linux-kernel - Re: [PATCH 1/3] ipc: Convert handmade 'max' to max().

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Date:	Fri, 04 Jan 2008 07:46:44 +0100
From:	Richard Knutsson <ricknu-0@...dent.ltu.se>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] ipc: Convert handmade 'max' to max().

Sorry for the late response, have been away during the holidays.

Andrew Morton wrote:
> On Mon, 17 Dec 2007 03:35:55 +0100 (MET) Richard Knutsson <ricknu-0@...dent.ltu.se> wrote:
>
>   
>> Convert handmade 'max' to max().
>>
>> ...
>>
>> --- a/ipc/msg.c
>> +++ b/ipc/msg.c
>> @@ -473,7 +473,7 @@ asmlinkage long sys_msgctl(int msqid, int cmd, struct msqid_ds __user *buf)
>>  		up_read(&msg_ids(ns).rw_mutex);
>>  		if (copy_to_user(buf, &msginfo, sizeof(struct msginfo)))
>>  			return -EFAULT;
>> -		return (max_id < 0) ? 0 : max_id;
>> +		return max(max_id, 0);
>>     
>
> I don't think I like that much.
>
> I tend to think of max() as being an arithmetic sort of thing: pick the
> largest of two scalars.
>
> But the code which you're changing is a _logical_ operation.  It says "if
> ipc_get_maxid() returned an error, then return zero.  Otherwise return
> whatever ipc_get_maxid() returned".
>
> Yes, max() will do the right thing here, but I think it's a bit of weird
> trick?
>
>
> I mean, if ipc_get_maxid() were a better function, it would return a -ve
> errno when something failed rather than the present dopey hard-coded -1. 
> In which case the code would read 
>
> 	return IS_ERR_VALUE(max_id) ? 0 : max_id;
>
> in which case, converting it to max() would be even less appropriate.  If
> you see what I mean...
>   
Yes, have to agree. Were too quick with the changing...

Thanks
Richard Knutsson

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