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[Xen-devel] [PATCH v2] Fix xl vcpu-set to decrease amount of vCPUS without warnining.


This patchset had been floating in the past. The aim for is to allow
the user to do 'xl vcpu-set <domain-id> X' where the X can be bigger
than the amount of physical CPUs the machine has. You can do this by
launching an guest with huge amount of virtual CPUs without issues.


Let me rehash what we had in set in stone way back in 4.4:
 - The guest config ('maxvcpus') is permitted to be greater than the pCPUs.
   Ditto for the initially allocated ('vcpus') amounts. It is also
   OK to be different - 'vcpus' < 'maxvcpus', etc.

 - If the 'vcpus' < pCPUs and we want to increase it above pCPUs we should
   error out and print out a warning telling them to use --ignore-host.
   Regardless of the dominfo.max_vcpu_id - so if the max_vpcu_id is
   greater than pCPU and 'vcpu' < pCPU, we should still warn the user
   when increasing.

 - If the 'vcpus' > pCPUs and we want to decrease to be below pCPUs then
   we should do that without the warning.
   (this is what the patchset is fixing).


However during the fixes an request was made to have libxl_domain_info
return a more proper return value when there are no domains found - hence:
 [PATCH v2 1/5] libxl: Add ERROR_NOTFOUND for libxl_domain_info when

is part of this patchset.

 tools/libxl/libxl.c         | 18 +++++++++------
 tools/libxl/libxl.h         |  4 +++-
 tools/libxl/libxl_types.idl |  1 +
 tools/libxl/xl_cmdimpl.c    | 55 +++++++++++++++++++++++++++++----------------
 4 files changed, 51 insertions(+), 27 deletions(-)

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