linux-kernel - Re: [PATCH] pstore/ftrace: Convert to its own enable/disable debugfs knob

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Message-ID: <50070789.7040601@codeaurora.org>
Date:	Wed, 18 Jul 2012 11:59:21 -0700
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Anton Vorontsov <anton.vorontsov@...aro.org>
CC:	Steven Rostedt <rostedt@...dmis.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Kees Cook <keescook@...omium.org>,
	Colin Cross <ccross@...roid.com>,
	Tony Luck <tony.luck@...el.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>, Arnd Bergmann <arnd@...db.de>,
	John Stultz <john.stultz@...aro.org>,
	Shuah Khan <shuahkhan@...il.com>, arve@...roid.com,
	Rebecca Schultz Zavin <rebecca@...roid.com>,
	Jesper Juhl <jj@...osbits.net>,
	Randy Dunlap <rdunlap@...otime.net>,
	Thomas Meyer <thomas@...3r.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Marco Stornelli <marco.stornelli@...il.com>,
	WANG Cong <xiyou.wangcong@...il.com>,
	linux-kernel@...r.kernel.org, devel@...verdev.osuosl.org,
	linaro-kernel@...ts.linaro.org, patches@...aro.org,
	kernel-team@...roid.com
Subject: Re: [PATCH] pstore/ftrace: Convert to its own enable/disable debugfs
 knob

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"?

-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

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