[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]
Subject: Re: [virtio-dev] virtio-spec: Clarify /wrt maintaining a split-queue descriptors
On Sat, Oct 12, 2019 at 09:20:02AM +0200, Jan Kiszka wrote: > Hi all, > > I'm wondering if the spec is clear enough regarding who is in charge of > setting fields in a descriptor of split virtqueues. Background: I just > made the mistake in an experimental backend of writing back the number > of bytes pushed into a buffer not only in virtq_used_elem but also the > referenced virtq_desc - with unpleasant effects for the guest. > > The spec in section 2.6.8 reads to me like virtq_used_elem.len is rather > informative. At least this section leaves it fuzzy to me whether there > are other sources from where a driver can find out how much a device has > delivered - and misled me to also update virtq_desc.len in the device. > > But maybe I'm missing a clear note in another section. > > Jan Well it does say this: When the driver wants to send a buffer to the device, it fills in a slot in the descriptor table (or chains several together), and writes the descriptor index into the available ring. It then notifies the device. When the device has finished a buffer, it writes the descriptor index into the used ring, and sends a used buffer notification. but for sure, documenting that descriptor area is read-only by device can't hurt. > -- > Siemens AG, Corporate Technology, CT RDA IOT SES-DE > Corporate Competence Center Embedded Linux > > --------------------------------------------------------------------- > To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org > For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org
[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]