diff mbox

[v2,2/3] kvm: cleanup io_device code

Message ID 20090527213744.24324.82745.stgit@dev.haskins.net (mailing list archive)
State New, archived
Headers show

Commit Message

Gregory Haskins May 27, 2009, 9:37 p.m. UTC 
We modernize the io_device code so that we use container_of() instead of
dev->private, and move the vtable to a separate ops structure
(theoretically allows better caching for multiple instances of the same
ops structure)

Signed-off-by: Gregory Haskins <ghaskins@novell.com>
---

 arch/x86/kvm/i8254.c      |   40 ++++++++++++++++++++++++++++------------
 arch/x86/kvm/i8259.c      |   20 ++++++++++++++------
 arch/x86/kvm/lapic.c      |   22 +++++++++++++++-------
 arch/x86/kvm/x86.c        |    2 +-
 virt/kvm/coalesced_mmio.c |   25 +++++++++++++++----------
 virt/kvm/ioapic.c         |   22 +++++++++++++++-------
 virt/kvm/iodev.h          |   25 ++++++++++++++++++-------
 virt/kvm/kvm_main.c       |    2 +-
 8 files changed, 107 insertions(+), 51 deletions(-)


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Comments

Chris Wright May 28, 2009, 5:49 a.m. UTC | #1 
* Gregory Haskins (ghaskins@novell.com) wrote:
> We modernize the io_device code so that we use container_of() instead of
> dev->private, and move the vtable to a separate ops structure
> (theoretically allows better caching for multiple instances of the same
> ops structure)

Looks like a nice cleanup.  Couple minor nits.

> +static struct kvm_io_device_ops pit_dev_ops = {
> +	.read     = pit_ioport_read,
> +	.write    = pit_ioport_write,
> +	.in_range = pit_in_range,
> +};
> +
> +static struct kvm_io_device_ops speaker_dev_ops = {
> +	.read     = speaker_ioport_read,
> +	.write    = speaker_ioport_write,
> +	.in_range = speaker_in_range,
> +};

kvm_io_device_ops instances could be made const.

> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2227,7 +2227,7 @@ static struct kvm_io_device *vcpu_find_pervcpu_dev(struct kvm_vcpu *vcpu,
>  
>  	if (vcpu->arch.apic) {
>  		dev = &vcpu->arch.apic->dev;
> -		if (dev->in_range(dev, addr, len, is_write))
> +		if (dev->ops->in_range(dev, addr, len, is_write))
>  			return dev;

> --- a/virt/kvm/iodev.h
> +++ b/virt/kvm/iodev.h
> @@ -18,7 +18,9 @@
>  
>  #include <linux/kvm_types.h>
>  
> -struct kvm_io_device {
> +struct kvm_io_device;
> +
> +struct kvm_io_device_ops {
>  	void (*read)(struct kvm_io_device *this,
>  		     gpa_t addr,
>  		     int len,
> @@ -30,16 +32,25 @@ struct kvm_io_device {
>  	int (*in_range)(struct kvm_io_device *this, gpa_t addr, int len,
>  			int is_write);
>  	void (*destructor)(struct kvm_io_device *this);
> +};
> +
>  
> -	void             *private;
> +struct kvm_io_device {
> +	struct kvm_io_device_ops *ops;
>  };

Did you plan to extend kvm_io_device struct?

> +static inline void kvm_iodevice_init(struct kvm_io_device *dev,
> +				     struct kvm_io_device_ops *ops)
> +{
> +	dev->ops = ops;
> +}

And similarly, did you have a plan to do more with kvm_iodevice_init()?
Otherwise looking a bit like overkill to me.

> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2456,7 +2456,7 @@ struct kvm_io_device *kvm_io_bus_find_dev(struct kvm_io_bus *bus,
>  	for (i = 0; i < bus->dev_count; i++) {
>  		struct kvm_io_device *pos = bus->devs[i];
>  
> -		if (pos->in_range(pos, addr, len, is_write))
> +		if (kvm_iodevice_inrange(pos, addr, len, is_write))
>  			return pos;
>  	}

You converted this to the helper but not vcpu_find_pervcpu_dev() (not
convinced it actually helps readability, but consistency is good).  BTW,
while there, s/kvm_iodevice_inrange/kvm_iodevice_in_range/ would be nice.

thanks,
-chris
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Gregory Haskins May 28, 2009, 11:59 a.m. UTC | #2 
Chris Wright wrote:
> * Gregory Haskins (ghaskins@novell.com) wrote:
>   
>> We modernize the io_device code so that we use container_of() instead of
>> dev->private, and move the vtable to a separate ops structure
>> (theoretically allows better caching for multiple instances of the same
>> ops structure)
>>     
>
> Looks like a nice cleanup.  Couple minor nits.
>
>   
>> +static struct kvm_io_device_ops pit_dev_ops = {
>> +	.read     = pit_ioport_read,
>> +	.write    = pit_ioport_write,
>> +	.in_range = pit_in_range,
>> +};
>> +
>> +static struct kvm_io_device_ops speaker_dev_ops = {
>> +	.read     = speaker_ioport_read,
>> +	.write    = speaker_ioport_write,
>> +	.in_range = speaker_in_range,
>> +};
>>     
>
> kvm_io_device_ops instances could be made const.
>   

Ack

>   
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -2227,7 +2227,7 @@ static struct kvm_io_device *vcpu_find_pervcpu_dev(struct kvm_vcpu *vcpu,
>>  
>>  	if (vcpu->arch.apic) {
>>  		dev = &vcpu->arch.apic->dev;
>> -		if (dev->in_range(dev, addr, len, is_write))
>> +		if (dev->ops->in_range(dev, addr, len, is_write))
>>  			return dev;
>>     
>
>   
>> --- a/virt/kvm/iodev.h
>> +++ b/virt/kvm/iodev.h
>> @@ -18,7 +18,9 @@
>>  
>>  #include <linux/kvm_types.h>
>>  
>> -struct kvm_io_device {
>> +struct kvm_io_device;
>> +
>> +struct kvm_io_device_ops {
>>  	void (*read)(struct kvm_io_device *this,
>>  		     gpa_t addr,
>>  		     int len,
>> @@ -30,16 +32,25 @@ struct kvm_io_device {
>>  	int (*in_range)(struct kvm_io_device *this, gpa_t addr, int len,
>>  			int is_write);
>>  	void (*destructor)(struct kvm_io_device *this);
>> +};
>> +
>>  
>> -	void             *private;
>> +struct kvm_io_device {
>> +	struct kvm_io_device_ops *ops;
>>  };
>>     
>
> Did you plan to extend kvm_io_device struct?
>
>   
>> +static inline void kvm_iodevice_init(struct kvm_io_device *dev,
>> +				     struct kvm_io_device_ops *ops)
>> +{
>> +	dev->ops = ops;
>> +}
>>     
>
> And similarly, did you have a plan to do more with kvm_iodevice_init()?
> Otherwise looking a bit like overkill to me.
>   

Yeah.  As of right now my plan is to wait for Marcelo's lock cleanup to
go in and integrate with that, and then convert the MMIO/PIO code to use
RCU to acquire a reference to the io_device (so we run as fine-graned
and lockless as possible).  When that happens, you will see an atomic_t
in the struct/init as well.

Even if that doesn't make the cut after review, I am thinking that we
may be making the structure more complex in the future (for instance, to
use a rbtree/hlist instead of the array, or to do tricks with caching
the MRU device, etc.) and this will simplify that effort by already
having all users call the abstracted init. 

That said, we could just defer these hunks until needed.  I just figured
"while Im in here" but its nbd either way.

>   
>> --- a/virt/kvm/kvm_main.c
>> +++ b/virt/kvm/kvm_main.c
>> @@ -2456,7 +2456,7 @@ struct kvm_io_device *kvm_io_bus_find_dev(struct kvm_io_bus *bus,
>>  	for (i = 0; i < bus->dev_count; i++) {
>>  		struct kvm_io_device *pos = bus->devs[i];
>>  
>> -		if (pos->in_range(pos, addr, len, is_write))
>> +		if (kvm_iodevice_inrange(pos, addr, len, is_write))
>>  			return pos;
>>  	}
>>     
>
> You converted this to the helper but not vcpu_find_pervcpu_dev() (not
> convinced it actually helps readability, but consistency is good).

Oops..oversight.  Will fix.

>   BTW,
> while there, s/kvm_iodevice_inrange/kvm_iodevice_in_range/ would be nice.
>   

Yeah, good idea.  Will fix.

Thanks Chris,
-Greg
diff mbox

Patch

diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index 584e3d3..d6a2b7d 100644
--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c
@@ -347,10 +347,20 @@  void kvm_pit_load_count(struct kvm *kvm, int channel, u32 val)
 	mutex_unlock(&kvm->arch.vpit->pit_state.lock);
 }
 
+static inline struct kvm_pit *dev_to_pit(struct kvm_io_device *dev)
+{
+	return container_of(dev, struct kvm_pit, dev);
+}
+
+static inline struct kvm_pit *speaker_to_pit(struct kvm_io_device *dev)
+{
+	return container_of(dev, struct kvm_pit, speaker_dev);
+}
+
 static void pit_ioport_write(struct kvm_io_device *this,
 			     gpa_t addr, int len, const void *data)
 {
-	struct kvm_pit *pit = (struct kvm_pit *)this->private;
+	struct kvm_pit *pit = dev_to_pit(this);
 	struct kvm_kpit_state *pit_state = &pit->pit_state;
 	struct kvm *kvm = pit->kvm;
 	int channel, access;
@@ -423,7 +433,7 @@  static void pit_ioport_write(struct kvm_io_device *this,
 static void pit_ioport_read(struct kvm_io_device *this,
 			    gpa_t addr, int len, void *data)
 {
-	struct kvm_pit *pit = (struct kvm_pit *)this->private;
+	struct kvm_pit *pit = dev_to_pit(this);
 	struct kvm_kpit_state *pit_state = &pit->pit_state;
 	struct kvm *kvm = pit->kvm;
 	int ret, count;
@@ -494,7 +504,7 @@  static int pit_in_range(struct kvm_io_device *this, gpa_t addr,
 static void speaker_ioport_write(struct kvm_io_device *this,
 				 gpa_t addr, int len, const void *data)
 {
-	struct kvm_pit *pit = (struct kvm_pit *)this->private;
+	struct kvm_pit *pit = speaker_to_pit(this);
 	struct kvm_kpit_state *pit_state = &pit->pit_state;
 	struct kvm *kvm = pit->kvm;
 	u32 val = *(u32 *) data;
@@ -508,7 +518,7 @@  static void speaker_ioport_write(struct kvm_io_device *this,
 static void speaker_ioport_read(struct kvm_io_device *this,
 				gpa_t addr, int len, void *data)
 {
-	struct kvm_pit *pit = (struct kvm_pit *)this->private;
+	struct kvm_pit *pit = speaker_to_pit(this);
 	struct kvm_kpit_state *pit_state = &pit->pit_state;
 	struct kvm *kvm = pit->kvm;
 	unsigned int refresh_clock;
@@ -560,6 +570,18 @@  static void pit_mask_notifer(struct kvm_irq_mask_notifier *kimn, bool mask)
 	}
 }
 
