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

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Date:	Mon, 9 Dec 2013 09:43:16 +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 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");
>
> 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.

Thanks,
Ethan

>
> thanks,
>
> greg k-h
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