Thank you for your explanation, David.
But pci_map_page should work fine if we have multiple contiguous pages
in one frag that are allocated using alloc_pages, ie:
frag->page = alloc_pages(GFP_KERNEL, 2); // get 4 pages
frag->page_offset = 0;
frag->size = 4 * PAGE_SIZE;
dma_addr = pci_map_page(frag->page, frag->page_offset, frag->size, ..);
The reason I asked this is that I saw the following code in forthdeth drvier:
#define NV_TX2_TSO_MAX_SHIFT) 14
/* add fragments to entries count */
for (i = 0; i < fragments; i++) {
entries += (skb_shinfo(skb)->frags[i].size >> NV_TX2_TSO_MAX_SHIFT) +
((skb_shinfo(skb)->frags[i].size &
(NV_TX2_TSO_MAX_SIZE-1)) ? 1 : 0);
}
This looks unnecessary if each frag is guaranteed not to span pages.
Ronghua
On 10/10/06, David Miller <[EMAIL PROTECTED]> wrote:
From: "Ronghua Zhang" <[EMAIL PROTECTED]>
Date: Tue, 10 Oct 2006 15:37:04 -0700
> >From the code of tcp_sendmsg, it seems to me that each frag is at most
> one page. Is it a guaranteed property or the driver should not assume
> it? Thanks
This assumption basically already exists everywhere since
all drivers that create DMA mappings of the frags call
pci_map_page().
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