Re: Support cloning of VMs - part 2

On Wed, Jul 09, 2025 at 11:27:45AM +0100, Daniel P. Berrangé via Devel wrote: Well it didn't take me long to uncover new info :-( Looking at the QEMU codebase for where 'qemu_uuid' is used reveals rather more than anticipated git grep -E '\bqemu_uuid(_set)?\b' hw/core/machine-qmp-cmds.c: info->UUID = qemu_uuid_unparse_strdup(&qemu_uuid); hw/i386/vmport.c: uint32_t *uuid_parts = (uint32_t *)(qemu_uuid.data); hw/nvram/fw_cfg.c: fw_cfg_add_bytes(s, FW_CFG_UUID, &qemu_uuid, 16); hw/ppc/pnv.c: buf = qemu_uuid_unparse_strdup(&qemu_uuid); hw/ppc/pnv.c: if (qemu_uuid_set) { hw/ppc/spapr.c: buf = qemu_uuid_unparse_strdup(&qemu_uuid); hw/ppc/spapr.c: if (qemu_uuid_set) { hw/ppc/spapr_rtas.c: ret = sysparm_st(buffer, length, (unsigned char *)&qemu_uuid, hw/ppc/spapr_rtas.c: (qemu_uuid_set ? 16 : 0)); hw/smbios/smbios.c: if (qemu_uuid_set) { hw/smbios/smbios.c: smbios_encode_uuid(&t->uuid, &qemu_uuid); hw/smbios/smbios.c: if (qemu_uuid_parse(val, &qemu_uuid) != 0) { hw/smbios/smbios.c: qemu_uuid_set = true; hw/smbios/smbios_legacy.c: if (qemu_uuid_set) { hw/smbios/smbios_legacy.c: &qemu_uuid, 16); include/hw/firmware/smbios.h: /* uuid is in qemu_uuid */ include/sysemu/sysemu.h:extern QemuUUID qemu_uuid; include/sysemu/sysemu.h:extern bool qemu_uuid_set; migration/multifd.c: memcpy(msg.uuid, &qemu_uuid.data, sizeof(msg.uuid)); migration/multifd.c: if (memcmp(msg.uuid, &qemu_uuid, sizeof(qemu_uuid))) { migration/multifd.c: char *uuid = qemu_uuid_unparse_strdup(&qemu_uuid); migration/savevm.c: state->uuid = qemu_uuid; migration/savevm.c: return qemu_uuid_set && migrate_validate_uuid(); migration/savevm.c: if (!qemu_uuid_set) { migration/savevm.c: if (!qemu_uuid_is_equal(&state->uuid, &qemu_uuid)) { migration/savevm.c: qemu_uuid_unparse(&qemu_uuid, uuid_dst); system/globals.c:/* The bytes in qemu_uuid are in the order specified by RFC4122, _not_ in the system/globals.c:QemuUUID qemu_uuid; system/globals.c:bool qemu_uuid_set; system/vl.c: if (qemu_uuid_parse(optarg, &qemu_uuid) < 0) { system/vl.c: qemu_uuid_set = true; target/s390x/kvm/kvm.c: memcpy(sysib.vm[0].uuid, &qemu_uuid, sizeof(sysib.vm[0].uuid)); target/s390x/tcg/misc_helper.c: memcpy(sysib.sysib_322.vm[0].uuid, &qemu_uuid, ui/dbus.c: g_autofree char *uuid = qemu_uuid_unparse_strdup(&qemu_uuid); ui/spice-core.c: spice_server_set_uuid(spice_server, (unsigned char *)&qemu_uuid); Only a small subset of those places have a directly exposed property that could override the default they obtain from the -uuid arg. The savevm code in particular is a sticking point as we need to use the migration code as the mechanism for cloning. So if we want to enable cloning, without the guest visible UUIDs changing, and with the savevm checks passing, we're pretty much stuck with having to set -uuid to a *different* value than the <uuid></uuid> in the XML :-( This probably takes us back to needing to have another element at the top level in the XML. <uuid>....</uuid> <hwuuid>...</hwuuid> where <uuid> is mandatory as today, and <hwuuid> can optionally be used to override what is exposed to the guest, defaulting to <uuid> if omitted. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|