linux-kernel - Re: [PATCH] debugfs: Document that debugfs_create functions need not be error checked

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Date:   Wed, 23 Feb 2022 09:49:15 +0100
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     Douglas Anderson <dianders@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Jani Nikula <jani.nikula@...ux.intel.com>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] debugfs: Document that debugfs_create functions need not
 be error checked

Hello Doug,

On 2/23/22 00:46, Douglas Anderson wrote:
> As talked about in commit b792e64021ec ("drm: no need to check return
> value of debugfs_create functions"), in many cases we can get away
> with totally skipping checking the errors of debugfs functions. Let's
> document that so people don't add new code that needlessly checks
> these errors.
> 
> Probably this note could be added to a boatload of functions, but
> that's a lot of duplication.  Let's just add it to the two most
> frequent ones and hope people will get the idea.
> 

Agreed. The first contact point for folks looking for the function's
return values will probably be these two, I second that is enough.

> Suggested-by: Javier Martinez Canillas <javierm@...hat.com>
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
> 
>  fs/debugfs/inode.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
> index 2f117c57160d..3dcf0b8b4e93 100644
> --- a/fs/debugfs/inode.c
> +++ b/fs/debugfs/inode.c
> @@ -450,6 +450,11 @@ static struct dentry *__debugfs_create_file(const char *name, umode_t mode,
>   *
>   * If debugfs is not enabled in the kernel, the value -%ENODEV will be
>   * returned.
> + *
> + * NOTE: it's expected that most callers should _ignore_ the errors returned
> + * by this function. Other debugfs functions handle the fact that the "dentry"
> + * passed to them could be an error and they don't crash in that case.
> + * Drivers should generally work fine even if debugfs fails to init anyway.
>   */

Thanks a lot for adding this. I was confused why the kernel doc didn't mention
anything like that, yet most drivers didn't check and just ignored the errors.

Reviewed-by: Javier Martinez Canillas <javierm@...hat.com>

Best regards,
-- 
Javier Martinez Canillas
Linux Engineering
Red Hat