[libvirt] [PATCH 0/3] add disk driver metadata_cache_size option

[Nikolay Shirokovskiy]

Hi, all.

This is a patch series after offlist agreement on introducing
metadata-cache-size option for disks. The options itself is described in 2nd
patch of the series.

There is a plenty of attempts to add option to set qcow2 metadata cache sizes in
past, see [1] [2] to name recent that has comments I tried to address or has
work I reused to some extent.

I would like to address Peter's comment in [1] that this option is image's
option rather then disk's here. While this makes sense if we set specific cache
value that covers disk only partially, here when we have maximum policy that
covers whole disk it makes sense to set same value for all images. The setted
value is only upper limit on cache size and thus cache for every image will
grow proportionally to image data size "visible from top" eventually I guess.
And these sizes are changing during guest lifetime - thus we need set whole
disk limit for every image for 'maxium' effect.

On the other hand if we add policies different from 'maximum' it may require
per image option. Well I can't imagine name for element for backing chain that
will have cache size attribute better then 'driver'). And driver is already
used for top image so I leave it this way.

  KNOWN ISSUES

1. when using -driver to configure disks in command line cache size does not
   get propagated thru backing chain

2. when making external disk snapshot cache size sneak into backing file
   filename and thus cache size for backing image became remembered there

3. blockcommit after such snapshot will not work because libvirt is not ready
   for backing file name is reported as json sometimes

Looks like 1 can be addressed in qemu. The reason for behaviour in 2
I do not understand honestly. And 3 will be naturally addessed after
blockjobs starts working with blockdev configuration I guess.

  LINKS

[1] [PATCH] qemu: Added support L2 table cache for qcow2 disk
https://www.redhat.com/archives/libvir-list/2018-July/msg00166.html

[2] [PATCH v6 0/2] Add support for qcow2 cache
 https://www.redhat.com/archives/libvir-list/2017-September/msg00553.html

Nikolay Shirokovskiy (3):
  qemu: caps: add drive.qcow2.l2-cache-size
  xml: add disk driver metadata_cache_size option
  qemu: support metadata-cache-size for blockdev

 docs/formatdomain.html.in                          |  7 ++++
 docs/schemas/domaincommon.rng                      | 10 +++++
 src/conf/domain_conf.c                             | 17 ++++++++
 src/conf/domain_conf.h                             |  9 ++++
 src/qemu/qemu_block.c                              |  5 ++-
 src/qemu/qemu_capabilities.c                       |  3 ++
 src/qemu/qemu_capabilities.h                       |  1 +
 src/qemu/qemu_command.c                            | 26 ++++++++++++
 src/qemu/qemu_domain.c                             |  2 +
 src/util/virstoragefile.c                          |  1 +
 src/util/virstoragefile.h                          |  1 +
 tests/qemucapabilitiesdata/caps_2.10.0.aarch64.xml |  1 +
 tests/qemucapabilitiesdata/caps_2.10.0.ppc64.xml   |  1 +
 tests/qemucapabilitiesdata/caps_2.10.0.s390x.xml   |  1 +
 tests/qemucapabilitiesdata/caps_2.10.0.x86_64.xml  |  1 +
 tests/qemucapabilitiesdata/caps_2.11.0.s390x.xml   |  1 +
 tests/qemucapabilitiesdata/caps_2.11.0.x86_64.xml  |  1 +
 tests/qemucapabilitiesdata/caps_2.12.0.aarch64.xml |  1 +
 tests/qemucapabilitiesdata/caps_2.12.0.ppc64.xml   |  1 +
 tests/qemucapabilitiesdata/caps_2.12.0.s390x.xml   |  1 +
 tests/qemucapabilitiesdata/caps_2.12.0.x86_64.xml  |  1 +
 tests/qemucapabilitiesdata/caps_2.5.0.x86_64.xml   |  1 +
 tests/qemucapabilitiesdata/caps_2.6.0.aarch64.xml  |  1 +
 tests/qemucapabilitiesdata/caps_2.6.0.ppc64.xml    |  1 +
 tests/qemucapabilitiesdata/caps_2.6.0.x86_64.xml   |  1 +
 tests/qemucapabilitiesdata/caps_2.7.0.s390x.xml    |  1 +
 tests/qemucapabilitiesdata/caps_2.7.0.x86_64.xml   |  1 +
 tests/qemucapabilitiesdata/caps_2.8.0.s390x.xml    |  1 +
 tests/qemucapabilitiesdata/caps_2.8.0.x86_64.xml   |  1 +
 tests/qemucapabilitiesdata/caps_2.9.0.ppc64.xml    |  1 +
 tests/qemucapabilitiesdata/caps_2.9.0.s390x.xml    |  1 +
 tests/qemucapabilitiesdata/caps_2.9.0.x86_64.xml   |  1 +
 tests/qemucapabilitiesdata/caps_3.0.0.ppc64.xml    |  1 +
 tests/qemucapabilitiesdata/caps_3.0.0.riscv32.xml  |  1 +
 tests/qemucapabilitiesdata/caps_3.0.0.riscv64.xml  |  1 +
 tests/qemucapabilitiesdata/caps_3.0.0.s390x.xml    |  1 +
 tests/qemucapabilitiesdata/caps_3.0.0.x86_64.xml   |  1 +
 .../qemuxml2argvdata/disk-metadata_cache_size.args | 34 +++++++++++++++
 .../qemuxml2argvdata/disk-metadata_cache_size.xml  | 42 +++++++++++++++++++
 tests/qemuxml2argvtest.c                           |  2 +
 .../disk-metadata_cache_size.xml                   | 48 ++++++++++++++++++++++
 tests/qemuxml2xmltest.c                            |  2 +
 42 files changed, 235 insertions(+), 1 deletion(-)
 create mode 100644 tests/qemuxml2argvdata/disk-metadata_cache_size.args
 create mode 100644 tests/qemuxml2argvdata/disk-metadata_cache_size.xml
 create mode 100644 tests/qemuxml2xmloutdata/disk-metadata_cache_size.xml

-- 
1.8.3.1