netdev - Re: [PATCH][RFC 23/23]: Support for zero-copy TCP transmit of user space data

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Date:	Fri, 19 Dec 2008 17:56:11 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Evgeniy Polyakov <zbr@...emap.net>
CC:	Vladislav Bolkhovitin <vst@...b.net>, linux-scsi@...r.kernel.org,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	Mike Christie <michaelc@...wisc.edu>,
	Jeff Garzik <jeff@...zik.org>,
	Boaz Harrosh <bharrosh@...asas.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, scst-devel@...ts.sourceforge.net,
	Bart Van Assche <bart.vanassche@...il.com>,
	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>,
	netdev@...r.kernel.org, Rusty Russell <rusty@...tcorp.com.au>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	David Miller <davem@...emloft.net>
Subject: Re: [PATCH][RFC 23/23]: Support for zero-copy TCP transmit of user
 space data

Evgeniy Polyakov wrote:
> Shared info is freed when there are no skbs referring to the shared info
> in question. Skb holds all pages in shared info in the fraglist array,
> so when it is about to be freed, it means that network stack does not
> use it (particulary it will putpage every page in fraglist). Usually
> there are two skbs in the network stack per packet in TCP (allocated at
> once though via fastclone mechanims): one is provided to the device
> (and will be freed there) and another one is placed into retransmit
> queue, where it will be located and freed when ack has been received.
>
> There may be another layers which may clone skb, but its shared info
> structure (shared between the clones) will only be freed when all users
> freed appropriate cloned skbs.
>   

I see.  One more question: how would I go about submitting some data 
with the callback attached to it?

    J
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