[$] Printbuf rebuffed for now

There is a long and growing list of options for getting information out ofthe kernel but, in the real world, print statements still tend to be thetool of choice. The kernel's printk()function often comes up short, despite the fact that it provides a set ofkernel-specific features, so there has, for some time, been interest inbetter APIs for textual output from the kernel. The "printbuf"proposal from Kent Overstreet is one step in that direction, but willneed some changes to make it work well with features the kernel alreadyhas.