Re: [PATCH v3 2/3] Introduce migration precopy policy

[Jennifer Herbert <Jennifer.Herbert@citrix.com>]

On 26/09/17 11:58, Andrew Cooper wrote:
> On 25/09/17 19:55, Jennifer Herbert wrote:
>> +/*
>> + * A precopy_policy callback may not be running in the same address
>> + * space as libxc an so precopy_stats is passed by value.
>> + */
> Please take a step back and thing about what is written here...
>
> As I've said repeatedly, the structure vs pointer argument here is
> entirely unrelated to the IPC boundary.
>
> I am also unhappy that, after multiple review requests saying "turn this
> into a pointer", its remained being passed by value.  It is not ok to
> hack things like this up simply because its the easier cause of action.

Passing tiny structures by value is not a hack - it is perfectly valid 
C.  Bare in mind that a pointer is not a zero
sized entity - it itself needs to be copied.  Passing by value here is 
quite possibly faster, and use less memory.   Furthermore, the multiple 
reviews concluded that this was related to IPC boundary, and that the 
tiny struct size was acceptable.

Maybe you could elaborate on why you do not think it is related to the 
IPC boundary.

Instead, we could pass each element of the structure, as an individual 
parameters.  This would seem a retrograde
step to me, but  would address your sensitivities.

-jenny

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