Commit 48ee0d11 authored by Charlie Jacobsen's avatar Charlie Jacobsen

static-cptr-cache: Changes cptr cache defs to use statically alloc'd bmaps.

That is, the bitmaps are now arrays inside the cptr cache, rather
than pointers. We need this for LCDs because the cptr cache needs
to be up and running before we even initialize the page allocator
and malloc.

I need to tweak the code slightly next.

Note: I considered using a packed struct for cptr's, with char
fields. But I realized the allocation algorithm would become a little
less efficient, due to extra required calculations. The advantage of
the current algorithm is that, because the cnode table size is
a power of 2 *and* the bits are packed (they would no longer be
packed if we used chars, unless the cnode table size was 512), translating
a bitmap index to a path in the cspace radix tree is really simple.
If we switched to a struct with char's, such as:

    struct cptr {
       char level;
       char path[CAP_CSPACE_DEPTH];
       char slot;

we would need to do a handful of bit shifts and masks to set up
these fields properly. (For the current algorithm, there's just
one bitwise OR to set the level bits.)

I also realized the bit-level ops we currently use are not that
bad/obscure. We just sacrifice a slight amount of clarity.
parent 96adabf2
Pipeline #390 skipped