Re: [Qemu-devel] [PATCH for-2.0] kvm_physical_sync_dirty_bitmap: ignore ENOENT from kvm_vm_ioctl

[Serge Hallyn <serge.hallyn@ubuntu.com>]

Quoting Paolo Bonzini (pbonzini@redhat.com):
> Il 11/04/2014 04:31, Michael Tokarev ha scritto:
> >ENOENT means the kernel has an empty dirty bitmap for this
> >slot.  Don't abort in that case.  This appears to solve
> >the bug reported at
> >
> >https://bugs.launchpad.net/ubuntu/+source/qemu/+bug/1303926
> >
> >which first showed up with commit b533f658a98325d: fix return
> >check for KVM_GET_DIRTY_LOG ioctl
> >
> >Cc: Serge Hallyn <serge.hallyn@ubuntu.com>
> >Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
> >---
> > kvm-all.c |   10 ++++++++--
> > 1 file changed, 8 insertions(+), 2 deletions(-)
> >
> >diff --git a/kvm-all.c b/kvm-all.c
> >index cd4111d..47fa948 100644
> >--- a/kvm-all.c
> >+++ b/kvm-all.c
> >@@ -441,13 +441,19 @@ static int kvm_physical_sync_dirty_bitmap(MemoryRegionSection *section)
> >
> >         d.slot = mem->slot;
> >
> >-        if (kvm_vm_ioctl(s, KVM_GET_DIRTY_LOG, &d) < 0) {
> >+        ret = kvm_vm_ioctl(s, KVM_GET_DIRTY_LOG, &d);
> >+        if (ret >= 0) {
> >+            /* regular case, process returned bitmap */
> >+            kvm_get_dirty_pages_log_range(section, d.dirty_bitmap);
> >+        } else if (ret == -ENOENT) {
> >+            /* kernel does not have dirty bitmap in this slot */
> >+            ret = 0;
> >+        } else {
> >             DPRINTF("ioctl failed %d\n", errno);
> >             ret = -1;
> >             break;
> >         }
> >
> >-        kvm_get_dirty_pages_log_range(section, d.dirty_bitmap);
> >         start_addr = mem->start_addr + mem->memory_size;
> >     }
> >     g_free(d.dirty_bitmap);
> >
> 
> I'd rather revert b533f658a98325d instead.

That seems wrong though.  If we want to ignore all errors that's one
thing, but before that commit we just ignored all errors other than
EPERM.