linux-kernel - Re: [PATCH] Fix debugfs_create_file's error checking method for usb/gadget/

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Date:	Mon, 20 Oct 2008 09:15:16 +0800
From:	"Zhaolei" <zhaolei@...fujitsu.com>
To:	"Alan Stern" <stern@...land.harvard.edu>
Cc:	<linux-kernel@...r.kernel.org>, <dbrownell@...rs.sourceforge.net>,
	<linux-usb@...r.kernel.org>
Subject: Re: [PATCH] Fix debugfs_create_file's error checking method for usb/gadget/

From: "Alan Stern" <stern@...land.harvard.edu>
To: "Zhaolei" <zhaolei@...fujitsu.com>
Cc: <linux-kernel@...r.kernel.org>; <dbrownell@...rs.sourceforge.net>; <linux-usb@...r.kernel.org>
Sent: Friday, October 17, 2008 11:18 PM
Subject: Re: [PATCH] Fix debugfs_create_file's error checking method for usb/gadget/


> On Fri, 17 Oct 2008, Zhaolei wrote:
> 
>> Hi,
>> 
>> debugfs_create_file() returns NULL if an error occurs, returns -ENODEV
>> when debugfs is not enabled in the kernel.
>> 
>> Signed-off-by: Zhao Lei <zhaolei@...fujitsu.com>
>> ---
>>  drivers/usb/gadget/s3c2410_udc.c |    2 +-
>>  1 files changed, 1 insertions(+), 1 deletions(-)
>> 
>> diff --git a/drivers/usb/gadget/s3c2410_udc.c b/drivers/usb/gadget/s3c2410_udc.c
>> index 29d13eb..4ba50ef 100644
>> --- a/drivers/usb/gadget/s3c2410_udc.c
>> +++ b/drivers/usb/gadget/s3c2410_udc.c
>> @@ -1894,7 +1894,7 @@ static int s3c2410_udc_probe(struct platform_device *pdev)
>>  udc->regs_info = debugfs_create_file("registers", S_IRUGO,
>>  s3c2410_udc_debugfs_root,
>>  udc, &s3c2410_udc_debugfs_fops);
>> - if (IS_ERR(udc->regs_info)) {
>> + if (IS_ERR(udc->regs_info) || !udc->regs_info) {
>>  dev_warn(dev, "debugfs file creation failed %ld\n",
>>  PTR_ERR(udc->regs_info));
>>  udc->regs_info = NULL;
> 
> In fact the original code and your patch are both wrong.  The test 
> should simply be:
> 
> if (!udc->regs_info) {
> dev_warn(dev, "debugfs file creation failed\n");
> 
Hello, Alan Stern

If we only check if (!udc->regs_info), that is no problem except that we
can't see dev_warn when debugfs isn't enabled in the kernel.
It this warning message is not necessary, I agree with you.

Thanks!
> (The line setting udc->regs_info to NULL can then be removed.)
> 
> The driver should be able to work even if debugfs isn't enabled in the 
> kernel.
> 
> Alan Stern
> 
> 
>