[libvirt PATCH 6/6] qemu: implement vhost-user-blk support

[Peter Krempa]

On Tue, Feb 02, 2021 at 16:04:12 +0100, Pavel Hrdina wrote:
> Implements QEMU support for vhost-user-blk together with live
> hotplug/unplug.
> 
> Signed-off-by: Pavel Hrdina <phrdina at redhat.com>
> ---
>  src/qemu/qemu_block.c                         | 16 ++++
>  src/qemu/qemu_block.h                         |  5 +
>  src/qemu/qemu_command.c                       | 91 +++++++++++++++++--
>  src/qemu/qemu_command.h                       |  8 ++
>  src/qemu/qemu_domain.c                        |  5 +
>  src/qemu/qemu_hotplug.c                       |  5 +-
>  src/qemu/qemu_validate.c                      | 13 +++
>  .../disk-vhostuser.x86_64-latest.args         | 41 +++++++++
>  tests/qemuxml2argvtest.c                      |  1 +
>  9 files changed, 176 insertions(+), 9 deletions(-)
>  create mode 100644 tests/qemuxml2argvdata/disk-vhostuser.x86_64-latest.args

[...]

> diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
> index 3e652e18b7..059126cfeb 100644
> --- a/src/qemu/qemu_command.c
> +++ b/src/qemu/qemu_command.c
> @@ -1712,9 +1712,16 @@ qemuBuildDiskDeviceStr(const virDomainDef *def,
>          break;
>  
>      case VIR_DOMAIN_DISK_BUS_VIRTIO:
> -        if (qemuBuildVirtioDevStr(&opt, "virtio-blk", qemuCaps,
> -                                  VIR_DOMAIN_DEVICE_DISK, disk) < 0) {
> -            return NULL;
> +        if (virStorageSourceGetActualType(disk->src) == VIR_STORAGE_TYPE_VHOST_USER) {
> +            if (qemuBuildVirtioDevStr(&opt, "vhost-user-blk", qemuCaps,
> +                                      VIR_DOMAIN_DEVICE_DISK, disk) < 0) {
> +                return NULL;
> +            }
> +        } else {
> +            if (qemuBuildVirtioDevStr(&opt, "virtio-blk", qemuCaps,
> +                                      VIR_DOMAIN_DEVICE_DISK, disk) < 0) {
> +                return NULL;
> +            }

Preferably, add a temporary string holding either "vhost-user-blk" or
"virtio-blk" and call qemuBuildVirtioDevStr just once, since all other
arguments are the same.

>          }
>  
>          if (disk->iothread)

[...]


> diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
> index 0c078a9388..aa6d539610 100644
> --- a/src/qemu/qemu_domain.c
> +++ b/src/qemu/qemu_domain.c
> @@ -10581,6 +10581,11 @@ qemuDomainPrepareDiskSource(virDomainDiskDefPtr disk,
>              disk->src->format = VIR_STORAGE_FILE_RAW;
>      }
>  
> +    /* Nothing else to prepare as it will use -chardev instead
> +     * of -blockdev/-drive option. */
> +    if (disk->src->type == VIR_STORAGE_TYPE_VHOST_USER)
> +        return 0;

The code above sets 'format' for storage pool backed disks, but since
format isn't something we'd be setting for vhost-user this exemption
should be at the beginning of the function.

> +
>      if (virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_BLOCKDEV) &&
>          !qemuDiskBusIsSD(disk->bus)) {
>          if (qemuDomainPrepareDiskSourceBlockdev(disk, priv, cfg) < 0)


Missing stuff from this commit:

- hot-unplug support
    - see qemuDomainRemoveDiskDevice where the chardev isn't deleted
- blockjob lockout
    - qemuDomainDiskBlockJobIsSupported
- block iotune lockout
- possible better lockout for qemuDomainBlockPeek
    - it will barf either that the file is not 'raw' or that it can't be
      initialized
- possible better lockout for qemuDomainSetBlockThreshold
    - "threshold currently can't be set for block device '%s'" <- it
      will never be possible
- lockout for qemuDomainGetBlockInfo
- lockout for qemuDomainBlockResize
- lockout for qemuDomainBlockStats(Flags)
- handling in bulk stats (qemuDomainGetStatsBlockExportDisk ?)