On 10/8/19 1:52 AM, Christian Ehrhardt wrote:
On Mon, Oct 7, 2019 at 11:49 PM Cole Robinson <crobinso@redhat.com> wrote:
This series is the first steps to teaching libvirt about qcow2 data_file support, aka external data files or qcow2 external metadata.
A bit about the feature: it was added in qemu 4.0. It essentially creates a two part image file: a qcow2 layer that just tracks the image metadata, and a separate data file which is stores the VM disk contents. AFAICT the driving use case is to keep a fully coherent raw disk image on disk, and only use qcow2 as an intermediate metadata layer when necessary, for things like incremental backup support.
The original qemu patch posting is here: https://lists.gnu.org/archive/html/qemu-devel/2019-02/msg07496.html
For testing, you can create a new qcow2+raw data_file image from an existing image, like:
qemu-img convert -O qcow2 \ -o data_file=NEW.raw,data_file_raw=yes EXISTING.raw NEW.qcow2
The goal of this series is to teach libvirt enough about this case so that we can correctly relabel the data_file on VM startup/shutdown. The main functional changes are
* Teach storagefile how to parse out data_file from the qcow2 header * Store the raw string as virStorageSource->externalDataStoreRaw * Track that as its out virStorageSource in externalDataStore * dac/selinux relabel externalDataStore as needed
From libvirt's perspective, externalDataStore is conceptually pretty close to a backingStore, but the main difference is its read/write permissions should match its parent image, rather than being readonly like backingStore.
This series has only been tested on top of the -blockdev enablement series, but I don't think it actually interacts with that work at the moment.
Future work: * Exposing this in the runtime XML. We need to figure out an XML schema. It will reuse virStorageSource obviously, but the main thing to figure out is probably 1) what the top element name should be ('dataFile' maybe?), 2) where it sits in the XML hierarchy (under <disk> or under <source> I guess)
* Exposing this on the qemu -blockdev command line. Similar to how in the blockdev world we are explicitly putting the disk backing chain on the command line, we can do that for data_file too. Then like persistent <backingStore> XML the user will have the power to overwrite the data_file location for an individual VM run.
* Figure out how we expect ovirt/rhev to be using this at runtime. Possibly taking a running VM using a raw image, doing blockdev-* magic to pivot it to qcow2+raw data_file, so it can initiate incremental backup on top of a previously raw only VM?
Known issues: * In the qemu driver, the qcow2 image metadata is only parsed in -blockdev world if no <backingStore> is specified in the persistent XML. So basically if there's a <backingStore> listed, we never parse the qcow2 header and detect the presence of data_file. Fixable I'm sure but I didn't look into it much yet.
Most of this is cleanups and refactorings to simplify the actual functional changes.
Cole Robinson (30): storagefile: Make GetMetadataInternal static storagefile: qcow1: Check for BACKING_STORE_OK storagefile: qcow1: Fix check for empty backing file storagefile: qcow1: Let qcowXGetBackingStore fill in format storagefile: Check version to determine if qcow2 or not storagefile: Drop now unused isQCow2 argument storagefile: Use qcowXGetBackingStore directly storagefile: Push 'start' into qcow2GetBackingStoreFormat storagefile: Push extension_end calc to qcow2GetBackingStoreFormat storagefile: Rename qcow2GetBackingStoreFormat storagefile: Rename qcow2GetExtensions 'format' argument storagefile: Fix backing format \0 check storagefile: Add externalDataStoreRaw member storagefile: Parse qcow2 external data file storagefile: Fill in meta->externalDataStoreRaw storagefile: Don't access backingStoreRaw directly in FromBackingRelative storagefile: Split out virStorageSourceNewFromChild storagefile: Add externalDataStore member storagefile: Fill in meta->externalDataStore security: dac: Drop !parent handling in SetImageLabelInternal security: dac: Add is_toplevel to SetImageLabelInternal security: dac: Restore image label for externalDataStore security: dac: break out SetImageLabelRelative security: dac: Label externalDataStore security: selinux: Simplify SetImageLabelInternal security: selinux: Drop !parent handling in SetImageLabelInternal security: selinux: Add is_toplevel to SetImageLabelInternal security: selinux: Restore image label for externalDataStore security: selinux: break out SetImageLabelRelative security: selinux: Label externalDataStore
Hi Cole, it seems the changes to dac/selinux follow a common pattern, in the past those changes then mostly applied to security-apparmor as well. Are you going to add patches for that security backend as well before this is final or do you expect the apparmor users Debian/Suse/Ubuntu to do so later on?
Furthermore for the static XML->Apparmor part it will most likely need an extension to [1] as well. Fortunately as you said it is very similar to backingDevices which means it should be rather easy to add this.
[1]: https://libvirt.org/git/?p=libvirt.git;a=blob;f=src/security/virt-aa-helper....
I forgot about apparmor, sorry. I just sent a series and CCd you that does some apparmor cleanups and tweaks so that for this series the data_file coverage is just this extra diff: diff --git a/src/security/virt-aa-helper.c b/src/security/virt-aa-helper.c index d9f6b5638b..fc095d2964 100644 --- a/src/security/virt-aa-helper.c +++ b/src/security/virt-aa-helper.c @@ -948,6 +948,10 @@ storage_source_add_files(virStorageSourcePtr src, if (add_file_path(tmp, depth, buf) < 0) return -1; + if (src->externalDataStore && + storage_source_add_files(src->externalDataStore, buf, depth) < 0) + return -1; + depth++; } I will add a proper patch for that when the prep work hits git Thanks, Cole