+static struct kvm_io_device_ops pit_dev_ops = {
+	.read     = pit_ioport_read,
+	.write    = pit_ioport_write,
+	.in_range = pit_in_range,
+};
+
+static struct kvm_io_device_ops speaker_dev_ops = {
+	.read     = speaker_ioport_read,
+	.write    = speaker_ioport_write,
+	.in_range = speaker_in_range,
+};
+
 struct kvm_pit *kvm_create_pit(struct kvm *kvm, u32 flags)
 {
 	struct kvm_pit *pit;
@@ -580,17 +602,11 @@  struct kvm_pit *kvm_create_pit(struct kvm *kvm, u32 flags)
 	spin_lock_init(&pit->pit_state.inject_lock);
 
 	/* Initialize PIO device */
-	pit->dev.read = pit_ioport_read;
-	pit->dev.write = pit_ioport_write;
-	pit->dev.in_range = pit_in_range;
-	pit->dev.private = pit;
+	kvm_iodevice_init(&pit->dev, &pit_dev_ops);
 	kvm_io_bus_register_dev(&kvm->pio_bus, &pit->dev);
 
 	if (flags & KVM_PIT_SPEAKER_DUMMY) {
-		pit->speaker_dev.read = speaker_ioport_read;
-		pit->speaker_dev.write = speaker_ioport_write;
-		pit->speaker_dev.in_range = speaker_in_range;
-		pit->speaker_dev.private = pit;
+		kvm_iodevice_init(&pit->speaker_dev, &speaker_dev_ops);
 		kvm_io_bus_register_dev(&kvm->pio_bus, &pit->speaker_dev);
 	}
 
diff --git a/arch/x86/kvm/i8259.c b/arch/x86/kvm/i8259.c
index 1ccb50c..63d9e5e 100644
--- a/arch/x86/kvm/i8259.c
+++ b/arch/x86/kvm/i8259.c
@@ -444,10 +444,15 @@  static int picdev_in_range(struct kvm_io_device *this, gpa_t addr,
 	}
 }
 
+static inline struct kvm_pic *to_pic(struct kvm_io_device *dev)
+{
+	return container_of(dev, struct kvm_pic, dev);
+}
+
 static void picdev_write(struct kvm_io_device *this,
 			 gpa_t addr, int len, const void *val)
 {
-	struct kvm_pic *s = this->private;
+	struct kvm_pic *s = to_pic(this);
 	unsigned char data = *(unsigned char *)val;
 
 	if (len != 1) {
@@ -474,7 +479,7 @@  static void picdev_write(struct kvm_io_device *this,
 static void picdev_read(struct kvm_io_device *this,
 			gpa_t addr, int len, void *val)
 {
-	struct kvm_pic *s = this->private;
+	struct kvm_pic *s = to_pic(this);
 	unsigned char data = 0;
 
 	if (len != 1) {
@@ -516,6 +521,12 @@  static void pic_irq_request(void *opaque, int level)
 	}
 }
 
+static struct kvm_io_device_ops picdev_ops = {
+	.read = picdev_read,
+	.write = picdev_write,
+	.in_range = picdev_in_range,
+};
+
 struct kvm_pic *kvm_create_pic(struct kvm *kvm)
 {
 	struct kvm_pic *s;
@@ -534,10 +545,7 @@  struct kvm_pic *kvm_create_pic(struct kvm *kvm)
 	/*
 	 * Initialize PIO device
 	 */
-	s->dev.read = picdev_read;
-	s->dev.write = picdev_write;
-	s->dev.in_range = picdev_in_range;
-	s->dev.private = s;
+	kvm_iodevice_init(&s->dev, &picdev_ops);
 	kvm_io_bus_register_dev(&kvm->pio_bus, &s->dev);
 	return s;
 }
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index ae99d83..496d2ad 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -522,10 +522,15 @@  static u32 __apic_read(struct kvm_lapic *apic, unsigned int offset)
 	return val;
 }
 
+static inline struct kvm_lapic *to_lapic(struct kvm_io_device *dev)
+{
+	return container_of(dev, struct kvm_lapic, dev);
+}
+
 static void apic_mmio_read(struct kvm_io_device *this,
 			   gpa_t address, int len, void *data)
 {
-	struct kvm_lapic *apic = (struct kvm_lapic *)this->private;
+	struct kvm_lapic *apic = to_lapic(this);
 	unsigned int offset = address - apic->base_address;
 	unsigned char alignment = offset & 0xf;
 	u32 result;
@@ -606,7 +611,7 @@  static void apic_manage_nmi_watchdog(struct kvm_lapic *apic, u32 lvt0_val)
 static void apic_mmio_write(struct kvm_io_device *this,
 			    gpa_t address, int len, const void *data)
 {
-	struct kvm_lapic *apic = (struct kvm_lapic *)this->private;
+	struct kvm_lapic *apic = to_lapic(this);
 	unsigned int offset = address - apic->base_address;
 	unsigned char alignment = offset & 0xf;
 	u32 val;
@@ -723,7 +728,7 @@  static void apic_mmio_write(struct kvm_io_device *this,
 static int apic_mmio_range(struct kvm_io_device *this, gpa_t addr,
 			   int len, int size)
 {
-	struct kvm_lapic *apic = (struct kvm_lapic *)this->private;
+	struct kvm_lapic *apic = to_lapic(this);
 	int ret = 0;
 
 
@@ -917,6 +922,12 @@  static struct kvm_timer_ops lapic_timer_ops = {
 	.is_periodic = lapic_is_periodic,
 };
 
+static struct kvm_io_device_ops apic_mmio_ops = {
+	.read     = apic_mmio_read,
+	.write    = apic_mmio_write,
+	.in_range = apic_mmio_range,
+};
+
 int kvm_create_lapic(struct kvm_vcpu *vcpu)
 {
 	struct kvm_lapic *apic;
@@ -951,10 +962,7 @@  int kvm_create_lapic(struct kvm_vcpu *vcpu)
 	vcpu->arch.apic_base = APIC_DEFAULT_PHYS_BASE;
 
 	kvm_lapic_reset(vcpu);
-	apic->dev.read = apic_mmio_read;
-	apic->dev.write = apic_mmio_write;
-	apic->dev.in_range = apic_mmio_range;
-	apic->dev.private = apic;
+	kvm_iodevice_init(&apic->dev, &apic_mmio_ops);
 
 	return 0;
 nomem_free_apic:
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 6d44dd5..b54159e 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2227,7 +2227,7 @@  static struct kvm_io_device *vcpu_find_pervcpu_dev(struct kvm_vcpu *vcpu,
 
 	if (vcpu->arch.apic) {
 		dev = &vcpu->arch.apic->dev;
-		if (dev->in_range(dev, addr, len, is_write))
+		if (dev->ops->in_range(dev, addr, len, is_write))
 			return dev;
 	}
 	return NULL;
diff --git a/virt/kvm/coalesced_mmio.c b/virt/kvm/coalesced_mmio.c
index 03ea280..f61a1d4 100644
--- a/virt/kvm/coalesced_mmio.c
+++ b/virt/kvm/coalesced_mmio.c
@@ -14,11 +14,15 @@ 
 
 #include "coalesced_mmio.h"
 
+static inline struct kvm_coalesced_mmio_dev *to_mmio(struct kvm_io_device *dev)
+{
+	return container_of(dev, struct kvm_coalesced_mmio_dev, dev);
+}
+
 static int coalesced_mmio_in_range(struct kvm_io_device *this,
 				   gpa_t addr, int len, int is_write)
 {
-	struct kvm_coalesced_mmio_dev *dev =
-				(struct kvm_coalesced_mmio_dev*)this->private;
+	struct kvm_coalesced_mmio_dev *dev = to_mmio(this);
 	struct kvm_coalesced_mmio_zone *zone;
 	int next;
 	int i;
@@ -63,8 +67,7 @@  static int coalesced_mmio_in_range(struct kvm_io_device *this,
 static void coalesced_mmio_write(struct kvm_io_device *this,
 				 gpa_t addr, int len, const void *val)
 {
-	struct kvm_coalesced_mmio_dev *dev =
-				(struct kvm_coalesced_mmio_dev*)this->private;
+	struct kvm_coalesced_mmio_dev *dev = to_mmio(this);
 	struct kvm_coalesced_mmio_ring *ring = dev->kvm->coalesced_mmio_ring;
 
