Vincent Hanquez wrote:
On 19/04/10 21:43, Andre Przywara wrote:
I am not fully convinced of this. There is quite a lot of information
copied (up to 4KB), and some fields (like pagesize or the version
numbers) are just plain integers. And this approach just propagates the
underlying design.
In the xl info implementation I used this feature to just get the
pagesize. One could think of just querying the version number, too. If
you don't like the additional parameter, what about a wrapping macro,
then?
I don't see the problem with the complexity, though, as it is hidden
inside the library.
The query mask is exposed to the user, and the structure is partially
filled. I can imagine that it's going to create those kind of issues,
where the wrong mask is passed, or change later, and then the field the
user was expecting would be left null.
The macro would help in the previous case, but I still feel it's
unnecessary. As a user, I would just not bother, and call the function
always with full mask, until I reach the optimisation phase, and its
appears on the graph.
A couple of K of data copied shouldn't make a difference, and would be
completely lost in noise, however if you really think it makes a
difference, you could have special dedicated info call to get specific
things like version number.
I just wanted to avoid introducing a lot of functions which could be
actually one. And if a user passes a wrong mask, then well, he is just
doing the wrong thing and cannot expect it to work. If Xen provides a
possibility to query single parts of the information, why should we hide
this capability from the upper layers?
Anyway, my plan was now to make the current mask function static and
create three exported functions, one for getting all the information,
one for getting the pagesize and one for getting the Xen version number
only. Together with a comment one could later expose the mask function
again if the need arises.
But when I was looking at the libxl_sprintf thing, I realized that all
the information in the info structure is static and will never change
during runtime. Am I right? If so, we can solve this whole thing by not
only storing the strings in libxl_ctx, but the whole structure. The
first call to the function would query all the members, subsequent calls
would just return the pointer. This avoids duplication should the
function be called multiple times. It would be automatically freed when
destroying the xl context.
What do you think of this?
Regards,
Andre.
--
Andre Przywara
AMD-Operating System Research Center (OSRC), Dresden, Germany
Tel: +49 351 448-3567-12
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