many times it will be the case that an allocation for a block of data
needs to be done in one alloc() call such that the members of a struct as well
as some extra trailing data are all in the same allocation like
```
struct Test {
unsigned a[4];
unsigned c;
};
unsigned *b; //ptr to uint[8]
```
should be allocated as a single block of (13 * sizeof(unsigned)) memory using
C pointer offsets to allocate the memory as
```
| Test | b |
```
with something like
```
struct Test *t = malloc(sizeof(struct Test) + (8 * sizeof(unsigned)));
```
and then set `b` with
```
t->b = ((uint8_t*)t) + sizeof(struct Test);
```
this is annoying, awful to read, and (at least for dum-dums like me) prone to errors,
however, so having some utility functions which can deliver the same
functionality with better readability helps out this case by transforming it to
```
unsigned *b;
void **ptrs[] = {(void*)&b};
size_t sizes[] = {8 * sizeof(unsigned));
struct Test *t = ptralloc(sizeof(struct Test), 1, sizes, ptrs);
```
where `b` is now set to the appropriate offset in memory
Acked-by: Dave Airlie <airlied@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/13678>
Erik Faye-Lund
Yonggang Luo
Mike Blumenkrantz