On Mon, 10 Nov 2014 15:34:50 -0600 Bill Fischofer <[email protected]>
wrote:
> As noted before, the application stipulated headroom and tailroom are the
> minimums it expects to see honored. If they cannot be, then the allocation
> fails. The implementation is free to give more than requested, but not
> less.
If that is the case, users must express their alignment requirements
explicitly.
Think of the following user code:
headroom = 32; /* suffices for my uses */
headroom += 2; /* make sure ETH ends in a word aligned boundary */
odp_buffer_pool_set_headroom(pool, headroom);
Now, if implementation is _free_ to give "more than requested" in an
implementation-specific arbitrary fashion, then user's _implicit_
alignment requirement gets lost.
Point is, if NO alignment requirement parameter is passed, meaning user
utilizes the headroom parameter to tell the implementation where data
needs to be placed, then the implementation must place the data exactly
at the point specified by the user ("head" + headroom).
Or alternatively, if implementation is allowed to add its own arbitrary
headroom, then it must also follow user's requested alignment which must
be stated explicitly.
Regards,
Shmulik
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