Re: [PATCH manager v3] fix #4503: ui: qemu: add detect zeroes disk option

["Daniel Kral" <d.kral@proxmox.com>]

On Fri Jun 19, 2026 at 1:01 PM CEST, David Riley wrote:
> On 6/18/26 1:49 PM, Lukas Sichert wrote:
>> When discard is enabled, qemu-server defaults to 'detect-zeroes=unmap'.
>> This can have a significant performance impact for zero writes on some
>> setups, while users might still want to keep guest discard/TRIM support
>> enabled.
>>
>> Allow configuring the option independently so 'discard' can stay enabled
>> while zero detection is disabled. Persist the checkbox state explicitly,
>> as the backend treats an absent value as default-enabled behavior,
>> resulting in 'detect-zeroes=unmap' when 'discard' is enabled.
>
> Thanks for submitting this patch.
>
> While it clearly addresses the performance issues reported in #4503
> [0], I was reading through the Bugzilla thread and noticed a request
> to support the third QEMU state for detect_zeroes [1]. Currently, the
> underlying parameter supports off, on, and unmap [2].
>
> Since we are already modifying this configuration in the UI, it might
> make sense to fully expose all three options to the user rather than
> just a binary toggle as there is a difference between "on" and
> "unmap".

This would need adapting the detect_zeroes option and parsing logic
(it's only boolean right now) so it can take any of the 3 valid values
by QEMU and be backwards compatible to the old values in our config.

This should probably also check the constraint that detect-zeroes=unmap
can only be set if discard=unmap, but the error message seems already be
quite clear for that [0].

[0] https://gitlab.com/qemu-project/qemu/-/blob/master/block.c?ref_type=heads#L1120

>
> [0] https://bugzilla.proxmox.com/show_bug.cgi?id=4503
> [1] https://bugzilla.proxmox.com/show_bug.cgi?id=4503#c8
> [2] https://www.qemu.org/docs/master/interop/qemu-storage-daemon-qmp-ref.html#enum-QSD-block-core.BlockdevDetectZeroesOptions
>
>> Link: https://bugzilla.proxmox.com/show_bug.cgi?id=4503
>> Signed-off-by: Lukas Sichert <l.sichert@proxmox.com>
>> ---
>>
>> Notes:
>>      changes from v2 to v3 (thanks @Fabian):
>>      - add a comment explaining why this property is handled differently from
>>        the others
>>      
>>      changes from v1 to v2:
>>      - added bug-numer to commit header
>>      - appended bug-link to commit body
>>
>>   www/manager6/qemu/HDEdit.js | 10 ++++++++++
>>   1 file changed, 10 insertions(+)
>>
>> [...]
>>