Re: [RFC PATCH v3 1/6] kvm: add device control API
On Thu, Apr 04, 2013 at 06:47:45PM -0500, Scott Wood wrote:
On 04/04/2013 05:41:35 AM, Gleb Natapov wrote:
On Tue, Apr 02, 2013 at 08:57:48PM -0500, Scott Wood wrote:
+struct kvm_device_attr {
+ __u32 flags; /* no flags currently defined */
+ __u32 group; /* device-defined */
+ __u64 attr; /* group-defined */
+ __u64 addr; /* userspace address of attr data */
+};
+
Since now each device has its own fd is it an advantage to enforce
common interface between different devices?
I think so, even if only to avoid repeating the various pains
surrounding adding ioctls. Not necessarily enforce, just enable.
If a device has some sort of command that does not fit neatly into
the set or get model, it could still add a new ioctl.
Make sense.
If we do so though why not handle file creation, ioctl and file
descriptor lifetime in the
common code. Common code will have struct kvm_device with struct
kvm_device_arch and struct kvm_device_ops members. Instead of
kvm_mpic_ioctl there will be kvm_device_ioctl which will despatch
ioctls
to a device using kvm_device-ops-(set|get|has)_attr pointers.
So make it more like the pre-fd version, except for the actual fd
usage? It would make destruction a bit simpler (assuming there's no
need for vcpu destruction code to access a device). Hopefully
nobody asks me to change it back again, though. :-)
--
Gleb.
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Re: [RFC PATCH v3 1/6] kvm: add device control API
On Fri, Apr 05, 2013 at 12:02:06PM +1100, Paul Mackerras wrote: On Thu, Apr 04, 2013 at 01:41:35PM +0300, Gleb Natapov wrote: Since now each device has its own fd is it an advantage to enforce common interface between different devices? If we do so though why not handle file creation, ioctl and file descriptor lifetime in the common code. Common code will have struct kvm_device with struct kvm_device_arch and struct kvm_device_ops members. Instead of kvm_mpic_ioctl there will be kvm_device_ioctl which will despatch ioctls to a device using kvm_device-ops-(set|get|has)_attr pointers. I thought about making the same request, but when I looked at it, the amount of code that could be made common in this way is pretty tiny, and doing that involves a bit of extra complexity, so I thought that on the whole it wouldn't be worthwhile. The value of doing so is not only in making some code common, but also moving fd lifetime management into the common code where it can be debugged once and for all potential users. I also expect the amount of shared code to grow when interface will be used by more architectures. -- Gleb. -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [RFC PATCH v3 1/6] kvm: add device control API
On 04/08/2013 12:33:13 AM, Paul Mackerras wrote:
On Tue, Apr 02, 2013 at 08:57:48PM -0500, Scott Wood wrote:
[snip]
+static int kvm_ioctl_create_device(struct kvm *kvm,
+ struct kvm_create_device *cd)
+{
+ bool test = cd-flags KVM_CREATE_DEVICE_TEST;
+
+ switch (cd-type) {
+ default:
+ return -ENODEV;
+ }
+}
This gives a compile error saying error: unused variable `test',
which is fatal since this gets compiled under arch/powerpc/kvm, and we
treat all warnings as errors there.
This still gives a compile error at the end of your series if you try
to compile with CONFIG_KVM_MPIC=n.
Ah, right. Will mark as __maybe_unused.
-Scott
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Re: [RFC PATCH v3 1/6] kvm: add device control API
On Thu, Apr 04, 2013 at 06:47:45PM -0500, Scott Wood wrote:
On 04/04/2013 05:41:35 AM, Gleb Natapov wrote:
On Tue, Apr 02, 2013 at 08:57:48PM -0500, Scott Wood wrote:
+struct kvm_device_attr {
+ __u32 flags; /* no flags currently defined */
+ __u32 group; /* device-defined */
+ __u64 attr; /* group-defined */
+ __u64 addr; /* userspace address of attr data */
+};
+
Since now each device has its own fd is it an advantage to enforce
common interface between different devices?
I think so, even if only to avoid repeating the various pains
surrounding adding ioctls. Not necessarily enforce, just enable.
If a device has some sort of command that does not fit neatly into
the set or get model, it could still add a new ioctl.
Make sense.
If we do so though why not handle file creation, ioctl and file
descriptor lifetime in the
common code. Common code will have struct kvm_device with struct
kvm_device_arch and struct kvm_device_ops members. Instead of
kvm_mpic_ioctl there will be kvm_device_ioctl which will despatch
ioctls
to a device using kvm_device-ops-(set|get|has)_attr pointers.
