[virtio-comment] [PATCH v3] virtio-net: Add support for the flexible driver notification structure

[virtio-comment] [PATCH v3] virtio-net: Add support for the flexible driver notification structure

[Vitaly Mireyno]

Currently, the driver notification (available buffer notification) has a fixed structure.
If VIRTIO_F_NOTIFICATION_DATA has been negotiated, it includes: vqn, next_off and next_wrap.
If notify_off_multiplier > 0, the VQ number can be derived by the device from the Queue Notify address, so vqn may be redundant.

Some devices benefit from receiving an additional data with driver notifications. This data can optionally replace the vqn field in the driver notification structure.
In its simplest form, it would be sufficient for this data to be a per-device constant value.

Changes from v2 - Defined a new feature flag instead of a PCI-specific flag.

Signed-off-by: Vitaly Mireyno <vmireyno@marvell.com>
---
 content.tex | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/content.tex b/content.tex
index b91a132..5223d5c 100644
--- a/content.tex
+++ b/content.tex
@@ -965,6 +965,8 @@ \subsubsection{Notification structure layout}\label{sec:Virtio Transport Options
 struct virtio_pci_notify_cap {
         struct virtio_pci_cap cap;
         le32 notify_off_multiplier; /* Multiplier for queue_notify_off. */
+        le16 notify_data; /* Data to be placed in the vqn field */
+        le16 padding; /* Pad to a dword */
 };
 \end{lstlisting}
 
@@ -984,6 +986,21 @@ \subsubsection{Notification structure layout}\label{sec:Virtio Transport Options
 the same Queue Notify address for all queues.
 \end{note}
 
+\field{notify_data} is the data that the driver will set in the \field{vqn}
+field in the available buffer notification, if
+VIRTIO_NET_F_NOTIF_EXTRA_DATA has been negotiated.
+
+\begin{note}
+If \field{notify_off_multiplier} > 0, the virtqueue number can potentially be
+derived by the device from the Queue Notify address, so \field{vqn} may be
+redundant. Some devices benefit from receiving the additional data with driver
+notifications. An example could be a hardware device implementing multiple
+protocols (with virtio being one of them), so extra notification data could
+serve as a notification type indication or a protocol indication.
+Another example could be using shared hardware memory space for driver
+notifications for multiple virtio devices in a trusted environment.
+\end{note}
+
 \devicenormative{\paragraph}{Notification capability}{Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Notification capability}
 The device MUST present at least one notification capability.
 
@@ -1020,6 +1037,10 @@ \subsubsection{Notification structure layout}\label{sec:Virtio Transport Options
 cap.length >= queue_notify_off * notify_off_multiplier + 4
 \end{lstlisting}
 
+If VIRTIO_NET_F_NOTIF_EXTRA_DATA has been negotiated, the device MUST set
+\field{notify_data} to a valid value, and SHOULD set
+\field{notify_off_multiplier} > 0.
+
 \subsubsection{ISR status capability}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / ISR status capability}
 
 The VIRTIO_PCI_CAP_ISR_CFG capability
@@ -1519,6 +1540,14 @@ \subsubsection{Available Buffer Notifications}\label{sec:Virtio Transport Option
 See \ref{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Notification capability}
 for how to calculate the Queue Notify address.
 
+\drivernormative{\paragraph}{Available Buffer Notifications}{Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Initialization And Device Operation / Available Buffer Notifications}
+The driver SHOULD accept the VIRTIO_NET_F_NOTIF_EXTRA_DATA feature if it has
+been offered.
+
+If VIRTIO_NET_F_NOTIF_EXTRA_DATA has been negotiated, the driver MUST set the
+\field{vqn} field of the available buffer notification structure to the
+\field{notify_data} value.
+
 \subsubsection{Used Buffer Notifications}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Initialization And Device Operation / Used Buffer Notifications}
 
 If a used buffer notification is necessary for a virtqueue, the device would typically act as follows:
@@ -2895,6 +2924,10 @@ \subsection{Feature bits}\label{sec:Device Types / Network Device / Feature bits
 \item[VIRTIO_NET_F_CTRL_MAC_ADDR(23)] Set MAC address through control
     channel.
 
+\item[VIRTIO_NET_F_NOTIF_EXTRA_DATA(57)] Driver provides an extra data with
+    available buffer notifications, to aid in notification processing by the
+    device.
+
 \item[VIRTIO_NET_F_GUEST_HDRLEN(59)] Driver can provide the exact \field{hdr_len}
     value. Device benefits from knowing the exact header length.
 
@@ -2934,6 +2967,7 @@ \subsubsection{Feature bit requirements}\label{sec:Device Types / Network Device
 \item[VIRTIO_NET_F_CTRL_MAC_ADDR] Requires VIRTIO_NET_F_CTRL_VQ.
 \item[VIRTIO_NET_F_RSC_EXT] Requires VIRTIO_NET_F_HOST_TSO4 or VIRTIO_NET_F_HOST_TSO6.
 \item[VIRTIO_NET_F_RSS] Requires VIRTIO_NET_F_CTRL_VQ.
+\item[VIRTIO_NET_F_NOTIF_EXTRA_DATA] Requires VIRTIO_F_NOTIFICATION_DATA.
 \end{description}
 
 \subsubsection{Legacy Interface: Feature bits}\label{sec:Device Types / Network Device / Feature bits / Legacy Interface: Feature bits}
--

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Re: [virtio-comment] [PATCH v3] virtio-net: Add support for the flexible driver notification structure

[Jason Wang]

On 2020/2/26 上午12:30, Vitaly Mireyno wrote:
> Currently, the driver notification (available buffer notification) has a fixed structure.
> If VIRTIO_F_NOTIFICATION_DATA has been negotiated, it includes: vqn, next_off and next_wrap.
> If notify_off_multiplier > 0, the VQ number can be derived by the device from the Queue Notify address, so vqn may be redundant.
>
> Some devices benefit from receiving an additional data with driver notifications. This data can optionally replace the vqn field in the driver notification structure.
> In its simplest form, it would be sufficient for this data to be a per-device constant value.
>
> Changes from v2 - Defined a new feature flag instead of a PCI-specific flag.
>
> Signed-off-by: Vitaly Mireyno <vmireyno@marvell.com>
> ---
>   content.tex | 34 ++++++++++++++++++++++++++++++++++
>   1 file changed, 34 insertions(+)
>
> diff --git a/content.tex b/content.tex
> index b91a132..5223d5c 100644
> --- a/content.tex
> +++ b/content.tex
> @@ -965,6 +965,8 @@ \subsubsection{Notification structure layout}\label{sec:Virtio Transport Options
>   struct virtio_pci_notify_cap {
>           struct virtio_pci_cap cap;
>           le32 notify_off_multiplier; /* Multiplier for queue_notify_off. */
> +        le16 notify_data; /* Data to be placed in the vqn field */
> +        le16 padding; /* Pad to a dword */
>   };
>   \end{lstlisting}
>   
> @@ -984,6 +986,21 @@ \subsubsection{Notification structure layout}\label{sec:Virtio Transport Options
>   the same Queue Notify address for all queues.
>   \end{note}
>   
> +\field{notify_data} is the data that the driver will set in the \field{vqn}
> +field in the available buffer notification, if
> +VIRTIO_NET_F_NOTIF_EXTRA_DATA has been negotiated.
> +
> +\begin{note}
> +If \field{notify_off_multiplier} > 0, the virtqueue number can potentially be
> +derived by the device from the Queue Notify address, so \field{vqn} may be
> +redundant. Some devices benefit from receiving the additional data with driver
> +notifications. An example could be a hardware device implementing multiple
> +protocols (with virtio being one of them), so extra notification data could
> +serve as a notification type indication or a protocol indication.
> +Another example could be using shared hardware memory space for driver
> +notifications for multiple virtio devices in a trusted environment.
> +\end{note}
> +
>   \devicenormative{\paragraph}{Notification capability}{Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Notification capability}
>   The device MUST present at least one notification capability.
>   
> @@ -1020,6 +1037,10 @@ \subsubsection{Notification structure layout}\label{sec:Virtio Transport Options
>   cap.length >= queue_notify_off * notify_off_multiplier + 4
>   \end{lstlisting}
>   
> +If VIRTIO_NET_F_NOTIF_EXTRA_DATA has been negotiated, the device MUST set
> +\field{notify_data} to a valid value, and SHOULD set
> +\field{notify_off_multiplier} > 0.
> +
>   \subsubsection{ISR status capability}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / ISR status capability}
>   
>   The VIRTIO_PCI_CAP_ISR_CFG capability
> @@ -1519,6 +1540,14 @@ \subsubsection{Available Buffer Notifications}\label{sec:Virtio Transport Option
>   See \ref{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Notification capability}
>   for how to calculate the Queue Notify address.
>   
> +\drivernormative{\paragraph}{Available Buffer Notifications}{Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Initialization And Device Operation / Available Buffer Notifications}
> +The driver SHOULD accept the VIRTIO_NET_F_NOTIF_EXTRA_DATA feature if it has
> +been offered.


I think we need use "MUST" here?

Other looks good to me.

Thanks


> +
> +If VIRTIO_NET_F_NOTIF_EXTRA_DATA has been negotiated, the driver MUST set the
> +\field{vqn} field of the available buffer notification structure to the
> +\field{notify_data} value.
> +
>   \subsubsection{Used Buffer Notifications}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Initialization And Device Operation / Used Buffer Notifications}
>   
>   If a used buffer notification is necessary for a virtqueue, the device would typically act as follows:
> @@ -2895,6 +2924,10 @@ \subsection{Feature bits}\label{sec:Device Types / Network Device / Feature bits
>   \item[VIRTIO_NET_F_CTRL_MAC_ADDR(23)] Set MAC address through control
>       channel.
>   
> +\item[VIRTIO_NET_F_NOTIF_EXTRA_DATA(57)] Driver provides an extra data with
> +    available buffer notifications, to aid in notification processing by the
> +    device.
> +
>   \item[VIRTIO_NET_F_GUEST_HDRLEN(59)] Driver can provide the exact \field{hdr_len}
>       value. Device benefits from knowing the exact header length.
>   
> @@ -2934,6 +2967,7 @@ \subsubsection{Feature bit requirements}\label{sec:Device Types / Network Device
>   \item[VIRTIO_NET_F_CTRL_MAC_ADDR] Requires VIRTIO_NET_F_CTRL_VQ.
>   \item[VIRTIO_NET_F_RSC_EXT] Requires VIRTIO_NET_F_HOST_TSO4 or VIRTIO_NET_F_HOST_TSO6.
>   \item[VIRTIO_NET_F_RSS] Requires VIRTIO_NET_F_CTRL_VQ.
> +\item[VIRTIO_NET_F_NOTIF_EXTRA_DATA] Requires VIRTIO_F_NOTIFICATION_DATA.
>   \end{description}
>   
>   \subsubsection{Legacy Interface: Feature bits}\label{sec:Device Types / Network Device / Feature bits / Legacy Interface: Feature bits}
> --
>
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[virtio-comment] Re: [PATCH v3] virtio-net: Add support for the flexible driver notification structure

[Michael S. Tsirkin]

On Tue, Feb 25, 2020 at 04:30:56PM +0000, Vitaly Mireyno wrote:
> Currently, the driver notification (available buffer notification) has a fixed structure.
> If VIRTIO_F_NOTIFICATION_DATA has been negotiated, it includes: vqn, next_off and next_wrap.
> If notify_off_multiplier > 0, the VQ number can be derived by the device from the Queue Notify address, so vqn may be redundant.
> 
> Some devices benefit from receiving an additional data with driver notifications. This data can optionally replace the vqn field in the driver notification structure.
> In its simplest form, it would be sufficient for this data to be a per-device constant value.
> 
> Changes from v2 - Defined a new feature flag instead of a PCI-specific flag.
> 
> Signed-off-by: Vitaly Mireyno <vmireyno@marvell.com>
> ---
>  content.tex | 34 ++++++++++++++++++++++++++++++++++
>  1 file changed, 34 insertions(+)
> 
> diff --git a/content.tex b/content.tex
> index b91a132..5223d5c 100644
> --- a/content.tex
> +++ b/content.tex
> @@ -965,6 +965,8 @@ \subsubsection{Notification structure layout}\label{sec:Virtio Transport Options
>  struct virtio_pci_notify_cap {
>          struct virtio_pci_cap cap;
>          le32 notify_off_multiplier; /* Multiplier for queue_notify_off. */
> +        le16 notify_data; /* Data to be placed in the vqn field */
> +        le16 padding; /* Pad to a dword */
>  };
>  \end{lstlisting}
>  
> @@ -984,6 +986,21 @@ \subsubsection{Notification structure layout}\label{sec:Virtio Transport Options
>  the same Queue Notify address for all queues.
>  \end{note}
>  
> +\field{notify_data} is the data that the driver will set in the \field{vqn}
> +field in the available buffer notification, if
> +VIRTIO_NET_F_NOTIF_EXTRA_DATA has been negotiated.
> +
> +\begin{note}
> +If \field{notify_off_multiplier} > 0, the virtqueue number can potentially be
> +derived by the device from the Queue Notify address, so \field{vqn} may be
> +redundant. Some devices benefit from receiving the additional data with driver
> +notifications. An example could be a hardware device implementing multiple
> +protocols (with virtio being one of them), so extra notification data could
> +serve as a notification type indication or a protocol indication.
> +Another example could be using shared hardware memory space for driver
> +notifications for multiple virtio devices in a trusted environment.
> +\end{note}
> +
>  \devicenormative{\paragraph}{Notification capability}{Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Notification capability}
>  The device MUST present at least one notification capability.
>  
> @@ -1020,6 +1037,10 @@ \subsubsection{Notification structure layout}\label{sec:Virtio Transport Options
>  cap.length >= queue_notify_off * notify_off_multiplier + 4
>  \end{lstlisting}
>  
> +If VIRTIO_NET_F_NOTIF_EXTRA_DATA has been negotiated, the device MUST set
> +\field{notify_data} to a valid value,

I'm not sure what would a valid value mean. Does this requirement
add any value (pun intended :) )?

> and SHOULD set
> +\field{notify_off_multiplier} > 0.

So I have a concern here. There could be multiple capabilities.
What if some have notify_off_multiplier and some aren't?
This is SHOULD so it seems to be legal.

Then below ...

> +
>  \subsubsection{ISR status capability}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / ISR status capability}
>  
>  The VIRTIO_PCI_CAP_ISR_CFG capability
> @@ -1519,6 +1540,14 @@ \subsubsection{Available Buffer Notifications}\label{sec:Virtio Transport Option
>  See \ref{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Notification capability}
>  for how to calculate the Queue Notify address.
>  
> +\drivernormative{\paragraph}{Available Buffer Notifications}{Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Initialization And Device Operation / Available Buffer Notifications}
> +The driver SHOULD accept the VIRTIO_NET_F_NOTIF_EXTRA_DATA feature if it has
> +been offered.
> +
> +If VIRTIO_NET_F_NOTIF_EXTRA_DATA has been negotiated, the driver MUST set the
> +\field{vqn} field of the available buffer notification structure to the
> +\field{notify_data} value.
> +

So if notify_off_multiplier for a given capability is actually 0,
when using this specific capability,
I think we need to keep vqn there as previously.

How about listing this behaviour out explicitly?



>  \subsubsection{Used Buffer Notifications}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Initialization And Device Operation / Used Buffer Notifications}
>  
>  If a used buffer notification is necessary for a virtqueue, the device would typically act as follows:
> @@ -2895,6 +2924,10 @@ \subsection{Feature bits}\label{sec:Device Types / Network Device / Feature bits
>  \item[VIRTIO_NET_F_CTRL_MAC_ADDR(23)] Set MAC address through control
>      channel.
>  
> +\item[VIRTIO_NET_F_NOTIF_EXTRA_DATA(57)] Driver provides an extra data with
> +    available buffer notifications, to aid in notification processing by the
> +    device.
> +
>  \item[VIRTIO_NET_F_GUEST_HDRLEN(59)] Driver can provide the exact \field{hdr_len}
>      value. Device benefits from knowing the exact header length.
>  
> @@ -2934,6 +2967,7 @@ \subsubsection{Feature bit requirements}\label{sec:Device Types / Network Device
>  \item[VIRTIO_NET_F_CTRL_MAC_ADDR] Requires VIRTIO_NET_F_CTRL_VQ.
>  \item[VIRTIO_NET_F_RSC_EXT] Requires VIRTIO_NET_F_HOST_TSO4 or VIRTIO_NET_F_HOST_TSO6.
>  \item[VIRTIO_NET_F_RSS] Requires VIRTIO_NET_F_CTRL_VQ.
> +\item[VIRTIO_NET_F_NOTIF_EXTRA_DATA] Requires VIRTIO_F_NOTIFICATION_DATA.
>  \end{description}
>  
>  \subsubsection{Legacy Interface: Feature bits}\label{sec:Device Types / Network Device / Feature bits / Legacy Interface: Feature bits}
> --


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[virtio-comment] Re: [PATCH v3] virtio-net: Add support for the flexible driver notification structure

[Vitaly Mireyno]

>-----Original Message-----
>From: Michael S. Tsirkin <mst@redhat.com>
>Sent: Thursday, 5 March, 2020 21:59
>To: Vitaly Mireyno <vmireyno@marvell.com>
>Cc: virtio-comment@lists.oasis-open.org; Jason Wang <jasowang@redhat.com>; Ariel Elior
><aelior@marvell.com>
>Subject: [EXT] Re: [PATCH v3] virtio-net: Add support for the flexible driver notification structure
>
>External Email
>
>----------------------------------------------------------------------
>On Tue, Feb 25, 2020 at 04:30:56PM +0000, Vitaly Mireyno wrote:
>> Currently, the driver notification (available buffer notification) has a fixed structure.
>> If VIRTIO_F_NOTIFICATION_DATA has been negotiated, it includes: vqn, next_off and next_wrap.
>> If notify_off_multiplier > 0, the VQ number can be derived by the device from the Queue Notify
>address, so vqn may be redundant.
>>
>> Some devices benefit from receiving an additional data with driver notifications. This data can
>optionally replace the vqn field in the driver notification structure.
>> In its simplest form, it would be sufficient for this data to be a per-device constant value.
>>
>> Changes from v2 - Defined a new feature flag instead of a PCI-specific flag.
>>
>> Signed-off-by: Vitaly Mireyno <vmireyno@marvell.com>
>> ---
>>  content.tex | 34 ++++++++++++++++++++++++++++++++++
>>  1 file changed, 34 insertions(+)
>>
>> diff --git a/content.tex b/content.tex index b91a132..5223d5c 100644
>> --- a/content.tex
>> +++ b/content.tex
>> @@ -965,6 +965,8 @@ \subsubsection{Notification structure
>> layout}\label{sec:Virtio Transport Options  struct virtio_pci_notify_cap {
>>          struct virtio_pci_cap cap;
>>          le32 notify_off_multiplier; /* Multiplier for
>> queue_notify_off. */
>> +        le16 notify_data; /* Data to be placed in the vqn field */
>> +        le16 padding; /* Pad to a dword */
>>  };
>>  \end{lstlisting}
>>
>> @@ -984,6 +986,21 @@ \subsubsection{Notification structure
>> layout}\label{sec:Virtio Transport Options  the same Queue Notify address for all queues.
>>  \end{note}
>>
>> +\field{notify_data} is the data that the driver will set in the
>> +\field{vqn} field in the available buffer notification, if
>> +VIRTIO_NET_F_NOTIF_EXTRA_DATA has been negotiated.
>> +
>> +\begin{note}
>> +If \field{notify_off_multiplier} > 0, the virtqueue number can
>> +potentially be derived by the device from the Queue Notify address,
>> +so \field{vqn} may be redundant. Some devices benefit from receiving
>> +the additional data with driver notifications. An example could be a
>> +hardware device implementing multiple protocols (with virtio being
>> +one of them), so extra notification data could serve as a notification type indication or a protocol
>indication.
>> +Another example could be using shared hardware memory space for
>> +driver notifications for multiple virtio devices in a trusted environment.
>> +\end{note}
>> +
>>  \devicenormative{\paragraph}{Notification capability}{Virtio
>> Transport Options / Virtio Over PCI Bus / PCI Device Layout / Notification capability}  The device MUST
>present at least one notification capability.
>>
>> @@ -1020,6 +1037,10 @@ \subsubsection{Notification structure
>> layout}\label{sec:Virtio Transport Options  cap.length >=
>> queue_notify_off * notify_off_multiplier + 4  \end{lstlisting}
>>
>> +If VIRTIO_NET_F_NOTIF_EXTRA_DATA has been negotiated, the device MUST
>> +set \field{notify_data} to a valid value,
>
>I'm not sure what would a valid value mean. Does this requirement add any value (pun intended :) )?
>
>> and SHOULD set
>> +\field{notify_off_multiplier} > 0.
>
>So I have a concern here. There could be multiple capabilities.
>What if some have notify_off_multiplier and some aren't?
>This is SHOULD so it seems to be legal.
>
>Then below ...
>
>> +
>>  \subsubsection{ISR status capability}\label{sec:Virtio Transport
>> Options / Virtio Over PCI Bus / PCI Device Layout / ISR status
>> capability}
>>
>>  The VIRTIO_PCI_CAP_ISR_CFG capability @@ -1519,6 +1540,14 @@
>> \subsubsection{Available Buffer Notifications}\label{sec:Virtio
>> Transport Option  See \ref{sec:Virtio Transport Options / Virtio Over
>> PCI Bus / PCI Device Layout / Notification capability}  for how to calculate the Queue Notify address.
>>
>> +\drivernormative{\paragraph}{Available Buffer Notifications}{Virtio
>> +Transport Options / Virtio Over PCI Bus / PCI-specific Initialization
>> +And Device Operation / Available Buffer Notifications} The driver SHOULD accept the
>VIRTIO_NET_F_NOTIF_EXTRA_DATA feature if it has been offered.
>> +
>> +If VIRTIO_NET_F_NOTIF_EXTRA_DATA has been negotiated, the driver MUST
>> +set the \field{vqn} field of the available buffer notification
>> +structure to the \field{notify_data} value.
>> +
>
>So if notify_off_multiplier for a given capability is actually 0, when using this specific capability, I think
>we need to keep vqn there as previously.
>
>How about listing this behaviour out explicitly?
>

