Re: [PATCH 5/5] qemu_validate: Deduplicate code for graphics type check

On Wed, Nov 18, 2020 at 09:12:26 +0100, Michal Privoznik wrote: > On 11/18/20 8:59 AM, Peter Krempa wrote: >> On Tue, Nov 17, 2020 at 12:28:27 +0100, Michal Privoznik wrote: >>> Similarly to previous commits, we can utilize domCaps to check if >>> graphics type is supported. >>> >>> Signed-off-by: Michal Privoznik <mprivozn(a)redhat.com&gt; >>> --- >>> src/qemu/qemu_capabilities.c | 2 +- >>> src/qemu/qemu_capabilities.h | 3 +++ >>> src/qemu/qemu_validate.c | 40 ++++++++++++------------------------ >>> 3 files changed, 17 insertions(+), 28 deletions(-) >> >> [...] >> >>> @@ -3903,15 +3892,12 @@ qemuValidateDomainDeviceDefGraphics(const virDomainGraphicsDef *graphics, >>> } >>> break; >>> + >>> + case VIR_DOMAIN_GRAPHICS_TYPE_VNC: >>> case VIR_DOMAIN_GRAPHICS_TYPE_RDP: >>> case VIR_DOMAIN_GRAPHICS_TYPE_DESKTOP: >>> - virReportError(VIR_ERR_CONFIG_UNSUPPORTED, >>> - _("unsupported graphics type '%s'"), >>> - virDomainGraphicsTypeToString(graphics->type)); >>> - return -1; >>> case VIR_DOMAIN_GRAPHICS_TYPE_LAST: >>> - default: >>> - return -1; >>> + break; >> >> Removing 'default: ' is not necessary once you use proper type for the >> variable in the switch statement, which is our usual approach. > > I guess I don't need to typecast ->type since it's already stored as > virDomainGraphicsType in the struct. > >> >> The default and _LAST case should use virReportEnumRangeError. >> >> > > I'm not sure it's adding useful code. In this very patch I'm adding a check > that rejects unknown values for ->type and thus I don't see a way how the > control could hit any of these 'case', or 'default'. You are right it won't . A drawback of using the capability code is that it relies on converting the type to a bit array stored in "unsigned int" without any overflow safeguards. Once a device model or type enum reaches 33 entries, the code will start failing without any obvious sign. virDomainCapsEnumSet which is internally used by the VIR_DOMAIN_CAPS_ENUM_SET which is used by virQEMUCapsFillDomainDeviceGraphicsCaps to fill the bitmap catches overflow but the callers neglect to propagate it.