Re: [PATCH v2] qemu: qemuDomainChangeNet: validity checks should be done before XML autocompletion

[Ján Tomko <jtomko@xxxxxxxxxx>]

On Thu, Aug 09, 2018 at 11:21:52AM +0200, Katerina Koukiou wrote:
> This patch ensures that changes in attributes of interfaces will be emit
> errors accept if they are missing from the XML.
> Previously we were falsely reporting successfull updates, because some

*successful

> changed attributes got overwritten before the validity checks.

The more I think about this 'feature' that allows you to omit parts of
the changed XML, the weirder it gets.

> https://bugzilla.redhat.com/show_bug.cgi?id=1599513
>
> Signed-off-by: Katerina Koukiou <kkoukiou@xxxxxxxxxx>
> ---
> src/qemu/qemu_hotplug.c | 42 +++++++++++++++++++++++++----------------
> 1 file changed, 26 insertions(+), 16 deletions(-)
>
> diff --git a/src/qemu/qemu_hotplug.c b/src/qemu/qemu_hotplug.c
> index 1488f0a7c2..76ab56a479 100644
> --- a/src/qemu/qemu_hotplug.c
> +++ b/src/qemu/qemu_hotplug.c
> @@ -3445,23 +3445,9 @@ qemuDomainChangeNet(virQEMUDriverPtr driver,
>         goto cleanup;
>     }
>
> -    /* info: if newdev->info is empty, fill it in from olddev,
> -     * otherwise verify that it matches - nothing is allowed to
> -     * change. (There is no helper function to do this, so
> -     * individually check the few feidls of virDomainDeviceInfo that
> -     * are relevant in this case).
> +    /* info: Nothing is allowed to change. First fill the missing newdev->info
> +     * from olddev and then check for changes.

Maybe the other way around (checking first - with respect to what was
specified in the XML, then overwriting) might be cleaner, see below.

>      */
> -    if (!virDomainDeviceAddressIsValid(&newdev->info,
> -                                       VIR_DOMAIN_DEVICE_ADDRESS_TYPE_PCI) &&
> -        virDomainDeviceInfoCopy(&newdev->info, &olddev->info) < 0) {
> -        goto cleanup;
> -    }
> -    if (!virPCIDeviceAddressEqual(&olddev->info.addr.pci,
> -                                  &newdev->info.addr.pci)) {
> -        virReportError(VIR_ERR_OPERATION_UNSUPPORTED, "%s",
> -                       _("cannot modify network device guest PCI address"));
> -        goto cleanup;
> -    }
>     /* grab alias from olddev if not set in newdev */
>     if (!newdev->info.alias &&
>         VIR_STRDUP(newdev->info.alias, olddev->info.alias) < 0)
> @@ -3469,26 +3455,50 @@ qemuDomainChangeNet(virQEMUDriverPtr driver,
>
>     /* device alias is checked already in virDomainDefCompatibleDevice */
>
> +    if (newdev->info.rombar == VIR_TRISTATE_BOOL_ABSENT)
> +        newdev->info.rombar = olddev->info.rombar;
>     if (olddev->info.rombar != newdev->info.rombar) {
>         virReportError(VIR_ERR_OPERATION_UNSUPPORTED, "%s",
>                        _("cannot modify network device rom bar setting"));
>         goto cleanup;
>     }
> +
> +    if (!newdev->info.romfile &&
> +        VIR_STRDUP(newdev->info.romfile, olddev->info.romfile) < 0)
> +        goto cleanup;
>     if (STRNEQ_NULLABLE(olddev->info.romfile, newdev->info.romfile)) {
>         virReportError(VIR_ERR_OPERATION_UNSUPPORTED, "%s",
>                        _("cannot modify network rom file"));
>         goto cleanup;
>     }
> +
> +    if (newdev->info.bootIndex == 0)
> +        newdev->info.bootIndex = olddev->info.bootIndex;
>     if (olddev->info.bootIndex != newdev->info.bootIndex) {
>         virReportError(VIR_ERR_OPERATION_UNSUPPORTED, "%s",
>                        _("cannot modify network device boot index setting"));
>         goto cleanup;
>     }
> +
> +    if (newdev->info.romenabled == VIR_TRISTATE_BOOL_ABSENT)
> +        newdev->info.romenabled = olddev->info.romenabled;
>     if (olddev->info.romenabled != newdev->info.romenabled) {
>         virReportError(VIR_ERR_OPERATION_UNSUPPORTED, "%s",
>                        _("cannot modify network device rom enabled setting"));
>         goto cleanup;
>     }
> +
> +    /* if pci addr is missing or is invalid we overwrite it from olddev */
> +    if (!virDomainDeviceAddressIsValid(&newdev->info,
> +                                       VIR_DOMAIN_DEVICE_ADDRESS_TYPE_PCI)) {
> +        newdev->info.addr.pci = olddev->info.addr.pci;

This is an insufficient way to copy the address. The 'addr' union might
be containing an address of a different type. And the 'info.type' attribute also
needs to be copied, either 1) manually or via a 2) DeviceInfoCopy call.

Also, the checks can be moved to a separate fuction first (qemuDomainChangeNet
is over 400 lines long now), e.g. qemuDomainChangeNetAllowed.

Then either:
1) change the unconditional copy of the attributes not present in newdev
  to call another helper (DeviceInfoCopyIfNeeded? MaybeCopy?) that only fills
  the missing parts; or
2) Make qemuDomainChangeNetAllowed only look at specified attributes and
  move the DeviceInfoCopy call after it. (Also, to prevent memory
  leaks, the original info should be cleared before calling copy)

Jano

> +    }
> +    if (!virPCIDeviceAddressEqual(&olddev->info.addr.pci,
> +                                  &newdev->info.addr.pci)) {

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