On Mon, Apr 14, 2003 at 07:12:37PM +0530, Deepankar Vidyarthi wrote:
> Hi,
>
> Require some more clarification to an older question :).
> I am attaching my original mail too for reference.
> As I understand, Linux first uses skb1->frags array to put data.
> Once it is full, it gets another skb (say skb2), fills its data
> area,
As far as I can recall, it does NOT fill its data area, only uses its
frags array. Let's see..
? then its frags area.
> So data is in this form (order):
>
> skb1->data, skb1->frags[1-MAX], skb1->fraglist (ie skb2),
> skb2->data, skb2->frags[1-MAX].
skb1->data, skb1->frags[1-MAX], skb1->fraglist (ie skb2)
skb2->frags[1-MAX], skb2->fraglist ...
> Suppose it needs more space, so it creates skb3.
> Now where will it keep skb3.
> It seems to me that it goes as:
> skb1->fraglist->next (=skb3)
> ie, same as skb2->next. (=skb3)
> Is this fine???
next and prev are used in a completely different context, to have
several skbs on a queue. So, to answer your question, once you add
skb3, you will have skb2->fraglist = skb3, and only the ->frags array
on skb3 will be used.
> Moreover, it seems to me that Linux uses this type of frag chaining only while it is
> getting fragments from the network. Does the code handle such sort of chaining if we
> create packet in that format on the output side?? As far as I could check, it seems
> this (skb_shared_info) is used only on the input side. I have checked in some flows,
> just wanted to make sure this is the case for all the output flows.
grepping around for NETIF_F_FRAGLIST in 2.5, it appears that only the
loopback device and ieee1394 use it.
Hope this helps,
Muli.
--
Muli Ben-Yehuda
http://www.mulix.org
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