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

[Fiona Ebner <f.ebner@proxmox.com>]

Am 23.06.26 um 4:06 PM schrieb Lukas Sichert:
> On 2026-06-22 10:51, Daniel Kral <d.kral@proxmox.com> wrote:
>> 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].
> 
> Already in src/PVE/QemuServer/Drive.pm in the qemu-server repo, this is
> checked and set accordingly.
> 
> Since detect-zeroes=unmap is essentially an extension of
> detect-zeroes=on [1], and detect-zeroes=unmap is currently the default
> when discard is enabled, I would keep this patch as is to preserve
> backward compatibility.

I also think it's fine to keep it as-is.