The default value of the granularity is the image cluster size clamped between 4096 and 65536. Libvirt should add a check for this otherwise qemu will report error like below: $ virsh blockcopy r7 vda /var/lib/libvirt/images/r7.s1 --granularity 32 error: internal error: unable to execute QEMU command 'drive-mirror': Parameter 'granularity' expects a value in range [512B, 64MB] Signed-off-by: Shanzhi Yu <shyu(a)redhat.com&gt; --- src/qemu/qemu_driver.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c index d1f195c..0eca8ed 100644 --- a/src/qemu/qemu_driver.c +++ b/src/qemu/qemu_driver.c @@ -16990,6 +16990,10 @@ qemuDomainBlockCopy(virDomainPtr dom, const char *disk, const char *destxml, virReportError(VIR_ERR_INVALID_ARG, "%s", _("granularity must be power of 2")); goto cleanup; + } else if (param->value.ui > 65536 || param->value.ui < 4096) { + virReportError(VIR_ERR_INVALID_ARG, "%s", + _("granularity expects value in range [4096 65536]")); + goto cleanup; } granularity = param->value.ui; } else if (STREQ(param->field, VIR_DOMAIN_BLOCK_COPY_BUF_SIZE)) { -- 2.4.3