v2:
This version made some modifications. (include suggestion of Jonathon)
- rebase on master
- assume QEMU support discard and write-zeroes and drop the capability
introduction and probe
- add validation for options, only allowing attributes be configured for
VIRTIO bus
- enrich the test case
- update NEWS

Thanks Jonathon for pointing out the redundant commit in time.
Please review!

Yong

DISCARD and WRITE_ZEROES commands has been implemented in virtio-blk
protocol since qemu >= 4.2.0, may be it's time to introduce discard and
write-zeroes options for virtio-blk device in libvirt so that the upper
layer can enable this feature at disk granularity.
To distinguish the discard option in block drive layer, use the 'virtio'
prefix to indicate that these attributes are specific for virtio-blk
disk.
To try this out, three things has done in this patchset:
1. introduce capabilities of discard and write-zeroes for virtio-blk
2. add virtio_discard and virtio_write_zeroes attributes of driver in
disk xml element
3. generate cmd line when launching vm

Hyman Huang(黄勇) (3):
  conf: Add 'virtio_discard' and 'virtio_write_zeroes' attributes
  qemu_command: Generate cmd line for discard and write-zeroes
    properties
  NEWS: Mention support for discard and write_zeroes of virtio-blk
    device

 NEWS.rst                                      |  8 +++
 docs/formatdomain.rst                         |  8 +++
 src/conf/domain_conf.c                        | 16 +++++
 src/conf/domain_conf.h                        |  2 +
 src/conf/schemas/domaincommon.rng             | 10 ++++
 src/conf/storage_source_conf.c                |  2 +
 src/conf/storage_source_conf.h                |  2 +
 src/qemu/qemu_command.c                       |  2 +
 src/qemu/qemu_domain.c                        |  2 +
 src/qemu/qemu_driver.c                        |  4 +-
 src/qemu/qemu_validate.c                      |  9 +++
 src/vz/vz_utils.c                             | 12 ++++
 .../disk-virtio-discard.x86_64-latest.args    | 45 ++++++++++++++
 .../qemuxml2argvdata/disk-virtio-discard.xml  | 45 ++++++++++++++
 tests/qemuxml2argvtest.c                      |  1 +
 .../disk-virtio-discard.x86_64-latest.xml     | 58 +++++++++++++++++++
 tests/qemuxml2xmltest.c                       |  1 +
 17 files changed, 226 insertions(+), 1 deletion(-)
 create mode 100644 tests/qemuxml2argvdata/disk-virtio-discard.x86_64-latest.args
 create mode 100644 tests/qemuxml2argvdata/disk-virtio-discard.xml
 create mode 100644 tests/qemuxml2xmloutdata/disk-virtio-discard.x86_64-latest.xml

-- 
2.38.5