* Philippe Mathieu-Daudé (phi...@redhat.com) wrote: > Cc'ing qemu-devel@ > > On 2/23/21 1:45 AM, Jiatong Shen wrote: > > Hello, > > > > we are faced with an issue where a changed sized romfile > > (efi-virtio.rom) fails live migration. Do qemu load this rom from its > > current host only? If yes, why cannot sync this from source vm?
Hi, For migration to work the ROM has to be the same size on the source and destination. The problem is that whne the destination starts up it allocates the size of the ROM based on the size of the file; but then the migration comes along and tries to copy the data from the source machine into that allocation; and isn't sure what should happen when it doesn't quite fit. There is some variation allowed (I think the allocated size gets rounded up, maybe to the next power of 2); but you still hit problems wehn the ROM size crosses certain thresholds. In the latest qemu, a 'romsize' property was added (see git commit 08b1df8ff463e72b0875538fb991d5393047606c ); that lets you specifiy a size that's big enough to hold some space for future expansion - e.g. lets say your ROM is currently 300k, you might specify romsize=512k and then it doesn't matter what size the actual file is, we'll always allocate 512k, and as long as the file is less than 512k migration will work. The more manual way to do that, is to arrange for your files to be padded to a larger boundary so that you leave room for growth. Some distros have done that for a while. Dave > > thank you. > > > > -- > > > > Best Regards, > > > > Jiatong Shen > -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
