| Message ID | 1ac81ba920b03d153f80236fea5aa81321e054fa.1547420060.git.crobinso@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | RFC: qemu: virtio-{non-}transitional support | expand |
On Sun, Jan 13, 2019 at 06:12:06PM -0500, Cole Robinson wrote: > Add new <disk> model values for virtio transitional devices. When > combined with bus='virtio': > > * "virtio-transitional" maps to qemu "virtio-blk-pci-transitional" > * "virtio-non-transitional" maps to qemu "virtio-blk-pci-non-transitional" > > Signed-off-by: Cole Robinson <crobinso@redhat.com> > --- > src/qemu/qemu_command.c | 31 ++++++++++++++++++- > src/qemu/qemu_domain_address.c | 2 ++ > ...virtio-non-transitional.x86_64-latest.args | 7 +++-- > .../virtio-transitional.x86_64-latest.args | 4 +-- > .../virtio-non-transitional.xml | 10 ++++-- > 5 files changed, 45 insertions(+), 9 deletions(-) > > diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c > index 822d5f8669..ca6abea227 100644 > --- a/src/qemu/qemu_command.c > +++ b/src/qemu/qemu_command.c > @@ -443,6 +443,33 @@ qemuBuildVirtioDevStr(virBufferPtr buf, > return 0; > } > > +static int > +qemuBuildVirtioTransitional(virBufferPtr buf, > + const char *baseName, > + virDomainDeviceAddressType type, > + bool transitional, > + bool nontransitional) > +{ > + if (qemuBuildVirtioDevStr(buf, baseName, type) < 0) > + return -1; > + > + if (type != VIR_DOMAIN_DEVICE_ADDRESS_TYPE_PCI && > + (transitional || nontransitional)) { > + virReportError(VIR_ERR_CONFIG_UNSUPPORTED, > + _("virtio transitional models are not supported " > + "for address type=%s"), > + virDomainDeviceAddressTypeToString(type)); > + return -1; > + } > + > + if (transitional) { > + virBufferAddLit(buf, "-transitional"); > + } else if (nontransitional) { > + virBufferAddLit(buf, "-non-transitional"); > + } > + return 0; So this only works on QEMU >= 4.0.0 - earlier versions will fail to start. We can, however, make it work correctly with old QEMU. A transitional device is 100% identical to the existing device types, so we can simply not add the "-transitional" suffix for old QEMU. The only difference is the way libvirt does PCI bus placement of the transitional device - we'd never use PCIe. A non-transitional device is identical to the existing device types, but with disable-legacy=true set. QEMU guarantees this compatibility of the different devices, but only for machine types < pc-i440fx-4.0.0 / pc-q35-4.0.0. So we should none the less make sure we use the modern device names for any QEMU which genuinely supports them. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :| -- libvir-list mailing list libvir-list@redhat.com https://www.redhat.com/mailman/listinfo/libvir-list
On Tue, 2019-01-15 at 16:56 +0000, Daniel P. Berrangé wrote: > On Sun, Jan 13, 2019 at 06:12:06PM -0500, Cole Robinson wrote: > > Add new <disk> model values for virtio transitional devices. When > > combined with bus='virtio': > > > > * "virtio-transitional" maps to qemu "virtio-blk-pci-transitional" > > * "virtio-non-transitional" maps to qemu "virtio-blk-pci-non-transitional" > > > > Signed-off-by: Cole Robinson <crobinso@redhat.com> > > --- > > src/qemu/qemu_command.c | 31 ++++++++++++++++++- > > src/qemu/qemu_domain_address.c | 2 ++ > > ...virtio-non-transitional.x86_64-latest.args | 7 +++-- > > .../virtio-transitional.x86_64-latest.args | 4 +-- > > .../virtio-non-transitional.xml | 10 ++++-- > > 5 files changed, 45 insertions(+), 9 deletions(-) > > > > diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c > > index 822d5f8669..ca6abea227 100644 > > --- a/src/qemu/qemu_command.c > > +++ b/src/qemu/qemu_command.c > > @@ -443,6 +443,33 @@ qemuBuildVirtioDevStr(virBufferPtr buf, > > return 0; > > } > > > > +static int > > +qemuBuildVirtioTransitional(virBufferPtr buf, > > + const char *baseName, > > + virDomainDeviceAddressType type, > > + bool transitional, > > + bool nontransitional) > > +{ > > + if (qemuBuildVirtioDevStr(buf, baseName, type) < 0) > > + return -1; > > + > > + if (type != VIR_DOMAIN_DEVICE_ADDRESS_TYPE_PCI && > > + (transitional || nontransitional)) { > > + virReportError(VIR_ERR_CONFIG_UNSUPPORTED, > > + _("virtio transitional models are not supported " > > + "for address type=%s"), > > + virDomainDeviceAddressTypeToString(type)); > > + return -1; > > + } > > + > > + if (transitional) { > > + virBufferAddLit(buf, "-transitional"); > > + } else if (nontransitional) { > > + virBufferAddLit(buf, "-non-transitional"); > > + } > > + return 0; > > So this only works on QEMU >= 4.0.0 - earlier versions will > fail to start. > > We can, however, make it work correctly with old QEMU. > > A transitional device is 100% identical