[$] Reimplementing printk()

The venerable printk() function has been part of Linux since the verybeginning, though it has undergone a fair number of changes along the way.Now, John Ogness is proposing to fundamentally rework printk() inorder to get rid of handful of issues that currently plague it. The proposed code does thisby adding yet another ring-buffer implementation to the kernel; this one is aimed atmaking printk() work better from hard-to-handle contexts. Fora task that seems conceptually simple-printing messages to theconsole-printk() is actually a rather complex beast; that won'tchange if these patches are merged, though many of the problems with the current implementationwill be removed.