[PATCH v2 1/2] conf: add support for discard_granularity

[Peter Krempa]

On Fri, Aug 25, 2023 at 13:52:14 +0200, Kristina Hanicova wrote:
> This introduces the ability to set the discard granularity option
> for a disk.  It defines the smallest amount of data that can be
> discarded in a single operation (useful for managing and
> optimizing storage).
> 
> Signed-off-by: Kristina Hanicova <khanicov at redhat.com>
> ---
>  docs/formatdomain.rst             |  6 +++++-
>  src/conf/domain_conf.c            | 19 ++++++++++++++++++-
>  src/conf/domain_conf.h            |  1 +
>  src/conf/domain_validate.c        |  3 ++-
>  src/conf/schemas/domaincommon.rng |  5 +++++
>  src/qemu/qemu_domain.c            |  2 ++
>  6 files changed, 33 insertions(+), 3 deletions(-)
> 
> diff --git a/docs/formatdomain.rst b/docs/formatdomain.rst
> index cd9cb02bf8..0d0812f08c 100644
> --- a/docs/formatdomain.rst
> +++ b/docs/formatdomain.rst
> @@ -2588,7 +2588,7 @@ paravirtualized driver is specified via the ``disk`` element.
>         <driver name='qemu' type='raw'/>
>         <source dev='/dev/sda'/>
>         <geometry cyls='16383' heads='16' secs='63' trans='lba'/>
> -       <blockio logical_block_size='512' physical_block_size='4096'/>
> +       <blockio logical_block_size='512' physical_block_size='4096' discard_granularity='4096'/>
>         <target dev='hdj' bus='ide'/>
>       </disk>
>       <disk type='volume' device='disk'>
> @@ -3435,6 +3435,10 @@ paravirtualized driver is specified via the ``disk`` element.
>        this would be the value returned by the BLKPBSZGET ioctl and describes the
>        disk's hardware sector size which can be relevant for the alignment of
>        disk data.
> +   ``discard_granularity``
> +      The smallest amount of data that can be discarded in a single operation.
> +      It impacts the unmap operations and it must be a multiple of a
> +      ``logical_block_size``.

Add a note that most hypervisors select the proper setting and users
don't really need to tweak this.

Reviewed-by: Peter Krempa <pkrempa at redhat.com>