class PhysIter

PhysIter -- An iterator yielding physical address and size pairs of a buffer, given as a

(zx_paddr_t, size_t) pair. These iterated pairs are suitable for hardware DMA transactions that

consume a physical address and length of bytes. The buffer need not be backed by physically

contiguous chunks (more below), or be chunk-aligned. The iterator will ensure chunk boundaries

are not crossed in given (addr, size) pairs unless the origin VMO was pinned with

ZX_BTI_CONTIGUOUS in effect.

The chunk list is given as a list of zx_paddr_t values, which is chunk-count in size. These

values are typically taken from the result of zx_bti_pin().

Chunks -- When pinned, a VMO may be subject to the effects of either ZX_BTI_CONTIGUOUS or

ZX_BTI_COMPRESS. These flags affect the size of contiguous bytes pointed at by the returned

zx_paddr_t list. There are three possibilities:

1. If neither flag was supplied, the returned list entries will point to page-sized chunks.

2. If ZX_BTI_CONTIGUOUS was given, the list will contain a single entry, pointing at a sequence

of (physically) contiguous pages. The chunk size isn't used in this case.

3. If ZX_BTI_COMPRESS was given, the list entries will point to minimum-contiguity-sized

chunks. This is an internal parameter, chosen by the kernel, which may be looked up via

zx_object_get_info().

Because this implementation seeks to not cross applicable chunk boundaries, it needs to know what

the chunk sizing actually is. The chunk size is a parameter given during construction, and

should be commensurate with how the origin VMO was actually pinned.