So make it more like the pre-fd version, except for the actual fd
usage? It would make destruction a bit simpler (assuming there's no
need for vcpu destruction code to access a device). Hopefully
nobody asks me to change it back again, though. :-)
--
Gleb.
--
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Re: [RFC PATCH v3 1/6] kvm: add device control API
On Fri, Apr 05, 2013 at 12:02:06PM +1100, Paul Mackerras wrote: On Thu, Apr 04, 2013 at 01:41:35PM +0300, Gleb Natapov wrote: Since now each device has its own fd is it an advantage to enforce common interface between different devices? If we do so though why not handle file creation, ioctl and file descriptor lifetime in the common code. Common code will have struct kvm_device with struct kvm_device_arch and struct kvm_device_ops members. Instead of kvm_mpic_ioctl there will be kvm_device_ioctl which will despatch ioctls to a device using kvm_device-ops-(set|get|has)_attr pointers. I thought about making the same request, but when I looked at it, the amount of code that could be made common in this way is pretty tiny, and doing that involves a bit of extra complexity, so I thought that on the whole it wouldn't be worthwhile. The value of doing so is not only in making some code common, but also moving fd lifetime management into the common code where it can be debugged once and for all potential users. I also expect the amount of shared code to grow when interface will be used by more architectures. -- Gleb. -- To unsubscribe from this list: send the line unsubscribe kvm-ppc in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [RFC PATCH v3 1/6] kvm: add device control API
On 04/08/2013 12:33:13 AM, Paul Mackerras wrote:
On Tue, Apr 02, 2013 at 08:57:48PM -0500, Scott Wood wrote:
[snip]
+static int kvm_ioctl_create_device(struct kvm *kvm,
+ struct kvm_create_device *cd)
+{
+ bool test = cd-flags KVM_CREATE_DEVICE_TEST;
+
+ switch (cd-type) {
+ default:
+ return -ENODEV;
+ }
+}
This gives a compile error saying error: unused variable `test',
which is fatal since this gets compiled under arch/powerpc/kvm, and we
treat all warnings as errors there.
This still gives a compile error at the end of your series if you try
to compile with CONFIG_KVM_MPIC=n.
Ah, right. Will mark as __maybe_unused.
-Scott
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Re: [RFC PATCH v3 1/6] kvm: add device control API
On Tue, Apr 02, 2013 at 08:57:48PM -0500, Scott Wood wrote:
[snip]
+static int kvm_ioctl_create_device(struct kvm *kvm,
+struct kvm_create_device *cd)
+{
+ bool test = cd-flags KVM_CREATE_DEVICE_TEST;
+
+ switch (cd-type) {
+ default:
+ return -ENODEV;
+ }
+}
This gives a compile error saying error: unused variable `test',
which is fatal since this gets compiled under arch/powerpc/kvm, and we
treat all warnings as errors there.
This still gives a compile error at the end of your series if you try
to compile with CONFIG_KVM_MPIC=n.
Paul.
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Re: [RFC PATCH v3 1/6] kvm: add device control API
On Tue, Apr 02, 2013 at 08:57:48PM -0500, Scott Wood wrote:
[snip]
+static int kvm_ioctl_create_device(struct kvm *kvm,
+struct kvm_create_device *cd)
+{
+ bool test = cd-flags KVM_CREATE_DEVICE_TEST;
+
+ switch (cd-type) {
+ default:
+ return -ENODEV;
+ }
+}
This gives a compile error saying error: unused variable `test',
which is fatal since this gets compiled under arch/powerpc/kvm, and we
treat all warnings as errors there.
This still gives a compile error at the end of your series if you try
to compile with CONFIG_KVM_MPIC=n.
Paul.
--
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Re: [RFC PATCH v3 1/6] kvm: add device control API
On Tue, Apr 02, 2013 at 08:57:48PM -0500, Scott Wood wrote:
Currently, devices that are emulated inside KVM are configured in a
hardcoded manner based on an assumption that any given architecture
only has one way to do it. If there's any need to access device state,
it is done through inflexible one-purpose-only IOCTLs (e.g.
KVM_GET/SET_LAPIC). Defining new IOCTLs for every little thing is
cumbersome and depletes a limited numberspace.
This API provides a mechanism to instantiate a device of a certain
type, returning an ID that can be used to set/get attributes of the
device. Attributes may include configuration parameters (e.g.
register base address), device state, operational commands, etc. It
is similar to the ONE_REG API, except that it acts on devices rather
than vcpus.
Both device types and individual attributes can be tested without having
to create the device or get/set the attribute, without the need for
separately managing enumerated capabilities.
Signed-off-by: Scott Wood scottw...@freescale.com
---
v3: remove some changes that were merged into this patch by accident,
and fix the error documentation for KVM_CREATE_DEVICE.
NOTE: I had some difficulty figuring out what ioctl numbers I should
assign... it seems that at one point care was taken to keep vcpu and
vm ioctls separate, but some overlap exists now (despite not exhausing
the ioctl space). Some of that was my fault, but not all of it. :-)
I moved to a new ioctl range for device control -- please let me know
if there's something else you'd prefer I do.
---
Documentation/virtual/kvm/api.txt| 70
++
Documentation/virtual/kvm/devices/README |1 +
include/uapi/linux/kvm.h | 27
virt/kvm/kvm_main.c | 31 +
4 files changed, 129 insertions(+)
create mode 100644 Documentation/virtual/kvm/devices/README
diff --git a/Documentation/virtual/kvm/api.txt
b/Documentation/virtual/kvm/api.txt
index 976eb65..d52f3f9 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -2173,6 +2173,76 @@ header; first `n_valid' valid entries with contents
from the data
written, then `n_invalid' invalid entries, invalidating any previously
valid entries found.
+4.79 KVM_CREATE_DEVICE
+
+Capability: KVM_CAP_DEVICE_CTRL
+Type: vm ioctl
+Parameters: struct kvm_create_device (in/out)
+Returns: 0 on success, -1 on error
+Errors:
+ ENODEV: The device type is unknown or unsupported
+ EEXIST: Device already created, and this type of device may not
+ be instantiated multiple times
+
+ Other error conditions may be defined by individual device types or
+ have their standard meanings.
+
+Creates an emulated device in the kernel. The file descriptor returned
+in fd can be used with KVM_SET/GET/HAS_DEVICE_ATTR.
+
+If the KVM_CREATE_DEVICE_TEST flag is set, only test whether the
+device type is supported (not necessarily whether it can be created
+in the current vm).
+
+Individual devices should not define flags. Attributes should be used
+for specifying any behavior that is not implied by the device type
+number.
+
+struct kvm_create_device {
+ __u32 type; /* in: KVM_DEV_TYPE_xxx */
+ __u32 fd; /* out: device handle */
+ __u32 flags; /* in: KVM_CREATE_DEVICE_xxx */
+};
+
+4.80 KVM_SET_DEVICE_ATTR/KVM_GET_DEVICE_ATTR
+
+Capability: KVM_CAP_DEVICE_CTRL
+Type: device ioctl
+Parameters: struct kvm_device_attr
+Returns: 0 on success, -1 on error
+Errors:
+ ENXIO: The group or attribute is unknown/unsupported for this device
+ EPERM: The attribute cannot (currently) be accessed this way
+ (e.g. read-only attribute, or attribute that only makes
+ sense when the device is in a different state)
+
+ Other error conditions may be defined by individual device types.
+
+Gets/sets a specified piece of device configuration and/or state. The
+semantics are device-specific. See individual device documentation in
+the devices directory. As with ONE_REG, the size of the data
+transferred is defined by the particular attribute.
+
+struct kvm_device_attr {
+ __u32 flags; /* no flags currently defined */
+ __u32 group; /* device-defined */
+ __u64 attr; /* group-defined */
+ __u64 addr; /* userspace address of attr data */
+};
+
Since now each device has its own fd is it an advantage to enforce
common interface between different devices? If we do so though why
not handle file creation, ioctl and file descriptor lifetime in the
common code. Common code will have struct kvm_device with struct
kvm_device_arch and struct kvm_device_ops members. Instead of
kvm_mpic_ioctl there will be kvm_device_ioctl which will despatch ioctls
to a device using kvm_device-ops-(set|get|has)_attr pointers.
--
Gleb.
--
Re: [RFC PATCH v3 1/6] kvm: add device control API
On 04/04/2013 05:41:35 AM, Gleb Natapov wrote:
On Tue, Apr 02, 2013 at 08:57:48PM -0500, Scott Wood wrote:
+struct kvm_device_attr {
+ __u32 flags; /* no flags currently defined */
+ __u32 group; /* device-defined */
+ __u64 attr; /* group-defined */
+ __u64 addr; /* userspace address of attr data */
+};
+
Since now each device has its own fd is it an advantage to enforce
common interface between different devices?
I think so, even if only to avoid repeating the various pains
surrounding adding ioctls. Not necessarily enforce, just enable. If
a device has some sort of command that does not fit neatly into the
set or get model, it could still add a new ioctl.
If we do so though why not handle file creation, ioctl and file
descriptor lifetime in the
common code. Common code will have struct kvm_device with struct
kvm_device_arch and struct kvm_device_ops members. Instead of
kvm_mpic_ioctl there will be kvm_device_ioctl which will despatch
ioctls
to a device using kvm_device-ops-(set|get|has)_attr pointers.
So make it more like the pre-fd version, except for the actual fd
usage? It would make destruction a bit simpler (assuming there's no
need for vcpu destruction code to access a device). Hopefully nobody
asks me to change it back again, though. :-)
-Scott
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the body of a message to majord...@vger.kernel.org
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Re: [RFC PATCH v3 1/6] kvm: add device control API
On Thu, Apr 04, 2013 at 01:41:35PM +0300, Gleb Natapov wrote: Since now each device has its own fd is it an advantage to enforce common interface between different devices? If we do so though why not handle file creation, ioctl and file descriptor lifetime in the common code. Common code will have struct kvm_device with struct kvm_device_arch and struct kvm_device_ops members. Instead of kvm_mpic_ioctl there will be kvm_device_ioctl which will despatch ioctls to a device using kvm_device-ops-(set|get|has)_attr pointers. I thought about making the same request, but when I looked at it, the amount of code that could be made common in this way is pretty tiny, and doing that involves a bit of extra complexity, so I thought that on the whole it wouldn't be worthwhile. Paul. -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [RFC PATCH v3 1/6] kvm: add device control API
On Tue, Apr 02, 2013 at 08:57:48PM -0500, Scott Wood wrote:
Currently, devices that are emulated inside KVM are configured in a
hardcoded manner based on an assumption that any given architecture
only has one way to do it. If there's any need to access device state,
it is done through inflexible one-purpose-only IOCTLs (e.g.
KVM_GET/SET_LAPIC). Defining new IOCTLs for every little thing is
cumbersome and depletes a limited numberspace.
This API provides a mechanism to instantiate a device of a certain
type, returning an ID that can be used to set/get attributes of the
device. Attributes may include configuration parameters (e.g.
register base address), device state, operational commands, etc. It
is similar to the ONE_REG API, except that it acts on devices rather
than vcpus.
Both device types and individual attributes can be tested without having
to create the device or get/set the attribute, without the need for
separately managing enumerated capabilities.
Signed-off-by: Scott Wood scottw...@freescale.com
---
v3: remove some changes that were merged into this patch by accident,
and fix the error documentation for KVM_CREATE_DEVICE.
NOTE: I had some difficulty figuring out what ioctl numbers I should
assign... it seems that at one point care was taken to keep vcpu and
vm ioctls separate, but some overlap exists now (despite not exhausing
the ioctl space). Some of that was my fault, but not all of it. :-)
I moved to a new ioctl range for device control -- please let me know
if there's something else you'd prefer I do.
---
Documentation/virtual/kvm/api.txt| 70
++
Documentation/virtual/kvm/devices/README |1 +
include/uapi/linux/kvm.h | 27
virt/kvm/kvm_main.c | 31 +
4 files changed, 129 insertions(+)
create mode 100644 Documentation/virtual/kvm/devices/README
diff --git a/Documentation/virtual/kvm/api.txt
b/Documentation/virtual/kvm/api.txt
index 976eb65..d52f3f9 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -2173,6 +2173,76 @@ header; first `n_valid' valid entries with contents
from the data
written, then `n_invalid' invalid entries, invalidating any previously
valid entries found.
+4.79 KVM_CREATE_DEVICE
+
+Capability: KVM_CAP_DEVICE_CTRL
+Type: vm ioctl
+Parameters: struct kvm_create_device (in/out)
+Returns: 0 on success, -1 on error
+Errors:
+ ENODEV: The device type is unknown or unsupported
+ EEXIST: Device already created, and this type of device may not
+ be instantiated multiple times
+
+ Other error conditions may be defined by individual device types or
+ have their standard meanings.
+
+Creates an emulated device in the kernel. The file descriptor returned
+in fd can be used with KVM_SET/GET/HAS_DEVICE_ATTR.
