FSSH_B_PAGE_SIZE
#define B_PAGE_SIZE FSSH_B_PAGE_SIZE
int32_t pageOffset = offset & (FSSH_B_PAGE_SIZE - 1);
const uint32_t kMaxChunkSize = MAX_IO_VECS * FSSH_B_PAGE_SIZE;
fssh_size_t(FSSH_B_PAGE_SIZE - pageOffset), bytesLeft);
offset += FSSH_B_PAGE_SIZE;
#define PAGE_ALIGN(x) (((x) + (FSSH_B_PAGE_SIZE - 1)) & ~(FSSH_B_PAGE_SIZE - 1))