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xen-devel
[Xen-devel] About the specification of the transmission processing of ne
Hi All,
Please teach us the specification of the transmission processing of netback
driver.
When the packet is transmitted by using VNIF on PV-domain and PV-ON-HVM,
the data of SKB is fragmented.
It is fragmented whenever the data of the packet is larger than that of 64
bytes.
It seems like the specification from at first.
Why is the packet fragmented by 64 bytes?
Details are as follows:
・linux-2.6.18-xen.hg/drivers/xen/netback/netback.c
-----------------------------------------------------------------------------
1177 /* Called after netfront has transmitted */
1178 static void net_tx_action(unsigned long unused)
1179 {
...
1285 data_len = (txreq.size > PKT_PROT_LEN &&
1286 ret < MAX_SKB_FRAGS) ?
1287 PKT_PROT_LEN : txreq.size;
1288
1289 skb = alloc_skb(data_len + 16 + NET_IP_ALIGN,
1290 GFP_ATOMIC | __GFP_NOWARN);
...
1324 if (data_len < txreq.size) {
1325 skb_shinfo(skb)->nr_frags++;
1326 skb_shinfo(skb)->frags[0].page =
1327 (void *)(unsigned long)pending_idx;
1328 } else {
-----------------------------------------------------------------------------
1285:
When packet is 64 bytes or less, data_len is the sizes of the packet.
But, it is 64 bytes that the packet is larger than 64 bytes
1324-1327:
In a packet that is larger than 64 bytes, the remainder of the packet is
fragmented.
Best Regards
--
Takanori Kasai
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