Re: [Xen-devel] [PATCH V2 3/6] [RFC] xen/common: Introduce _xrealloc function

[Oleksandr <olekstysh@xxxxxxxxx>]

Hi, Jan, Volodymyr.


> >   c. re-allocate struct with flexible buffer.
> >
> > option c. is about structures like this:
> >
> > struct arrlen
> > {
> >          size_t len;
> >          int data[1];
> > };
> >
> > This is Oleksandr's case.
> >
> > So for option a. we can use _xreallocate(ptr, size, align)
> > For option b. we can use xrealloc_array(_ptr, _type, _num)
> > And for option c. I propose to implement the following macro:
> >
> > #define realloc_flex_struct(_ptr, _type, _field, 
> > _len)                        \
> >   ((_type *)_xrealloc(_ptr, offsetof(_type, _field[_len]) , 
> > __alignof__(_type)))
> > It can be used in the following way:
> >
> > newptr = realloc_flex_struct(ptr, struct arrlen, newsize);
> >
> > As you can see, this approach is type-safe and covers Oleksanrd's case.
> This looks fine to me, but then wants to be accompanied by a
> similar xmalloc_flex_struct(), which could be used right away
> to replace a number of open-coded instances of the above.
Thank you Volodymyr for the idea. Looks like we can get a type-safe 
approach which looks suitable for my particular case.
So, I need to focus on the proper implementation of non type-safe 
(_xrealloc) variant in the first place taking into the account Jan's 
comments. Then I will be back to the suggested type-safe marco 
(realloc_flex_struct).

> There's one more thing for the re-alloc case though (besides
> cosmetic aspects): The incoming pointer should also be verified
> to be of correct type.
Jan, how this could be technically implemented, or are these any 
existing examples in Xen?

> Jan
--
Regards,

Oleksandr Tyshchenko


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