> revalidation.
>
> There's an assumption that sizeof(unsigned long) <= sizeof(pointer)
> on all architectures and as far as I know that assumption holds.
>
> So adding a revision counter to the struct kernfs_elem_dir variant of
> the kernfs_node type union won't increase the size of the kernfs_node
> struct. This is because struct kernfs_elem_dir is at least
> sizeof(pointer) smaller than the largest union variant. It's tempting
> to make the revision counter a u64 but that would increase the size of
> kernfs_node on archs where sizeof(pointer) is smaller than the revision
> counter.
>
> Signed-off-by: Ian Kent <raven@themaw.net>

Reviewed-by: Miklos Szeredi <mszeredi@redhat.com>