On 2013-10-21 22:37, Eric Blake wrote:
On 10/20/2013 08:52 PM, Max Reitz wrote:
Saving the VM state is done using bdrv_pwrite. This function may perform
a read-modify-write, which in this case results in data being read from
beyond the end of the virtual disk. Since we are actually trying to
access an area which is not a part of the virtual disk, zero_beyond_eof
has to be set to false before performing the partial write, otherwise
the VM state may become corrupted.
Signed-off-by: Max Reitz <mre...@redhat.com>
---
Follow-up to (depends on):
- qcow2: Restore total_sectors value in save_vmstate
Reviewed-by: Eric Blake <ebl...@redhat.com>
Do you have test cases that demonstrate the corruption pre-patch?
I could write a test case for the other patch, but for this one it would
probably be rather difficult. What I did to bisect the bug was just
starting a VM over and over while saving a snapshot at some time during
boot-up and trying to load that snapshot again. Sometimes, qemu itself
would report a corrupted VM state, but most of the time, the guest
simply hang or paniced. This is something I can detect interactively,
but I don't know if I could write a test for this (at least not for
hanging).
Max
