Function getnewbuf

freebsd/kern/vfs_bio.c:3276–3326

* getnewbuf: * * Find and initialize a new buffer header, freeing up existing buffers * in the bufqueues as necessary. The new buffer is returned locked. * * We block if: * We have insufficient buffer headers * We have insufficient buffer space * buffer_arena is too fragmented ( space reservation fails ) * If we have to flush dirty buffers ( but we try to avoid this ) * * The calle

 *	allocbuf() is called.
 */
static struct buf *
getnewbuf(struct vnode *vp, int slpflag, int slptimeo, int maxsize, int gbflags)
{
	struct bufdomain *bd;
	struct buf *bp;
	bool metadata, reserved;

	bp = NULL;
	KASSERT((gbflags & (GB_UNMAPPED | GB_KVAALLOC)) != GB_KVAALLOC,
	    ("GB_KVAALLOC only makes sense with GB_UNMAPPED"));
	if (!unmapped_buf_allowed)
		gbflags &= ~(GB_UNMAPPED | GB_KVAALLOC);

	if (vp == NULL || (vp->v_vflag & (VV_MD | VV_SYSTEM)) != 0 ||
	    vp->v_type == VCHR)
		metadata = true;
	else
		metadata = false;
	if (vp == NULL)
		bd = &bdomain[0];
	else
		bd = &bdomain[vp->v_bufobj.bo_domain];

	counter_u64_add(getnewbufcalls, 1);
	reserved = false;
	do {
		if (reserved == false &&
		    bufspace_reserve(bd, maxsize, metadata) != 0) {
			counter_u64_add(getnewbufrestarts, 1);
			continue;
		}
		reserved = true;
		if ((bp = buf_alloc(bd)) == NULL) {
			counter_u64_add(getnewbufrestarts, 1);
			continue;
		}
		if (getnewbuf_kva(bp, gbflags, maxsize) == 0)
			return (bp);
		break;
	} while (buf_recycle(bd, false) == 0);

	if (reserved)
		bufspace_release(bd, maxsize);
	if (bp != NULL) {
		bp->b_flags |= B_INVAL;
		brelse(bp);
	}
	bufspace_wait(bd, vp, gbflags, slpflag, slptimeo);

	return (NULL);
}

/*
 *	buf_daemon: