[$] SPDX identifiers in the kernel

Observers of the kernel's commit stream or mailing lists will have seen acertain amount of traffic referring to the addition of SPDX licenseidentifiers to kernel source files. For many, this may be their first encounter with SPDX. Butthe SPDX effort has been going on for some years; this article describesSPDX, along with why and how the kernel community intends to use it.