> It looks to me as though the skb-pull() function is what I want. I can pull
> each 1K chunk off at a time. Is it really that simple? However, an element
> of doubt has been put in my mind by the description of the function in the
> Linux Device Drivers book ("Removes data from the head of the packet. The
> driver won't need to use this function, but is included for completeness.")
> Hopefully, it is complete.
I think "completeness" refers to the book, not to the functionality of
skb_pull(). I think it is most unsual to use skb_pull() in a network device
driver.
> Will I be able to use skb_push()
> function to assemble a 4K frame in a similar manner on the receive side?
Normally, you'd use skb_put(). This assumes that the first chunk is received
first:
skb = dev_alloc_skb (4K + alignment);
skb_reserve (skb, alignment);
insl (ioaddr + x, skb_put (skb, 1K), 1K); /* 1st chunk. */
...
insl (ioaddr + x, skb_put (skb, 1K), 1K); /* 2nd chunk. */
...
insl (ioaddr + x, skb_put (skb, 1K), 1K); /* 3rd chunk. */
...
insl (ioaddr + x, skb_put (skb, 1K), 1K); /* 4th chunk. */
If you get the first chunk last, then use skb_push():
skb = dev_alloc_skb (4K + alignment);
skb_reserve (skb, 4K + alignment);
insl (ioaddr + x, skb_push (skb, 1K), 1K); /* 4th chunk. */
...
insl (ioaddr + x, skb_push (skb, 1K), 1K); /* 3rd chunk. */
...
insl (ioaddr + x, skb_push (skb, 1K), 1K); /* 2nd chunk. */
...
insl (ioaddr + x, skb_push (skb, 1K), 1K); /* 1st chunk. */
(I don't know what skb_push() returns, I'm assuming it returns a pointer to
the new 1K chunk in skb_put() style. If not, modify accordingly.)
This should work fine with 2.2 kernels too.
All of the above assumed that you use PIO transfers. With a DMA device,
you'll need to manage the pointers yourself on the receive side when dealing
with the chunks. Something like:
skb = dev_alloc_skb (4K + alignment);
skb_reserve (skb, alignment);
dma_pointer = pci_map_single (pdev, skb->head, 4K, PCI_DMA_FROMDEVICE);
/* await completion of DMA */
skb_put (skb, length_of_whole_packet);
pci_unmap_single (pdev, dma_pointer, skb->head, 4K, PCI_DMA_FROMDEVICE);
(Please the the order of the arguments.)
Regards,
Rask Ingemann Lambertsen
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