For frames bigger than a single page, the NETRXF more data ?¬‚ag will be set,
and the next receive request in the queue will be used to contain the remainder.
Note that the virtual network interface is not the only solution for interdomain
communication, although it is the easiest to use. The XenSocket mechanism,
which is under development, includes a mechanism for using a shared-memory
transport for communicating between two userspace processes in cooperating domains.
If you just need to move a lot of data between two domains, you might
174 Chapter 9. Supporting the Core Devices
Copying versus Flipping
For the size of data of an average network packet, it is faster to copy the data
than su?¬?er the hit from invalidating the cache. If the feature-rx-copy key in
the back end??™s XenStore subtree is set to ???1???, it supports copying instead of
transferring the page. If this is not used, the back end swaps the page o?¬?ered
by the grant reference with the one containing the bu?¬?er. Depending on where
the packet was DMA??™d to by the physical interface, this may require a copy
operation in the back end.
Pages:
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373