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Subject: Re: [PATCH] virtio-net: Add equal-sized receive buffers feature
On 2019/10/31 äå5:23, Vitaly Mireyno wrote:
Some devices benefit from working with receive buffers of a predefined constant length. Add a feature for drivers that allocate equal-sized receive buffers, and devices that benefit from predefined receive buffers length. Signed-off-by: Vitaly Mireyno <vmireyno@marvell.com> --- content.tex | 29 +++++++++++++++++++++++++++-- 1 file changed, 27 insertions(+), 2 deletions(-)
Is there any other networking device that has this feature?
diff --git a/content.tex b/content.tex index b1ea9b9..c9e67c8 100644 --- a/content.tex +++ b/content.tex @@ -2811,6 +2811,10 @@ \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_CONST_RXBUF_LEN(58)] Driver allocates all receive buffers+ of the same constant length. Device benefits from working with + receive buffers of equal length. + \item[VIRTIO_NET_F_RSC_EXT(61)] Device can process duplicated ACKs and report number of coalesced segments and duplicated ACKs@@ -2854,8 +2858,8 @@ \subsubsection{Legacy Interface: Feature bits}\label{sec:Device Types / Network\subsection{Device configuration layout}\label{sec:Device Types / Network Device / Device configuration layout} \label{sec:Device Types / Block Device / Feature bits / Device configuration layout}-Three driver-read-only configuration fields are currently defined. The \field{mac} address field-always exists (though is only valid if VIRTIO_NET_F_MAC is set), and +The driver-read-only \field{mac} address field always exists +(though is only valid if VIRTIO_NET_F_MAC is set), and \field{status} only exists if VIRTIO_NET_F_STATUS is set. Two read-only bits (for the driver) are currently defined for the status field: VIRTIO_NET_S_LINK_UP and VIRTIO_NET_S_ANNOUNCE. @@ -2875,12 +2879,17 @@ \subsection{Device configuration layout}\label{sec:Device Types / Network Device VIRTIO_NET_F_MTU is set. This field specifies the maximum MTU for the driver to use.+The device-read-only field \field{rx_buf_len} only exists if
Should be driver-read-only.
+VIRTIO_NET_F_CONST_RXBUF_LEN is negotiated. This field specifies the receive +buffers length. + \begin{lstlisting} struct virtio_net_config { u8 mac[6]; le16 status; le16 max_virtqueue_pairs; le16 mtu; + le32 rx_buf_len; }; \end{lstlisting}@@ -2933,6 +2942,13 @@ \subsection{Device configuration layout}\label{sec:Device Types / Network Device A driver SHOULD negotiate the VIRTIO_NET_F_STANDBY feature if the device offers it. +A driver SHOULD accept the VIRTIO_NET_F_CONST_RXBUF_LEN feature if offered.+ +If VIRTIO_NET_F_CONST_RXBUF_LEN feature has been negotiated, the driver MUST +set \field{rx_buf_len}.
I think it's device that set the field?
+ +A driver MUST NOT modify \field{rx_buf_len} once it has been set. + \subsubsection{Legacy Interface: Device configuration layout}\label{sec:Device Types / Network Device / Device configuration layout / Legacy Interface: Device configuration layout} \label{sec:Device Types / Block Device / Feature bits / Device configuration layout / Legacy Interface: Device configuration layout} When using the legacy interface, transitional devices and drivers @@ -3241,6 +3257,11 @@ \subsubsection{Setting Up Receive Buffers}\label{sec:Device Types / Network Devi If VIRTIO_NET_F_MQ is negotiated, each of receiveq1\ldots receiveqN that will be used SHOULD be populated with receive buffers.+If VIRTIO_NET_F_CONST_RXBUF_LEN feature has been negotiated, the driver+MUST initialize all receive virtqueue descriptors \field{len} field with +the value configured in \field{rx_buf_len} device configuration field, +and allocate receive buffers accordingly. + \devicenormative{\paragraph}{Setting Up Receive Buffers}{Device Types / Network Device / Device Operation / Setting Up Receive Buffers}The device MUST set \field{num_buffers} to the number of descriptors used to@@ -3396,6 +3417,10 @@ \subsubsection{Processing of Incoming Packets}\label{sec:Device Types / Network checksum (in case of multiple encapsulated protocols, one level of checksums is validated).+If VIRTIO_NET_F_CONST_RXBUF_LEN has been negotiated, the device MAY+use \field{rx_buf_len} as a buffer length (instead of reading it from +virtqueue descriptor \field{len} field).
Is this safe? What if driver submit a small buffer, then device can read more than what is allowed?
Thanks
+ \drivernormative{\paragraph}{Processing of Incoming Packets}{Device Types / Network Device / Device Operation / Processing of Incoming Packets} --
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