to the existing device > types, so we can simply not add the "-transitional" suffix for > old QEMU. The only difference is the way libvirt does PCI bus > placement of the transitional device - we'd never use PCIe. > > A non-transitional device is identical to the existing device > types, but with disable-legacy=true set. Again, the relationship between existing and new devices is not quite this straighforward because of the reasons I outlined in https://www.redhat.com/archives/libvir-list/2019-January/msg00514.html But the idea of using disable-{legacy,modern} instead of the new virtio-*-{non,}-transitional devices is one I had already suggested in https://bugzilla.redhat.com/show_bug.cgi?id=1614127 so I'm obviously on board with it :) > QEMU guarantees this compatibility of the different devices, > but only for machine types < pc-i440fx-4.0.0 / pc-q35-4.0.0. > So we should none the less make sure we use the modern device > names for any QEMU which genuinely supports them. As I already mentioned in the bug report linked above, I'm not quite convinced that's the case, and I don't see why we wouldn't just use the options and basically ignore the QEMU-level devices, as the former approach would work on old QEMU releases as well as recent ones with no drawback I can think of.
On Wed, Jan 16, 2019 at 12:31:04PM +0100, Andrea Bolognani wrote: > On Tue, 2019-01-15 at 16:56 +0000, Daniel P. Berrangé wrote: > > On Sun, Jan 13, 2019 at 06:12:06PM -0500, Cole Robinson wrote: > > > Add new <disk> model values for virtio transitional devices. When > > > combined with bus='virtio': > > > > > > * "virtio-transitional" maps to qemu "virtio-blk-pci-transitional" > > > * "virtio-non-transitional" maps to qemu "virtio-blk-pci-non-transitional" > > > > > > Signed-off-by: Cole Robinson <crobinso@redhat.com> > > > --- > > > src/qemu/qemu_command.c | 31 ++++++++++++++++++- > > > src/qemu/qemu_domain_address.c | 2 ++ > > > ...virtio-non-transitional.x86_64-latest.args | 7 +++-- > > > .../virtio-transitional.x86_64-latest.args | 4 +-- > > > .../virtio-non-transitional.xml | 10 ++++-- > > > 5 files changed, 45 insertions(+), 9 deletions(-) > > > > > > diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c > > > index 822d5f8669..ca6abea227 100644 > > > --- a/src/qemu/qemu_command.c > > > +++ b/src/qemu/qemu_command.c > > > @@ -443,6 +443,33 @@ qemuBuildVirtioDevStr(virBufferPtr buf, > > > return 0; > > > } > > > > > > +static int > > > +qemuBuildVirtioTransitional(virBufferPtr buf, > > > + const char *baseName, > > > + virDomainDeviceAddressType type, > > > + bool transitional, > > > + bool nontransitional) > > > +{ > > > + if (qemuBuildVirtioDevStr(buf, baseName, type) < 0) > > > + return -1; > > > + > > > + if (type != VIR_DOMAIN_DEVICE_ADDRESS_TYPE_PCI && > > > + (transitional || nontransitional)) { > > > + virReportError(VIR_ERR_CONFIG_UNSUPPORTED, > > > + _("virtio transitional models are not supported " > > > + "for address type=%s"), > > > + virDomainDeviceAddressTypeToString(type)); > > > + return -1; > > > + } > > > + > > > + if (transitional) { > > > + virBufferAddLit(buf, "-transitional"); > > > + } else if (nontransitional) { > > > + virBufferAddLit(buf, "-non-transitional"); > > > + } > > > + return 0; > > > > So this only works on QEMU >= 4.0.0 - earlier versions will > > fail to start. > > > > We can, however, make it work correctly with old QEMU. > > > > A transitional device is 100% identical to the existing device > > types, so we can simply not add the "-transitional" suffix for > > old QEMU. The only difference is the way libvirt does PCI bus > > placement of the transitional device - we'd never use PCIe. > > > > A non-transitional device is identical to the existing device > > types, but with disable-legacy=true set. > > Again, the relationship between existing and new devices is not > quite this straighforward because of the reasons I outlined in > > https://www.redhat.com/archives/libvir-list/2019-January/msg00514.html When told to use virtio-transitional for a device, libvirt would only plug it into a PCI slot, never a PCI-X slot. Given this constraint, it is functionally identical / interchangable with the existing device. > But the idea of using disable-{legacy,modern} instead of the new > virtio-*-{non,}-transitional devices is one I had already suggested > in > > https://bugzilla.redhat.com/show_bug.cgi?id=1614127 > > so I'm obviously on board with it :) > > > QEMU guarantees this compatibility of the different devices, > > but only for machine types < pc-i440fx-4.0.0 / pc-q35-4.0.0. > > So we should none the less make sure we use the modern device > > names for any QEMU which genuinely supports them. > > As I already mentioned in the bug report linked above, I'm not > quite convinced that's the case, and I don't see why we wouldn't > just use the options and basically ignore the QEMU-level devices, > as the former approach would work on old QEMU releases as well as > recent ones with no drawback I can think of. The QEMU maintainers were against the idea of us doing that. In the future they may add properties to, or change the defaults on, the -transitional or -non-transitional devices only, associated with new machine type versions. If libvirt forever uses the old devices, then we loose ability to take advantage of that. Indeed if QEMU maintainers wanted us to use the disable-legacy/modern features long term, there would be no point in them even adding the new device types in the first place. We should only ever use the disable- flags if the new devices do not exist in QEMU. Regards, Daniel
On Wed, 2019-01-16 at 11:39 +0000, Daniel P. Berrangé wrote: > On Wed, Jan 16, 2019 at 12:31:04PM +0100, Andrea Bolognani wrote: > > On Tue, 2019-01-15 at 16:56 +0000, Daniel P. Berrangé wrote: > > > A transitional device is 100% identical to the existing device > > > types, so we can simply not add the "-transitional" suffix for > > > old QEMU. The only difference is the way libvirt does PCI bus > > > placement of the transitional device - we'd never use PCIe. > > > > > > A non-transitional device is identical to the existing device > > > types, but with disable-legacy=true set. > > > > Again, the relationship between existing and new devices is not > > quite this straighforward because of the reasons I outlined in > > > > https://www.redhat.com/archives/libvir-list/2019-January/msg00514.html > > When told to use virtio-transitional for a device, libvirt would > only plug it into a PCI slot, never a PCI-X slot. Given this > constraint, it is functionally identical / interchangable with > the existing device. Right, but you didn't spell out the constraint the first time around, thus making your (broader) statement that a "transitional device is 100% identical to the existing device" incorrect :) > > But the idea of using disable-{legacy,modern} instead of the new > > virtio-*-{non,}-transitional devices is one I had already suggested > > in > > > > https://bugzilla.redhat.com/show_bug.cgi?id=1614127 > > > > so I'm obviously on board with it :) > > > > > QEMU guarantees this compatibility of the different devices, > > > but only for machine types < pc-i440fx-4.0.0 / pc-q35-4.0.0. > > > So we should none the less make sure we use the modern device > > > names for any QEMU which genuinely supports them. > > > > As I already mentioned in the bug report linked above, I'm not > > quite convinced that's the case, and I don't see why we wouldn't > > just use the options and basically ignore the QEMU-level devices, > > as the former approach would work on old QEMU releases as well as > > recent ones with no drawback I can think of. > > The QEMU maintainers were against the idea of us doing that. I don't recall any QEMU developer specifically saying that, but that might be just a case of my memory sucking :) CC'ing Eduardo so he can weigh in. > In the > future they may add properties to, or change the defaults on, the > -transitional or -non-transitional devices only, associated with > new machine type versions. If libvirt forever uses the old devices, > then we loose ability to take advantage of that. Regardless of what libvirt ends up doing, from the QEMU user point of view I think it would be very surprising if eg. virtio-blk-pci plugged into a PCIe slot behaved differently from virtio-blk-pci-non-transitional plugged into the very same slot, or if virtio-net-pci,disable-legacy=false,disable-modern=false behaved differently from virtio-net-pci-transitional regardless of the slot it's plugged into, so moving away from that consistency should be a non-goal IMHO. > Indeed if QEMU maintainers wanted us to use the disable-legacy/modern > features long term, there would be no point in them even adding the > new device types in the first place. Yeah, after commenting on the bug report mentioned above I indeed started thinking that we could have gotten away with not adding those devices. They might still be useful to people running QEMU directly, though. > We should only ever use the disable- flags if the new devices do > not exist in QEMU. Wouldn't that potentially cause issues when migrating from QEMU < 4.0.0, where we'd use disable-*, to QEMU >= 4.0.0, where we'd use *-{,non}transitional instead? I guess not if the changes in device behavior are gated by the machine type version.
On Wed, Jan 16, 2019 at 01:29:13PM +0100, Andrea Bolognani wrote: > On Wed, 2019-01-16 at 11:39 +0000, Daniel P. Berrangé wrote: > > On Wed, Jan 16, 2019 at 12:31:04PM +0100, Andrea Bolognani wrote: > > > On Tue, 2019-01-15 at 16:56 +0000, Daniel P. Berrangé wrote: > > > > A transitional device is 100% identical to the existing device > > > > types, so we can simply not add the "-transitional" suffix for > > > > old QEMU. The only difference is the way libvirt does PCI bus > > > > placement of the transitional device - we'd never use PCIe. > > > > > > > > A non-transitional device is identical to the existing device > > > > types, but with disable-legacy=true set. > > > > > > Again, the relationship between existing and new devices is not > > > quite this straighforward because of the reasons I outlined in > > > > > > https://www.redhat.com/archives/libvir-list/2019-January/msg00514.html > > > > When told to use virtio-transitional for a device, libvirt would > > only plug it into a PCI slot, never a PCI-X slot. Given this > > constraint, it is functionally identical / interchangable with > > the existing device. > > Right, but you didn't spell out the constraint the first time > around, thus making your (broader) statement that a "transitional > device is 100% identical to the existing device" incorrect :) > > > > But the idea of using disable-{legacy,modern} instead of the new > > > virtio-*-{non,}-transitional devices is one I had already suggested > > > in > > > > > > https://bugzilla.redhat.com/show_bug.cgi?id=1614127 > > > > > > so I'm obviously on board with it :) > > > > > > > QEMU guarantees this compatibility of the different devices, > > > > but only for machine types < pc-i440fx-4.0.0 / pc-q35-4.0.0. > > > > So we should none the less make sure we use the modern device > > > > names for any QEMU which genuinely supports them. > > > > > > As I already mentioned in the bug report linked above, I'm not > > > quite convinced that's the case, and I don't see why we wouldn't > > > just use the options and basically ignore the QEMU-level devices, > > > as the former approach would work on old QEMU releases as well as > > > recent ones with no drawback I can think of. > > > > The QEMU maintainers were against the idea of us doing that. > > I don't recall any QEMU developer specifically saying that, but > that might be just a case of my memory sucking :) CC'ing Eduardo > so he can weigh in. It was somewhere in one of the many mail threads, but I'm not finding the archive link right now. > > In the > > future they may add properties to, or change the defaults on, the > > -transitional or -non-transitional devices only, associated with > > new machine type versions. If libvirt forever uses the old devices, > > then we loose ability to take advantage of that. > > Regardless of what libvirt ends up doing, from the QEMU user point > of view I think it would be very surprising if eg. virtio-blk-pci > plugged into a PCIe slot behaved differently from > virtio-blk-pci-non-transitional plugged into the very same slot, or > if virtio-net-pci,disable-legacy=false,disable-modern=false behaved > differently from virtio-net-pci-transitional regardless of the slot > it's plugged into, so moving away from that consistency should be a > non-goal IMHO. > > > Indeed if QEMU maintainers wanted us to use the disable-legacy/modern > > features long term, there would be no point in them even adding the > > new device types in the first place. > > Yeah, after commenting on the bug report mentioned above I indeed > started thinking that we could have gotten away with not adding > those devices. They might still be useful to people running QEMU > directly, though. > > > We should only ever use the disable- flags if the new devices do > > not exist in QEMU. > > Wouldn't that potentially cause issues when migrating from QEMU > < 4.0.0, where we'd use disable-*, to QEMU >= 4.0.0, where we'd > use *-{,non}transitional instead? I guess not if the changes in > device behavior are gated by the machine type version. In this message Eduardo said virtio-blk-pci,disable-legacy and virtio-blk-pci-non-transitional are only compatible with the pc-4.0 machine types and earlier. There's no compat guarantee of compat for future machine types: https://lists.gnu.org/archive/html/qemu-devel/2018-11/msg03762.html If we didn't use the new QEMU device models right now, we could end up trapped forever. The safe futureproof approach is to always use the new devices models if available, and use disable-legacy for old QEMU versions only, which we know will have old machine types for which the compat guarantee is available. Regards, Daniel
