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

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Date:   Wed, 20 Dec 2017 09:16:01 +0900
From:   "Prashant Bhole" <bhole_prashant_q7@....ntt.co.jp>
To:     "'David Miller'" <davem@...emloft.net>
Cc:     <jakub.kicinski@...ronome.com>, <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: Tue, 19 Dec 2017 13:45:47 +0900
> 
> > I tried to evaluate whether fixing return value of
> > debugfs_create_dir() (and
> > friends) will be useful or not because it has not been changed since
> > very long time. Now I am not much convinced about changing this api.
> >
> > Important and possible error codes could be -EEXIST and -ENOMEM.
> > Suppose -EEXIST is returned, IMO the directory shouldn't exists in the
> > first place because it is specific to particular module. Also, there
> > is no point in creating file in such directory, because directory
> > owner (creator) might remove it too. This means there are less chances
> > that api change will be useful. Please let me know your opinion on it.
> >
> > If you are ok with above explanation, shall I submit v2 for this patch?
> 
> Well, something is seriously wrong if the directory exists already.
> 
> It could be that two netdevsim modules, independantly compiled, are trying
to
> be loaded.
> 
> Wouldn't it clearly be desirable to fail and not load the module in that
case?
> 
> This is why I think ignoring debugfs errors is foolish.

Right. I am planning to do following (quoting previous mail), In debugfs
error will not be ignored in modules load.
-----------
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.
-----------

Shall I submit v2?

-Prashant