[Xen-devel] Re: [PATCH] Fox for pcnet device model data corruption

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 25 Feb 2006, at 00:10, Kamble, Nitin A wrote:

> Hi Ian,
>    The attached patch fixes pcnet data corruption for VMX guests as 
> reported by you.
> All the packets go through the qemu generic packet interface to the 
> specific device model. In this case the device model is pcnet.
>    The pcnet device model receiver is registered with it like this.
> qemu_add_read_packet(nd, pcnet_can_receive, pcnet_receive, d);
>    pcnet_can_receive function is used to tell the generic qemu 
> framework that the DM can receive packets. It is suppose block 
> incoming packets in the cases such as when the pcnet driver is not yet 
> started by the OS or pcnet device is suspended or stopped by the OS or 
> it is not ready to receive more packets.
>     When the traffic is heavy on the DM, its receive rings can get 
> filled up, and it will has to drop the receiving packets. This patch 
> detects this situation in the pcnet_can_receive() function and avoids 
> dropping of packets. This mechanism is working as a bandwidth 
> handshaking between device model and the sender. Dm is saying send me 
> up to the rate at which I can handle it.
I can see that this may avoid packet loss, but does pcnet_receive 
really get confused and corrupt data if there is no spare space? It 
appears to check the same status flag that you check in your patch?
 -- Keir


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel