KVM: Clarify KVM_ASSIGN_PCI_DEVICE documentation

Neither host_irq nor the guest_msi struct are used anymore today.
Tag the former, drop the latter to avoid confusion.
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

Documentation/virtual/kvm/api.txt

@@ -1143,15 +1143,10 @@ Assigns an IRQ to a passed-through device.
 
 struct kvm_assigned_irq {
 	__u32 assigned_dev_id;
-	__u32 host_irq;
+	__u32 host_irq; /* ignored (legacy field) */
 	__u32 guest_irq;
 	__u32 flags;
 	union {
-		struct {
-			__u32 addr_lo;
-			__u32 addr_hi;
-			__u32 data;
-		} guest_msi;
 		__u32 reserved[12];
 	};
 };

include/linux/kvm.h

@@ -773,20 +773,14 @@ struct kvm_assigned_pci_dev {
 
 struct kvm_assigned_irq {
 	__u32 assigned_dev_id;
-	__u32 host_irq;
+	__u32 host_irq; /* ignored (legacy field) */
 	__u32 guest_irq;
 	__u32 flags;
 	union {
-		struct {
-			__u32 addr_lo;
-			__u32 addr_hi;
-			__u32 data;
-		} guest_msi;
 		__u32 reserved[12];
 	};
 };
 
-
 struct kvm_assigned_msix_nr {
 	__u32 assigned_dev_id;
 	__u16 entry_nr;