ARM: add QMP command to query GIC version
cover ARM: add QMP command to query GIC version
For ARM platform, we still do not have any interface to query whether current QEMU/host support specific GIC version. This patchset is trying to add one QMP interface for that. By querying the GIC capability using the new interface, one should know exactly what GIC version(s) the platform will support. The capability bits will be decided by both QEMU and host kernel.
The current patchset only provides interface for review. Its handler is a fake one which returns empty always.
The command interface I am planning to add is something like this:
-> { "execute": "query-gic-capability" }
<- { "return": [ "gicv2", "gicv2-kvm", "gicv3-kvm" ] }
Currently, all the possible supported GIC versions are:
- gicv2: GIC version 2 without kernel IRQ chip - gicv2-kvm: GIC version 2 with kernel IRQ chip - gicv3: GIC version 3 without kernel IRQ chip (not supported) - gicv3-kvm: GIC version 3 with kernel IRQ chip
Since "gicv3" is still not supported (to use GICv3, kernel irqchip support is required for now, which corresponds to "gicv3-kvm"), currently the maximum superset of the result should be:
["gicv2", "gicv2-kvm", "gicv3-kvm"]
Please help review whether the interface suits our need, also please point out any error I have made.
One question: how should I make this command "ARM only"? I see that in qmp-commands.hx, I can use something like "#if defined TARGET_ARM" to block out ARM specified commands, however how should I do the similiar thing in qapi-schema.json?
Thanks!
Peter
Peter Xu (2):
arm: gic: add GICType
arm: gic: add "query-gic-capability" interface
qapi-schema.json | 28 ++++++++++++++++++++++++++++ qmp-commands.hx | 25 +++++++++++++++++++++++++ qmp.c | 5 +++++ scripts/qapi.py | 1 + 4 files changed, 59 insertions(+)
Signature · 1 line
2.4.3
RFC PATCH 1/2 arm: gic: add GICType
A new enum type is added to define ARM GIC types.
--- qapi-schema.json | 17 +++++++++++++++++ 1 file changed, 17 insertions(+)
qapi-schema.json +17 -0
@@ -4083,3 +4083,20 @@ ## { 'enum': 'ReplayMode', 'data': [ 'none', 'record', 'play' ] } + +## +# @GICType: +# +# An enumeration of GIC types +# +# @gicv2: GICv2 support without kernel irqchip +# +# @gicv3: GICv3 support without kernel irqchip +# +# @gicv2-kvm: GICv3 support with kernel irqchip +# +# @gicv3-kvm: GICv3 support with kernel irqchip +# +# Since: 2.6 +## +{ 'enum': 'GICType', 'data': [ 'gicv2', 'gicv3', 'gicv2-kvm', 'gicv3-kvm' ] }
Signature · 1 line
2.4.3
RFC PATCH 2/2 arm: gic: add "query-gic-capability" interface
In reply to Peter Xu--- qapi-schema.json | 11 +++++++++++ qmp-commands.hx | 25 +++++++++++++++++++++++++ qmp.c | 5 +++++ scripts/qapi.py | 1 + 4 files changed, 42 insertions(+)
qapi-schema.json +11 -0
@@ -4100,3 +4100,14 @@ # Since: 2.6 ## { 'enum': 'GICType', 'data': [ 'gicv2', 'gicv3', 'gicv2-kvm', 'gicv3-kvm' ] } + +## +# @query-gic-capability: +# +# Return a list of supported GIC types +# +# Returns: a list of GICType +# +# Since: 2.6 +## +{ 'command': 'query-gic-capability', 'returns': ['GICType'] }
qmp-commands.hx +25 -0
@@ -4818,3 +4818,28 @@ Example: {"type": 0, "out-pport": 0, "pport": 0, "vlan-id": 3840, "pop-vlan": 1, "id": 251658240} ]} + +EQMP + +#if defined TARGET_ARM + { + .name = "query-gic-capability", + .args_type = "", + .mhandler.cmd_new = qmp_marshal_query_gic_capability, + }, +#endif + +SQMP +query-gic-capability +--------------- + +Return a list of supported ARM GIC types. + +Arguments: None + +Example: + +-> { "execute": "query-gic-capability" } +<- { "return": [ "gicv2", "gicv2-kvm", "gicv3-kvm" ] } + +EQMP
qmp.c +5 -0
@@ -753,3 +753,8 @@ ACPIOSTInfoList *qmp_query_acpi_ospm_status(Error **errp)return head; } + +GICTypeList *qmp_query_gic_capability (Error **errp) +{ +return NULL ; +}
scripts/qapi.py +1 -0
@@ -46,6 +46,7 @@ returns_whitelist = [ 'query-tpm-models', 'query-tpm-types', 'ringbuf-read', + 'query-gic-capability', # From QGA: 'guest-file-open',
Signature · 1 line
2.4.3
Quoted 22 lines · Peter Xu
For ARM platform, we still do not have any interface to query whether current QEMU/host support specific GIC version. This patchset is trying to add one QMP interface for that. By querying the GIC capability using the new interface, one should know exactly what GIC version(s) the platform will support. The capability bits will be decided by both QEMU and host kernel.
The current patchset only provides interface for review. Its handler is a fake one which returns empty always.
The command interface I am planning to add is something like this:
-> { "execute": "query-gic-capability" }
<- { "return": [ "gicv2", "gicv2-kvm", "gicv3-kvm" ] }Currently, all the possible supported GIC versions are:
- gicv2: GIC version 2 without kernel IRQ chip - gicv2-kvm: GIC version 2 with kernel IRQ chip - gicv3: GIC version 3 without kernel IRQ chip (not supported) - gicv3-kvm: GIC version 3 with kernel IRQ chip
Quoted 8 lines
Since "gicv3" is still not supported (to use GICv3, kernel irqchip support is required for now, which corresponds to "gicv3-kvm"), currently the maximum superset of the result should be:
["gicv2", "gicv2-kvm", "gicv3-kvm"]
Please help review whether the interface suits our need, also please point out any error I have made.
I tested QEMU with these patches and they were able to work on a native ARM64 machine.
Quoted 5 lines
One question: how should I make this command "ARM only"? I see that in qmp-commands.hx, I can use something like "#if defined
TARGET_ARM" to block out ARM specified commands, however how should I do the similiar thing in qapi-schema.json?
This situation is similar to "rtc-reset-reinjection", right? I think You can disable this feature on other arch's by setting QERR_FEATURE_DISABLED in file like monitor.c.
Quoted 14 lines
Thanks!
PeterPeter Xu (2):
arm: gic: add GICType
arm: gic: add "query-gic-capability" interfaceqapi-schema.json | 28 ++++++++++++++++++++++++++++ qmp-commands.hx | 25 +++++++++++++++++++++++++ qmp.c | 5 +++++ scripts/qapi.py | 1 + 4 files changed, 59 insertions(+)
Quoted 6 lines · Wei Huang
Quoted 2 lines · Peter Xu
Please help review whether the interface suits our need, also please point out any error I have made.
I tested QEMU with these patches and they were able to work on a native ARM64 machine.
Thanks for the verification. :)
Quoted 10 lines
Quoted 6 lines
One question: how should I make this command "ARM only"? I see that in qmp-commands.hx, I can use something like "#if defined
TARGET_ARM" to block out ARM specified commands, however how should I do the similiar thing in qapi-schema.json?This situation is similar to "rtc-reset-reinjection", right? I think You can disable this feature on other arch's by setting
QERR_FEATURE_DISABLEDin file likemonitor.c.
Yes. Will include this when post the real patches.
Thanks!
Peter
Quoted 7 lines · Peter Xu
Quoted 6 lines · Wei Huang
Quoted 4 lines · Peter Xu
One question: how should I make this command "ARM only"? I see that in qmp-commands.hx, I can use something like "#if defined
TARGET_ARM" to block out ARM specified commands, however how should I do the similiar thing in qapi-schema.json?
Quoted 5 lines
Quoted 3 lines
This situation is similar to "rtc-reset-reinjection", right? I think You can disable this feature on other arch's by setting
QERR_FEATURE_DISABLEDin file likemonitor.c.Yes. Will include this when post the real patches.
Yes, I think returning an error for non-ARM targets suffices.
Fam
Quoted 22 lines · Peter Xu
For ARM platform, we still do not have any interface to query whether current QEMU/host support specific GIC version. This patchset is trying to add one QMP interface for that. By querying the GIC capability using the new interface, one should know exactly what GIC version(s) the platform will support. The capability bits will be decided by both QEMU and host kernel.
The current patchset only provides interface for review. Its handler is a fake one which returns empty always.
The command interface I am planning to add is something like this:
-> { "execute": "query-gic-capability" }
<- { "return": [ "gicv2", "gicv2-kvm", "gicv3-kvm" ] }Currently, all the possible supported GIC versions are:
- gicv2: GIC version 2 without kernel IRQ chip - gicv2-kvm: GIC version 2 with kernel IRQ chip - gicv3: GIC version 3 without kernel IRQ chip (not supported) - gicv3-kvm: GIC version 3 with kernel IRQ chip
Quoted 9 lines
Since "gicv3" is still not supported (to use GICv3, kernel irqchip support is required for now, which corresponds to "gicv3-kvm"), currently the maximum superset of the result should be:
["gicv2", "gicv2-kvm", "gicv3-kvm"]
Please help review whether the interface suits our need, also please point out any error I have made.
This looks nice. I have some questions, but I'm not an expert in this area, so excuse me if they are stupid.
So hardware itself supports some GIC version, let's say 3 for our case. Does that mean it can be triggered to do v2 as well? I mean is it possible that HW supports multiple versions? If yes, then I suspect there is (will be) HW that does *not* do it and that's where QEMU (or KVM) must emulate that version. If all I'm having in mind is true, then you are trying to reply with two orthogonal types of information. A) versions kernel/HW supports and B) qemu/kvm can emulate. That is fine if libvirt can choose all the versions specified (e.g. gicv2-kvm, gicv2), but if we can only select a version, then it might be worth just returning those two types of information separately, e.g.:
["v2": {"emulated": true, "kvm":true}, "v3": {"emulated": false, "kvm": true}]
But as I said, I don't know the pre-requisites for this and mainly I'm not dealing with arm support now in libvirt, I'm just curious about it.
Quoted 5 lines
One question: how should I make this command "ARM only"? I see that in qmp-commands.hx, I can use something like "#if defined
TARGET_ARM" to block out ARM specified commands, however how should I do the similiar thing in qapi-schema.json?
As mentioned in the other thread, making it available everywhere and just returning a proper error message (so we can parse the class and not the error message itself) is the best choice, IMHO.
Quoted 20 lines
Thanks!
PeterPeter Xu (2):
arm: gic: add GICType
arm: gic: add "query-gic-capability" interfaceqapi-schema.json | 28 ++++++++++++++++++++++++++++ qmp-commands.hx | 25 +++++++++++++++++++++++++ qmp.c | 5 +++++ scripts/qapi.py | 1 + 4 files changed, 59 insertions(+)--
2.4.3--
libvir-list mailing list
[email protected]
https://www.redhat.com/mailman/listinfo/libvir-list
Quoted 4 lines · Martin Kletzander
So hardware itself supports some GIC version, let's say 3 for our case. Does that mean it can be triggered to do v2 as well? I mean is it possible that HW supports multiple versions? If yes, then I suspect there is (will be) HW that does *not* do it
Hardware may be:
GICv2 only
GICv3 only
GICv3 with v2 backwards-compatibility support
Quoted 2 lines
and that's where QEMU (or
KVM) must emulate that version.
If the hardware doesn't support the version that we are trying to provide to the guest then we can't run KVM at all. (KVM with an emulated interrupt controller is not a supported setup, because you wouldn't get CPU timer interrupts in the guest.)
thanks
-- PMM
Quoted 11 lines · Peter Maydell
Quoted 4 lines · Martin Kletzander
So hardware itself supports some GIC version, let's say 3 for our case. Does that mean it can be triggered to do v2 as well? I mean is it possible that HW supports multiple versions? If yes, then I suspect there is (will be) HW that does *not* do it
Hardware may be:
GICv2 only
GICv3 only
GICv3 with v2 backwards-compatibility support
Quoted 7 lines
Quoted 2 lines
and that's where QEMU (or
KVM) must emulate that version.If the hardware doesn't support the version that we are trying to provide to the guest then we can't run KVM at all. (KVM with an emulated interrupt controller is not a supported setup, because you wouldn't get CPU timer interrupts in the guest.)
I know Pavel Fedin was trying to revive kernel_irqchip=off once, but I don't know if that effort was abandoned or not. I think it could be a nice-to-have, in order to help isolate bugs with KVM, but I agree running that way wouldn't be the norm.
Thanks,
drew
Hello!
Quoted 2 lines
I know Pavel Fedin was trying to revive kernel_irqchip=off once, but I don't know if that effort was abandoned or not.
It should work with the latest kernel, at least i posted patches and all of them were applied. If nothing got broken during later
rewrites.
The only missing part is generic timer support. There were problems with it, however, after rewrite, they can be clearly addressed,
without need for any hacks. The following patchset implements this on kernel side, but it has never been reviewed:
http://www.spinics.net/lists/kvm/msg124539.html. I also have qemu support in my experimental tree and it works great, i can run "virt" guest on a Samsung's proprietary board with FrankenGIC, but since there was no interest, i never polished it up and published.
Quoted 3 lines
I think it
could be a nice-to-have, in order to help isolate bugs with KVM, but I agree running that way wouldn't be the norm.
IMHO it depends on what you want to achieve. If you strive for performance, then yes, of course. But, if you want to emulate some
particular hardware on another hardware, then this can be the only way to do it if, for example, you have GICv3-only hardware. KVM without irqchip is still much better than TCG.
But yes, i never included it into Libvirt. Once i was thinking about something like <gic version=off>, but perhaps it's not good
idea because this option is not ARM-specific, it's architecture-agnostic and applicable to any KVM acceleration for IRQ controller. Whether it works or not for the given platform, it is IMHO different story.
Kind regards,
Pavel Fedin
Senior Engineer
Samsung Electronics Research center Russia
Quoted 22 lines · Martin Kletzander
Quoted 6 lines · Peter Xu
["gicv2", "gicv2-kvm", "gicv3-kvm"]
Please help review whether the interface suits our need, also please point out any error I have made.
This looks nice. I have some questions, but I'm not an expert in this area, so excuse me if they are stupid.
So hardware itself supports some GIC version, let's say 3 for our case. Does that mean it can be triggered to do v2 as well? I mean is it possible that HW supports multiple versions? If yes, then I suspect there is (will be) HW that does *not* do it and that's where QEMU (or KVM) must emulate that version. If all I'm having in mind is true, then you are trying to reply with two orthogonal types of information. A) versions kernel/HW supports and B) qemu/kvm can emulate. That is fine if libvirt can choose all the versions specified (e.g. gicv2-kvm, gicv2), but if we can only select a version, then it might be worth just returning those two types of information separately, e.g.:
Quoted 1 line
["v2": {"emulated": true, "kvm":true}, "v3": {"emulated": false, "kvm": true}]
Yes, I'd say that this is more clear especially when the matrix is very big. Luckily for GIC versions, there is only 2x2 (2x3 if there is v4) and it keeps a small one. So IMHO this is a flavor issue and both work for me. :)
Thanks.
Peter
Quoted 22 lines · Peter Xu
For ARM platform, we still do not have any interface to query whether current QEMU/host support specific GIC version. This patchset is trying to add one QMP interface for that. By querying the GIC capability using the new interface, one should know exactly what GIC version(s) the platform will support. The capability bits will be decided by both QEMU and host kernel.
The current patchset only provides interface for review. Its handler is a fake one which returns empty always.
The command interface I am planning to add is something like this:
-> { "execute": "query-gic-capability" }
<- { "return": [ "gicv2", "gicv2-kvm", "gicv3-kvm" ] }Currently, all the possible supported GIC versions are:
- gicv2: GIC version 2 without kernel IRQ chip - gicv2-kvm: GIC version 2 with kernel IRQ chip - gicv3: GIC version 3 without kernel IRQ chip (not supported) - gicv3-kvm: GIC version 3 with kernel IRQ chip
Quoted 8 lines
Since "gicv3" is still not supported (to use GICv3, kernel irqchip support is required for now, which corresponds to "gicv3-kvm"), currently the maximum superset of the result should be:
["gicv2", "gicv2-kvm", "gicv3-kvm"]
Please help review whether the interface suits our need, also please point out any error I have made.
Adding ad hoc queries as we go won't scale. Is there really no generic way to get this information, e.g. with qom-get?
Quoted 4 lines
One question: how should I make this command "ARM only"? I see that in qmp-commands.hx, I can use something like "#if defined
TARGET_ARM" to block out ARM specified commands, however how should I do the similiar thing in qapi-schema.json?
Have a look at the #if in qmp-commands.hx.
Quoted 28 lines · Markus Armbruster
Quoted 26 lines · Peter Xu
For ARM platform, we still do not have any interface to query whether current QEMU/host support specific GIC version. This patchset is trying to add one QMP interface for that. By querying the GIC capability using the new interface, one should know exactly what GIC version(s) the platform will support. The capability bits will be decided by both QEMU and host kernel.
The current patchset only provides interface for review. Its handler is a fake one which returns empty always.
The command interface I am planning to add is something like this:
-> { "execute": "query-gic-capability" }
<- { "return": [ "gicv2", "gicv2-kvm", "gicv3-kvm" ] }Currently, all the possible supported GIC versions are:
- gicv2: GIC version 2 without kernel IRQ chip - gicv2-kvm: GIC version 2 with kernel IRQ chip - gicv3: GIC version 3 without kernel IRQ chip (not supported) - gicv3-kvm: GIC version 3 with kernel IRQ chipSince "gicv3" is still not supported (to use GICv3, kernel irqchip support is required for now, which corresponds to "gicv3-kvm"), currently the maximum superset of the result should be:
Quoted 7 lines
Quoted 4 lines
["gicv2", "gicv2-kvm", "gicv3-kvm"]
Please help review whether the interface suits our need, also please point out any error I have made.
Adding ad hoc queries as we go won't scale. Is there really no generic way to get this information, e.g. with qom-get?
Haven't used "qom-get" before, but it seems to fetch one property for a specific object. If so, will it be strange to hide some capability bits into every GIC objects (though there is possibly one object)?
I agree that we should keep the interface as simple as possible. I see that there are already commands that works just like this one, which is to query some capabilities from QEMU, like:
- query-dump-guest-memory-capability
- query-migrate-capabilities
So... besides the original proposal, what about adding a generic QMP command to query all kinds of capabilities (and let GIC be the first item)? Or any other way to avoid adding a new command?
Thanks.
Peter
Quoted 7 lines
Quoted 5 lines
One question: how should I make this command "ARM only"? I see that in qmp-commands.hx, I can use something like "#if defined
TARGET_ARM" to block out ARM specified commands, however how should I do the similiar thing in qapi-schema.json?Have a look at the #if in qmp-commands.hx.
Quoted 34 lines · Peter Xu
Quoted 33 lines · Markus Armbruster
Quoted 30 lines · Peter Xu
For ARM platform, we still do not have any interface to query whether current QEMU/host support specific GIC version. This patchset is trying to add one QMP interface for that. By querying the GIC capability using the new interface, one should know exactly what GIC version(s) the platform will support. The capability bits will be decided by both QEMU and host kernel.
The current patchset only provides interface for review. Its handler is a fake one which returns empty always.
The command interface I am planning to add is something like this:
-> { "execute": "query-gic-capability" }
<- { "return": [ "gicv2", "gicv2-kvm", "gicv3-kvm" ] }Currently, all the possible supported GIC versions are:
- gicv2: GIC version 2 without kernel IRQ chip - gicv2-kvm: GIC version 2 with kernel IRQ chip - gicv3: GIC version 3 without kernel IRQ chip (not supported) - gicv3-kvm: GIC version 3 with kernel IRQ chipSince "gicv3" is still not supported (to use GICv3, kernel irqchip support is required for now, which corresponds to "gicv3-kvm"), currently the maximum superset of the result should be:
["gicv2", "gicv2-kvm", "gicv3-kvm"]
Please help review whether the interface suits our need, also please point out any error I have made.
Quoted 7 lines
Quoted 2 lines
Adding ad hoc queries as we go won't scale. Is there really no generic way to get this information, e.g. with qom-get?
Haven't used "qom-get" before, but it seems to fetch one property for a specific object. If so, will it be strange to hide some capability bits into every GIC objects (though there is possibly one object)?
Pardon my ignorance... what are these "GIC objects"?
What exactly is the "GIC type", and how would the result of query-gic-capability be used?
Quoted 6 lines
I agree that we should keep the interface as simple as possible. I see that there are already commands that works just like this one, which is to query some capabilities from QEMU, like:
- query-dump-guest-memory-capability
- query-migrate-capabilities
I'm not saying we must not add another ad hoc query. I'm trying to figure out whether existing generic infrastructure can serve, or be adapted to serve. Once we establish the answer is "no" or "badly", I'm willing to consider the ad hoc query.
Quoted 3 lines
So... besides the original proposal, what about adding a generic QMP command to query all kinds of capabilities (and let GIC be the first item)? Or any other way to avoid adding a new command?
[...]
Quoted 11 lines · Markus Armbruster
Quoted 9 lines · Peter Xu
Quoted 3 lines · Markus Armbruster
Peter Xu <[email protected]> writes:
Adding ad hoc queries as we go won't scale. Is there really no generic way to get this information, e.g. with qom-get?Haven't used "qom-get" before, but it seems to fetch one property for a specific object. If so, will it be strange to hide some capability bits into every GIC objects (though there is possibly one object)?
Quoted 4 lines
Pardon my ignorance... what are these "GIC objects"?
What exactly is the "GIC type", and how would the result of query-gic-capability be used?
The GIC type (for our purposes) is the revision of the interrupt controller supported by the host, which comes in two versions (v2 and v3). These are not compatible, unless your host has the v3-with-v2-compat flavour. If a host is v3-only, it is not possible for it to give the guest a v2 virtual interrupt controller; if v2, it can't give the guest a v3 virtual interrupt controller. (If you ask QEMU to do this via command line options we will report an error at startup.)
The underlying aim is to allow libvirt to say "this VM config won't work on this host", rather than ploughing blindly on and creating a VM config that always errors on startup.
The "GIC object" presumably is the GIC QOM device object. However we do the "does this host support this GIC version?" check in QEMU before we ever create the GIC device object, so trying to probe it for properties isn't going to work.
The only other QOM object potentially available to probe would be the machine (board) object. However as I understand it libvirt does all its probing with the "none" machine type, and it seems a bit odd to put a bunch of properties on the "none" machine type. It would be possible though I guess.
thanks
-- PMM
Quoted 17 lines · Peter Maydell
Quoted 11 lines · Markus Armbruster
Quoted 9 lines · Peter Xu
Quoted 3 lines · Markus Armbruster
Peter Xu <[email protected]> writes:
Adding ad hoc queries as we go won't scale. Is there really no generic way to get this information, e.g. with qom-get?Haven't used "qom-get" before, but it seems to fetch one property for a specific object. If so, will it be strange to hide some capability bits into every GIC objects (though there is possibly one object)?
Quoted 4 lines
Pardon my ignorance... what are these "GIC objects"?
What exactly is the "GIC type", and how would the result of query-gic-capability be used?
Quoted 8 lines
The GIC type (for our purposes) is the revision of the interrupt controller supported by the host, which comes in two versions (v2 and v3). These are not compatible, unless your host has the v3-with-v2-compat flavour. If a host is v3-only, it is not possible for it to give the guest a v2 virtual interrupt controller; if v2, it can't give the guest a v3 virtual interrupt controller. (If you ask QEMU to do this via command line options we will report an error at startup.)
How would the command line look like?
I'm asking because the answer will point us to the introspection problem to solve.
Quoted 3 lines
The underlying aim is to allow libvirt to say "this VM config won't work on this host", rather than ploughing blindly on and creating a VM config that always errors on startup.
Yes, finding out with a suitable introspection interface is easier and more robust than "try and guess what the error message might mean".
Quoted 4 lines
The "GIC object" presumably is the GIC QOM device object. However we do the "does this host support this GIC version?" check in QEMU before we ever create the GIC device object, so trying to probe it for properties isn't going to work.
QMP introspection would ideally cover introspecting device objects:
simply introspect device_add. But it doesn't cover it now, because QMP introspection is really a special case of QAPI schema introspection, and the QAPI schema cannot express device_add for two reasons:
1. The QAPI schema is fixed at compile time, but the device models aren't. Instead, whatever device models are linked into QEMU register themselves during startup. Collecting them at compile time is a solvable problem, but unlikely to be fun.
2. The QAPI schema is data, but general QOM properties are code. As always, code is much harder to work with than data. You can't extract properties from code at compile time, you have to run the code.
To introspect QOM properties, you have to instantiate an object, examine it, then destroy it. Aside: this requires instantiate + destroy to have no lasting side effects, and experience tells that device model code gets that wrong easily.
Paolo suggested that we special-case device introspection instead of somehow hook it into QMP introsprection. Even if we do that, developing it will take time.
It'll always be easier and more expedient to add another ad hoc query instead. But it leaves the generic problem unsolved while the ad hoc queries pile up.
Quoted 5 lines
The only other QOM object potentially available to probe would be the machine (board) object. However as I understand it libvirt does all its probing with the "none" machine type, and it seems a bit odd to put a bunch of properties on the "none" machine type. It would be possible though I guess.
Quoted 28 lines · Markus Armbruster
Quoted 17 lines · Peter Maydell
Quoted 11 lines · Markus Armbruster
Quoted 9 lines · Peter Xu
Quoted 3 lines · Markus Armbruster
Peter Xu <[email protected]> writes:
Adding ad hoc queries as we go won't scale. Is there really no generic way to get this information, e.g. with qom-get?Haven't used "qom-get" before, but it seems to fetch one property for a specific object. If so, will it be strange to hide some capability bits into every GIC objects (though there is possibly one object)?
Quoted 4 lines
Pardon my ignorance... what are these "GIC objects"?
What exactly is the "GIC type", and how would the result of query-gic-capability be used?
Quoted 8 lines
The GIC type (for our purposes) is the revision of the interrupt controller supported by the host, which comes in two versions (v2 and v3). These are not compatible, unless your host has the v3-with-v2-compat flavour. If a host is v3-only, it is not possible for it to give the guest a v2 virtual interrupt controller; if v2, it can't give the guest a v3 virtual interrupt controller. (If you ask QEMU to do this via command line options we will report an error at startup.)
Quoted 2 lines
How would the command line look like?
Here is what is available today
# select gicv2 (this work with and without KVM) qemu-system-aarch64 -M virt # v2 is the default qemu-system-aarch64 -M virt,gic-version=2 ...
# select gicv3 (only works with KVM) qemu-system-aarch64 -M virt,gic-version=3 ...
# select whatever the host has qemu-system-aarch64 -M virt,gic-version=host ...
Thanks,
drew
Quoted 4 lines · Andrew Jones
Quoted 2 lines · Markus Armbruster
How would the command line look like?
Quoted 8 lines
Here is what is available today
# select gicv2 (this work with and without KVM) qemu-system-aarch64 -M virt # v2 is the default qemu-system-aarch64 -M virt,gic-version=2 ...# select gicv3 (only works with KVM) qemu-system-aarch64 -M virt,gic-version=3 ...
This will work with TCG once we get the GICv3 emulation upstream.
Quoted 2 lines
# select whatever the host has qemu-system-aarch64 -M virt,gic-version=host ...
This only works with KVM (like -cpu host).
thanks
-- PMM
Quoted 14 lines · Peter Maydell
Quoted 4 lines · Andrew Jones
Quoted 2 lines · Markus Armbruster
How would the command line look like?
Quoted 8 lines
Here is what is available today
# select gicv2 (this work with and without KVM) qemu-system-aarch64 -M virt # v2 is the default qemu-system-aarch64 -M virt,gic-version=2 ...# select gicv3 (only works with KVM) qemu-system-aarch64 -M virt,gic-version=3 ...
Quoted 6 lines
This will work with TCG once we get the GICv3 emulation upstream.
Quoted 2 lines
# select whatever the host has qemu-system-aarch64 -M virt,gic-version=host ...This only works with KVM (like -cpu host).
Aha, it's a machine option. Therefore, the generic direct solution would be command line introspection. A couple of remarks.
We don't have comprehensive command line introspection. There's only query-command-line-options, but it's incomplete and insufficiently expressive. We usually sidestep command line introspection and introspect the corresponding QMP command, or we "look for a witness" in QMP, i.e. some introspectible indicator for the non-introspectible feature we need to know.
The is no QMP command corresponding to --machine. There's a long term vision to start QEMU with a blank slate, then configure everything via QMP. With that, QMP introspection would cover machine options. Of course, visions aren't going to help you now.
Even if there was a QMP command, the way we do --machine options would defeat QMP introspection: they're QOM properties, defined in code.
Defining things in code is the most flexible solution, but it makes reasoning about them *much* harder: the only general way to learn what code does is run it. This is fundamentally incompatible with introspection. In other words, QOM's design sacrifices introspectability for flexibility. The flexibility isn't actually needed most of the time, but it defeats introspection all of the time. For me, this was an design mistake. We made the same mistake before, with migration.
I figure we'll need to crack the QOM introspection problem to at least some useful degree. But it's going to be a lot of work.
A less flexible, introspectible, data-driven interface could be layered on top of the code-driven one. With as many users as possible converted to the data-driven interface, the flexibility then defeats introspection only where we actually use the flexibility.
Back to GIV. Recognized values of gic-version are fixed at compile
time: 2, 3, host. Once again, QOM does things in code rather than data:
the set of values is defined in the setter function virt_set_gic_version().
Some values are accepted only together with other configuration: 3 requires accel=kvm (for now), host requires -cpu host. Static introspection can't show such constraints.
Would the proposed query-gic-capability show them? How?
Quoted 63 lines · Markus Armbruster
Quoted 14 lines · Peter Maydell
Quoted 4 lines · Andrew Jones
Quoted 2 lines · Markus Armbruster
How would the command line look like?
Quoted 8 lines
Here is what is available today
# select gicv2 (this work with and without KVM) qemu-system-aarch64 -M virt # v2 is the default qemu-system-aarch64 -M virt,gic-version=2 ...# select gicv3 (only works with KVM) qemu-system-aarch64 -M virt,gic-version=3 ...Quoted 6 lines
This will work with TCG once we get the GICv3 emulation upstream.
Quoted 2 lines
# select whatever the host has qemu-system-aarch64 -M virt,gic-version=host ...This only works with KVM (like -cpu host).
Aha, it's a machine option. Therefore, the generic direct solution would be command line introspection. A couple of remarks.
We don't have comprehensive command line introspection. There's only query-command-line-options, but it's incomplete and insufficiently expressive. We usually sidestep command line introspection and introspect the corresponding QMP command, or we "look for a witness" in QMP, i.e. some introspectible indicator for the non-introspectible feature we need to know.
The is no QMP command corresponding to --machine. There's a long term vision to start QEMU with a blank slate, then configure everything via QMP. With that, QMP introspection would cover machine options. Of course, visions aren't going to help you now.
Even if there was a QMP command, the way we do --machine options would defeat QMP introspection: they're QOM properties, defined in code.
Defining things in code is the most flexible solution, but it makes reasoning about them *much* harder: the only general way to learn what code does is run it. This is fundamentally incompatible with introspection. In other words, QOM's design sacrifices introspectability for flexibility. The flexibility isn't actually needed most of the time, but it defeats introspection all of the time. For me, this was an design mistake. We made the same mistake before, with migration.
I figure we'll need to crack the QOM introspection problem to at least some useful degree. But it's going to be a lot of work.
A less flexible, introspectible, data-driven interface could be layered on top of the code-driven one. With as many users as possible converted to the data-driven interface, the flexibility then defeats introspection only where we actually use the flexibility.
Back to GIV. Recognized values of gic-version are fixed at compile
time: 2, 3, host. Once again, QOM does things in code rather than data:
the set of values is defined in the setter functionvirt_set_gic_version().
Quoted 5 lines
Some values are accepted only together with other configuration: 3 requires accel=kvm (for now), host requires -cpu host. Static introspection can't show such constraints.
Would the proposed query-gic-capability show them? How?
Also bear in mind that libvirt probes capabilities using '-m none' so you're not going to have any 'virt' machine type instantiated when probing is done.
Regards,
Daniel
Signature · 4 lines
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Quoted 10 lines · Daniel P. Berrange
Quoted 10 lines
Back to GIV. Recognized values of gic-version are fixed at compile
time: 2, 3, host. Once again, QOM does things in code rather than data:
the set of values is defined in the setter functionvirt_set_gic_version().
Some values are accepted only together with other configuration: 3 requires accel=kvm (for now), host requires -cpu host. Static introspection can't show such constraints.
Would the proposed query-gic-capability show them? How?
Quoted 4 lines
Also bear in mind that libvirt probes capabilities using '-m none' so you're not going to have any 'virt' machine type instantiated when probing is done.
The idea is to add this information to domain capabilities, which already have virtualization type, architecture and machine type as inputs.
Since GIC is only available for the virt machine type on ARM hosts, and the GIC versions might be limited by using TCG instead of KVM, it seems like it would fit nicely...
Cheers.
--
Andrea Bolognani
Software Engineer - Virtualization Team
Quoted 7 lines · Andrea Bolognani
The idea is to add this information to domain capabilities, which already have virtualization type, architecture and machine type as inputs.
Since GIC is only available for the virt machine type on ARM hosts, and the GIC versions might be limited by using TCG instead of KVM, it seems like it would fit nicely...
The GIC is available for more than just "virt". It's just that at the moment "virt" is the only machine type which lets you pick which GIC version you want, and so the only machine type with that machine property. (For instance vexpress-a15 is always GICv2, since the hardware we're modelling there is always GICv2.)
Other board models in future might support a choice of GIC versions. (The obvious possibility would be the Android 'ranchu' board if that is ever upstreamed.)
thanks
-- PMM
Quoted 8 lines · Peter Maydell
Quoted 7 lines · Andrea Bolognani
The idea is to add this information to domain capabilities, which already have virtualization type, architecture and machine type as inputs.
Since GIC is only available for the virt machine type on ARM hosts, and the GIC versions might be limited by using TCG instead of KVM, it seems like it would fit nicely...
Quoted 11 lines
The GIC is available for more than just "virt". It's just that at the moment "virt" is the only machine type which lets you pick which GIC version you want, and so the only machine type with that machine property. (For instance vexpress-a15 is always GICv2, since the hardware we're modelling there is always GICv2.)
Other board models in future might support a choice of GIC versions. (The obvious possibility would be the Android 'ranchu' board if that is ever upstreamed.)
Yeah, I didn't express myself properly: I meant to say that the ability to pick a GIC version is limited to the virt machine type so far. Sorry about that :)
Cheers.
--
Andrea Bolognani
Software Engineer - Virtualization Team
Quoted 11 lines · Andrea Bolognani
Quoted 10 lines · Daniel P. Berrange
Quoted 10 lines
Back to GIV. Recognized values of gic-version are fixed at compile
time: 2, 3, host. Once again, QOM does things in code rather than data:
the set of values is defined in the setter functionvirt_set_gic_version().
Some values are accepted only together with other configuration: 3 requires accel=kvm (for now), host requires -cpu host. Static introspection can't show such constraints.
Would the proposed query-gic-capability show them? How?
Quoted 8 lines
Quoted 4 lines
Also bear in mind that libvirt probes capabilities using '-m none' so you're not going to have any 'virt' machine type instantiated when probing is done.The idea is to add this information to domain capabilities, which already have virtualization type, architecture and machine type as inputs.
Regardless of the way it is exposed in libvirt API, when libvirt probes for capabilities it will *always* use '-m none'.
Regards,
Daniel
Signature · 4 lines
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Quoted 16 lines · Daniel P. Berrange
Quoted 15 lines · Andrea Bolognani
Quoted 14 lines · Daniel P. Berrange
Quoted 10 lines
Back to GIV. Recognized values of gic-version are fixed at compile
time: 2, 3, host. Once again, QOM does things in code rather than data:
the set of values is defined in the setter functionvirt_set_gic_version().
Some values are accepted only together with other configuration: 3 requires accel=kvm (for now), host requires -cpu host. Static introspection can't show such constraints.
Would the proposed query-gic-capability show them? How?
Also bear in mind that libvirt probes capabilities using '-m none' so you're not going to have any 'virt' machine type instantiated when probing is done.
Quoted 7 lines
Quoted 4 lines
The idea is to add this information to domain capabilities, which already have virtualization type, architecture and machine type as inputs.
Regardless of the way it is exposed in libvirt API, when libvirt probes for capabilities it will *always* use '-m none'.
Domain capabilities are currently derived almost entirely from data taken from virQEMUCaps, but is there anything stopping us from calling QEMU with the appropriate machine type from qemuConnectGetDomainCapabilities() to query for machine type dependent domain capabilities such as supported values for the gic-version property?
Cheers.
--
Andrea Bolognani
Software Engineer - Virtualization Team
Quoted 25 lines · Andrea Bolognani
Quoted 16 lines · Daniel P. Berrange
Quoted 15 lines · Andrea Bolognani
Quoted 14 lines · Daniel P. Berrange
Quoted 10 lines
Back to GIV. Recognized values of gic-version are fixed at compile
time: 2, 3, host. Once again, QOM does things in code rather than data:
the set of values is defined in the setter functionvirt_set_gic_version().
Some values are accepted only together with other configuration: 3 requires accel=kvm (for now), host requires -cpu host. Static introspection can't show such constraints.
Would the proposed query-gic-capability show them? How?
Also bear in mind that libvirt probes capabilities using '-m none' so you're not going to have any 'virt' machine type instantiated when probing is done.Quoted 7 lines
Quoted 4 lines
The idea is to add this information to domain capabilities, which already have virtualization type, architecture and machine type as inputs.
Regardless of the way it is exposed in libvirt API, when libvirt probes for capabilities it will *always* use '-m none'.
Quoted 6 lines
Domain capabilities are currently derived almost entirely from data taken from virQEMUCaps, but is there anything stopping us from calling QEMU with the appropriate machine type from
qemuConnectGetDomainCapabilities()to query for machine type dependent domain capabilities such as supported values for the gic-version property?
The cost of invoking QEMU for each architecture and probing capabilities is already higher than we would like. If we multiply that cost by the number of machine types, it makes the problem orders of magnitude worse, so we cannot go that route.
This is a key reason why we would like to be able to probe properties against QEMU classses without instantiating them. ie so we can launch QEMU once with "-m none" and still be able to query specific properties we want from the 'virt' machine type. A small step towards this was made with a patch we landed to let us register properties against classes in QOM, instead of against objects. We've not done work to convert code internally to use this facility yet though.
Regards,
Daniel
Signature · 4 lines
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Quoted 9 lines · Daniel P. Berrange
Quoted 9 lines
Quoted 2 lines
Regardless of the way it is exposed in libvirt API, when libvirt probes for capabilities it will *always* use '-m none'.
Domain capabilities are currently derived almost entirely from data taken from virQEMUCaps, but is there anything stopping us from calling QEMU with the appropriate machine type fromqemuConnectGetDomainCapabilities()to query for machine type dependent domain capabilities such as supported values for the gic-version property?
Quoted 13 lines
The cost of invoking QEMU for each architecture and probing capabilities is already higher than we would like. If we multiply that cost by the number of machine types, it makes the problem orders of magnitude worse, so we cannot go that route.
This is a key reason why we would like to be able to probe properties against QEMU classses without instantiating them. ie so we can launch QEMU once with "-m none" and still be able to query specific properties we want from the 'virt' machine type. A small step towards this was made with a patch we landed to let us register properties against classes in QOM, instead of against objects. We've not done work to convert code internally to use this facility yet though.
So, until such support lands in QEMU, is there really anything we can do in libvirt beside passing through whatever value the user has specified in the domain XML and report QEMU's error on failure?
I had underestimated the performance implications of spawning more QEMU processes, thanks for highlighting them.
Cheers.
--
Andrea Bolognani
Software Engineer - Virtualization Team
Quoted 53 lines · Markus Armbruster
Quoted 34 lines · Peter Xu
Quoted 33 lines · Markus Armbruster
Quoted 30 lines · Peter Xu
For ARM platform, we still do not have any interface to query whether current QEMU/host support specific GIC version. This patchset is trying to add one QMP interface for that. By querying the GIC capability using the new interface, one should know exactly what GIC version(s) the platform will support. The capability bits will be decided by both QEMU and host kernel.
The current patchset only provides interface for review. Its handler is a fake one which returns empty always.
The command interface I am planning to add is something like this:
-> { "execute": "query-gic-capability" }
<- { "return": [ "gicv2", "gicv2-kvm", "gicv3-kvm" ] }Currently, all the possible supported GIC versions are:
- gicv2: GIC version 2 without kernel IRQ chip - gicv2-kvm: GIC version 2 with kernel IRQ chip - gicv3: GIC version 3 without kernel IRQ chip (not supported) - gicv3-kvm: GIC version 3 with kernel IRQ chipSince "gicv3" is still not supported (to use GICv3, kernel irqchip support is required for now, which corresponds to "gicv3-kvm"), currently the maximum superset of the result should be:
["gicv2", "gicv2-kvm", "gicv3-kvm"]
Please help review whether the interface suits our need, also please point out any error I have made.
Quoted 7 lines
Quoted 2 lines
Adding ad hoc queries as we go won't scale. Is there really no generic way to get this information, e.g. with qom-get?
Haven't used "qom-get" before, but it seems to fetch one property for a specific object. If so, will it be strange to hide some capability bits into every GIC objects (though there is possibly one object)?
Pardon my ignorance... what are these "GIC objects"?
What exactly is the "GIC type", and how would the result of query-gic-capability be used?
Quoted 4 lines
I agree that we should keep the interface as simple as possible. I see that there are already commands that works just like this one, which is to query some capabilities from QEMU, like:
Quoted 7 lines
Quoted 2 lines
- query-dump-guest-memory-capability
- query-migrate-capabilitiesI'm not saying we must not add another ad hoc query. I'm trying to figure out whether existing generic infrastructure can serve, or be adapted to serve. Once we establish the answer is "no" or "badly", I'm willing to consider the ad hoc query.
Looking at this from the POV of solving the generic problem, what we have here is an object with an integer property, for which only certain values are permitted based on what host kernel/hardware we're runing on.
So to solve this generically, we would need a way to provide information in QOM as to what permitted values are for any given property. This would make sense for at least bool, int and enum properties, since they can all potentially have scenarios where the possible range of values is greater than the currently permissible range of values.
Regards,
Daniel
Signature · 4 lines
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Quoted 67 lines · Daniel P. Berrange
Quoted 53 lines · Markus Armbruster
Quoted 34 lines · Peter Xu
Quoted 33 lines · Markus Armbruster
Quoted 30 lines · Peter Xu
For ARM platform, we still do not have any interface to query whether current QEMU/host support specific GIC version. This patchset is trying to add one QMP interface for that. By querying the GIC capability using the new interface, one should know exactly what GIC version(s) the platform will support. The capability bits will be decided by both QEMU and host kernel.
The current patchset only provides interface for review. Its handler is a fake one which returns empty always.
The command interface I am planning to add is something like this:
-> { "execute": "query-gic-capability" }
<- { "return": [ "gicv2", "gicv2-kvm", "gicv3-kvm" ] }Currently, all the possible supported GIC versions are:
- gicv2: GIC version 2 without kernel IRQ chip - gicv2-kvm: GIC version 2 with kernel IRQ chip - gicv3: GIC version 3 without kernel IRQ chip (not supported) - gicv3-kvm: GIC version 3 with kernel IRQ chipSince "gicv3" is still not supported (to use GICv3, kernel irqchip support is required for now, which corresponds to "gicv3-kvm"), currently the maximum superset of the result should be:
["gicv2", "gicv2-kvm", "gicv3-kvm"]
Please help review whether the interface suits our need, also please point out any error I have made.
Quoted 7 lines
Quoted 2 lines
Adding ad hoc queries as we go won't scale. Is there really no generic way to get this information, e.g. with qom-get?
Haven't used "qom-get" before, but it seems to fetch one property for a specific object. If so, will it be strange to hide some capability bits into every GIC objects (though there is possibly one object)?
Pardon my ignorance... what are these "GIC objects"?
What exactly is the "GIC type", and how would the result of query-gic-capability be used?
Quoted 4 lines
I agree that we should keep the interface as simple as possible. I see that there are already commands that works just like this one, which is to query some capabilities from QEMU, like:
Quoted 7 lines
Quoted 2 lines
- query-dump-guest-memory-capability
- query-migrate-capabilitiesI'm not saying we must not add another ad hoc query. I'm trying to figure out whether existing generic infrastructure can serve, or be adapted to serve. Once we establish the answer is "no" or "badly", I'm willing to consider the ad hoc query.
Looking at this from the POV of solving the generic problem, what we have here is an object with an integer property, for which only certain values are permitted based on what host kernel/hardware we're runing on.
Quoted 5 lines
So to solve this generically, we would need a way to provide information in QOM as to what permitted values are for any given property. This would make sense for at least bool, int and enum properties, since they can all potentially have scenarios where the possible range of values is greater than the currently permissible range of values.
Is this work on any of our todo list (or anyone has started the prototyping)?
It seems reasonable to provide such a generic interface, rather than adding a "query-gic-capability" for GIC versions only. The problem is that, I am not sure how eagerly we are wanting this GIC interface, and when will this framework be there in QOM.
Thanks.
Peter
Quoted 8 lines
Regards,
DanielSignature · 4 lines
|: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :|
Quoted 74 lines · Peter Xu
Quoted 67 lines · Daniel P. Berrange
Quoted 53 lines · Markus Armbruster
Quoted 34 lines · Peter Xu
Quoted 33 lines · Markus Armbruster
Quoted 30 lines · Peter Xu
For ARM platform, we still do not have any interface to query whether current QEMU/host support specific GIC version. This patchset is trying to add one QMP interface for that. By querying the GIC capability using the new interface, one should know exactly what GIC version(s) the platform will support. The capability bits will be decided by both QEMU and host kernel.
The current patchset only provides interface for review. Its handler is a fake one which returns empty always.
The command interface I am planning to add is something like this:
-> { "execute": "query-gic-capability" }
<- { "return": [ "gicv2", "gicv2-kvm", "gicv3-kvm" ] }Currently, all the possible supported GIC versions are:
- gicv2: GIC version 2 without kernel IRQ chip - gicv2-kvm: GIC version 2 with kernel IRQ chip - gicv3: GIC version 3 without kernel IRQ chip (not supported) - gicv3-kvm: GIC version 3 with kernel IRQ chipSince "gicv3" is still not supported (to use GICv3, kernel irqchip support is required for now, which corresponds to "gicv3-kvm"), currently the maximum superset of the result should be:
["gicv2", "gicv2-kvm", "gicv3-kvm"]
Please help review whether the interface suits our need, also please point out any error I have made.
Quoted 7 lines
Quoted 2 lines
Adding ad hoc queries as we go won't scale. Is there really no generic way to get this information, e.g. with qom-get?
Haven't used "qom-get" before, but it seems to fetch one property for a specific object. If so, will it be strange to hide some capability bits into every GIC objects (though there is possibly one object)?
Pardon my ignorance... what are these "GIC objects"?
What exactly is the "GIC type", and how would the result of query-gic-capability be used?
Quoted 4 lines
I agree that we should keep the interface as simple as possible. I see that there are already commands that works just like this one, which is to query some capabilities from QEMU, like:
Quoted 7 lines
Quoted 2 lines
- query-dump-guest-memory-capability
- query-migrate-capabilitiesI'm not saying we must not add another ad hoc query. I'm trying to figure out whether existing generic infrastructure can serve, or be adapted to serve. Once we establish the answer is "no" or "badly", I'm willing to consider the ad hoc query.
Looking at this from the POV of solving the generic problem, what we have here is an object with an integer property, for which only certain values are permitted based on what host kernel/hardware we're runing on.
Quoted 5 lines
So to solve this generically, we would need a way to provide information in QOM as to what permitted values are for any given property. This would make sense for at least bool, int and enum properties, since they can all potentially have scenarios where the possible range of values is greater than the currently permissible range of values.
Quoted 7 lines
Is this work on any of our todo list (or anyone has started the prototyping)?
It seems reasonable to provide such a generic interface, rather than adding a "query-gic-capability" for GIC versions only. The problem is that, I am not sure how eagerly we are wanting this GIC interface, and when will this framework be there in QOM.
We want it eagerly :-) This type of a rabbit hole is likely why Daniel was suggesting we do more in libvirt. I'm still not sure we want to probe both kvm and qemu from libvirt though, so I'm still in favor of an improved qemu probing method being worked out.
I don't know what the policy is for deprecating QMP commands, but I wonder if we can't introduce a QMP command now, and then, after working out the QOM extensions, we could shift to it, deprecating this QMP command and any others that would no longer be needed.
Thanks,
drew
Quoted 13 lines
Thanks.
PeterQuoted 8 lines
Regards,
DanielSignature · 4 lines
|: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :|
Quoted 7 lines · Andrew Jones
Quoted 7 lines
Is this work on any of our todo list (or anyone has started the prototyping)?
It seems reasonable to provide such a generic interface, rather than adding a "query-gic-capability" for GIC versions only. The problem is that, I am not sure how eagerly we are wanting this GIC interface, and when will this framework be there in QOM.
Quoted 10 lines
We want it eagerly :-) This type of a rabbit hole is likely why Daniel was suggesting we do more in libvirt. I'm still not sure we want to probe both kvm and qemu from libvirt though, so I'm still in favor of an improved qemu probing method being worked out.
I don't know what the policy is for deprecating QMP commands, but I wonder if we can't introduce a QMP command now, and then, after working out the QOM extensions, we could shift to it, deprecating this QMP command and any others that would no longer be needed.
AFAIK, the current situation of libvirt passing the GIC version to QEMU and simply reporting in case of failure is not unprecedented and there are a few cases where probing in advance would simply not be feasible.
Any probing code added to libvirt would have to be kept around forever to ensure compatibility with current QEMU versions, so it should IMHO be seen as a last resort in case we can't live without GIC version probing while it's being implemented, properly, in QEMU.
Cheers.
--
Andrea Bolognani
Software Engineer - Virtualization Team
Quoted 24 lines · Andrea Bolognani
Quoted 7 lines · Andrew Jones
Quoted 7 lines
Is this work on any of our todo list (or anyone has started the prototyping)?
It seems reasonable to provide such a generic interface, rather than adding a "query-gic-capability" for GIC versions only. The problem is that, I am not sure how eagerly we are wanting this GIC interface, and when will this framework be there in QOM.Quoted 10 lines
We want it eagerly :-) This type of a rabbit hole is likely why Daniel was suggesting we do more in libvirt. I'm still not sure we want to probe both kvm and qemu from libvirt though, so I'm still in favor of an improved qemu probing method being worked out.
I don't know what the policy is for deprecating QMP commands, but I wonder if we can't introduce a QMP command now, and then, after working out the QOM extensions, we could shift to it, deprecating this QMP command and any others that would no longer be needed.AFAIK, the current situation of libvirt passing the GIC version to QEMU and simply reporting in case of failure is not unprecedented and there are a few cases where probing in advance would simply not be feasible.
Quoted 4 lines
Any probing code added to libvirt would have to be kept around forever to ensure compatibility with current QEMU versions, so it should IMHO be seen as a last resort in case we can't live without GIC version probing while it's being implemented, properly, in QEMU.
If libvirt is the most possible consumer for the new command, I think it might not be too hard to keep the compatibility of all possible versions of QEMU. E.g., after we have got a better way to query GIC version other than query-gic-capability, we can do something like this in libvirt:
- try query-gic-capability
- if supported -> [got GIC version]
- if not supported -> try the new method
- if supported -> [got GIC version]
- if not supported -> [not support]
During the time when QEMU has both methods working (before obsoleting the query-gic-capability QMP command), QEMU will make sure querying in both way will get exactly the same results.
Does this work?
Thanks.
Peter
Quoted 9 lines · Peter Xu
Quoted 9 lines
AFAIK, the current situation of libvirt passing the GIC version to QEMU and simply reporting in case of failure is not unprecedented and there are a few cases where probing in advance would simply not be feasible.
Any probing code added to libvirt would have to be kept around forever to ensure compatibility with current QEMU versions, so it should IMHO be seen as a last resort in case we can't live without GIC version probing while it's being implemented, properly, in QEMU.
Quoted 16 lines
If libvirt is the most possible consumer for the new command, I think it might not be too hard to keep the compatibility of all possible versions of QEMU. E.g., after we have got a better way to query GIC version other than query-gic-capability, we can do something like this in libvirt:
- try query-gic-capability
- if supported -> [got GIC version]
- if not supported -> try the new method
- if supported -> [got GIC version]
- if not supported -> [not support]
During the time when QEMU has both methods working (before obsoleting the query-gic-capability QMP command), QEMU will make sure querying in both way will get exactly the same results.
I didn't say it would be hard :)
I just said that such compatibility code would have to be kept around forever. We already support lots and lots of similar cases in libvirt, the difference being that in this case we would add support for a new command *knowing in advance* that it will become obsolete as soon as a proper implementation is available.
It might still be the right thing to do! I just want to make sure everything's been properly considered and discussed beforehand.
Cheers.
--
Andrea Bolognani
Software Engineer - Virtualization Team
Quoted 10 lines · Andrea Bolognani
I didn't say it would be hard :)
I just said that such compatibility code would have to be kept around forever. We already support lots and lots of similar cases in libvirt, the difference being that in this case we would add support for a new command *knowing in advance* that it will become obsolete as soon as a proper implementation is available.
It might still be the right thing to do! I just want to make sure everything's been properly considered and discussed beforehand.
I totally agree with you to think more before doing. :)
Then I will try to move on. Appreciate for all the review comments!
Peter
Quoted 12 lines · Peter Xu
Quoted 11 lines · Andrea Bolognani
I didn't say it would be hard :)
I just said that such compatibility code would have to be kept around forever. We already support lots and lots of similar cases in libvirt, the difference being that in this case we would add support for a new command *knowing in advance* that it will become obsolete as soon as a proper implementation is available.
It might still be the right thing to do! I just want to make sure everything's been properly considered and discussed beforehand.
Quoted 2 lines
I totally agree with you to think more before doing. :)
So, anyone else willing to give their $0.2 on how to implement this The Right Way™?
I just skimmed the whole thread again and it doesn't look to me like any consensus has been reached.
Cheers.
--
Andrea Bolognani
Software Engineer - Virtualization Team
Quoted 13 lines · Andrea Bolognani
Quoted 12 lines · Peter Xu
Quoted 11 lines · Andrea Bolognani
I didn't say it would be hard :)
I just said that such compatibility code would have to be kept around forever. We already support lots and lots of similar cases in libvirt, the difference being that in this case we would add support for a new command *knowing in advance* that it will become obsolete as soon as a proper implementation is available.
It might still be the right thing to do! I just want to make sure everything's been properly considered and discussed beforehand.
Quoted 8 lines
Quoted 2 lines
I totally agree with you to think more before doing. :)So, anyone else willing to give their $0.2 on how to implement this The Right Way™?
I just skimmed the whole thread again and it doesn't look to me like any consensus has been reached.
Hi, Andrea,
I have sent another non-rfc patchset about this already:
https://lists.gnu.org/archive/html/qemu-devel/2016-02/msg05270.html
I am not sure whether you have received it or not (you should be in the CC list :), just pasting it again here. Do you think this would work for us?
Btw, the thread is receiving none reviews till now. Looking forward to have any of your further comments!
Thanks!
Peter
Quoted 6 lines
Cheers.
--
Andrea Bolognani
Software Engineer - Virtualization Team