Internships/ProjectIdeas/VirtIOBlkZonedBlockDevices

Add zoned device support to QEMU's virtio-blk emulation

Summary:

The goal of this project is to let guests (virtual machines) access zoned storage devices on the host (hypervisor) through a virtio-blk device. This involves extending QEMU's block layer and virtio-blk emulation code.

Zoned devices are a special type of block device (hard-disks or SSDs) that are split into regions called zones. Any sector from any zone can be read in any order (sequentially or randomly) but zones can only be written sequentially and do not accept random writes. The "Links" section below contains more information about zoned devices and how they fit into the software stack.

QEMU's block layer needs new APIs that call Linux ZBD ioctls when disk images are located on zoned devices. The virtio-blk emulation code then needs to be extended to handle zoned device commands by calling the new block layer APIs to perform zoned device I/O on behalf of the guest. The virtio-blk zoned device command VIRTIO specification is currently being drafted and you will implement it in QEMU.

This project will expose you to device emulation and zoned storage. You will gain experience in systems programming and especially how storage devices work in the context of Linux and QEMU.

The concrete goals are:

• Add QEMU block layer APIs resembling Linux ZBD ioctls.
• Extend QEMU virtio-blk emulation to implement zoned device commands using new QEMU block layer zoned storage APIs.
• Add qemu-iotests test cases covering zoned block devices.

Stretch goals (if there is enough time):

• Implement zoned storage emulation in QEMU's block/null.c driver so it's easy to run tests without root (needed for Linux null or scsi_debug drivers) or nested guests (needed for QEMU NVMe ZNS).
• Implement SCSI ZBC support in QEMU's SCSI target to enable zoned devices in QEMU's emulated SCSI HBAs.
• Implement NVMe ZNS using new QEMU block layer zoned storage APIs (currently it emulates fake zones but doesn't call actual Linux ZBD ioctls).

You do not need to have a physical zoned storage device for this project because there are several ways to simulate zoned devices in software (Linux null_blk, Linux scsi_debug, tcmu-runner, and QEMU NVMe ZNS emulation).

Links:

• Overview of zoned storage
• Linux ZBD ioctls
• VIRTIO 1.1 specification Block device section
• QEMU virtio-blk emulation code

Details:

• Project size: 350 hours
• Difficulty: intermediate
• Required skills: C programming
• Mentors: Damien Le Moal <Damien.LeMoal@wdc.com>, Dmitry Fomichev <Dmitry.Fomichev@wdc.com>, Hannes Reinecke <hare@suse.de>, Stefan Hajnoczi <stefanha@redhat.com>