[libvirt] [PATCH v3 3/3] qemu: Use the correct vm def on cold attach

[Michal Privoznik]

On 07/16/2018 11:14 PM, John Ferlan wrote:
> https://bugzilla.redhat.com/show_bug.cgi?id=1559867
> 
> When attaching a device to the domain we need to be sure
> to use the correct domain definition (vm->def or vm->newDef)
> when calling virDomainDeviceDefParse because the post parse
> processing algorithms that may assign an address for the
> device will use whatever domain definition was passed in.
> 
> Additionally, some devices (SCSI hostdev and SCSI disk) use
> algorithms that rely on knowing what already exists of the
> other type when generating the new device's address. Using
> the wrong VM definition could result in duplicated addresses.
> 
> In the case of the bz, two hostdev's with no domain address
> provided were added to the running domain's config only.
> However, the parsing algorithm used the live domain in
> order to figure out the host device address resulting in
> the same address being used and a subsequent start failing
> due to duplicate address.
> 
> Fix this by separating the checks/code into CONFIG and LIVE
> processing using the correct definition for each block and
> performing cleanup for both options as necessary.
> 
> Signed-off-by: John Ferlan <jferlan at redhat.com>
> ---
>  src/qemu/qemu_driver.c | 52 +++++++++++++++++++-----------------------
>  1 file changed, 23 insertions(+), 29 deletions(-)
> 
> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
> index 7d519c0714..3dbd5c62d2 100644
> --- a/src/qemu/qemu_driver.c
> +++ b/src/qemu/qemu_driver.c
> @@ -8473,7 +8473,8 @@ qemuDomainAttachDeviceLiveAndConfig(virDomainObjPtr vm,
>  {
>      virDomainDefPtr vmdef = NULL;
>      virQEMUDriverConfigPtr cfg = NULL;
> -    virDomainDeviceDefPtr dev = NULL, dev_copy = NULL;
> +    virDomainDeviceDefPtr devConf = NULL;
> +    virDomainDeviceDefPtr devLive = NULL;
>      int ret = -1;
>      virCapsPtr caps = NULL;
>      unsigned int parse_flags = VIR_DOMAIN_DEF_PARSE_INACTIVE |
> @@ -8487,49 +8488,43 @@ qemuDomainAttachDeviceLiveAndConfig(virDomainObjPtr vm,
>      if (!(caps = virQEMUDriverGetCapabilities(driver, false)))
>          goto cleanup;
>  
> -    dev = dev_copy = virDomainDeviceDefParse(xml, vm->def,
> -                                             caps, driver->xmlopt,
> -                                             parse_flags);
> -    if (dev == NULL)
> -        goto cleanup;
> -
> -    if (virDomainDeviceValidateAliasForHotplug(vm, dev, flags) < 0)
> -        goto cleanup;
> -
> -    if (flags & VIR_DOMAIN_AFFECT_CONFIG &&
> -        flags & VIR_DOMAIN_AFFECT_LIVE) {
> -        /* If we are affecting both CONFIG and LIVE
> -         * create a deep copy of device as adding
> -         * to CONFIG takes one instance.
> -         */
> -        dev_copy = virDomainDeviceDefCopy(dev, vm->def, caps, driver->xmlopt);
> -        if (!dev_copy)
> -            goto cleanup;
> -    }
> -
> +    /* The config and live post processing address auto-generation algorithms
> +     * rely on the correct vm->def or vm->newDef being passed, so call the
> +     * device parse based on which definition is in use */
>      if (flags & VIR_DOMAIN_AFFECT_CONFIG) {
> -        /* Make a copy for updated domain. */
>          vmdef = virDomainObjCopyPersistentDef(vm, caps, driver->xmlopt);
>          if (!vmdef)
>              goto cleanup;
>  
> -        if (virDomainDefCompatibleDevice(vmdef, dev, NULL,
> +        if (!(devConf = virDomainDeviceDefParse(xml, vmdef, caps,
> +                                                driver->xmlopt, parse_flags)))
> +            goto cleanup;
> +
> +        if (virDomainDefCompatibleDevice(vmdef, devConf, NULL,
>                                           VIR_DOMAIN_DEVICE_ACTION_ATTACH,
>                                           false) < 0)
>              goto cleanup;
> -        if ((ret = qemuDomainAttachDeviceConfig(vmdef, dev, caps,
> +
> +        if ((ret = qemuDomainAttachDeviceConfig(vmdef, devConf, caps,
>                                                  parse_flags,
>                                                  driver->xmlopt)) < 0)
>              goto cleanup;
>      }
>  
>      if (flags & VIR_DOMAIN_AFFECT_LIVE) {
> -        if (virDomainDefCompatibleDevice(vm->def, dev_copy, NULL,
> +        if (!(devLive = virDomainDeviceDefParse(xml, vm->def, caps,
> +                                                driver->xmlopt, parse_flags)))
> +            goto cleanup;
> +
> +        if (virDomainDeviceValidateAliasForHotplug(vm, devLive, flags) < 0)
> +            goto cleanup;
> +
> +        if (virDomainDefCompatibleDevice(vm->def, devLive, NULL,
>                                           VIR_DOMAIN_DEVICE_ACTION_ATTACH,
>                                           true) < 0)
>              goto cleanup;
>  
> -        if ((ret = qemuDomainAttachDeviceLive(vm, dev_copy, driver)) < 0)
> +        if ((ret = qemuDomainAttachDeviceLive(vm, devLive, driver)) < 0)
>              goto cleanup;
>          /*
>           * update domain status forcibly because the domain status may be
> @@ -8553,9 +8548,8 @@ qemuDomainAttachDeviceLiveAndConfig(virDomainObjPtr vm,
>  
>   cleanup:
>      virDomainDefFree(vmdef);
> -    if (dev != dev_copy)
> -        virDomainDeviceDefFree(dev_copy);
> -    virDomainDeviceDefFree(dev);
> +    virDomainDeviceDefFree(devConf);
> +    virDomainDeviceDefFree(devLive);
>      virObjectUnref(cfg);
>      virObjectUnref(caps);
>  
> 

I'm failing to see why the other patches are necessary. I'm unable to
reproduce the bug after I applied only this single patch.
It also makes sense, because the source of error is that when parsing
device XML wrong vmdef was passed. Therefore, when postParse callback
tried to fill device address it was looking at wrong data (thinking
there's no such drive address) and returned the next free address which
was the same all the time.

ACK to this patch.

Michal