linux-ext4 - Re: [PATCH v5 04/23] fsnotify: Reserve mark bits for backends

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Message-ID: <20210805091407.GB14483@quack2.suse.cz>
Date:   Thu, 5 Aug 2021 11:14:07 +0200
From:   Jan Kara <jack@...e.cz>
To:     Gabriel Krisman Bertazi <krisman@...labora.com>
Cc:     jack@...e.com, amir73il@...il.com, djwong@...nel.org,
        tytso@....edu, david@...morbit.com, dhowells@...hat.com,
        khazhy@...gle.com, linux-fsdevel@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-api@...r.kernel.org,
        kernel@...labora.com
Subject: Re: [PATCH v5 04/23] fsnotify: Reserve mark bits for backends

On Wed 04-08-21 12:05:53, Gabriel Krisman Bertazi wrote:
> Split out the final bits of struct fsnotify_mark->flags for use by a
> backend.
> 
> Signed-off-by: Gabriel Krisman Bertazi <krisman@...labora.com>
> ---
>  include/linux/fsnotify_backend.h | 19 ++++++++++++++++---
>  1 file changed, 16 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
> index 1ce66748a2d2..9d5586445c65 100644
> --- a/include/linux/fsnotify_backend.h
> +++ b/include/linux/fsnotify_backend.h
> @@ -363,6 +363,21 @@ struct fsnotify_mark_connector {
>  	struct hlist_head list;
>  };
>  
> +#define FSNOTIFY_MARK_FLAG(flag)	\
> +static const unsigned int FSNOTIFY_MARK_FLAG_##flag = \
> +	(1 << FSN_MARK_FL_BIT_##flag)

Static variable declaration in a header file makes me a bit uneasy. I know
it is const so a compiler should optimize this to a constant but still
there will likely be some side-effects (see the 0-day warning).

Honestly, given these are just three flags I'd just don't overengineer this
and have:

#define FSNOTIFY_MARK_FLAG_IGNORED_SURV_MODIFY \
			(1 << FSN_MARK_FL_BIT_IGNORED_SURV_MODIFY)
...

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR