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Re: [libvirt] [PATCH 3/3] Stop accessing driver->caps directly in QEMU driver



On Wed, Feb 06, 2013 at 11:54:51 +0000, Daniel P. Berrange wrote:
> From: "Daniel P. Berrange" <berrange redhat com>
> 
> The 'driver->caps' pointer can be changed on the fly. Accessing
> it currently requires the global driver lock. Isolate this
> access in a single helper, so a future patch can relax the
> locking constraints.
...
I checked that no direct access to driver->caps remained.

There are quite a few places where virQEMUDriverGetCapabilities is
called on an unlocked driver but that's not your fault. The bug has been
there even for years in some cases. Anyway, I guess one of your next
series will fix all these issues by changing the way we use qemu driver
lock.

...
> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
> index 18c4d3c..7ada7c3 100644
> --- a/src/qemu/qemu_driver.c
> +++ b/src/qemu/qemu_driver.c
...
> @@ -956,20 +888,25 @@ static void qemuNotifyLoadDomain(virDomainObjPtr vm, int newVM, void *opaque)
>  static int
>  qemuReload(void) {
>      virQEMUDriverConfigPtr cfg;
> +    virCapsPtr caps;
>  
>      if (!qemu_driver)
>          return 0;
>  
> +    if (!(caps = virQEMUDriverGetCapabilities(qemu_driver, false)))
> +        return -1;
> +

I know you're going to revisit qemu_driver locking in a future series
but you can still add virQEMUDriverGetCapabilities call after
qemu_driver is actually locked here.

>      qemuDriverLock(qemu_driver);
>      cfg = virQEMUDriverGetConfig(qemu_driver);
>      virDomainObjListLoadAllConfigs(qemu_driver->domains,
> -                                   qemu_driver->caps,
> +                                   caps,
>                                     cfg->configDir,
>                                     cfg->autostartDir,
>                                     0, QEMU_EXPECTED_VIRT_TYPES,
>                                     qemuNotifyLoadDomain, qemu_driver);
>      qemuDriverUnlock(qemu_driver);
>      virObjectUnref(cfg);
> +    virObjectUnref(caps);
>      return 0;
>  }
>
...

ACK with this small change.

Jirka


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