Re: [Qemu-devel] Block layer roadmap

[Anthony Liguori]

On 07/27/2011 07:37 AM, Stefan Hajnoczi wrote:
> Hi,
> Here is a list of block layer and storage changes that have been discussed.  It
> is useful to have a roadmap of changes in order to avoid duplication, allow
> more developers to contribute, and to communicate the direction of storage in
> QEMU.

Thanks for writing this up Stefan!

> I suggest we first do a braindump of all changes that have been discussed.
> Later we can discuss specific changes and if/when they fit into the roadmap -
> please don't jump into discussion about specific changes yet.
>
> Kevin: I hope this a useful starting point.  Here are all the items
> that I am aware of:
>
> =Material for next QEMU release=
>
> Coroutines in the block layer [Kevin]
>   * Programming model to simplify block drivers without blocking QEMU threads
>
> Generic copy-on-read [Stefan]
>   * Populate image file to avoid fetching same block from backing file
> again later
>
> Generic image streaming [Stefan]
>   * Make block_stream commands available for all image formats that
> support backing files
>
> Live block copy [Marcelo/Kevin/Stefan?]
>   * Copy the contents of an image file while a guest is using it
>
> In-place qcow2<->  qed conversion [Devin, GSoC 2011]:
>   * Fast conversion between qcow2 and qed image formats without copy all data
>
> VMDK enhancements [Fam, GSoC 2011]
>   * Implement latest VMDK specs to support modern image files
>
> Block I/O limits [Zhi Yong]
>   * Resource control for guest I/O bandwidth/iops consumption
>
> =Changes where I am not aware of firm plans=
>
> Cow overlay [Dong Xu "Robert"]
>   * Allow live block copy and image streaming to raw destination files
>
> snapshot_blkdev and Backup API [Jes, Jagane]
>   * Support for consistent disk snapshots and dirty block tracking
>   * Allow backup software to integrate with QEMU
>
> -blockdev [Markus?]
>   * Explicit user control over block device trees

I'm planning on helping out here however I can.

Regards,

Anthony Liguori

> QCOW3
>   * Extend qcow2 format to address current and future image format challenges
>
> iSCSI/NBD/Remote block device integration
>   * Enable remote access to disk images for live migration and other tasks
>
> Pre/post block copy
>   * Working block migration
>
> Avoid blocking QEMU threads
>   * Today loss of NFS connectivity can hang guests
>   * It's critical never to block the vcpu thread
>   * The iothread should also not block while the qemu mutex is held
>   * All blocking operations must be done asynchronously or in a worker thread
>
> virtio-scsi [Paolo/Stefan]
>   * The next step after virtio-blk, full SCSI command set and appears
> as SCSI HBA in guest
>
> tcm_vhost [Stefan]
>   * Directly connect virtio-scsi with Linux in-kernel SCSI target
>   * Pass-through of host SCSI devices