On Wed, Aug 17, 2011 at 08:12:03AM -0600, Eric Blake wrote:
On 08/17/2011 07:10 AM, Osier Yang wrote:
If one tries to restore a domain from a corrupt save image, we blindly goes forward to restore from it, this can cause many different errors, depending on how much the image is saved. E.g.
https://bugzilla.redhat.com/show_bug.cgi?id=730750
So I'm thinking if we can introduce a new feild to struct qemud_save_header, such as "bool complete;", and set it true if succeeded to save the image, false if not. So that could do some checking while trying to open the image (qemuDomainSaveImageOpen), and quit early if "complete" is false, with a sensiable error message.
Almost. I think we can reuse one of the existing spare fields in the header (that is, change unused[15] to instead be unused[14] and make the new field a uint32_t), and I also think we need to have a tri-state value:
0 - save image was created with older libvirt, no idea if image is sane 1 - save image created by current libvirt, but not yet marked complete; attempts to restore from this image should fail with sensible message suggesting nuking the save image since it is broken - value written at start of save process 2 - save image created by current libvirt and completed - value written at end of save process
And of course, we have to update the bswap_header routine to treat it with the same endianness as the rest of the header.
The downside to adding a new header field, is that old libvirt won't look for it. A slightly more evil approach is to 1. Write header, but with 'magic' set to all zerso 2. do migration 3. Re-write header to set correct 'magic' On the plus side old livirt will refuse to restore from this. On the downside new libvirt will give less good errors "not a known save file" instad of "save file is corrupt" Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :|