Re: [Qemu-devel] container_of() vs DO_UPCAST() (was: [PATCH 2/3] Clean up upcast from PCIDevice to I6300State)

[Paul Brook]

On Monday 24 August 2009, Markus Armbruster wrote:
> We got container_of() in osdep.h.
>
> We also got DO_UPCAST() in qdev.h.  Odd place, as it's not really
> specific to qdev (except for the naming of the last parameter).  It
> takes the same parameters as container_of(), but in a different order,
> which I find needlessly confusing.  The last parameter is insufficiently
> parenthesized in the macro expansion.  Finally, I don't really like the
> name --- I find container_of() much clearer --- but that's just me.
>
> Why do we have two macros to do essentially the same thing?
>
> When should container_of() be used, and when DO_UPCAST()?

DO_UPCAST requires that the child object be at offset zero.

Paul