[libvirt] [PATCH] Don't parse/format vram attribute for cirrus video
Since the cirrus vga memory size isn't configurable, we can ignore any 'vram' attribute when parsing a domain definition. However, when no value is specified, it ends up getting set to a default value of 16MB. This 16MB value is not used anywhere (for example, it is not passed as an argument to qemu), but is displayed in the XML definition. So by changing this default value to 0, it will also be omitted from the XML definition of the domain. Fixes: rhbz#1447831 Signed-off-by: Jonathon Jongsma <jjongsma@redhat.com> --- This is an attempt to apply the fix suggested by Gerd at https://bugzilla.redhat.com/show_bug.cgi?id=1447831#c2. I'm not totally confident that this is the right approach, since I'm relatively new to the code. Another approach might be to simply close the bug as NOTABUG since it doesn't seem that having this unused attribute in the domain definition has any significant drawbacks. src/conf/domain_conf.c | 2 +- src/qemu/qemu_domain.c | 3 +++ 2 files changed, 4 insertions(+), 1 deletion(-) diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c index c69d382d70..d06e094b11 100644 --- a/src/conf/domain_conf.c +++ b/src/conf/domain_conf.c @@ -15154,7 +15154,6 @@ virDomainVideoDefaultRAM(const virDomainDef *def, { switch (type) { case VIR_DOMAIN_VIDEO_TYPE_VGA: - case VIR_DOMAIN_VIDEO_TYPE_CIRRUS: case VIR_DOMAIN_VIDEO_TYPE_VMVGA: if (def->virtType == VIR_DOMAIN_VIRT_VBOX) return 8 * 1024; @@ -15172,6 +15171,7 @@ virDomainVideoDefaultRAM(const virDomainDef *def, /* QEMU use 64M as the minimal video memory for qxl device */ return 64 * 1024; + case VIR_DOMAIN_VIDEO_TYPE_CIRRUS: case VIR_DOMAIN_VIDEO_TYPE_DEFAULT: case VIR_DOMAIN_VIDEO_TYPE_VBOX: case VIR_DOMAIN_VIDEO_TYPE_PARALLELS: diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c index e5c6ef3fda..7f0baf57ac 100644 --- a/src/qemu/qemu_domain.c +++ b/src/qemu/qemu_domain.c @@ -6835,6 +6835,9 @@ qemuDomainDeviceVideoDefPostParse(virDomainVideoDefPtr video, if (video->type == VIR_DOMAIN_VIDEO_TYPE_QXL && !video->vgamem) { video->vgamem = QEMU_QXL_VGAMEM_DEFAULT; + } else if (video->type == VIR_DOMAIN_VIDEO_TYPE_CIRRUS) { + /* cirrus vram is not configurable. Ignore it */ + video->vram = 0; } return 0; -- 2.20.1
On Thu, Jun 20, 2019 at 14:51:12 -0500, Jonathon Jongsma wrote:
Since the cirrus vga memory size isn't configurable, we can ignore any 'vram' attribute when parsing a domain definition. However, when no value is specified, it ends up getting set to a default value of 16MB. This 16MB value is not used anywhere (for example, it is not passed as an argument to qemu), but is displayed in the XML definition. So by changing this default value to 0, it will also be omitted from the XML definition of the domain.
Fixes: rhbz#1447831
Please always use the full link so that it's clickable and users don't have to figure out what 'rhbz' is.
Signed-off-by: Jonathon Jongsma <jjongsma@redhat.com> --- This is an attempt to apply the fix suggested by Gerd at https://bugzilla.redhat.com/show_bug.cgi?id=1447831#c2. I'm not totally confident that this is the right approach, since I'm relatively new to the code. Another approach might be to simply close the bug as NOTABUG since it doesn't seem that having this unused attribute in the domain definition has any significant drawbacks.
We certainly should not set any default if it's not used. There's not much else we can do though as we did put a default into the configuration. Doing any validation would mean that any VM which had the default errorneously configured in the XML would fail to start. Whether it's worth clearing the default or not I'm not so certain but I don't think it should hurt. You definitely should fix the docs though: https://libvirt.org/formatdomain.html#elementsVideo As it says 'For a guest of type "kvm", the default video is: type with value "cirrus", vram with value "16384" and heads with value "1".' (see docs/formatdomain.html.in )
On Fri, 2019-06-21 at 08:13 +0200, Peter Krempa wrote:
On Thu, Jun 20, 2019 at 14:51:12 -0500, Jonathon Jongsma wrote:
Since the cirrus vga memory size isn't configurable, we can ignore any 'vram' attribute when parsing a domain definition. However, when no value is specified, it ends up getting set to a default value of 16MB. This 16MB value is not used anywhere (for example, it is not passed as an argument to qemu), but is displayed in the XML definition. So by changing this default value to 0, it will also be omitted from the XML definition of the domain.
Fixes: rhbz#1447831
Please always use the full link so that it's clickable and users don't have to figure out what 'rhbz' is.
Signed-off-by: Jonathon Jongsma <jjongsma@redhat.com> --- This is an attempt to apply the fix suggested by Gerd at https://bugzilla.redhat.com/show_bug.cgi?id=1447831#c2. I'm not totally confident that this is the right approach, since I'm relatively new to the code. Another approach might be to simply close the bug as NOTABUG since it doesn't seem that having this unused attribute in the domain definition has any significant drawbacks.
We certainly should not set any default if it's not used. There's not much else we can do though as we did put a default into the configuration.
I'm not sure I understand what you're suggesting here. This sentence seems to imply that you think we should *not* set a default, but down below you say that you're not certain whether we should clear the default? It seems a bit contradictory, but perhaps I'm simply misunderstanding.
Doing any validation would mean that any VM which had the default errorneously configured in the XML would fail to start.
Yeah, I did not do any 'validation' of cirrus vram attributes because I didn't want existing VMs to fail to start. And all existing VMs that use the cirrus device presumably have this attribute set in their XML definition. So I simply ignored this parameter rather than rejecting it. But as I said, I'm not sure whether that's the correct approach for libvirt.
Whether it's worth clearing the default or not I'm not so certain but I don't think it should hurt.
You definitely should fix the docs though:
https://libvirt.org/formatdomain.html#elementsVideo
As it says 'For a guest of type "kvm", the default video is: type with value "cirrus", vram with value "16384" and heads with value "1".'
(see docs/formatdomain.html.in )
Thanks, will do. Jonathon
On Fri, Jun 21, 2019 at 09:53:59 -0500, Jonathon Jongsma wrote:
On Fri, 2019-06-21 at 08:13 +0200, Peter Krempa wrote:
On Thu, Jun 20, 2019 at 14:51:12 -0500, Jonathon Jongsma wrote:
Since the cirrus vga memory size isn't configurable, we can ignore any 'vram' attribute when parsing a domain definition. However, when no value is specified, it ends up getting set to a default value of 16MB. This 16MB value is not used anywhere (for example, it is not passed as an argument to qemu), but is displayed in the XML definition. So by changing this default value to 0, it will also be omitted from the XML definition of the domain.
Fixes: rhbz#1447831
Please always use the full link so that it's clickable and users don't have to figure out what 'rhbz' is.
Signed-off-by: Jonathon Jongsma <jjongsma@redhat.com> --- This is an attempt to apply the fix suggested by Gerd at https://bugzilla.redhat.com/show_bug.cgi?id=1447831#c2. I'm not totally confident that this is the right approach, since I'm relatively new to the code. Another approach might be to simply close the bug as NOTABUG since it doesn't seem that having this unused attribute in the domain definition has any significant drawbacks.
We certainly should not set any default if it's not used. There's not much else we can do though as we did put a default into the configuration.
I'm not sure I understand what you're suggesting here. This sentence seems to imply that you think we should *not* set a default, but down below you say that you're not certain whether we should clear the default? It seems a bit contradictory, but perhaps I'm simply misunderstanding.
I actually meant 'clearing the memory size', thus basically just omitting the whole second hunk of your patch. So any previously set value would be kept intact. Clearing it itself is not a problem for libvirt but might be potentially unexpected by higher level management apps. But I'm not really sure whether't that's a valid case.
Doing any validation would mean that any VM which had the default errorneously configured in the XML would fail to start.
Yeah, I did not do any 'validation' of cirrus vram attributes because I didn't want existing VMs to fail to start. And all existing VMs that use the cirrus device presumably have this attribute set in their XML definition. So I simply ignored this parameter rather than rejecting it. But as I said, I'm not sure whether that's the correct approach for libvirt.
I don't think there's much to do besides ignoring it.
Whether it's worth clearing the default or not I'm not so certain but I don't think it should hurt.
You definitely should fix the docs though:
https://libvirt.org/formatdomain.html#elementsVideo
As it says 'For a guest of type "kvm", the default video is: type with value "cirrus", vram with value "16384" and heads with value "1".'
(see docs/formatdomain.html.in )
Thanks, will do.
Jonathon
On Fri, 2019-06-21 at 17:05 +0200, Peter Krempa wrote:
On Fri, Jun 21, 2019 at 09:53:59 -0500, Jonathon Jongsma wrote:
On Fri, 2019-06-21 at 08:13 +0200, Peter Krempa wrote:
On Thu, Jun 20, 2019 at 14:51:12 -0500, Jonathon Jongsma wrote:
Since the cirrus vga memory size isn't configurable, we can ignore any 'vram' attribute when parsing a domain definition. However, when no value is specified, it ends up getting set to a default value of 16MB. This 16MB value is not used anywhere (for example, it is not passed as an argument to qemu), but is displayed in the XML definition. So by changing this default value to 0, it will also be omitted from the XML definition of the domain.
Fixes: rhbz#1447831
Please always use the full link so that it's clickable and users don't have to figure out what 'rhbz' is.
Signed-off-by: Jonathon Jongsma <jjongsma@redhat.com> --- This is an attempt to apply the fix suggested by Gerd at https://bugzilla.redhat.com/show_bug.cgi?id=1447831#c2. I'm not totally confident that this is the right approach, since I'm relatively new to the code. Another approach might be to simply close the bug as NOTABUG since it doesn't seem that having this unused attribute in the domain definition has any significant drawbacks.
We certainly should not set any default if it's not used. There's not much else we can do though as we did put a default into the configuration.
I'm not sure I understand what you're suggesting here. This sentence seems to imply that you think we should *not* set a default, but down below you say that you're not certain whether we should clear the default? It seems a bit contradictory, but perhaps I'm simply misunderstanding.
I actually meant 'clearing the memory size', thus basically just omitting the whole second hunk of your patch. So any previously set value would be kept intact.
Clearing it itself is not a problem for libvirt but might be potentially unexpected by higher level management apps. But I'm not really sure whether't that's a valid case.
I'm starting to wonder if I'm not falling into the trap of only thinking about things from a qemu/kvm perspective. It looks like a cirrus device can also be used in the libxl driver, and perhaps it is configurable under that hypervisor? I don't have any experience there. In that case, maybe it's safest to simply drop this patch and close the bug as WONTFIX. Any thoughts? Jonathon
participants (2)
-
Jonathon Jongsma -
Peter Krempa