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Date: Wed, 18 Jul 2012 11:59:21 -0700
From: Stephen Boyd <sboyd@codeaurora.org>
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To: Anton Vorontsov <anton.vorontsov@linaro.org>
CC: Steven Rostedt <rostedt@goodmis.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Kees Cook <keescook@chromium.org>, Colin Cross <ccross@android.com>,
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Subject: Re: [PATCH] pstore/ftrace: Convert to its own enable/disable debugfs
 knob
References: <20120710001004.GA22744@lizard> <1341879046-5197-3-git-send-email-anton.vorontsov@linaro.org> <1342553898.10332.9.camel@gandalf.stny.rr.com> <20120717200130.GA31678@lizard> <1342561102.10332.18.camel@gandalf.stny.rr.com> <20120718034722.GA18081@lizard> <5006EE8C.20304@codeaurora.org> <20120718185029.GA4184@lizard>
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On 07/18/12 11:50, Anton Vorontsov wrote:
> On Wed, Jul 18, 2012 at 10:12:44AM -0700, Stephen Boyd wrote:
>> On 07/17/12 20:47, Anton Vorontsov wrote:
>>> +
>>> +	file = debugfs_create_file("record_ftrace", 0600, dir, NULL,
>>> +				   &pstore_knob_fops);
>>> +	if (IS_ERR_OR_NULL(file)) {
>>> +		err = PTR_ERR(file);
>>> +		pr_err("%s: unable to create pstore/ftrace file: %d\n",
>>> +		       __func__, err);
>>> +		goto err_file;
>>> +	}
>> debugfs only returns NULL on failure.
> Well, techincally, with DEBUG_FS=y, yes. (And we have dependency on
> it.)
>
> But see include/linux/debugfs.h for DEBUG_FS=n case:
>
> static inline struct dentry *debugfs_create_file(const char *name, umode_t mode,
>                                         struct dentry *parent, void *data,
>                                         const struct file_operations *fops)
> {
>         return ERR_PTR(-ENODEV);
> }
>
> So, I think it is fine to check for IS_ERR_OR_NULL(), although today
> it's always NULL for our case, true.

What does PTR_ERR(NULL) mean then? It will always print "unable to
create pstore/ftrace file: 0"?

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