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-rw-r--r--Documentation/virtual/kvm/api.txt16
1 files changed, 11 insertions, 5 deletions
diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 158805532083..88ecbc7645db 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -13,7 +13,7 @@ of a virtual machine. The ioctls belong to three classes:
- VM ioctls: These query and set attributes that affect an entire virtual
machine, for example memory layout. In addition a VM ioctl is used to
- create virtual cpus (vcpus).
+ create virtual cpus (vcpus) and devices.
VM ioctls must be issued from the same process (address space) that was
used to create the VM.
@@ -26,6 +26,11 @@ of a virtual machine. The ioctls belong to three classes:
the documentation. Otherwise, the first ioctl after switching threads
could see a performance impact.
+ - device ioctls: These query and set attributes that control the operation
+ of a single device.
+
+ device ioctls must be issued from the same process (address space) that
+ was used to create the VM.
2. File descriptors
-------------------
@@ -34,10 +39,11 @@ The kvm API is centered around file descriptors. An initial
open("/dev/kvm") obtains a handle to the kvm subsystem; this handle
can be used to issue system ioctls. A KVM_CREATE_VM ioctl on this
handle will create a VM file descriptor which can be used to issue VM
-ioctls. A KVM_CREATE_VCPU ioctl on a VM fd will create a virtual cpu
-and return a file descriptor pointing to it. Finally, ioctls on a vcpu
-fd can be used to control the vcpu, including the important task of
-actually running guest code.
+ioctls. A KVM_CREATE_VCPU or KVM_CREATE_DEVICE ioctl on a VM fd will
+create a virtual cpu or device and return a file descriptor pointing to
+the new resource. Finally, ioctls on a vcpu or device fd can be used
+to control the vcpu or device. For vcpus, this includes the important
+task of actually running guest code.
In general file descriptors can be migrated among processes by means
of fork() and the SCM_RIGHTS facility of unix domain socket. These