Function bp_unmapped_get_kva

freebsd/kern/vfs_bio.c:3769–3822

* Allocate the KVA mapping for an existing buffer. * If an unmapped buffer is provided but a mapped buffer is requested, take * also care to properly setup mappings between pages and KVA. */

 * also care to properly setup mappings between pages and KVA.
 */
static void
bp_unmapped_get_kva(struct buf *bp, daddr_t blkno, int size, int gbflags)
{
	int bsize, maxsize, need_mapping, need_kva;
	off_t offset;

	need_mapping = bp->b_data == unmapped_buf &&
	    (gbflags & GB_UNMAPPED) == 0;
	need_kva = bp->b_kvabase == unmapped_buf &&
	    bp->b_data == unmapped_buf &&
	    (gbflags & GB_KVAALLOC) != 0;
	if (!need_mapping && !need_kva)
		return;

	BUF_CHECK_UNMAPPED(bp);

	if (need_mapping && bp->b_kvabase != unmapped_buf) {
		/*
		 * Buffer is not mapped, but the KVA was already
		 * reserved at the time of the instantiation.  Use the
		 * allocated space.
		 */
		goto has_addr;
	}

	/*
	 * Calculate the amount of the address space we would reserve
	 * if the buffer was mapped.
	 */
	bsize = vn_isdisk(bp->b_vp) ? DEV_BSIZE : bp->b_bufobj->bo_bsize;
	KASSERT(bsize != 0, ("bsize == 0, check bo->bo_bsize"));
	offset = blkno * bsize;
	maxsize = size + (offset & PAGE_MASK);
	maxsize = imax(maxsize, bsize);

	while (bufkva_alloc(bp, maxsize, gbflags) != 0) {
		if ((gbflags & GB_NOWAIT_BD) != 0) {
			/*
			 * XXXKIB: defragmentation cannot
			 * succeed, not sure what else to do.
			 */
			panic("GB_NOWAIT_BD and GB_UNMAPPED %p", bp);
		}
		counter_u64_add(mappingrestarts, 1);
		bufspace_wait(bufdomain(bp), bp->b_vp, gbflags, 0, 0);
	}
has_addr:
	if (need_mapping) {
		/* b_offset is handled by bpmap_qenter. */
		bp->b_data = bp->b_kvabase;
		BUF_CHECK_MAPPED(bp);
		bpmap_qenter(bp);
	}
}

struct buf *
getblk(struct vnode *vp, daddr_t blkno, int size, int slpflag, int slptimeo,