linux-kernel - Re: [PATCH 1/5] kernfs: implement i

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Message-ID: <20170523150946.GA6123@smirco-mbp.DHCP.thefacebook.com>
Date:   Tue, 23 May 2017 08:09:48 -0700
From:   Shaohua Li <shli@...com>
To:     Christoph Hellwig <hch@...radead.org>
CC:     <linux-kernel@...r.kernel.org>, <tj@...nel.org>,
        <gregkh@...uxfoundation.org>, <viro@...iv.linux.org.uk>,
        <Kernel-team@...com>
Subject: Re: [PATCH 1/5] kernfs: implement i_generation

On Tue, May 23, 2017 at 12:41:12AM -0700, Christoph Hellwig wrote:
> On Mon, May 22, 2017 at 03:53:05PM -0700, Shaohua Li wrote:
> > Set i_generation for kernfs inod. This is required to implement exportfs
> > operations.
> > 
> > Signed-off-by: Shaohua Li <shli@...com>
> > ---
> >  fs/kernfs/dir.c        | 2 ++
> >  fs/kernfs/inode.c      | 1 +
> >  include/linux/kernfs.h | 2 ++
> >  3 files changed, 5 insertions(+)
> > 
> > diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
> > index db5900aaa..09d093e 100644
> > --- a/fs/kernfs/dir.c
> > +++ b/fs/kernfs/dir.c
> > @@ -634,6 +634,7 @@ static struct kernfs_node *__kernfs_new_node(struct kernfs_root *root,
> >  	if (ret < 0)
> >  		goto err_out2;
> >  	kn->ino = ret;
> > +	kn->generation = atomic_inc_return(&root->next_generation);
> 
> i_generation is only supposed to be valid on a per-inode basis, so this
> global counter seems really odd.

What's the difference between per-inode or per-super? The i_generation doesn't
need to be consecutive for an inode. I checked other fs, a lot of filesystems
implement i_generation in this way, for example, f2fs, ext4.

Thanks,
Shaohua