> -----Original Message----- > From: Francois Romieu <romieu@xxxxxxxxxxxxx> > Sent: Sunday, March 19, 2023 6:47 PM > To: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx> > Cc: linux-hyperv@xxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; Dexuan Cui > <decui@xxxxxxxxxxxxx>; KY Srinivasan <kys@xxxxxxxxxxxxx>; Paul Rosswurm > <paulros@xxxxxxxxxxxxx>; olaf@xxxxxxxxx; vkuznets@xxxxxxxxxx; > davem@xxxxxxxxxxxxx; wei.liu@xxxxxxxxxx; edumazet@xxxxxxxxxx; > kuba@xxxxxxxxxx; pabeni@xxxxxxxxxx; leon@xxxxxxxxxx; Long Li > <longli@xxxxxxxxxxxxx>; ssengar@xxxxxxxxxxxxxxxxxxx; linux- > kernel@xxxxxxxxxxxxxxx > Subject: Re: [PATCH net-next] net: mana: Add support for jumbo frame > > [Some people who received this message don't often get email from > romieu@xxxxxxxxxxxxx. Learn why this is important at > https://aka.ms/LearnAboutSenderIdentification ] > > Haiyang Zhang <haiyangz@xxxxxxxxxxxxx> : > [...] > > diff --git a/drivers/net/ethernet/microsoft/mana/mana_en.c > b/drivers/net/ethernet/microsoft/mana/mana_en.c > > index 492474b4d8aa..07738b7e85f2 100644 > > --- a/drivers/net/ethernet/microsoft/mana/mana_en.c > > +++ b/drivers/net/ethernet/microsoft/mana/mana_en.c > > @@ -427,6 +427,34 @@ static u16 mana_select_queue(struct net_device > *ndev, struct sk_buff *skb, > > return txq; > > } > > > > +static int mana_change_mtu(struct net_device *ndev, int new_mtu) > > +{ > > + unsigned int old_mtu = ndev->mtu; > > + int err, err2; > > + > > + err = mana_detach(ndev, false); > > + if (err) { > > + netdev_err(ndev, "mana_detach failed: %d\n", err); > > + return err; > > + } > > + > > + ndev->mtu = new_mtu; > > + > > + err = mana_attach(ndev); > > + if (!err) > > + return 0; > > + > > + netdev_err(ndev, "mana_attach failed: %d\n", err); > > + > > + /* Try to roll it back to the old configuration. */ > > + ndev->mtu = old_mtu; > > + err2 = mana_attach(ndev); > > + if (err2) > > + netdev_err(ndev, "mana re-attach failed: %d\n", err2); > > + > > + return err; > > +} > > I do not see where the driver could depend on the MTU. Even if it fails, > a single call to mana_change_mtu should thus never wreck the old working > state/configuration. > > Stated differently, the detach/attach implementation is simple but > it makes the driver less reliable than it could be. > > No ? No, it doesn't make the driver less reliable. To safely remove and reallocate DMA buffers with different size, we have to stop the traffic. So, mana_detach() is called. We also call mana_detach() in mana_close(). So the process in mana_change_mtu() is no more risky than ifdown/ifup of the NIC. In some rare cases, if the system memory is running really low, the bigger buffer allocation may fail, so we re-try with the previous MTU. I don't expect it to fail again. But we still check & log the error code for completeness and debugging. Thanks, - Haiyang
