netdev - Re: [PATCH v8] net: ethernet: add driver for Aurora VLSI NB8800 Ethernet controller

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Date:	Wed, 25 Nov 2015 14:00:15 +0100
From:	Mason <slash.tmp@...e.fr>
To:	Mans Rullgard <mans@...sr.com>,
	Alexander Duyck <alexander.duyck@...il.com>
Cc:	netdev@...r.kernel.org, Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH v8] net: ethernet: add driver for Aurora VLSI NB8800
 Ethernet controller

On 25/11/2015 13:45, Måns Rullgård wrote:

> Mason wrote:
> 
>> On 19/11/2015 14:02, Mans Rullgard wrote:
>>
>>> +	if (dma_mapping_error(&dev->dev, dma_addr)) {
>>> +		skb_free_frag(data);
>>> +		return -ENOMEM;
>>> +	}
>>
>> I'm back-porting this driver to 4.1
>>
>> skb_free_frag() was introduced in 4.2 by 181edb2bfa22b IIUC.
>>
>> +static inline void skb_free_frag(void *addr)
>> +{
>> +       __free_page_frag(addr);
>> +}
>>
>> Should I just copy the definition of __free_page_frag() ?
> 
> Looks like it ought to work.  Try and find out.  Not that you'll ever
> hit that error condition unless you fake it.

Turns out __free_pages_ok() is static and I'd rather not touch
mm/page_alloc.c in my back-port.

Since you say the error condition is rare, I think I'll go with
the code that 181edb2bfa22b replaced (put_page, IIUC).

#include <linux/version.h>
#if LINUX_VERSION_CODE < KERNEL_VERSION(4,2,0)
#define skb_free_frag(data) put_page(virt_to_head_page(data))
#else
#error DELETE ME NOW (see commit 181edb2bfa22b)
#endif

Alexander, does that look correct?

Regards.

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