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

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Date:   Tue, 2 Feb 2021 13:07:50 +0100
From:   Ilya Dryomov <idryomov@...il.com>
To:     Jiapeng Chong <jiapeng.chong@...ux.alibaba.com>
Cc:     Jeff Layton <jlayton@...nel.org>,
        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 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.

Thanks,

                Ilya