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

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Date:   Mon, 11 Dec 2017 13:46:48 +0900
From:   "Prashant Bhole" <bhole_prashant_q7@....ntt.co.jp>
To:     "'David Miller'" <davem@...emloft.net>,
        <jakub.kicinski@...ronome.com>
Cc:     <netdev@...r.kernel.org>
Subject: RE: [PATCH net-next] netdevsim: correctly check return value of debugfs_create_dir


> 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.

-Prashant