netdev - Re: [PATCH net-next] netdevsim: correctly check return value of debugfs_create

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Date:   Mon, 11 Dec 2017 10:40:29 -0800
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     "Prashant Bhole" <bhole_prashant_q7@....ntt.co.jp>
Cc:     "'David Miller'" <davem@...emloft.net>, <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] netdevsim: correctly check return value of
 debugfs_create_dir

On Mon, 11 Dec 2017 13:46:48 +0900, Prashant Bhole wrote:
> > From: David Miller [mailto:davem@...emloft.net]
> > 
> > From: Prashant Bhole <bhole_prashant_q7@....ntt.co.jp>
> > Date: Fri,  8 Dec 2017 09:52:50 +0900
> >   
> > > Return value is now checked with IS_ERROR_OR_NULL because
> > > debugfs_create_dir doesn't return error value. It either returns NULL
> > > or a valid pointer.
> > >
> > > Signed-off-by: Prashant Bhole <bhole_prashant_q7@....ntt.co.jp>
> > > ---
> > >  drivers/net/netdevsim/netdev.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/net/netdevsim/netdev.c
> > > b/drivers/net/netdevsim/netdev.c index eb8c679fca9f..88d8ee2c89da
> > > 100644
> > > --- a/drivers/net/netdevsim/netdev.c
> > > +++ b/drivers/net/netdevsim/netdev.c
> > > @@ -469,7 +469,7 @@ static int __init nsim_module_init(void)
> > >  	int err;
> > >
> > >  	nsim_ddir = debugfs_create_dir(DRV_NAME, NULL);
> > > -	if (IS_ERR(nsim_ddir))
> > > +	if (IS_ERR_OR_NULL(nsim_ddir))
> > >  		return PTR_ERR(nsim_ddir);  
> > 
> > debugfs_create_dir() should really be fixed, either it uses error pointers
> > consistently and therefore always provides a suitable error code to return  
> or it
> > always uses NULL.
> > 
> > This in-between behavior makes using it as an interface painful because no  
> clear
> > meaning is given to NULL.
> > 
> > So please do the work necessary to make debugfs_create_dir()'s return
> > semantics clearer and more useful.
> > 
> > Thank you.  
> 
> Dave,
> Thanks for comments. I will try to fix error handling in netdevsim first.
> 
> Jakub,
> Let's decide with an example. The typical directory structure for netdevsim
> interface is as below:
> /sys/kernel/debug/netdevsim/sim0/bpf_bound_progs/
> Please let me know if you are ok with following:
> 
> 1) If debugfs_create_dir() fails in module_init, let's keep it fatal error
> with corrected condition:
> +	if (IS_ERR_OR_NULL(nsim_ddir))
> +		return -ENOMEM;
> 
> 2) In case sim0 or bpf_bound_progs are  fail to create, we need to add
> checks before creating any file in them.

Fine with me, although if you fix DebugFS first you could use the real
error from the start here.