Re: [libvirt] [re-send][PATCH 1/3] add qemu driver hook

On Mon, Oct 08, 2012 at 08:05:21PM -0600, Eric Blake wrote: > On 10/08/2012 07:51 PM, liguang wrote: > > this hook aimed at migration only, it supposed > > to be used as a helper of migrate --copy-storage-* > > features to remove the unreasonable limitation > > of pre-exist disk images at migration target. > > someone can add more functions to hook files. > > NACK. Instead of writing a hook that runs outside of libvirt and has to > be installed to be of use, we should instead fix libvirt to do the file > creation itself. That is, you should be patching > src/qemu/qemu_migration.c to detect when copy-storage-* has been passed, > and to then pre-create the proper empty files and give them correct > SELinux labels. Correctly doing auto-creation of disk images on the target host is alot more complicated that you might assume, and the hook script here misses alot of the hard bits - If the migration fails, you need to clean up these disk images you just created, because the data in them may be incomplete or corrupt. - If the source image is using encryption, then the target image should use encryption too - If the source image uses a backing file, then when incremental copy is requested, we might need to maintain the backing store. - if the migration API did not have either of the --copy-* flags set we should not be doing any creation of disk images - We need to handling of non-file based disk images, because even block devices may be local-only. - If the user passed a custom XML for the target that differs from the source, this may affect decisions we need to make above wrt encryption or backing files Finally, we should *not* do auto-creation by default - we need to add a new migrate flag to allow apps to turn it on, only if they want it. Daniel