On Wed, 2019-01-16 at 12:44 +0000, Daniel P. Berrangé wrote: > On Wed, Jan 16, 2019 at 01:29:13PM +0100, Andrea Bolognani wrote: > > On Wed, 2019-01-16 at 11:39 +0000, Daniel P. Berrangé wrote: > > > In the > > > future they may add properties to, or change the defaults on, the > > > -transitional or -non-transitional devices only, associated with > > > new machine type versions. If libvirt forever uses the old devices, > > > then we loose ability to take advantage of that. > > > > Regardless of what libvirt ends up doing, from the QEMU user point > > of view I think it would be very surprising if eg. virtio-blk-pci > > plugged into a PCIe slot behaved differently from > > virtio-blk-pci-non-transitional plugged into the very same slot, or > > if virtio-net-pci,disable-legacy=false,disable-modern=false behaved > > differently from virtio-net-pci-transitional regardless of the slot > > it's plugged into, so moving away from that consistency should be a > > non-goal IMHO. > > [...] > > In this message Eduardo said virtio-blk-pci,disable-legacy and > virtio-blk-pci-non-transitional are only compatible with the > pc-4.0 machine types and earlier. There's no compat guarantee > of compat for future machine types: > > https://lists.gnu.org/archive/html/qemu-devel/2018-11/msg03762.html > > If we didn't use the new QEMU device models right now, we could end > up trapped forever. The safe futureproof approach is to always use > the new devices models if available, and use disable-legacy for old > QEMU versions only, which we know will have old machine types for > which the compat guarantee is available. Well, let's see if Eduardo is willing to reconsider the policy on compatibility between virtio-*-pci-{,non-}transitional and plain virtio-*-pci going forward based on the principle-of-least-surprise rationale outlined above :)
On Wed, Jan 16, 2019 at 03:31:49PM +0100, Andrea Bolognani wrote: > On Wed, 2019-01-16 at 12:44 +0000, Daniel P. Berrangé wrote: > > On Wed, Jan 16, 2019 at 01:29:13PM +0100, Andrea Bolognani wrote: > > > On Wed, 2019-01-16 at 11:39 +0000, Daniel P. Berrangé wrote: > > > > In the > > > > future they may add properties to, or change the defaults on, the > > > > -transitional or -non-transitional devices only, associated with > > > > new machine type versions. If libvirt forever uses the old devices, > > > > then we loose ability to take advantage of that. > > > > > > Regardless of what libvirt ends up doing, from the QEMU user point > > > of view I think it would be very surprising if eg. virtio-blk-pci > > > plugged into a PCIe slot behaved differently from > > > virtio-blk-pci-non-transitional plugged into the very same slot, or > > > if virtio-net-pci,disable-legacy=false,disable-modern=false behaved > > > differently from virtio-net-pci-transitional regardless of the slot > > > it's plugged into, so moving away from that consistency should be a > > > non-goal IMHO. > > > > [...] > > > > In this message Eduardo said virtio-blk-pci,disable-legacy and > > virtio-blk-pci-non-transitional are only compatible with the > > pc-4.0 machine types and earlier. There's no compat guarantee > > of compat for future machine types: > > > > https://lists.gnu.org/archive/html/qemu-devel/2018-11/msg03762.html > > > > If we didn't use the new QEMU device models right now, we could end > > up trapped forever. The safe futureproof approach is to always use > > the new devices models if available, and use disable-legacy for old > > QEMU versions only, which we know will have old machine types for > > which the compat guarantee is available. > > Well, let's see if Eduardo is willing to reconsider the policy on > compatibility between virtio-*-pci-{,non-}transitional and plain > virtio-*-pci going forward based on the principle-of-least-surprise > rationale outlined above :) I think we should use the new devices no matter what. Libvirt generally always strives to follow the latest QEMU best practice, even when new & old way of doing something are functionally identical. Eventually we would drop support for QEU < 4.0 and the old way would go away entirely. Regards, Daniel
On Wed, Jan 16, 2019 at 02:37:22PM +0000, Daniel P. Berrangé wrote: > On Wed, Jan 16, 2019 at 03:31:49PM +0100, Andrea Bolognani wrote: > > On Wed, 2019-01-16 at 12:44 +0000, Daniel P. Berrangé wrote: > > > On Wed, Jan 16, 2019 at 01:29:13PM +0100, Andrea Bolognani wrote: > > > > On Wed, 2019-01-16 at 11:39 +0000, Daniel P. Berrangé wrote: > > > > > In the > > > > > future they may add properties to, or change the defaults on, the > > > > > -transitional or -non-transitional devices only, associated with > > > > > new machine type versions. If libvirt forever uses the old devices, > > > > > then we loose ability to take advantage of that. > > > > > > > > Regardless of what libvirt ends up doing, from the QEMU user point > > > > of view I think it would be very surprising if eg. virtio-blk-pci > > > > plugged into a PCIe slot behaved differently from > > > > virtio-blk-pci-non-transitional plugged into the very same slot, or > > > > if virtio-net-pci,disable-legacy=false,disable-modern=false behaved > > > > differently from virtio-net-pci-transitional regardless of the slot > > > > it's plugged into, so moving away from that consistency should be a > > > > non-goal IMHO. > > > > > > [...] > > > > > > In this message Eduardo said virtio-blk-pci,disable-legacy and > > > virtio-blk-pci-non-transitional are only compatible with the > > > pc-4.0 machine types and earlier. There's no compat guarantee > > > of compat for future machine types: > > > > > > https://lists.gnu.org/archive/html/qemu-devel/2018-11/msg03762.html > > > > > > If we didn't use the new QEMU device models right now, we could end > > > up trapped forever. The safe futureproof approach is to always use > > > the new devices models if available, and use disable-legacy for old > > > QEMU versions only, which we know will have old machine types for > > > which the compat guarantee is available. > > > > Well, let's see if Eduardo is willing to reconsider the policy on > > compatibility between virtio-*-pci-{,non-}transitional and plain > > virtio-*-pci going forward based on the principle-of-least-surprise > > rationale outlined above :) > > I think we should use the new devices no matter what. Libvirt generally > always strives to follow the latest QEMU best practice, even when new & > old way of doing something are functionally identical. Eventually we > would drop support for QEU < 4.0 and the old way would go away entirely. It would also allow us to deprecate the old devices, which would be welcome. Always using the new devices when available would be my recommendation. But I don't want to create unnecessary obstacles for libvirt, so if there's a real benefit in promising compatibility between both device types, we can still promise that on the QEMU side. Breaking compatibility on purpose is very unlikely, and the most likely accidents could be detected by tests/acceptance/virtio_version.py. -- Eduardo -- libvir-list mailing list libvir-list@redhat.com https://www.redhat.com/mailman/listinfo/libvir-list
On Wed, Jan 16, 2019 at 12:45:43PM -0200, Eduardo Habkost wrote: > On Wed, Jan 16, 2019 at 02:37:22PM +0000, Daniel P. Berrangé wrote: > > On Wed, Jan 16, 2019 at 03:31:49PM +0100, Andrea Bolognani wrote: > > > On Wed, 2019-01-16 at 12:44 +0000, Daniel P. Berrangé wrote: > > > > On Wed, Jan 16, 2019 at 01:29:13PM +0100, Andrea Bolognani wrote: > > > > > On Wed, 2019-01-16 at 11:39 +0000, Daniel P. Berrangé wrote: > > > > > > In the > > > > > > future they may add properties to, or change the defaults on, the > > > > > > -transitional or -non-transitional devices only, associated with > > > > > > new machine type versions. If libvirt forever uses the old devices, > > > > > > then we loose ability to take advantage of that. > > > > > > > > > > Regardless of what libvirt ends up doing, from the QEMU user point > > > > > of view I think it would be very surprising if eg. virtio-blk-pci > > > > > plugged into a PCIe slot behaved differently from > > > > > virtio-blk-pci-non-transitional plugged into the very same slot, or > > > > > if virtio-net-pci,disable-legacy=false,disable-modern=false behaved > > > > > differently from virtio-net-pci-transitional regardless of the slot > > > > > it's plugged into, so moving away from that consistency should be a > > > > > non-goal IMHO. > > > > > > > > [...] > > > > > > > > In this message Eduardo said virtio-blk-pci,disable-legacy and > > > > virtio-blk-pci-non-transitional are only compatible with the > > > > pc-4.0 machine types and earlier. There's no compat guarantee > > > > of compat for future machine types: > > > > > > > > https://lists.gnu.org/archive/html/qemu-devel/2018-11/msg03762.html > > > > > > > > If we didn't use the new QEMU device models right now, we could end > > > > up trapped forever. The safe futureproof approach is to always use > > > > the new devices models if available, and use disable-legacy for old > > > > QEMU versions only, which we know will have old machine types for > > > > which the compat guarantee is available. > > > > > > Well, let's see if Eduardo is willing to reconsider the policy on > > > compatibility between virtio-*-pci-{,non-}transitional and plain > > > virtio-*-pci going forward based on the principle-of-least-surprise > > > rationale outlined above :) > > > > I think we should use the new devices no matter what. Libvirt generally > > always strives to follow the latest QEMU best practice, even when new & > > old way of doing something are functionally identical. Eventually we > > would drop support for QEU < 4.0 and the old way would go away entirely. > > It would also allow us to deprecate the old devices, which would > be welcome. Always using the new devices when available would be > my recommendation. I don't really see QEMU upstream deprecating the old devices any time. There is sooooo much documentation that refers to them that will never be fixed. 99% of users won't get any benefit from using the new devices either, so there's no compelling reason to update their existing configs or docs. They're not going to be a huge maint burden to QEMU devs either given its just a toggle of a few props. I might see a downstream distro deprecating them at some point though, since they have a much tighter controlled usage scenario than upstream. > But I don't want to create unnecessary obstacles for libvirt, so > if there's a real benefit in promising compatibility between both > device types, we can still promise that on the QEMU side. I don't think there's an obstacle for libvirt, as I don't see any compelling reason to avoid the new devices when we have QEMU >= 4.0. > Breaking compatibility on purpose is very unlikely, and the most > likely accidents could be detected by > tests/acceptance/virtio_version.py. Regards, Daniel
On Wed, 2019-01-16 at 15:40 +0000, Daniel P. Berrangé wrote: > On Wed, Jan 16, 2019 at 12:45:43PM -0200, Eduardo Habkost wrote: > > But I don't want to create unnecessary obstacles for libvirt, so > > if there's a real benefit in promising compatibility between both > > device types, we can still promise that on the QEMU side. > > I don't think there's an obstacle for libvirt, as I don't see any > compelling reason to avoid the new devices when we have QEMU >= 4.0. Alright, let's do it that way then. I still think it's important to maintain the relationship between old and new devices consistent going forward, because not doing so will certainly result in confusion for those using QEMU directly.