 	/* kvm->lock must be taken by caller before call to in_range()*/
@@ -80,12 +83,17 @@  static void coalesced_mmio_write(struct kvm_io_device *this,
 
 static void coalesced_mmio_destructor(struct kvm_io_device *this)
 {
-	struct kvm_coalesced_mmio_dev *dev =
-		(struct kvm_coalesced_mmio_dev *)this->private;
+	struct kvm_coalesced_mmio_dev *dev = to_mmio(this);
 
 	kfree(dev);
 }
 
+static struct kvm_io_device_ops coalesced_mmio_ops = {
+	.write = coalesced_mmio_write,
+	.in_range = coalesced_mmio_in_range,
+	.destructor = coalesced_mmio_destructor,
+};
+
 int kvm_coalesced_mmio_init(struct kvm *kvm)
 {
 	struct kvm_coalesced_mmio_dev *dev;
@@ -93,10 +101,7 @@  int kvm_coalesced_mmio_init(struct kvm *kvm)
 	dev = kzalloc(sizeof(struct kvm_coalesced_mmio_dev), GFP_KERNEL);
 	if (!dev)
 		return -ENOMEM;
-	dev->dev.write  = coalesced_mmio_write;
-	dev->dev.in_range  = coalesced_mmio_in_range;
-	dev->dev.destructor  = coalesced_mmio_destructor;
-	dev->dev.private  = dev;
+	kvm_iodevice_init(&dev->dev, &coalesced_mmio_ops);
 	dev->kvm = kvm;
 	kvm->coalesced_mmio_dev = dev;
 	kvm_io_bus_register_dev(&kvm->mmio_bus, &dev->dev);
diff --git a/virt/kvm/ioapic.c b/virt/kvm/ioapic.c
index 1eddae9..0c17270 100644
--- a/virt/kvm/ioapic.c
+++ b/virt/kvm/ioapic.c
@@ -220,10 +220,15 @@  void kvm_ioapic_update_eoi(struct kvm *kvm, int vector, int trigger_mode)
 			__kvm_ioapic_update_eoi(ioapic, i, trigger_mode);
 }
 
+static inline struct kvm_ioapic *to_ioapic(struct kvm_io_device *dev)
+{
+	return container_of(dev, struct kvm_ioapic, dev);
+}
+
 static int ioapic_in_range(struct kvm_io_device *this, gpa_t addr,
 			   int len, int is_write)
 {
-	struct kvm_ioapic *ioapic = (struct kvm_ioapic *)this->private;
+	struct kvm_ioapic *ioapic = to_ioapic(this);
 
 	return ((addr >= ioapic->base_address &&
 		 (addr < ioapic->base_address + IOAPIC_MEM_LENGTH)));
@@ -232,7 +237,7 @@  static int ioapic_in_range(struct kvm_io_device *this, gpa_t addr,
 static void ioapic_mmio_read(struct kvm_io_device *this, gpa_t addr, int len,
 			     void *val)
 {
-	struct kvm_ioapic *ioapic = (struct kvm_ioapic *)this->private;
+	struct kvm_ioapic *ioapic = to_ioapic(this);
 	u32 result;
 
 	ioapic_debug("addr %lx\n", (unsigned long)addr);
@@ -269,7 +274,7 @@  static void ioapic_mmio_read(struct kvm_io_device *this, gpa_t addr, int len,
 static void ioapic_mmio_write(struct kvm_io_device *this, gpa_t addr, int len,
 			      const void *val)
 {
-	struct kvm_ioapic *ioapic = (struct kvm_ioapic *)this->private;
+	struct kvm_ioapic *ioapic = to_ioapic(this);
 	u32 data;
 
 	ioapic_debug("ioapic_mmio_write addr=%p len=%d val=%p\n",
@@ -314,6 +319,12 @@  void kvm_ioapic_reset(struct kvm_ioapic *ioapic)
 	ioapic->id = 0;
 }
 
