[$] Toward a reverse splice()

The splice()system call is, at its core, a write operation; it attempts to implementzero-copy I/O by moving pages from a pipe to a file. At the 2019 LinuxStorage, Filesystem, and Memory-Management Summit, Miklos Szeredi describeda nascent idea for rsplice() - a "reverse splice" system call.There were not a lot of definitive outcomes from this discussion, but onething was clear: rsplice() needs a much better description (andsome code posted) before the development community can begin to form anopinion on it.