+
+If the KVM_CREATE_DEVICE_TEST flag is set, only test whether the
+device type is supported (not necessarily whether it can be created
+in the current vm).
+
+Individual devices should not define flags. Attributes should be used
+for specifying any behavior that is not implied by the device type
+number.
+
+struct kvm_create_device {
+ __u32 type; /* in: KVM_DEV_TYPE_xxx */
+ __u32 fd; /* out: device handle */
+ __u32 flags; /* in: KVM_CREATE_DEVICE_xxx */
+};
+
+4.80 KVM_SET_DEVICE_ATTR/KVM_GET_DEVICE_ATTR
+
+Capability: KVM_CAP_DEVICE_CTRL
+Type: device ioctl
+Parameters: struct kvm_device_attr
+Returns: 0 on success, -1 on error
+Errors:
+ ENXIO: The group or attribute is unknown/unsupported for this device
+ EPERM: The attribute cannot (currently) be accessed this way
+ (e.g. read-only attribute, or attribute that only makes
+ sense when the device is in a different state)
+
+ Other error conditions may be defined by individual device types.
+
+Gets/sets a specified piece of device configuration and/or state. The
+semantics are device-specific. See individual device documentation in
+the devices directory. As with ONE_REG, the size of the data
+transferred is defined by the particular attribute.
+
+struct kvm_device_attr {
+ __u32 flags; /* no flags currently defined */
+ __u32 group; /* device-defined */
+ __u64 attr; /* group-defined */
+ __u64 addr; /* userspace address of attr data */
+};
+
Since now each device has its own fd is it an advantage to enforce
common interface between different devices? If we do so though why
not handle file creation, ioctl and file descriptor lifetime in the
common code. Common code will have struct kvm_device with struct
kvm_device_arch and struct kvm_device_ops members. Instead of
kvm_mpic_ioctl there will be kvm_device_ioctl which will despatch ioctls
to a device using kvm_device-ops-(set|get|has)_attr pointers.
--
Gleb.
--
Re: [RFC PATCH v3 1/6] kvm: add device control API
On 04/04/2013 05:41:35 AM, Gleb Natapov wrote:
On Tue, Apr 02, 2013 at 08:57:48PM -0500, Scott Wood wrote:
+struct kvm_device_attr {
+ __u32 flags; /* no flags currently defined */
+ __u32 group; /* device-defined */
+ __u64 attr; /* group-defined */
+ __u64 addr; /* userspace address of attr data */
+};
+
Since now each device has its own fd is it an advantage to enforce
common interface between different devices?
I think so, even if only to avoid repeating the various pains
surrounding adding ioctls. Not necessarily enforce, just enable. If
a device has some sort of command that does not fit neatly into the
set or get model, it could still add a new ioctl.
If we do so though why not handle file creation, ioctl and file
descriptor lifetime in the
common code. Common code will have struct kvm_device with struct
kvm_device_arch and struct kvm_device_ops members. Instead of
kvm_mpic_ioctl there will be kvm_device_ioctl which will despatch
ioctls
to a device using kvm_device-ops-(set|get|has)_attr pointers.
So make it more like the pre-fd version, except for the actual fd
usage? It would make destruction a bit simpler (assuming there's no
need for vcpu destruction code to access a device). Hopefully nobody
asks me to change it back again, though. :-)
-Scott
--
To unsubscribe from this list: send the line unsubscribe kvm-ppc in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [RFC PATCH v3 1/6] kvm: add device control API
On Thu, Apr 04, 2013 at 01:41:35PM +0300, Gleb Natapov wrote: Since now each device has its own fd is it an advantage to enforce common interface between different devices? If we do so though why not handle file creation, ioctl and file descriptor lifetime in the common code. Common code will have struct kvm_device with struct kvm_device_arch and struct kvm_device_ops members. Instead of kvm_mpic_ioctl there will be kvm_device_ioctl which will despatch ioctls to a device using kvm_device-ops-(set|get|has)_attr pointers. I thought about making the same request, but when I looked at it, the amount of code that could be made common in this way is pretty tiny, and doing that involves a bit of extra complexity, so I thought that on the whole it wouldn't be worthwhile. Paul. -- To unsubscribe from this list: send the line unsubscribe kvm-ppc in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [RFC PATCH v3 1/6] kvm: add device control API
On 03.04.2013, at 03:57, Scott Wood wrote:
Currently, devices that are emulated inside KVM are configured in a
hardcoded manner based on an assumption that any given architecture
only has one way to do it. If there's any need to access device state,
it is done through inflexible one-purpose-only IOCTLs (e.g.