I see your point. Will send a fixed patch.

>
>
>>  \subsubsection{Used Buffer Notifications}\label{sec:Virtio Transport
>> Options / Virtio Over PCI Bus / PCI-specific Initialization And Device
>> Operation / Used Buffer Notifications}
>>
>>  If a used buffer notification is necessary for a virtqueue, the device would typically act as follows:
>> @@ -2895,6 +2924,10 @@ \subsection{Feature bits}\label{sec:Device
>> Types / Network Device / Feature bits  \item[VIRTIO_NET_F_CTRL_MAC_ADDR(23)] Set MAC
>address through control
>>      channel.
>>
>> +\item[VIRTIO_NET_F_NOTIF_EXTRA_DATA(57)] Driver provides an extra data with
>> +    available buffer notifications, to aid in notification processing by the
>> +    device.
>> +
>>  \item[VIRTIO_NET_F_GUEST_HDRLEN(59)] Driver can provide the exact \field{hdr_len}
>>      value. Device benefits from knowing the exact header length.
>>
>> @@ -2934,6 +2967,7 @@ \subsubsection{Feature bit
>> requirements}\label{sec:Device Types / Network Device  \item[VIRTIO_NET_F_CTRL_MAC_ADDR]
>Requires VIRTIO_NET_F_CTRL_VQ.
>>  \item[VIRTIO_NET_F_RSC_EXT] Requires VIRTIO_NET_F_HOST_TSO4 or VIRTIO_NET_F_HOST_TSO6.
>>  \item[VIRTIO_NET_F_RSS] Requires VIRTIO_NET_F_CTRL_VQ.
>> +\item[VIRTIO_NET_F_NOTIF_EXTRA_DATA] Requires VIRTIO_F_NOTIFICATION_DATA.
>>  \end{description}
>>
>>  \subsubsection{Legacy Interface: Feature bits}\label{sec:Device Types
>> / Network Device / Feature bits / Legacy Interface: Feature bits}
>> --


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