> -----Original Message----- > From: David Miller [mailto:davem@xxxxxxxxxxxxx] > Sent: Friday, July 3, 2015 12:17 PM > To: dan.carpenter@xxxxxxxxxx > Cc: Haiyang Zhang; netdev@xxxxxxxxxxxxxxx; olaf@xxxxxxxxx; > jasowang@xxxxxxxxxx; driverdev-devel@xxxxxxxxxxxxxxxxxxxxxx; linux- > kernel@xxxxxxxxxxxxxxx > Subject: Re: [PATCH net-next] hv_netvsc: Add support to set MTU > reservation from guest side > > From: Dan Carpenter <dan.carpenter@xxxxxxxxxx> > Date: Fri, 3 Jul 2015 14:28:47 +0300 > > > On Thu, Jul 02, 2015 at 01:17:35PM -0700, Haiyang Zhang wrote: > >> When packet encapsulation is in use, the MTU needs to be reduced for > >> headroom reservation. > >> The existing code takes the updated MTU value only from the host side. > >> But vSwitch extensions, such as Open vSwitch, require the flexibility > >> to change the MTU to different values from within a guest during the > >> lifecycle of a vNIC, when the encapsulation protocol is changed. The > >> patch supports this kind of MTU changes. > >> > >> Signed-off-by: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx> > >> Reviewed-by: K. Y. Srinivasan <kys@xxxxxxxxxxxxx> > >> --- > >> drivers/net/hyperv/netvsc_drv.c | 3 +-- > >> drivers/net/hyperv/rndis_filter.c | 2 +- > >> 2 files changed, 2 insertions(+), 3 deletions(-) > >> > >> diff --git a/drivers/net/hyperv/netvsc_drv.c > b/drivers/net/hyperv/netvsc_drv.c > >> index 358475e..68e7ece 100644 > >> --- a/drivers/net/hyperv/netvsc_drv.c > >> +++ b/drivers/net/hyperv/netvsc_drv.c > >> @@ -743,8 +743,7 @@ static int netvsc_change_mtu(struct net_device > *ndev, int mtu) > >> if (nvdev->nvsp_version >= NVSP_PROTOCOL_VERSION_2) > >> limit = NETVSC_MTU - ETH_HLEN; > >> > >> - /* Hyper-V hosts don't support MTU < ETH_DATA_LEN (1500) */ > >> - if (mtu < ETH_DATA_LEN || mtu > limit) > >> + if (mtu < 68 || mtu > limit) > > > > How did you calculate 68? Avoid magic numbers like this, make it a > > define. > > Agreed. The number 68 is same as the common code in eth_change_mtu(). I think it came from the protocol requirement: https://en.wikipedia.org/wiki/Maximum_transmission_unit Sure, I will put the number in a define, and resubmit the patch. Thanks, - Haiyang _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
