Re: [Qemu-devel] [RFC 1/3] block: Add ImageRotationalInfo

[Alberto Garcia]

On Mon 27 May 2019 02:16:53 PM CEST, Max Reitz wrote:
> On 26.05.19 17:08, Alberto Garcia wrote:
>> On Fri 24 May 2019 07:28:10 PM CEST, Max Reitz <address@hidden> wrote:
>>> +##
>>> +# @ImageRotationalInfo:
>>> +#
>>> +# Indicates whether an image is stored on a rotating disk or not.
>>> +#
>>> +# @solid-state: Image is stored on a solid-state drive
>>> +#
>>> +# @rotating:    Image is stored on a rotating disk
>> 
>> What happens when you cannot tell? You assume it's solid-state?
>
> When *I* cannot tell?  This field is generally optional, so in that case
> it just will not be present.
>
> (When Linux cannot tell?  I don’t know :-))
>
> Do you think there should be an explicit value for that?

I'll try to rephrase:

we have a new optimization that improves performance on SSDs but reduces
performance on HDDs, so this series would detect where an image is
stored in order to enable the faster code path for each case.

What happens if QEMU cannot detect if we have a solid drive or a
rotational drive? (e.g. a remote storage backend). Will it default to
enabling preallocation using write_zeroes()?

Berto