linux-kernel - Re: [PATCH] ceph: Replace DEFINE_SIMPLE_ATTRIBUTE with DEFINE_DEBUGFS

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Date:   Tue, 02 Feb 2021 11:01:14 -0500
From:   Jeff Layton <jlayton@...nel.org>
To:     Ilya Dryomov <idryomov@...il.com>,
        Jiapeng Chong <jiapeng.chong@...ux.alibaba.com>
Cc:     Ceph Development <ceph-devel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ceph: Replace DEFINE_SIMPLE_ATTRIBUTE with
 DEFINE_DEBUGFS_ATTRIBUTE

On Tue, 2021-02-02 at 07:45 -0500, Jeff Layton wrote:
> On Tue, 2021-02-02 at 13:07 +0100, Ilya Dryomov wrote:
> > On Mon, Feb 1, 2021 at 8:52 AM Jiapeng Chong
> > <jiapeng.chong@...ux.alibaba.com> wrote:
> > > 
> > > Fix the following coccicheck warning:
> > > 
> > > ./fs/ceph/debugfs.c:347:0-23: WARNING: congestion_kb_fops should be
> > > defined with DEFINE_DEBUGFS_ATTRIBUTE.
> > > 
> > > Reported-by: Abaci Robot <abaci@...ux.alibaba.com>
> > > Signed-off-by: Jiapeng Chong <jiapeng.chong@...ux.alibaba.com>
> > > ---
> > >  fs/ceph/debugfs.c | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/fs/ceph/debugfs.c b/fs/ceph/debugfs.c
> > > index 66989c8..617327e 100644
> > > --- a/fs/ceph/debugfs.c
> > > +++ b/fs/ceph/debugfs.c
> > > @@ -344,8 +344,8 @@ static int congestion_kb_get(void *data, u64 *val)
> > >         return 0;
> > >  }
> > > 
> > > -DEFINE_SIMPLE_ATTRIBUTE(congestion_kb_fops, congestion_kb_get,
> > > -                       congestion_kb_set, "%llu\n");
> > > +DEFINE_DEBUGFS_ATTRIBUTE(congestion_kb_fops, congestion_kb_get,
> > > +                         congestion_kb_set, "%llu\n");
> > > 
> > > 
> > >  void ceph_fs_debugfs_cleanup(struct ceph_fs_client *fsc)
> > 
> > Hi Jiapeng,
> > 
> > What is the benefit of this conversion?
> > 
> > From a quick look, with DEFINE_DEBUGFS_ATTRIBUTE writeback_congestion_kb
> > file would no longer be seekable.  It may not matter much, but something
> > that should have been mentioned.
> > 
> > Futher, debugfs_create_file() creates a full proxy for fops, protecting
> > against removal races.  DEFINE_DEBUGFS_ATTRIBUTE adds its own protection
> > but just for ->read() and ->write().  I don't think we need both.
> > 
> 
> 
> The coccinelle script clarifies some of this. See the commit log here:
> 
>     https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=5103068eaca290f890a30aae70085fac44cecaf6
> 
> That said, it also mentions that the file should be converted to use
> debugfs_create_file_unsafe now as well, and that wasn't done in this
> patch. Jiapeng, was that intentional? If so, why?
> 

For now, I've dropped this patch until the situation with
debugfs_create_file_unsafe is clear.
-- 
Jeff Layton <jlayton@...nel.org>