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Re: [libvirt] [PATCH v2 5/7] lock_driver_sanlock: Handle metadata flag gracefully




On 08/14/2018 07:19 AM, Michal Privoznik wrote:
> No real support implemented here. But hey, at least we will not
> fail.
> 
> Signed-off-by: Michal Privoznik <mprivozn redhat com>
> ---
>  src/locking/lock_driver_sanlock.c | 25 ++++++++++++++++++-------
>  1 file changed, 18 insertions(+), 7 deletions(-)
> 
> diff --git a/src/locking/lock_driver_sanlock.c b/src/locking/lock_driver_sanlock.c
> index 3e5f0e37b0..c1996fb937 100644
> --- a/src/locking/lock_driver_sanlock.c
> +++ b/src/locking/lock_driver_sanlock.c
> @@ -791,7 +791,8 @@ static int virLockManagerSanlockAddResource(virLockManagerPtr lock,
>      virLockManagerSanlockPrivatePtr priv = lock->privateData;
>  
>      virCheckFlags(VIR_LOCK_MANAGER_RESOURCE_READONLY |
> -                  VIR_LOCK_MANAGER_RESOURCE_SHARED, -1);
> +                  VIR_LOCK_MANAGER_RESOURCE_SHARED |
> +                  VIR_LOCK_MANAGER_RESOURCE_METADATA, -1);
>  
>      if (priv->res_count == SANLK_MAX_RESOURCES) {
>          virReportError(VIR_ERR_INTERNAL_ERROR,
> @@ -804,6 +805,11 @@ static int virLockManagerSanlockAddResource(virLockManagerPtr lock,
>      if (flags & VIR_LOCK_MANAGER_RESOURCE_READONLY)
>          return 0;
>  
> +    /* No metadata locking support for now.
> +     * TODO: implement it. */
> +    if (flags & VIR_LOCK_MANAGER_RESOURCE_METADATA)
> +        return 0;
> +

Doesn't this give someone the false impression that their resource is
locked if they choose METADATA?

Something doesn't feel right about that - giving the impression that
it's supported and the consumer is protected, but when push comes to
shove they aren't.

I'd be inclined to believe that we may want to do nothing with/for
sanlock allowing the virCheckFlags above take care of the consumer.

>      switch (type) {
>      case VIR_LOCK_MANAGER_RESOURCE_TYPE_DISK:
>          if (driver->autoDiskLease) {
> @@ -953,12 +959,17 @@ static int virLockManagerSanlockAcquire(virLockManagerPtr lock,
>      virCheckFlags(VIR_LOCK_MANAGER_ACQUIRE_RESTRICT |
>                    VIR_LOCK_MANAGER_ACQUIRE_REGISTER_ONLY, -1);
>  
> -    if (priv->res_count == 0 &&
> -        priv->hasRWDisks &&
> -        driver->requireLeaseForDisks) {
> -        virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
> -                       _("Read/write, exclusive access, disks were present, but no leases specified"));
> -        return -1;
> +    if (priv->res_count == 0) {
> +        if (priv->hasRWDisks &&
> +            driver->requireLeaseForDisks) {
> +            virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
> +                           _("Read/write, exclusive access, disks were present, but no leases specified"));
> +            return -1;
> +        }
> +
> +        /* We are not handling METADATA flag yet. So no resources
> +         * case is no-op for now. */
> +        return 0;

Similar comment to patch4 w/r/t resource type (e.g. disk or lease), but
now at least it's more obvious to me that hasRWDisks means lock for disk
vs. not.

Still it's odd to think that returning 0, but not actually getting the
lock is the "right" thing to do. "Theoretically", if AddResource failed,
then would Acquire ever be called w/ this flag?

>      }
>  
>      /* We only initialize 'sock' if we are in the real
> 

BTW:

Now that I think about them together...

  - lock_driver_lockd.h - extract from patch4 and merge to patch3. I
suppose it could be separate too to keep mgmt vs. space separate, but
they're related enough to keep them together. Perhaps this is where a
few more "words" about usage expectations as part of the commit message.

  - lock_daemon_dispatch.c - extract from patch4 and whether it goes
before or after is one of those chicken/egg type quandaries. Keeping it
with the fcntl/lockd as opposed to the sanlock implementation doesn't
feel right (even though sanlock doesn't use any LOCK_SPACE symbols).

I can be swayed otherwise... maybe someone else will pipe in.

John


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