Re: [PATCH v6 1/2] KVM: resize kvm_io_range array dynamically

[Marcelo Tosatti <mtosatti@redhat.com>]

On Thu, Mar 08, 2012 at 10:03:55AM +0800, Amos Kong wrote:
> This patch makes the kvm_io_range array can be resized dynamically.
> 
> Signed-off-by: Amos Kong <akong@redhat.com>
> ---
>  include/linux/kvm_host.h |    5 +++--
>  virt/kvm/kvm_main.c      |   38 ++++++++++++++++++--------------------
>  2 files changed, 21 insertions(+), 22 deletions(-)
> 
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index e42d85a..8a6c1a3 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -67,10 +67,11 @@ struct kvm_io_range {
>  	struct kvm_io_device *dev;
>  };
>  
> +#define NR_IOBUS_DEVS 300
> +
>  struct kvm_io_bus {
>  	int                   dev_count;
> -#define NR_IOBUS_DEVS 300
> -	struct kvm_io_range range[NR_IOBUS_DEVS];
> +	struct kvm_io_range range[];
>  };
>  
>  enum kvm_bus {
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 94e148e..f6ee1e2 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2393,9 +2393,6 @@ int kvm_io_bus_sort_cmp(const void *p1, const void *p2)
>  int kvm_io_bus_insert_dev(struct kvm_io_bus *bus, struct kvm_io_device *dev,
>  			  gpa_t addr, int len)
>  {
> -	if (bus->dev_count == NR_IOBUS_DEVS)
> -		return -ENOSPC;
> -
>  	bus->range[bus->dev_count++] = (struct kvm_io_range) {
>  		.addr = addr,
>  		.len = len,
> @@ -2495,12 +2492,15 @@ int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
>  	struct kvm_io_bus *new_bus, *bus;
>  
>  	bus = kvm->buses[bus_idx];
> -	if (bus->dev_count > NR_IOBUS_DEVS-1)
> +	if (bus->dev_count > NR_IOBUS_DEVS - 1)
>  		return -ENOSPC;
>  
> -	new_bus = kmemdup(bus, sizeof(struct kvm_io_bus), GFP_KERNEL);
> +	new_bus = kzalloc(sizeof(*bus) + ((bus->dev_count + 1) *
> +			  sizeof(struct kvm_io_range)), GFP_KERNEL);
>  	if (!new_bus)
>  		return -ENOMEM;
> +	memcpy(new_bus, bus, sizeof(*bus) + (bus->dev_count *
> +	       sizeof(struct kvm_io_range)));
>  	kvm_io_bus_insert_dev(new_bus, dev, addr, len);
>  	rcu_assign_pointer(kvm->buses[bus_idx], new_bus);
>  	synchronize_srcu_expedited(&kvm->srcu);
> @@ -2517,27 +2517,25 @@ int kvm_io_bus_unregister_dev(struct kvm *kvm, enum kvm_bus bus_idx,
>  	struct kvm_io_bus *new_bus, *bus;
>  
>  	bus = kvm->buses[bus_idx];
> -
> -	new_bus = kmemdup(bus, sizeof(*bus), GFP_KERNEL);
> -	if (!new_bus)
> -		return -ENOMEM;
> -
>  	r = -ENOENT;
> -	for (i = 0; i < new_bus->dev_count; i++)
> -		if (new_bus->range[i].dev == dev) {
> +	for (i = 0; i < bus->dev_count; i++)
> +		if (bus->range[i].dev == dev) {
>  			r = 0;
> -			new_bus->dev_count--;
> -			new_bus->range[i] = new_bus->range[new_bus->dev_count];
> -			sort(new_bus->range, new_bus->dev_count,
> -			     sizeof(struct kvm_io_range),
> -			     kvm_io_bus_sort_cmp, NULL);
>  			break;
>  		}
>  
> -	if (r) {
> -		kfree(new_bus);
> +	if (r)
>  		return r;
> -	}
> +
> +	new_bus = kzalloc(sizeof(*bus) + ((bus->dev_count - 1) *
> +			  sizeof(struct kvm_io_range)), GFP_KERNEL);
> +	if (!new_bus)
> +		return -ENOMEM;
> +
> +	new_bus->dev_count--;

Was just zeroed above?

> +	memcpy(new_bus->range, bus->range, i * sizeof(struct kvm_io_range));
> +	memcpy(new_bus->range + i, bus->range + i + 1,
> +	       (new_bus->dev_count - i) * sizeof(struct kvm_io_range));

Did you mean "i" as an indice for ->range[] ?