+static struct kvm_io_device_ops ioapic_mmio_ops = {
+	.read = ioapic_mmio_read,
+	.write = ioapic_mmio_write,
+	.in_range = ioapic_in_range,
+};
+
 int kvm_ioapic_init(struct kvm *kvm)
 {
 	struct kvm_ioapic *ioapic;
@@ -323,10 +334,7 @@  int kvm_ioapic_init(struct kvm *kvm)
 		return -ENOMEM;
 	kvm->arch.vioapic = ioapic;
 	kvm_ioapic_reset(ioapic);
-	ioapic->dev.read = ioapic_mmio_read;
-	ioapic->dev.write = ioapic_mmio_write;
-	ioapic->dev.in_range = ioapic_in_range;
-	ioapic->dev.private = ioapic;
+	kvm_iodevice_init(&ioapic->dev, &ioapic_mmio_ops);
 	ioapic->kvm = kvm;
 	kvm_io_bus_register_dev(&kvm->mmio_bus, &ioapic->dev);
 	return 0;
diff --git a/virt/kvm/iodev.h b/virt/kvm/iodev.h
index 55e8846..0e1d60a 100644
--- a/virt/kvm/iodev.h
+++ b/virt/kvm/iodev.h
@@ -18,7 +18,9 @@ 
 
 #include <linux/kvm_types.h>
 
-struct kvm_io_device {
+struct kvm_io_device;
+
+struct kvm_io_device_ops {
 	void (*read)(struct kvm_io_device *this,
 		     gpa_t addr,
 		     int len,
@@ -30,16 +32,25 @@  struct kvm_io_device {
 	int (*in_range)(struct kvm_io_device *this, gpa_t addr, int len,
 			int is_write);
 	void (*destructor)(struct kvm_io_device *this);
+};
+
 
-	void             *private;
+struct kvm_io_device {
+	struct kvm_io_device_ops *ops;
 };
 
+static inline void kvm_iodevice_init(struct kvm_io_device *dev,
+				     struct kvm_io_device_ops *ops)
+{
+	dev->ops = ops;
+}
+
 static inline void kvm_iodevice_read(struct kvm_io_device *dev,
 				     gpa_t addr,
 				     int len,
 				     void *val)
 {
-	dev->read(dev, addr, len, val);
+	dev->ops->read(dev, addr, len, val);
 }
 
 static inline void kvm_iodevice_write(struct kvm_io_device *dev,
@@ -47,19 +58,19 @@  static inline void kvm_iodevice_write(struct kvm_io_device *dev,
 				      int len,
 				      const void *val)
 {
-	dev->write(dev, addr, len, val);
+	dev->ops->write(dev, addr, len, val);
 }
 
 static inline int kvm_iodevice_inrange(struct kvm_io_device *dev,
 				       gpa_t addr, int len, int is_write)
 {
-	return dev->in_range(dev, addr, len, is_write);
+	return dev->ops->in_range(dev, addr, len, is_write);
 }
 
 static inline void kvm_iodevice_destructor(struct kvm_io_device *dev)
 {
-	if (dev->destructor)
-		dev->destructor(dev);
+	if (dev->ops->destructor)
+		dev->ops->destructor(dev);
 }
 
 #endif /* __KVM_IODEV_H__ */
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index de042cb..ca2034a 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2456,7 +2456,7 @@  struct kvm_io_device *kvm_io_bus_find_dev(struct kvm_io_bus *bus,
 	for (i = 0; i < bus->dev_count; i++) {
 		struct kvm_io_device *pos = bus->devs[i];
 
-		if (pos->in_range(pos, addr, len, is_write))
+		if (kvm_iodevice_inrange(pos, addr, len, is_write))
 			return pos;
 	}