netdev - Re: [PATCH] Packet socket: mmapped IO: PACKET_TX

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Date:	Tue, 11 Nov 2008 19:59:17 +0100
From:	"Johann Baudy" <johaahn@...il.com>
To:	"Lovich, Vitali" <vlovich@...lcomm.com>
Cc:	"Evgeniy Polyakov" <zbr@...emap.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH] Packet socket: mmapped IO: PACKET_TX_RING

Hi Vitali,

> I'm saying that that frame's status should just be set to TP_STATUS_KERNEL, not user.  The kernel wants nothing to do with this frame any more and the user needs to know that.  I was going to add statistics tracking to keep track of how many packets were sent vs rejected.  This was more of an issue with my approach where I had a dedicated kernel thread doing all of this.

In all cases of error, Kernel is blocking on the same frame until
update, indeed packet_increment_head() is only called on success.
I've done this in order to not skip a packet in case of
skb_alloc_send_skb error().

I believe, we have 3 options on all failure, if we set packet to:
- TP_STATUS_KERNEL: User can consider that buffer is free and it will
fill it again.
If we choose TP_STATUS_KERNEL by default, that's means content is lost
even for sock_alloc_send_skb() error. Such behavior is not acceptable,
User is not able to show the difference between packet success and
packet failure on a specific frame (same status).
- TP_STATUS_USER: Kernel will try to send it again and again,
especially if send() is called in a loop (even it is impossible).
This is current way of working, It looks like a manner to block on issue.
- TP_STATUS_LOOSING(or other): as TP_STATUS_USER with more info for user.
Whereas TP_STATUS_USER, this one provides user with the buffer where
error has occurred.

Thanks,
Johann
-- 
Johann Baudy
johaahn@...il.com
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