netdev - Re: [PATCH net v3 4/9] tun: Decouple vnet from tun

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Message-ID: <678a30c2df05f_3ef8eb29481@willemb.c.googlers.com.notmuch>
Date: Fri, 17 Jan 2025 05:28:18 -0500
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>, 
 Akihiko Odaki <akihiko.odaki@...nix.com>, 
 Jonathan Corbet <corbet@....net>, 
 Willem de Bruijn <willemdebruijn.kernel@...il.com>, 
 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, 
 Akihiko Odaki <akihiko.odaki@...nix.com>
Subject: Re: [PATCH net v3 4/9] tun: Decouple vnet from tun_struct

Willem de Bruijn wrote:
> Akihiko Odaki wrote:
> > Decouple vnet-related functions from tun_struct so that we can reuse
> > them for tap in the future.
> > 
> > Signed-off-by: Akihiko Odaki <akihiko.odaki@...nix.com>
> > ---
> >  drivers/net/tun.c | 53 +++++++++++++++++++++++++++--------------------------
> >  1 file changed, 27 insertions(+), 26 deletions(-)
> > 
> > diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> > index ec56ac865848..add09dfdada5 100644
> > --- a/drivers/net/tun.c
> > +++ b/drivers/net/tun.c
> > @@ -298,16 +298,16 @@ static bool tun_napi_frags_enabled(const struct tun_file *tfile)
> >  	return tfile->napi_frags_enabled;
> >  }
> >  
> > -static inline bool tun_legacy_is_little_endian(struct tun_struct *tun)
> > +static inline bool tun_legacy_is_little_endian(unsigned int flags)
> >  {
> >  	return !(IS_ENABLED(CONFIG_TUN_VNET_CROSS_LE) &&
> > -		 (tun->flags & TUN_VNET_BE)) &&
> > +		 (flags & TUN_VNET_BE)) &&
> >  		virtio_legacy_is_little_endian();
> >  }
> >  
> > -static long tun_get_vnet_be(struct tun_struct *tun, int __user *argp)
> > +static long tun_get_vnet_be(unsigned int flags, int __user *argp)
> >  {
> > -	int be = !!(tun->flags & TUN_VNET_BE);
> > +	int be = !!(flags & TUN_VNET_BE);
> >  
> >  	if (!IS_ENABLED(CONFIG_TUN_VNET_CROSS_LE))
> >  		return -EINVAL;
> > @@ -318,7 +318,7 @@ static long tun_get_vnet_be(struct tun_struct *tun, int __user *argp)
> >  	return 0;
> >  }
> >  
> > -static long tun_set_vnet_be(struct tun_struct *tun, int __user *argp)
> > +static long tun_set_vnet_be(unsigned int *flags, int __user *argp)
> >  {
> >  	int be;
> >  
> > @@ -329,27 +329,26 @@ static long tun_set_vnet_be(struct tun_struct *tun, int __user *argp)
> >  		return -EFAULT;
> >  
> >  	if (be)
> > -		tun->flags |= TUN_VNET_BE;
> > +		*flags |= TUN_VNET_BE;
> >  	else
> > -		tun->flags &= ~TUN_VNET_BE;
> > +		*flags &= ~TUN_VNET_BE;
> >  
> >  	return 0;
> >  }
> >  
> > -static inline bool tun_is_little_endian(struct tun_struct *tun)
> > +static inline bool tun_is_little_endian(unsigned int flags)
> >  {
> > -	return tun->flags & TUN_VNET_LE ||
> > -		tun_legacy_is_little_endian(tun);
> > +	return flags & TUN_VNET_LE || tun_legacy_is_little_endian(flags);
> >  }
> >  
> > -static inline u16 tun16_to_cpu(struct tun_struct *tun, __virtio16 val)
> > +static inline u16 tun16_to_cpu(unsigned int flags, __virtio16 val)
> >  {
> > -	return __virtio16_to_cpu(tun_is_little_endian(tun), val);
> > +	return __virtio16_to_cpu(tun_is_little_endian(flags), val);
> >  }
> >  
> > -static inline __virtio16 cpu_to_tun16(struct tun_struct *tun, u16 val)
> > +static inline __virtio16 cpu_to_tun16(unsigned int flags, u16 val)
> >  {
> > -	return __cpu_to_virtio16(tun_is_little_endian(tun), val);
> > +	return __cpu_to_virtio16(tun_is_little_endian(flags), val);
> >  }
> >  
> >  static inline u32 tun_hashfn(u32 rxhash)
> > @@ -1764,6 +1763,7 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
> >  
> >  	if (tun->flags & IFF_VNET_HDR) {
> >  		int vnet_hdr_sz = READ_ONCE(tun->vnet_hdr_sz);
> > +		int flags = tun->flags;
> 
> Here and elsewhere: instead of passing around and repeatedly parsing
> flags, have a variable is_little_endian (or is_le)?

I guess this will not work everywhere, because endianness is not a
boolean flag.. Code checks both TUN_VNET_LE and TUN_VNET_BE.