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Date:   Thu, 13 Jun 2019 17:59:06 +0200
From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     Jason Baron <jbaron@akamai.com>
Cc:     linux-kernel@vger.kernel.org
Subject: Re: [PATCH] lib: dynamic_debug: no need to check return value of
 debugfs_create functions
Message-ID: <20190613155906.GB4632@kroah.com>
References: <20190612153534.GA21141@kroah.com>
 <4936c8d8-9b69-1385-1bbf-9d19ac08d061@akamai.com>
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On Thu, Jun 13, 2019 at 10:33:23AM -0400, Jason Baron wrote:
> On 6/12/19 11:35 AM, Greg Kroah-Hartman wrote:
> > When calling debugfs functions, there is no need to ever check the
> > return value.  The function can work or not, but the code logic should
> > never do something different based on this.
> > 
> > Cc: Jason Baron <jbaron@akamai.com>
> > Cc: linux-kernel@vger.kernel.org
> > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > ---
> >  lib/dynamic_debug.c | 12 +++---------
> >  1 file changed, 3 insertions(+), 9 deletions(-)
> > 
> > diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
> > index 8a16c2d498e9..c60409138e13 100644
> > --- a/lib/dynamic_debug.c
> > +++ b/lib/dynamic_debug.c
> > @@ -993,20 +993,14 @@ static __initdata int ddebug_init_success;
> >  
> >  static int __init dynamic_debug_init_debugfs(void)
> >  {
> > -	struct dentry *dir, *file;
> > +	struct dentry *dir;
> >  
> >  	if (!ddebug_init_success)
> >  		return -ENODEV;
> >  
> >  	dir = debugfs_create_dir("dynamic_debug", NULL);
> > -	if (!dir)
> > -		return -ENOMEM;
> > -	file = debugfs_create_file("control", 0644, dir, NULL,
> > -					&ddebug_proc_fops);
> > -	if (!file) {
> > -		debugfs_remove(dir);
> > -		return -ENOMEM;
> > -	}
> > +	debugfs_create_file("control", 0644, dir, NULL, &ddebug_proc_fops);
> > +
> >  	return 0;
> >  }
> >  
> > 
> 
> Looks like debugfs_create_dir() can return NULL,

No it can not.

> and in that case if its passed to debugfs_create_file() then the
> 'control' file ends up in the root of debugfs?

If it could, yes, that is what would happen.

> I think its better to just not create the file then have it in the
> wrong place so maybe the file creation should be guarded by
> if(IS_ERR_OR_NULL(dir)).

As debugfs_create_dir() can not return NULL, you don't have to worry
about this :)

thanks,

greg k-h