[libvirt] [PATCH 2/2] qemu: Validate the domain after marking the current domain as transient

[Michal Privoznik]

On 02/23/2017 10:44 AM, Marc Hartmayer wrote:
> Validate the domain that actually will be started. It's semantically
> more clear and also it can detect failures that may have happened in
> virDomainObjSetDefTransient().
> 
> Signed-off-by: Marc Hartmayer <mhartmay at linux.vnet.ibm.com>
> Reviewed-by: Bjoern Walk <bwalk at linux.vnet.ibm.com>
> Reviewed-by: Boris Fiuczynski <fiuczy at linux.vnet.ibm.com>
> ---
>  src/qemu/qemu_process.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
> index a57d136..bd3a8b8 100644
> --- a/src/qemu/qemu_process.c
> +++ b/src/qemu/qemu_process.c
> @@ -4746,9 +4746,6 @@ qemuProcessInit(virQEMUDriverPtr driver,
>                                                        vm->def->os.machine)))
>          goto cleanup;
>  
> -    if (qemuProcessStartValidate(driver, vm, priv->qemuCaps, caps, flags) < 0)
> -        goto cleanup;
> -
>      /* Do this upfront, so any part of the startup process can add
>       * runtime state to vm->def that won't be persisted. This let's us
>       * report implicit runtime defaults in the XML, like vnc listen/socket
> @@ -4757,6 +4754,9 @@ qemuProcessInit(virQEMUDriverPtr driver,
>      if (virDomainObjSetDefTransient(caps, driver->xmlopt, vm) < 0)
>          goto cleanup;
>  
> +    if (qemuProcessStartValidate(driver, vm, priv->qemuCaps, caps, flags) < 0)
> +        goto cleanup;
> +

This needs to be goto stop for the reasons described in the previous e-mail.

>      if (flags & VIR_QEMU_PROCESS_START_PRETEND) {
>          if (qemuDomainSetPrivatePaths(driver, vm) < 0)
>              goto cleanup;
> 

Honestly, I like what we have now better. I mean, SetDefTransient() is
very unlikely to fail. It's just doing a copy of domain definition (in a
very stupid way, but lets save that for a different discussion).
Basically, it will fail on OOM only (which you will not get on a Linux
system, unless you really try).
However, the StartValidate() just reads some data without any
allocation. Thus, from memory management POV, should your domain be
unable to start we don't allocate any memory just to find that out.

Michal