KVM_GET/SET_LAPIC). Defining new IOCTLs for every little thing is
cumbersome and depletes a limited numberspace.
This API provides a mechanism to instantiate a device of a certain
type, returning an ID that can be used to set/get attributes of the
device. Attributes may include configuration parameters (e.g.
register base address), device state, operational commands, etc. It
is similar to the ONE_REG API, except that it acts on devices rather
than vcpus.
Both device types and individual attributes can be tested without having
to create the device or get/set the attribute, without the need for
separately managing enumerated capabilities.
Signed-off-by: Scott Wood scottw...@freescale.com
---
v3: remove some changes that were merged into this patch by accident,
and fix the error documentation for KVM_CREATE_DEVICE.
NOTE: I had some difficulty figuring out what ioctl numbers I should
assign... it seems that at one point care was taken to keep vcpu and
vm ioctls separate, but some overlap exists now (despite not exhausing
the ioctl space). Some of that was my fault, but not all of it. :-)
I moved to a new ioctl range for device control -- please let me know
if there's something else you'd prefer I do.
---
Documentation/virtual/kvm/api.txt| 70 ++
Documentation/virtual/kvm/devices/README |1 +
include/uapi/linux/kvm.h | 27
virt/kvm/kvm_main.c | 31 +
4 files changed, 129 insertions(+)
create mode 100644 Documentation/virtual/kvm/devices/README
diff --git a/Documentation/virtual/kvm/api.txt
b/Documentation/virtual/kvm/api.txt
index 976eb65..d52f3f9 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -2173,6 +2173,76 @@ header; first `n_valid' valid entries with contents
from the data
written, then `n_invalid' invalid entries, invalidating any previously
valid entries found.
+4.79 KVM_CREATE_DEVICE
+
+Capability: KVM_CAP_DEVICE_CTRL
+Type: vm ioctl
+Parameters: struct kvm_create_device (in/out)
+Returns: 0 on success, -1 on error
+Errors:
+ ENODEV: The device type is unknown or unsupported
+ EEXIST: Device already created, and this type of device may not
+ be instantiated multiple times
+
+ Other error conditions may be defined by individual device types or
+ have their standard meanings.
+
+Creates an emulated device in the kernel. The file descriptor returned
+in fd can be used with KVM_SET/GET/HAS_DEVICE_ATTR.
+
+If the KVM_CREATE_DEVICE_TEST flag is set, only test whether the
+device type is supported (not necessarily whether it can be created
+in the current vm).
+
+Individual devices should not define flags. Attributes should be used
+for specifying any behavior that is not implied by the device type
+number.
+
+struct kvm_create_device {
+ __u32 type; /* in: KVM_DEV_TYPE_xxx */
+ __u32 fd; /* out: device handle */
+ __u32 flags; /* in: KVM_CREATE_DEVICE_xxx */
+};
+
+4.80 KVM_SET_DEVICE_ATTR/KVM_GET_DEVICE_ATTR
+
+Capability: KVM_CAP_DEVICE_CTRL
+Type: device ioctl
+Parameters: struct kvm_device_attr
+Returns: 0 on success, -1 on error
+Errors:
+ ENXIO: The group or attribute is unknown/unsupported for this device
+ EPERM: The attribute cannot (currently) be accessed this way
+ (e.g. read-only attribute, or attribute that only makes
+ sense when the device is in a different state)
+
+ Other error conditions may be defined by individual device types.
+
+Gets/sets a specified piece of device configuration and/or state. The
+semantics are device-specific. See individual device documentation in
+the devices directory. As with ONE_REG, the size of the data
+transferred is defined by the particular attribute.
+
+struct kvm_device_attr {
+ __u32 flags; /* no flags currently defined */
+ __u32 group; /* device-defined */
+ __u64 attr; /* group-defined */
+ __u64 addr; /* userspace address of attr data */
+};
+
+4.81 KVM_HAS_DEVICE_ATTR
+
+Capability: KVM_CAP_DEVICE_CTRL
+Type: device ioctl
+Parameters: struct kvm_device_attr
+Returns: 0 on success, -1 on error
+Errors:
+ ENXIO: The group or attribute is unknown/unsupported for this device
+
+Tests whether a device supports a particular attribute. A successful
+return indicates the attribute is implemented. It does not necessarily
+indicate that the attribute can be read or written in the device's
+current state. addr is ignored.
4.77 KVM_ARM_VCPU_INIT
