Strange error messages from xnb on dom0. What do they mean?

[Roger Pau Monné]

On Mon, Apr 26, 2021 at 11:41:13AM -0700, Brian Buhrow wrote:
> 	hello.  Occasionally I see messages like the following from my FreeBSD-12.2/dom0 machine.
> Is this related to the issue of the NetBSD domu's seeing bursts of oversized packets, which I assume
> is caused by packets getting sent from the dom0 to the domu in batches rather than one at a
> time, each with an interrupt signal, or, the xen equivalent?
> 
> On the domu's I see:
> xennet0: discarding oversize frame (len=1518)
> 
> I see the following messages on the dom0, but not necessarily at the same time as the above
> messages appear in the domu's.
> 
> Any ideas?
> -thanks
> -Brian
> 
> 
> Apr 25 14:56:35 xen-lothlorien kernel: xnb(xnb_ring2pkt:1532): Unknown extra info type 255.  Discarding packet
> Apr 25 14:56:35 xen-lothlorien kernel: xnb(xnb_dump_txreq:302): netif_tx_request index =0
> Apr 25 14:56:35 xen-lothlorien kernel: xnb(xnb_dump_txreq:303): netif_tx_request.gref  =0
> Apr 25 14:56:35 xen-lothlorien kernel: xnb(xnb_dump_txreq:304): netif_tx_request.offset=0
> Apr 25 14:56:35 xen-lothlorien kernel: xnb(xnb_dump_txreq:305): netif_tx_request.flags =8
> Apr 25 14:56:35 xen-lothlorien kernel: xnb(xnb_dump_txreq:306): netif_tx_request.id    =69
> Apr 25 14:56:35 xen-lothlorien kernel: xnb(xnb_dump_txreq:307): netif_tx_request.size  =1000
> Apr 25 14:56:35 xen-lothlorien kernel: xnb(xnb_dump_txreq:302): netif_tx_request index =1
> Apr 25 14:56:35 xen-lothlorien kernel: xnb(xnb_dump_txreq:303): netif_tx_request.gref  =255
> Apr 25 14:56:35 xen-lothlorien kernel: xnb(xnb_dump_txreq:304): netif_tx_request.offset=0
> Apr 25 14:56:35 xen-lothlorien kernel: xnb(xnb_dump_txreq:305): netif_tx_request.flags =0
> Apr 25 14:56:35 xen-lothlorien kernel: xnb(xnb_dump_txreq:306): netif_tx_request.id    =0
> Apr 25 14:56:35 xen-lothlorien kernel: xnb(xnb_dump_txreq:307): netif_tx_request.size  =0
> Apr 25 14:56:35 xen-lothlorien kernel: xnb(xnb_rxpkt2rsp:2066): Got error -1 for hypervisor gnttab_copy status

Those are from netback failing to recognize or process a packet.
Likely netback is being too verbose here, as those should only appear
on debug builds or with boot_verbose. It might help identify what's
going wrong between NetBSD netfront and FreeBSD netback.

Roger.