Re: [PATCH 3/5] conf: Introduce <metadata_cache> subelement of <disk><driver>
On Fri, Jan 08, 2021 at 13:13:30 +0000, Daniel Berrange wrote:
On Thu, Jan 07, 2021 at 03:59:36PM +0100, Peter Krempa wrote:
> In certain specific cases it might be beneficial to be able to control
> the metadata caching of storage image format drivers of a hypervisor.
>
> Introduce XML machinery to set the maximum size of the metadata cache
> which will be used by qemu's qcow2 driver.
>
> Signed-off-by: Peter Krempa <pkrempa(a)redhat.com>
> ---
> docs/formatdomain.rst | 43 ++++++++++++++
> docs/schemas/domaincommon.rng | 20 ++++++-
> src/conf/domain_conf.c | 51 ++++++++++++++--
> src/util/virstoragefile.c | 1 +
> src/util/virstoragefile.h | 2 +
> .../qemuxml2argvdata/disk-metadata-cache.xml | 46 +++++++++++++++
> .../disk-metadata-cache.x86_64-latest.xml | 58 +++++++++++++++++++
> tests/qemuxml2xmltest.c | 1 +
> 8 files changed, 216 insertions(+), 6 deletions(-)
> create mode 100644 tests/qemuxml2argvdata/disk-metadata-cache.xml
> create mode 100644 tests/qemuxml2xmloutdata/disk-metadata-cache.x86_64-latest.xml
> + <disk type='file' device='disk'>
> + <driver name='qemu' type='qcow2'
cache='none'/>
> + <source file='/tmp/QEMUGuest2.img'/>
> + <backingStore type='file'>
> + <format type='qcow2'>
> + <metadata_cache>
> + <max_size unit='kiB'>1024</max_size>
> + </metadata_cache>
I only wonder if this is uneccessarily verbose XML nesting ?
I actually had the same feeling, but adding it just as an attribute to
<disk><driver ... >(the other case besides <backingStore> felt worse
since we have a huge list of attributes there.
I specifically want that it points to metadata cache maximum size so
that there isn't any unnecessary ambiguity.
Possibilities are to merge the <max_size> subelement into the parent
element so that we decrease the amount of lines. Or possibly go with
Jano's suggestion of dropping 'size' since that is obvious when
unit=''
is present (but note that unit is optional on input).