linux-kernel - Re: [PATCH] xen/debugfs: Check debugfs initialization before using it

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Date:	Mon, 9 Dec 2013 16:44:05 +0800
From:	Ethan Zhao <ethan.kernel@...il.com>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	konrad.wilk@...cle.com, raghavendra.kt@...ux.vnet.ibm.com,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] xen/debugfs: Check debugfs initialization before using it

On Mon, Dec 9, 2013 at 4:25 PM, Greg KH <gregkh@...uxfoundation.org> wrote:
> On Mon, Dec 09, 2013 at 09:43:16AM +0800, Ethan Zhao wrote:
>> On Sun, Dec 8, 2013 at 10:01 PM, Greg KH <gregkh@...uxfoundation.org> wrote:
>> > On Sun, Dec 08, 2013 at 07:31:02PM +0800, ethan.zhao wrote:
>> >> Should check debugfs initialization with debugfs_initialized() before using it,
>> >> Because if it isn't initialized, the return value of fake debugfs_create_dir() etc
>> >> functions would be ERR_PTR(-ENODEV), checking with NULL will not work.
>> >
>> > So?  It should "just work" without this check, right?  What happens if
>> > your patch isn't applied and debugfs isn't enabled?
>>
>> If debugfs isn't  configured, debugfs_initialized() and other
>> functions are defined as following,
>>
>> static inline bool debugfs_initialized(void)
>> {
>> return false;
>> }
>>
>> 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);
>> }
>>
>> static inline struct dentry *debugfs_create_dir(const char *name,
>> struct dentry *parent)
>> {
>> return ERR_PTR(-ENODEV);
>> }
>>
>> And the checking code in xen\debugfs.c xen_init_debugfs() will not
>> work, the return value is not NULL.
>> d_xen_debug = debugfs_create_dir("xen", NULL);
>>
>> if (!d_xen_debug)
>> pr_warning("Could not create 'xen' debugfs directory\n");
>
> Which is just fine, what is wrong with this?

If we no check with debugfs_initialized(),  the above code should be
if  (!d_xen_debug || IS_ERR (d_xen_debug))
    pr_warning("Could not create 'xen' debugfs directory\n");

>
>> >
>> > greg k-h
>> >
>> >> Signed-off-by: ethan.zhao <ethan.kernel@...il.com>
>> >
>> > Please put your "real" name here, not one with a '.' in it.
>>
>> The real name used in company is ethan.zhao@...cle.com,  but I
>> couldn't send and receive mails of
>> community with that mailbox for some reason you may know.
>
> I mean the "ethan.zhao" part, it should be "Ethan Zhao" :)

You got the my real name, thanks. :>

Ethan
>
> thanks,
>
> greg k-h
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