linux-kernel - Re: [PATCH 3/3] mm/damon/dbgfs: print DAMON debugfs interface deprecation message

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Date:   Thu, 9 Feb 2023 19:26:43 -0800
From:   Randy Dunlap <rdunlap@...radead.org>
To:     SeongJae Park <sj@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     damon@...ts.linux.dev, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] mm/damon/dbgfs: print DAMON debugfs interface
 deprecation message

Hi,

On 2/9/23 11:20, SeongJae Park wrote:
> DAMON debugfs interface has announced to be deprecated after >v5.15 LTS
> kernel is released.  And, v6.1.y has announced to be an LTS[1].
> 
> Though the announcement was there for a while, some people might not
> noticed that so far.  Also, some users could depend on it and have
> problems at  movng to the alternative (DAMON sysfs interface).
> 
> For such cases, warn DAMON debugfs interface deprecation with contacts
> to ask helps when any DAMON debugfs interface file is opened.
> 
> [1] https://git.kernel.org/pub/scm/docs/kernel/website.git/commit/?id=332e9121320bc7461b2d3a79665caf153e51732c
> 
> Signed-off-by: SeongJae Park <sj@...nel.org>
> ---
>  mm/damon/dbgfs.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/mm/damon/dbgfs.c b/mm/damon/dbgfs.c
> index b3f454a5c682..e551a20b35e3 100644
> --- a/mm/damon/dbgfs.c
> +++ b/mm/damon/dbgfs.c
> @@ -20,6 +20,11 @@ static int dbgfs_nr_ctxs;
>  static struct dentry **dbgfs_dirs;
>  static DEFINE_MUTEX(damon_dbgfs_lock);
>  
> +static void damon_dbgfs_warn_deprecation(void)
> +{
> +	pr_warn_once("DAMON debugfs interface is deprecated, so users should move to the sysfs interface (DAMON_SYSFS).  If you depend on this and cannot move, please report your usecase to damon@...ts.linux.dev and linux-mm@...ck.org.\n");
> +}

Line length of 234 is a bit over the limit.
I think it would be OK to split it at the end of the first sentence, like:

	pr_warn_once("DAMON debugfs interface is deprecated, so users should move to the sysfs interface (DAMON_SYSFS).\n");
	pr_warn_once("If you depend on this and cannot move, please report your usecase to damon@...ts.linux.dev and linux-mm@...ck.org.\n");

or would that [2 pr_warn_once() calls] not work for some reason?

Or even:

	pr_warn_once(
"DAMON debugfs interface is deprecated, so users should move to the sysfs interface (DAMON_SYSFS).\n");
	pr_warn_once(
"If you depend on this and cannot move, please report your usecase to damon@...ts.linux.dev and linux-mm@...ck.org.\n");

although some people might gag at that one.


-- 
~Randy