On Wed, Jan 16, 2019 at 05:24:02PM +0100, Andrea Bolognani wrote: > On Wed, 2019-01-16 at 15:40 +0000, Daniel P. Berrangé wrote: > > On Wed, Jan 16, 2019 at 12:45:43PM -0200, Eduardo Habkost wrote: > > > But I don't want to create unnecessary obstacles for libvirt, so > > > if there's a real benefit in promising compatibility between both > > > device types, we can still promise that on the QEMU side. > > > > I don't think there's an obstacle for libvirt, as I don't see any > > compelling reason to avoid the new devices when we have QEMU >= 4.0. > > Alright, let's do it that way then. > > I still think it's important to maintain the relationship between > old and new devices consistent going forward, because not doing so > will certainly result in confusion for those using QEMU directly. Agreed that it's a good thing to have. I will extend the existing virtio_version.py test case to be more strict and try to catch mistakes that would break compatibility between the two device types in the future. -- Eduardo -- libvir-list mailing list libvir-list@redhat.com https://www.redhat.com/mailman/listinfo/libvir-list
diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c index 822d5f8669..ca6abea227 100644 --- a/src/qemu/qemu_command.c +++ b/src/qemu/qemu_command.c @@ -443,6 +443,33 @@ qemuBuildVirtioDevStr(virBufferPtr buf, return 0; } +static int +qemuBuildVirtioTransitional(virBufferPtr buf, + const char *baseName, + virDomainDeviceAddressType type, + bool transitional, + bool nontransitional) +{ + if (qemuBuildVirtioDevStr(buf, baseName, type) < 0) + return -1; + + if (type != VIR_DOMAIN_DEVICE_ADDRESS_TYPE_PCI && + (transitional || nontransitional)) { + virReportError(VIR_ERR_CONFIG_UNSUPPORTED, + _("virtio transitional models are not supported " + "for address type=%s"), + virDomainDeviceAddressTypeToString(type)); + return -1; + } + + if (transitional) { + virBufferAddLit(buf, "-transitional"); + } else if (nontransitional) { + virBufferAddLit(buf, "-non-transitional"); + } + return 0; +} + static int qemuBuildVirtioOptionsStr(virBufferPtr buf, @@ -2049,7 +2076,9 @@ qemuBuildDiskDeviceStr(const virDomainDef *def, break; case VIR_DOMAIN_DISK_BUS_VIRTIO: - if (qemuBuildVirtioDevStr(&opt, "virtio-blk", disk->info.type) < 0) + if (qemuBuildVirtioTransitional(&opt, "virtio-blk", disk->info.type, + disk->model == VIR_DOMAIN_DISK_MODEL_VIRTIO_TRANSITIONAL, + disk->model == VIR_DOMAIN_DISK_MODEL_VIRTIO_NON_TRANSITIONAL) < 0) goto error; if (disk->iothread) diff --git a/src/qemu/qemu_domain_address.c b/src/qemu/qemu_domain_address.c index bd6c4031e0..1a77b74ad1 100644 --- a/src/qemu/qemu_domain_address.c +++ b/src/qemu/qemu_domain_address.c @@ -723,6 +723,8 @@ qemuDomainDeviceCalculatePCIConnectFlags(virDomainDeviceDefPtr dev, case VIR_DOMAIN_DEVICE_DISK: switch ((virDomainDiskBus) dev->data.disk->bus) { case VIR_DOMAIN_DISK_BUS_VIRTIO: + if (dev->data.disk->model == VIR_DOMAIN_DISK_MODEL_VIRTIO_NON_TRANSITIONAL) + return pciFlags; return virtioFlags; /* only virtio disks use PCI */ case VIR_DOMAIN_DISK_BUS_IDE: diff --git a/tests/qemuxml2argvdata/virtio-non-transitional.x86_64-latest.args b/tests/qemuxml2argvdata/virtio-non-transitional.x86_64-latest.args index 070b4b8334..a8f878c99c 100644 --- a/tests/qemuxml2argvdata/virtio-non-transitional.x86_64-latest.args +++ b/tests/qemuxml2argvdata/virtio-non-transitional.x86_64-latest.args @@ -25,10 +25,11 @@ file=/tmp/lib/domain--1-QEMUGuest1/master-key.aes \ -boot strict=on \ -device pcie-root-port,port=0x8,chassis=1,id=pci.1,bus=pcie.0,multifunction=on,\ addr=0x1 \ --device pcie-root-port,port=0x9,chassis=2,id=pci.2,bus=pcie.0,addr=0x1.0x1 \ +-device pcie-pci-bridge,id=pci.2,bus=pci.1,addr=0x0 \ +-device pcie-root-port,port=0x9,chassis=3,id=pci.3,bus=pcie.0,addr=0x1.0x1 \ -drive file=/dev/HostVG/QEMUGuest1,format=raw,if=none,id=drive-virtio-disk0 \ --device virtio-blk-pci,scsi=off,bus=pci.1,addr=0x0,drive=drive-virtio-disk0,\ -id=virtio-disk0,bootindex=1 \ +-device virtio-blk-pci-non-transitional,scsi=off,bus=pci.2,addr=0x1,\ +drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1 \ -sandbox on,obsolete=deny,elevateprivileges=deny,spawn=deny,\ resourcecontrol=deny \ -msg timestamp=on diff --git a/tests/qemuxml2argvdata/virtio-transitional.x86_64-latest.args b/tests/qemuxml2argvdata/virtio-transitional.x86_64-latest.args index 070b4b8334..7730b177e7 100644 --- a/tests/qemuxml2argvdata/virtio-transitional.x86_64-latest.args +++ b/tests/qemuxml2argvdata/virtio-transitional.x86_64-latest.args @@ -27,8 +27,8 @@ file=/tmp/lib/domain--1-QEMUGuest1/master-key.aes \ addr=0x1 \ -device pcie-root-port,port=0x9,chassis=2,id=pci.2,bus=pcie.0,addr=0x1.0x1 \ -drive file=/dev/HostVG/QEMUGuest1,format=raw,if=none,id=drive-virtio-disk0 \ --device virtio-blk-pci,scsi=off,bus=pci.1,addr=0x0,drive=drive-virtio-disk0,\ -id=virtio-disk0,bootindex=1 \ +-device virtio-blk-pci-transitional,scsi=off,bus=pci.1,addr=0x0,\ +drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1 \ -sandbox on,obsolete=deny,elevateprivileges=deny,spawn=deny,\ resourcecontrol=deny \ -msg timestamp=on diff --git a/tests/qemuxml2xmloutdata/virtio-non-transitional.xml b/tests/qemuxml2xmloutdata/virtio-non-transitional.xml index 1c00365edf..a64a84d145 100644 --- a/tests/qemuxml2xmloutdata/virtio-non-transitional.xml +++ b/tests/qemuxml2xmloutdata/virtio-non-transitional.xml @@ -18,7 +18,7 @@ <driver name='qemu' type='raw'/> <source dev='/dev/HostVG/QEMUGuest1'/> <target dev='vda' bus='virtio'/> - <address type='pci' domain='0x0000' bus='0x01' slot='0x00' function='0x0'/> + <address type='pci' domain='0x0000' bus='0x02' slot='0x01' function='0x0'/> </disk> <controller type='usb' index='0' model='none'/> <controller type='sata' index='0'> @@ -30,9 +30,13 @@ <target chassis='1' port='0x8'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x0' multifunction='on'/> </controller> - <controller type='pci' index='2' model='pcie-root-port'> + <controller type='pci' index='2' model='pcie-to-pci-bridge'> + <model name='pcie-pci-bridge'/> + <address type='pci' domain='0x0000' bus='0x01' slot='0x00' function='0x0'/> + </controller> + <controller type='pci' index='3' model='pcie-root-port'> <model name='pcie-root-port'/> - <target chassis='2' port='0x9'/> + <target chassis='3' port='0x9'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x1'/> </controller> <input type='mouse' bus='ps2'/>
Add new <disk> model values for virtio transitional devices. When combined with bus='virtio': * "virtio-transitional" maps to qemu "virtio-blk-pci-transitional" * "virtio-non-transitional" maps to qemu "virtio-blk-pci-non-transitional" Signed-off-by: Cole Robinson <crobinso@redhat.com> --- src/qemu/qemu_command.c | 31 ++++++++++++++++++- src/qemu/qemu_domain_address.c | 2 ++ ...virtio-non-transitional.x86_64-latest.args | 7 +++-- .../virtio-transitional.x86_64-latest.args | 4 +-- .../virtio-non-transitional.xml | 10 ++++-- 5 files changed, 45 insertions(+), 9 deletions(-) -- 2.20.1 -- libvir-list mailing list libvir-list@redhat.com https://www.redhat.com/mailman/listinfo/libvir-list