On 10/8/19 1:52 AM, Christian Ehrhardt wrote:
On Mon, Oct 7, 2019 at 11:49 PM Cole Robinson <crobinso@xxxxxxxxxx> 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.c;h=5853ad985fe17c91af3f1dc39d179f22a1dca5b7;hb=HEAD#l980
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
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