[Qemu-devel] [Bug 1294227] Re: migration wrong handling of KVM_GET_DIRTY_LOG ioctl

[Peter Maydell]

The apparently obvious fix was applied as commit b533f658a98325d0e4 but
then reverted in commit 50212d6346f33d6e19, because not all errno
returns from this ioctl should be treated as errors.

That commit message said "Revert that patch instead of fixing it
properly this late in the release process.  I disagree with this
approach, but let's make things move _somewhere_, instead of arguing
endlessly whch of the 2 proposed fixes is better." -- and then we never
did a proper fix, so 5 years later we're still making an incorrect == -1
check...

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https://bugs.launchpad.net/bugs/1294227

Title:
  migration wrong handling of KVM_GET_DIRTY_LOG ioctl

Status in QEMU:
  In Progress

Bug description:
  In the code below kvm_vm_ioctl(...) can return --errno != -1 from ioctl call, 
 but return only checks for -1. 
  Found during KVM-ARM migration which apperead to go through but was actually 
failing getting 
  memslot dirty bitmap.

  static int kvm_physical_sync_dirty_bitmap(....)
  {
   ....
   if(kvm_vm_ioctl(s, KVM_GET_DIRTY_LOG, &d) == -1) {
     - err out
   }
   ... continue
  }

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