On Mon, May 20, 2019 at 03:01:24PM +0200, Kevin Wolf wrote: > Am 17.05.2019 um 10:42 hat Klaus Birkelund Jensen geschrieben: > > Hi, > > > > This series of patches contains a number of refactorings to the emulated > > nvme device, adds additional features, such as support for metadata and > > scatter gather lists, and bumps the supported NVMe version to 1.3. > > Lastly, it contains a new 'ocssd' device. > > > > The motivation for the first seven patches is to set everything up for > > the final patch that adds a new 'ocssd' device and associated block > > driver that implements the OpenChannel 2.0 specification[1]. Many of us > > in the OpenChannel comunity have used a qemu fork[2] for emulation of > > OpenChannel devices. The fork is itself based on Keith's qemu-nvme > > tree[3] and we recently merged mainline qemu into it, but the result is > > still a "hybrid" nvme device that supports both conventional nvme and > > the OCSSD 2.0 spec through a 'dialect' mechanism. Merging instead of > > rebasing also created a pretty messy commit history and my efforts to > > try and rebase our work onto mainline was getting hairy to say the > > least. And I was never really happy with the dialect approach anyway. > > > > I have instead prepared this series of fresh patches that incrementally > > adds additional features to the nvme device to bring it into shape for > > finally introducing a new (and separate) 'ocssd' device that emulates an > > OpenChannel 2.0 device by reusing core functionality from the nvme > > device. Providing a separate ocssd device ensures that no ocssd specific > > stuff creeps into the nvme device. > > > > The ocssd device is backed by a new 'ocssd' block driver that holds > > internal meta data and keeps state permanent across power cycles. In the > > future I think we could use the same approach for the nvme device to > > keep internal metadata such as utilization and deallocated blocks. > > A backend driver that is specific for a guest device model (i.e. the > device model requires this driver, and the backend is useless without > the device) sounds like a very questionable design. > > Metadata like OcssdFormatHeader that is considered part of the image > data, which means that the _actual_ image content without metadata isn't > directly accessible any more feels like a bad idea, too. Simple things > like what a resize operation means (change only the actual disk size as > usual, or is the new size disk + metadata?) become confusing. Attaching > an image to a different device becomes impossible. > > The block format driver doesn't seem to actually add much functionality > to a specially crafted raw image: It provides a convenient way to create > such special images and it dumps some values in 'qemu-img info', but the > actual interpretation of the data is left to the device model. > > Looking at the options it does provide, my impression is that these > should really be qdev properties, and the place to store them > persistently is something like the libvirt XML. The device doesn't > change any of the values, so there is nothing that QEMU actually needs > to store. What you invented is a one-off way to pass a config file to a > device, but only for one specific device type. > > I think this needs to use a much more standard approach to be mergable. > > Markus (CCed) as the maintainer for the configuration mechanisms may > have an opinion on this, too.
Hi Kevin, Thank you for going through my motivations. I see what you mean. And yes, the main reason I did it like that was for the convenience of being able to `qemu-img create`'ing the image. I'll reconsider how to do this. > > > For now, the nvme device does not support the Deallocated and > > Unwritten Logical Block Error (DULBE) feature or the Data Set > > Management command as this would require such support. > > Doesn't bdrv_co_block_status() provide all the information you need for > that? > That does look useful. I'll look into it. Thanks!
