wrap copy in 8139too.c

tkmsr · 11-13-2010, 10:14 PM

I came across a function wrap_copy on http://lxr.free-electrons.com/source.../net/8139too.c
Can some one help to understand what it is doing.
What I interpret it is that some how the person is tying to copy
payload from DMA to sk buffer.Is this interpretation correct?
What exactly are we trying to achieve via wrap_copy function call?

neonsignal · 11-14-2010, 05:00 AM

The function is copying from a ring (circular) buffer into the skb buffer. Since the memcpy may go off the end of the ring buffer, the function sometimes has to break up the copy into two parts (wrapping back around to the beginning of the ring buffer for the rest of the data).

tkmsr · 11-14-2010, 07:01 AM

Hi, thanks for your reply

orgcandman · 11-16-2010, 09:58 AM

Also note - I don't see how that code will ever be called. The only valid _user_ configurable values are 0 and 2. RX_BUF_IDX of 3 is not defined anywhere.

neonsignal · 11-16-2010, 05:53 PM

Quote:

Originally Posted by orgcandman

Also note - I don't see how that code will ever be called.

True. It looks like this used to be handled by a configurable define called CONFIG_8139_RXBUF_IDX, which could take the values 0 to 3. I'm guessing that buffer sizes of 16k and 64k are no longer supported, and the comment in the file says that "Warning: 64K ring has hardware issues and may lock up."

It makes some sense to leave the code there in case the 64k buffer option is ever reinstated.