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Re: [Xen-devel] Freeing skbs (again)

To: Jacob Gorm Hansen <jacob@xxxxxxxx>
Subject: Re: [Xen-devel] Freeing skbs (again)
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Tue, 27 Apr 2004 17:47:10 +0100
Cc: Xen list <xen-devel@xxxxxxxxxxxxxxxxxxxxx>
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In-reply-to: Your message of "Tue, 27 Apr 2004 18:40:40 +0200." <1083084040.25203.230.camel@jacobg>
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> I guess I know why now. The skb->head ptrs all point to pages that are
> no longer mapped, this is why accessing data pointed to by skb_shinfo()
> (which the dealloc routine does) is bad. I could manually
> kfree(skb->head); but this still leaves empty mappings in the virtual
> memory map :-(
> I guess I need to flush the rings instead, but I suppose that means
> xen-queued outgoing packets will be dropped? Maybe I will just have to
> live with that.

NETOP_FLUSH_BUFFERS causes Xen to flush all the buffers it can. This
is every transmit buffer and every receive buffer /except/ for
trasnmit buffers that have been queued at the physical NIC. For these
the guest OS must spin/block until responses have been received some
(short) time later.

If you want all pending tx packets be to be sent then you should spin
on the tx_cons and _prod indexes /before/ calling NETOP_FLUSH_BUFFERS.

 -- Keir

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