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Subject: RE: [PATCH v2 4/4] Add support for MSI-X vectors configuration for PCI VFs
> From: Jason Wang <jasowang@redhat.com> > Sent: Friday, January 28, 2022 8:54 AM > vxlan part actually. Right. > > > > > Similarly, we prefer the ability and flexibility to set more fields in one > command. > > I understood this motivation. But what I want to say is: > > struct virtio_cmd { > u64 attr_mask; > field_X; > field_Y; > field_Z; > } > > What's the default value if one of the X,Y, Z is not specified? If minimum default values are not provided, HV cannot proceed to do configuration and ENOSUPPORT error code is returned by kernel to user. > How to get those default values? > By doing identify or _get respective command. > And suppose we add a new field > > struct virtio_cmd { > u64 attr_mask; > field_X; > field_Y; > field_Z; > field_M; > } > > How can the driver know it can use field_M? If attribute mask is present for field_M, driver can use it. > And if field_M is supported in src > but not dst, how can we keep the migration compatibility? This is HV level command to query and provision a VF. Migration compatibility is high level check where it will identify on which HV to migrate where I can provision X vectors for a VF. > > Would it be simple to just mandate all the fields in this case? > May be, attribute mask is basically to let expand structure without inventing new fields. For a given command few minimal attributes to be set and driver can verify, that if they are not, a given functionality is unsupported.
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