Re: [libvirt] [PATCH 8/8] qemu: enable blockdev support

On Mon, Nov 18, 2019 at 06:02:08PM +0100, Peter Krempa wrote: > Now that all pieces are in place (hopefully) let's enable -blockdev. > > We base the capability on presence of the fix for 'auto-read-only' on > files so that blockdev works properly, mandate that qemu supports > explicit SCSI id strings to avoid ABI regression and that the fix for > 'savevm' is present so that internal snapshots work. IIUC, once we enable this, we are fully committed to blockdev hereafter.... > diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c > index 6f23400f95..b5fa0fba7e 100644 > --- a/src/qemu/qemu_capabilities.c > +++ b/src/qemu/qemu_capabilities.c > @@ -4476,13 +4476,15 @@ virQEMUCapsInitProcessCaps(virQEMUCapsPtr qemuCaps) > virQEMUCapsClear(qemuCaps, QEMU_CAPS_DEVICE_VFIO_CCW); > } > > - /* To avoid guest ABI regression, blockdev shall be enabled only when > - * we are able to pass the custom 'device_id' for SCSI disks and cdroms. */ > - if (!virQEMUCapsGet(qemuCaps, QEMU_CAPS_SCSI_DISK_DEVICE_ID)) > - virQEMUCapsClear(qemuCaps, QEMU_CAPS_BLOCKDEV); > - > if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_CPU_UNAVAILABLE_FEATURES)) > virQEMUCapsSet(qemuCaps, QEMU_CAPS_CANONICAL_CPU_FEATURES); > + > + /* To avoid guest ABI regression, blockdev shall be enabled only when > + * we are able to pass the custom 'device_id' for SCSI disks and cdroms. */ > + if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_BLOCK_FILE_AUTO_READONLY_DYNAMIC) && > + virQEMUCapsGet(qemuCaps, QEMU_CAPS_SCSI_DISK_DEVICE_ID) && > + virQEMUCapsGet(qemuCaps, QEMU_CAPS_SAVEVM_MONITOR_NODES)) .... we must *not* add more capabilities in future to this list of three that we're checking, as that would cause us to regress in use of blockdev

> + virQEMUCapsSet(qemuCaps, QEMU_CAPS_BLOCKDEV); I don't think that's a problem really - we'll just treat anything else we find as a normal bug & make an effort to fix it as possible. We dont want to continually turn off blockdev over & over every time we find a new bug.