kvm: drop unsupported capabilities, fix documentation

No kernel ever reported KVM_CAP_DEVICE_MSIX, KVM_CAP_DEVICE_MSI,
KVM_CAP_DEVICE_ASSIGNMENT, KVM_CAP_DEVICE_DEASSIGNMENT.

This makes the documentation wrong, and no application ever
written to use these capabilities has a chance to work correctly.
The only way to detect support is to try, and test errno for ENOTTY.
That's unfortunate, but we can't fix the past.

Document the actual semantics, and drop the definitions from
the exported header to make it easier for application
developers to note and fix the bug.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 33 insertions, 7 deletions

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 7610eaa..7a943c2 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -68,9 +68,12 @@ description:
 
   Capability: which KVM extension provides this ioctl.  Can be 'basic',
       which means that is will be provided by any kernel that supports
-      API version 12 (see section 4.1), or a KVM_CAP_xyz constant, which
+      API version 12 (see section 4.1), a KVM_CAP_xyz constant, which
       means availability needs to be checked with KVM_CHECK_EXTENSION
-      (see section 4.4).
+      (see section 4.4), or 'none' which means that while not all kernels
+      support this ioctl, there's no capability bit to check its
+      availability: for kernels that don't support the ioctl,
+      the ioctl returns -ENOTTY.
 
   Architectures: which instruction set architectures provide this ioctl.
       x86 includes both i386 and x86_64.
@@ -1257,7 +1260,7 @@ The flags bitmap is defined as:
 
 4.48 KVM_ASSIGN_PCI_DEVICE
 
-Capability: KVM_CAP_DEVICE_ASSIGNMENT
+Capability: none
 Architectures: x86 ia64
 Type: vm ioctl
 Parameters: struct kvm_assigned_pci_dev (in)
@@ -1298,10 +1301,16 @@ Only PCI header type 0 devices with PCI BAR resources are supported by
 device assignment.  The user requesting this ioctl must have read/write
 access to the PCI sysfs resource files associated with the device.
 
+Errors:
+  ENOTTY: kernel does not support this ioctl
+
+  Other error conditions may be defined by individual device types or
+  have their standard meanings.
+
 
 4.49 KVM_DEASSIGN_PCI_DEVICE
 
-Capability: KVM_CAP_DEVICE_DEASSIGNMENT
+Capability: none
 Architectures: x86 ia64
 Type: vm ioctl
 Parameters: struct kvm_assigned_pci_dev (in)
@@ -1309,9 +1318,14 @@ Returns: 0 on success, -1 on error
 
 Ends PCI device assignment, releasing all associated resources.
 
-See KVM_CAP_DEVICE_ASSIGNMENT for the data structure. Only assigned_dev_id is
+See KVM_ASSIGN_PCI_DEVICE for the data structure. Only assigned_dev_id is
 used in kvm_assigned_pci_dev to identify the device.
 
+Errors:
+  ENOTTY: kernel does not support this ioctl
+
+  Other error conditions may be defined by individual device types or
+  have their standard meanings.
 
 4.50 KVM_ASSIGN_DEV_IRQ
 
@@ -1346,6 +1360,12 @@ The following flags are defined:
 It is not valid to specify multiple types per host or guest IRQ. However, the
 IRQ type of host and guest can differ or can even be null.
 
+Errors:
+  ENOTTY: kernel does not support this ioctl
+
+  Other error conditions may be defined by individual device types or
+  have their standard meanings.
+
 
 4.51 KVM_DEASSIGN_DEV_IRQ
 
@@ -1423,7 +1443,7 @@ struct kvm_irq_routing_s390_adapter {
 
 4.53 KVM_ASSIGN_SET_MSIX_NR
 
-Capability: KVM_CAP_DEVICE_MSIX
+Capability: none
 Architectures: x86 ia64
 Type: vm ioctl
 Parameters: struct kvm_assigned_msix_nr (in)
@@ -1445,7 +1465,7 @@ struct kvm_assigned_msix_nr {
 
 4.54 KVM_ASSIGN_SET_MSIX_ENTRY
 
-Capability: KVM_CAP_DEVICE_MSIX
+Capability: none
 Architectures: x86 ia64
 Type: vm ioctl
 Parameters: struct kvm_assigned_msix_entry (in)
@@ -1461,6 +1481,12 @@ struct kvm_assigned_msix_entry {
 	__u16 padding[3];
 };
 
+Errors:
+  ENOTTY: kernel does not support this ioctl
+
+  Other error conditions may be defined by individual device types or
+  have their standard meanings.
+
 
 4.55 KVM_SET_TSC_KHZ