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Message-ID: <20150422120129.275c0bc6@bahia.local> Date: Wed, 22 Apr 2015 12:01:29 +0200 From: Greg Kurz <gkurz@...ux.vnet.ibm.com> To: "Michael S. Tsirkin" <mst@...hat.com> Cc: Rusty Russell <rusty@...tcorp.com.au>, Cornelia Huck <cornelia.huck@...ibm.com>, linux-api@...r.kernel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org Subject: Re: [PATCH v4 8/8] macvtap/tun: add VNET_BE flag On Tue, 21 Apr 2015 20:30:23 +0200 "Michael S. Tsirkin" <mst@...hat.com> wrote: > On Tue, Apr 21, 2015 at 06:22:20PM +0200, Greg Kurz wrote: > > On Tue, 21 Apr 2015 16:06:33 +0200 > > "Michael S. Tsirkin" <mst@...hat.com> wrote: > > > > > On Fri, Apr 10, 2015 at 12:20:21PM +0200, Greg Kurz wrote: > > > > The VNET_LE flag was introduced to fix accesses to virtio 1.0 headers > > > > that are always little-endian. It can also be used to handle the special > > > > case of a legacy little-endian device implemented by a big-endian host. > > > > > > > > Let's add a flag and ioctls for big-endian devices as well. If both flags > > > > are set, little-endian wins. > > > > > > > > Since this is isn't a common usecase, the feature is controlled by a kernel > > > > config option (not set by default). > > > > > > > > Both macvtap and tun are covered by this patch since they share the same > > > > API with userland. > > > > > > > > Signed-off-by: Greg Kurz <gkurz@...ux.vnet.ibm.com> > > > > --- > > > > drivers/net/Kconfig | 12 ++++++++ > > > > drivers/net/macvtap.c | 60 +++++++++++++++++++++++++++++++++++++++++- > > > > drivers/net/tun.c | 62 ++++++++++++++++++++++++++++++++++++++++++- > > > > include/uapi/linux/if_tun.h | 2 + > > > > 4 files changed, 134 insertions(+), 2 deletions(-) > > > > > > > > diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig > > > > index df51d60..f0e23a0 100644 > > > > --- a/drivers/net/Kconfig > > > > +++ b/drivers/net/Kconfig > > > > @@ -244,6 +244,18 @@ config TUN > > > > > > > > If you don't know what to use this for, you don't need it. > > > > > > > > +config TUN_VNET_BE > > > > + bool "Support for big-endian vnet headers" > > > > + default n > > > > + ---help--- > > > > + This option allows TUN/TAP and MACVTAP device drivers to parse > > > > + vnet headers that are in big-endian byte order. It is useful > > > > + when the headers come from a big-endian legacy virtio driver and > > > > + the host is little-endian. > > > > + > > > > + Unless you have a little-endian system hosting a big-endian virtual > > > > + machine with a virtio NIC, you should say N. > > > > + > > > > > > should mention cross-endian, not big-endian, right? > > > > > > > The current TUN_VNET_LE related code is already doing cross-endian: without > > this patch, one can already run a LE guest on a BE host... wouldn't it be > > confusing to mention cross-endian only when the guest is BE ? > > Hmm I think no - LE is also useful for virtio 1 - this is what it was > intended for after all. > > > What about having a completely distinct implementation for cross-endian that > > don't reuse the existing code and defines then ? > > I think implementation and interface are fine, just the documentation > can be improved a bit. > > How about: > "Support for cross-endian vnet headers on little-endian kernels". > > Accordingly CONFIG_TUN_VNET_CROSS_LE > > ? > Sure. And what about also renaming the ioctl to TUNSETVNETCROSSLE then ? -- Greg -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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