linux-kernel - Re: [PATCH net-next v5 1/7] tun: Refactor CONFIG_TUN_VNET_CROSS

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Message-ID: <12dbfa5e-32cc-4355-89e4-6c1cd4e12d1a@daynix.com>
Date: Thu, 6 Feb 2025 15:53:26 +0900
From: Akihiko Odaki <akihiko.odaki@...nix.com>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>,
 Jonathan Corbet <corbet@....net>, Jason Wang <jasowang@...hat.com>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 "Michael S. Tsirkin" <mst@...hat.com>, Xuan Zhuo
 <xuanzhuo@...ux.alibaba.com>, Shuah Khan <shuah@...nel.org>,
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
 netdev@...r.kernel.org, kvm@...r.kernel.org,
 virtualization@...ts.linux-foundation.org, linux-kselftest@...r.kernel.org,
 Yuri Benditovich <yuri.benditovich@...nix.com>,
 Andrew Melnychenko <andrew@...nix.com>,
 Stephen Hemminger <stephen@...workplumber.org>, gur.stavi@...wei.com,
 devel@...nix.com
Cc: Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net-next v5 1/7] tun: Refactor CONFIG_TUN_VNET_CROSS_LE

On 2025/02/06 6:06, Willem de Bruijn wrote:
> Akihiko Odaki wrote:
>> Check IS_ENABLED(CONFIG_TUN_VNET_CROSS_LE) to save some lines and make
>> future changes easier.
>>
>> Signed-off-by: Akihiko Odaki <akihiko.odaki@...nix.com>
>> Reviewed-by: Willem de Bruijn <willemb@...gle.com>
>> ---
>>   drivers/net/tun.c | 26 ++++++++------------------
>>   1 file changed, 8 insertions(+), 18 deletions(-)
>>
>> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
>> index e816aaba8e5f2ed06f8832f79553b6c976e75bb8..452fc5104260fe7ff5fdd5cedc5d2647cbe35c79 100644
>> --- a/drivers/net/tun.c
>> +++ b/drivers/net/tun.c
>> @@ -298,10 +298,10 @@ static bool tun_napi_frags_enabled(const struct tun_file *tfile)
>>   	return tfile->napi_frags_enabled;
>>   }
>>   
>> -#ifdef CONFIG_TUN_VNET_CROSS_LE
>>   static inline bool tun_legacy_is_little_endian(struct tun_struct *tun)
>>   {
>> -	return tun->flags & TUN_VNET_BE ? false :
>> +	return !(IS_ENABLED(CONFIG_TUN_VNET_CROSS_LE) &&
>> +		 (tun->flags & TUN_VNET_BE)) &&
>>   		virtio_legacy_is_little_endian();
> 
> Since I have other comments to the series:
> 
> Can we make this a bit simpler to the reader, by splitting the test:
> 
>      if (IS_ENABLED(CONFIG_TUN_VNET_CROSS_LE) && tun->flags & TUN_VNET_BE)
>              return false;
> 
>      return virtio_legacy_is_little_endian();
> 

I kept all in one expression to show how different variables are reduced 
into one bool value, but I agree it is too complicated.

I'm adding a new variable to simplify this. The return statement will 
look like: return !be && virtio_legacy_is_little_endian();

It means: for tun, whether the legacy format is in little endian will be 
determined from the tun-specific big-endian flag and the virtio's common 
logic.