ToDo/Block/old

QEMU 1.0

Coroutines in the block layer [Kevin]

• Programming model to simplify block drivers without blocking QEMU threads
• All synchronous drivers converted to asynchronous

VMDK enhancements [Fam, GSoC 2011]

• Implement latest VMDK specs to support modern image files
• Patches currently being reviewed and merged

iSCSI block device integration

• Enable userspace-only remote access to disk images

QEMU 1.1

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

Block I/O limits [Zhi Yong]

• Resource control for guest I/O bandwidth/iops consumption
• Usable with virtio on QEMU 1.0

snapshot_blkdev and Backup API [Jeff]

• Support for consistent disk snapshots

NBD asynchronous I/O [Paolo]

• Improved performance

virtio-scsi [Paolo/Stefan]

• The next step after virtio-blk, full SCSI command set and appears as SCSI HBA in guest
• Real /dev/sda devices in guest
• No more modifying guest drivers to add simple storage protocol features

Material for next QEMU release

Live block operations

• Copy the contents of an image file while a guest is using it
  • Various implementations: active/synchronous (guest sees I/O completion when data reaches both source and destination), passive/asynchronous (guest sees I/O completion when data reaches source only)
• Improved error handling, similar to -drive rerror/werror
  • Errors can pause or cancel the job (with possibly separate handling for ENOSPC)

In-place qcow2 <-> qed conversion [Devin, GSoC 2011]:

• Fast conversion between qcow2 and qed image formats without copy all data
• Patches currently being reviewed and merged

Runtime WCE toggling [Paolo, mst?]

• wce=none|on|off and run-time guest toggling support
  • Is wce=... an option for guest devices or block devices?
• Prerequisite to switching away from cache=writethrough by default
• Idea: replace O_DSYNC with manual bdrv_flush calls after each write
  • Possible to get some speedups on qcow2 metadata updates too (certainly with respect to O_SYNC; not sure how much with O_DSYNC)

Block migration [?]

• Block migration working with a separate migration thread
• Perhaps just drop it.

IDE CD-ROM passthrough

• Track host tray state

virtio-scsi [Paolo/Stefan]

• multiqueue (in the kernel)
• MODE SELECT (WCE enable, perhaps something else?)

Future changes

Cow overlay [Dong Xu "Robert"]

• Allow live block copy and image streaming to raw destination files

-blockdev [Markus?]

• Explicit user control over block device trees
• Perhaps base this on QEMU Object Model right away

QCOW3

• Extend qcow2 format to address current and future image format challenges
  • Feature bits for fine-grained file format extensions
  • Sub-clusters to reduce metadata size and fragmentation
  • Zero clusters for efficient sparse images and copy-on-read
  • luks-like key scheme that allows changing passphrase without re-encrypting data

NBD server for block device migration

• Enable remote access to live disk images for external backup software

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

tcm_vhost [Zhi Yong]

• Directly connect virtio-scsi with Linux in-kernel SCSI target
• Pass-through of host SCSI devices

qcow2 online resize [Zhi Yong]

• Handle snapshots
• Support shrinking

qed online resize [Zhi Yong]

• Support shrinking