netdev - Re: [PATCH 1/2] [RFC] NET: Implement a standard ndev

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Date:	Fri, 08 Jun 2007 20:06:30 -0700
From:	"Kok, Auke" <auke-jan.h.kok@...el.com>
To:	Stephen Hemminger <shemminger@...ux-foundation.org>
CC:	netdev@...r.kernel.org, jeff@...zik.org, davem@...emloft.net,
	arjan@...ux.intel.com
Subject: Re: [PATCH 1/2] [RFC] NET: Implement a standard ndev_printk family

Stephen Hemminger wrote:
> On Fri, 08 Jun 2007 16:42:31 -0700
> "Kok, Auke" <auke-jan.h.kok@...el.com> wrote:
> 
>> Stephen Hemminger wrote:
>>>>  
>>>> +#define ndev_printk(kern_level, netif_level, netdev, format, arg...) \
>>>> +	do { if ((netdev)->msg_enable & NETIF_MSG_##netif_level) { \
>>>> +		printk(kern_level "%s: " format, \
>>>> +		(netdev)->name, ## arg); } } while (0)
>>> Could you make a version that doesn't evaluate the arguments twice?
>> hmm you lost me there a bit; Do you want me to duplicate this code for all the 
>> ndev_err/ndev_info functions instead so that ndev_err doesn't direct back to 
>> ndev_printk?
> 
> It is good practice in a macro to avoid potential problems with usage
> by only touching the arguments once. Otherwise, something (bogus) like
> 	ndev_printk(KERN_DEBUG, NETIF_MSG_PKTDATA, "got %d\n",
> 		    dev++, skb->len)
> would increment dev twice.

agreed, but

> My preference would be something more like dev_printk or even use that?
> You want to show both device name, and physical attachment in the message.

actually these ndev_* macros are almost an exact copy of dev_printk, which is 
how I modeled them in the first place!

See for yourself - here's the relevant snipplet from linux/device.h:

500 #define dev_printk(level, dev, format, arg...)  \
501         printk(level "%s %s: " format , dev_driver_string(dev) , 
(dev)->bus_id , ## arg)
502
503 #ifdef DEBUG
504 #define dev_dbg(dev, format, arg...)            \
505         dev_printk(KERN_DEBUG , dev , format , ## arg)
506 #else
507 #define dev_dbg(dev, format, arg...) do { (void)(dev); } while (0)
508 #endif
509
510 #define dev_err(dev, format, arg...)            \
511         dev_printk(KERN_ERR , dev , format , ## arg)
512 #define dev_info(dev, format, arg...)           \
513         dev_printk(KERN_INFO , dev , format , ## arg)
514 #define dev_warn(dev, format, arg...)           \
515         dev_printk(KERN_WARNING , dev , format , ## arg)
516 #define dev_notice(dev, format, arg...)         \
517         dev_printk(KERN_NOTICE , dev , format , ## arg)

using dev_printk however ignores msg_enable completely and also omits 
netdev->name, which may even change, so for netdevices it's much less suitable, 
maybe only at init time.

We can fix the dev_printk macro family as well, that's allright, but the need 
for a netdev-centric printk should be obvious: almost every netdevice driver has 
it's own variant :)

Auke
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