Re: [Qemu-devel] [PATCH for-2.4 00/12] hw/net: Fix .can_receive() for NICs

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Tue, Jul 14, 2015 at 03:53:29PM +0800, Fam Zheng wrote:
> Since a90a742 "tap: Drop tap_can_send", all nics that returns false from
> .can_receive() are required to explicitly flush the incoming queue when the
> status of it is changing back to true, otherwise the backend will sop
> processing more rx packets.
> 
> The purpose of this callback is to tell the peer backend (tap, socket, etc)
> "hold on until guest consumes old data because my buffer is not ready". More
> often than not NICs also do this when driver deactivated the card or disabled
> rx, causing the packets being unnessarily queued, where they should actualy be
> dropped.
> 
> This series adds such missing qemu_flush_queued_packets calls for all NICs, and
> drops such unnecessary conditions in .can_receive(), so that NICs now:
> 
>   - returns false from .can_receive when guest buffers are busy.
>   - calls qemu_flush_queued_packets when buffers are available again.
>   - returns -1 from .receive when rx is not enabled.
> 
> e1000, ne2000, rocker and vmxnet3 are not included because they're fixed by
> other patches on the list and applied to Stefan's tree.
> 
> virtio-net is covered by another thread:
> 
> https://lists.gnu.org/archive/html/qemu-devel/2015-06/msg07377.html
> 
> All other NICs are okay, as they already do the flush on the state transition
> points.
> 
> Please review.
> 
> Fam Zheng (12):
>   xgmac: Drop packets with eth_can_rx is false.
>   pcnet: Drop pcnet_can_receive
>   eepro100: Drop nic_can_receive
>   usbnet: Drop usbnet_can_receive
>   etsec: Move etsec_can_receive into etsec_receive
>   etsec: Flush queue when rx buffer is consumed
>   mcf_fec: Drop mcf_fec_can_receive
>   milkymist-minimac2: Flush queued packets when link comes up
>   mipsnet: Flush queued packets when receiving is enabled
>   stellaris_enet: Flush queued packets when read done
>   dp8393x: Flush packets when link comes up
>   axienet: Flush queued packets when rx is done
> 
>  hw/net/dp8393x.c            |  8 ++++++++
>  hw/net/eepro100.c           | 11 -----------
>  hw/net/fsl_etsec/etsec.c    | 20 ++++++++++----------
>  hw/net/fsl_etsec/etsec.h    |  4 +++-
>  hw/net/fsl_etsec/rings.c    | 15 +++++++++------
>  hw/net/lance.c              |  1 -
>  hw/net/mcf_fec.c            |  9 +--------
>  hw/net/milkymist-minimac2.c | 12 ++++++------
>  hw/net/mipsnet.c            |  9 +++++++--
>  hw/net/pcnet-pci.c          |  1 -
>  hw/net/pcnet.c              |  9 ---------
>  hw/net/pcnet.h              |  1 -
>  hw/net/stellaris_enet.c     | 14 +++++---------
>  hw/net/xgmac.c              |  8 ++++----
>  hw/net/xilinx_axienet.c     | 22 ++++++++++++++++++++++
>  hw/usb/dev-network.c        | 20 ++++----------------
>  16 files changed, 79 insertions(+), 85 deletions(-)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

I'm waiting to see if Michael is happy with the virtio-net changes, then
we can apply these + hub + virtio-net + other outstanding fixes.

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