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SubjectRe: [PATCH 2/4 2.6.28] cxgb3 - handle ARP replies for private iSCSI IP address
On Fri, 22 Aug 2008 12:12:50 -0700
Andrew Morton <akpm@linux-foundation.org> wrote:

> On Fri, 22 Aug 2008 11:39:08 -0700
> Karen Xie <kxie@chelsio.com> wrote:
>
> > [PATCH 2/4 2.6.28] cxgb3 - handle ARP replies for private iSCSI IP address
> >
> > From: Karen Xie <kxie@chelsio.com>
> >
> > stg can be tricky ...
> > [adding @adapter in cxgb3_arp_process doxygen header]
> > The accelerated iSCSI traffic uses a private IP address unknown to the OS.
> > The driver has to reply to ARP requests dedicated to the private IP address.
> >
> > Signed-off-by: Divy Le Ray <divy@chelsio.com>
> > ---
> >
> > drivers/net/cxgb3/sge.c | 71 ++++++++++++++++++++++++++++++++++++++++++++---
> > 1 files changed, 66 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/net/cxgb3/sge.c b/drivers/net/cxgb3/sge.c
> > index 1b0861d..d2a9285 100644
> > --- a/drivers/net/cxgb3/sge.c
> > +++ b/drivers/net/cxgb3/sge.c
> > @@ -36,6 +36,7 @@
> > #include <linux/ip.h>
> > #include <linux/tcp.h>
> > #include <linux/dma-mapping.h>
> > +#include <net/arp.h>
> > #include "common.h"
> > #include "regs.h"
> > #include "sge_defs.h"
> > @@ -1859,6 +1860,54 @@ static void restart_tx(struct sge_qset *qs)
> > }
> >
> > /**
> > + * cxgb3_arp_process - process an ARP request probing a private IP address
> > + * @adapter: the adapter
> > + * @skb: the skbuff containing the ARP request
> > + *
> > + * Check if the ARP request is probing the private IP address
> > + * dedicated to iSCSI, generate an ARP reply if so.
> > + */
> > +static void cxgb3_arp_process(struct adapter *adapter, struct sk_buff *skb)
> > +{
> > + struct net_device *dev = skb->dev;
> > + struct port_info *pi;
> > + struct arphdr *arp;
> > + unsigned char *arp_ptr;
> > + unsigned char *sha;
> > + u32 sip, tip;
> > +
> > + if (!dev)
> > + return;
>
> Can this happen?
>
> > + skb_reset_network_header(skb);
> > + arp = arp_hdr(skb);
> > +
> > + if (arp->ar_op != htons(ARPOP_REQUEST))
> > + return;
> > +
> > + arp_ptr = (unsigned char *)(arp + 1);
> > + sha = arp_ptr;
> > + arp_ptr += dev->addr_len;
> > + memcpy(&sip, arp_ptr, 4);
> > + arp_ptr += 4;
> > + arp_ptr += dev->addr_len;
> > + memcpy(&tip, arp_ptr, 4);
>
> Should arp_hdr_len() be used here?
>
> > + pi = netdev_priv(dev);
> > + if (ntohl(tip) != pi->iscsi_ipaddr)
> > + return;
> > +
> > + arp_send(ARPOP_REPLY, ETH_P_ARP, sip, dev, tip, sha,
> > + dev->dev_addr, sha);
> > +
> > +}
> > +
> > +static inline int is_arp(struct sk_buff *skb)
> > +{
> > + return skb->protocol == htons(ETH_P_ARP);
>
> Other net code uses __constant_htons() for this.

htons() goes through several levels of indirection to make sure
that if argument is constant, no code is necessary. The practice is
reserve __constant_htons() only for those cases like initialization and case
statements where C won't allow it.


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