[$] Two new ways to read a file quickly

System calls on Linux are relatively cheap, though the mitigations forspeculative-execution vulnerabilities have made them more expensive thanthey once were. But even cheap system calls add up if one has to make alarge number of them. Thus, developers have been working on ways to avoidsystem calls for a long time. Currently under discussion is a pair of waysto reduce the number of system calls required to read a file's contents,one of which is rather simpler than the other.