linux-kernel - Re: [Patch] compat ioctl: fix some build warnings

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Date:	Mon, 08 Feb 2010 10:56:26 +0800
From:	Cong Wang <amwang@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	linux-kernel@...r.kernel.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Arnd Bergmann <arnd@...db.de>
Subject: Re: [Patch] compat ioctl: fix some build warnings

Andrew Morton wrote:
> On Fri, 5 Feb 2010 02:05:56 -0500
> Amerigo Wang <amwang@...hat.com> wrote:
> 
>> I got these warnings:
>>
>> fs/compat_ioctl.c: In function ___compat_sys_ioctl':
>> fs/compat_ioctl.c:534: warning: ___karg' may be used uninitialized in this function
>> fs/compat_ioctl.c:533: warning: ___kcmd' may be used uninitialized in this function
>> fs/compat_ioctl.c:656: warning: ___ret' may be used uninitialized in this function
>>
>> These warnings are harmless, so just shut gcc up.
>>
>> Signed-off-by: WANG Cong <amwang@...hat.com>
>> Cc: Alexander Viro <viro@...iv.linux.org.uk>
>> Cc: Arnd Bergmann <arnd@...db.de>
>>
>> ---
>> diff --git a/fs/compat_ioctl.c b/fs/compat_ioctl.c
>> index c5c45de..2468f80 100644
>> --- a/fs/compat_ioctl.c
>> +++ b/fs/compat_ioctl.c
>> @@ -543,6 +543,8 @@ static int mt_ioctl_trans(unsigned int fd, unsigned int cmd, void __user *argp)
>>  		kcmd = MTIOCGET;
>>  		karg = &get;
>>  		break;
>> +	default:
>> +		return -EINVAL;
>>  	}
>>  	set_fs (KERNEL_DS);
>>  	err = sys_ioctl (fd, kcmd, (unsigned long)karg);
>> @@ -653,7 +655,7 @@ static int set_raw32_request(struct raw_config_request *req, struct raw32_config
>>  static int raw_ioctl(unsigned fd, unsigned cmd,
>>  		struct raw32_config_request __user *user_req)
>>  {
>> -        int ret;
>> +        int ret = -EINVAL;
>>  
>>          switch (cmd) {
>>          case RAW_SETBIND:
> 
> Unfortunately that adds more code for something which cannot happen at
> runtime.
> 
> I guess we could do this trick:
> 
> --- a/fs/compat_ioctl.c~a
> +++ a/fs/compat_ioctl.c
> @@ -539,7 +539,7 @@ static int mt_ioctl_trans(unsigned int f
>  		kcmd = MTIOCPOS;
>  		karg = &pos;
>  		break;
> -	case MTIOCGET32:
> +	default:	/* MTIOCGET32 */
>  		kcmd = MTIOCGET;
>  		karg = &get;
>  		break;
> @@ -657,7 +657,7 @@ static int raw_ioctl(unsigned fd, unsign
>  
>          switch (cmd) {
>          case RAW_SETBIND:
> -        case RAW_GETBIND: {
> +        default: {	/* RAW_GETBIND */
>                  struct raw_config_request req;
>                  mm_segment_t oldfs = get_fs();
>  
> _
> 
> 
> Which actually reduces code:
> 
> akpm:/usr/src/25> size fs/compat_ioctl.o
>    text    data     bss     dec     hex filename
>    9012    2232    2864   14108    371c fs/compat_ioctl.o
> 
>    8968    2232    2848   14048    36e0 fs/compat_ioctl.o
> 

Yeah! Definitely better.

Thanks, Andrew!

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