On Wed, Feb 05, 2014 at 09:49:18AM +1030, Rusty Russell wrote:
> "Michael S. Tsirkin" <> writes:
> > On Tue, Feb 04, 2014 at 01:35:55PM +1030, Rusty Russell wrote:
> >> "Michael S. Tsirkin" <> writes:
> >> 2) Add the concept of a "live" virtqueue, and explicitly disallow
> >> moving it backwards or changing descriptors. Make it clear that
> >> taking the net device out of mq mode makes the extra vq's not-live.
> >
> > This last part doesn't apply anymore, does it?
>
> Yes, indeed.
>
> Here's what I'm proposing to apply, if noone objects:
>
> Subject: Cleanup and setup clarifications
> From: Rusty Russell <>
>
> 1) Explicitly allow drivers to read config space during feature
> negotiation.
>
> 2) Add the concept of a "live" virtqueue, and explicitly disallow
> moving it backwards or changing descriptors.
>
> Signed-off-by: Rusty Russell <>
ACK
> diff --git a/content.tex b/content.tex
> index fa33435..413a4ad 100644
> --- a/content.tex
> +++ b/content.tex
> @@ -524,7 +524,11 @@ The driver MUST follow this sequence to initialize a device:
> \item Set the DRIVER status bit: the guest OS knows how to drive the device.
>
> \item Read device feature bits, and write the subset of feature bits
> - understood by the OS and driver to the device.
> + understood by the OS and driver to the device. During this step the
> + driver MAY read (but MUST NOT write) the device-specific configuration fields to check that it can support the device before accepting it.
> + The device MUST allow reading of any device-specific configuration field
> + before FEATURES_OK is set. This includes fields which are conditional
> + on feature bits, as long as those feature bits are offered by the device.
>
> \item\label{itm:General Initialization And Device Operation / Device Initialization / Set FEATURES-OK} Set the FEATURES_OK status bit. The driver MUST not accept
> new feature bits after this step.
> @@ -544,9 +548,9 @@ The driver MUST follow this sequence to initialize a device:
> If any of these steps go irrecoverably wrong, the driver SHOULD
> set the FAILED status bit to indicate that it has given up on the
> device (it can reset the device later to restart if desired). The
> -driver MUST not continue initialization in that case.
> +driver MUST NOT continue initialization in that case.
>
> -The device MUST NOT consume buffers before DRIVER_OK, and the driver
> +The device MUST NOT consume buffers or notify the driver before DRIVER_OK, and the driver
> MUST NOT notify the device before it sets DRIVER_OK.
>
> Devices SHOULD support all valid combinations of features, but we know
> @@ -769,7 +773,18 @@ suppressed by the device:
> For devices where the configuration information can be changed, an
> interrupt is delivered when a configuration change occurs.
>
> +\section{Device Cleanup}\label{sec:General Initialization And Device Operation / Device Cleanup}
>
> +Once the driver has set the DRIVER_OK status bit, all the configured virtqueue of the device are considered live. All of a device's virtqueues are no longer live once the device has been reset.
> +
> +A driver MUST NOT alter descriptor table entries which have been
> +exposed in the available ring (and not marked consumed by the device
> +in the used ring) of a live virtqueue.
> +
> +A driver MUST NOT decrement the available index on a live virtqueue (ie.
> +do not try to "unexpose" buffers).
> +
> +Thus a driver MUST ensure a virtqueue isn't live (by device reset) before removing exposed buffers.
>
> \chapter{Virtio Transport Options}\label{sec:Virtio Transport Options}
>
