Now that you've implemented the OS/161 system calls, let's improve their performance. Might as well start with getpid(), since it's simple. First, brie?y explain the overhead of performing a call to getpid() (1 point). Second, propose a way to reduce this overhead by exploiting properties of the getpid() system call . Finally, will this improve performance? If so, why? If not, why not? Justify
your answer
2.Versioning is an attractive feature for ?lesystems to provide. It means that not only does the ?lesystem provide access to the most recent ?le content through the familiar API, but also uses available disk space to store older version of ?les and directories as well as deleted ?les and directories.
Let's consider how to add this feature to the traditional hierarchical ?lesystem designs we've discussed. Here are design requirements for Our Versioned Filesystem (OVFS):
-OVFS does not track every change to every ?le. Instead, it creates periodic snapshots that record the state of the ?lesystem at a particular point in time
-OVFS provides access to old ?le versions without changing the familiar UNIX ?le API-through open(), close(), read()-with the exception that old ?le versions cannot be written to, only read from. (Attempts to open ?le versions with write permissions or perform writes can fail with an error.)
-OVFS utilizes all available space to store old ?le versions. Once the disk capacity is reached, it should apply a reasonable policy to remove old versions and create space for new ?le content.
Present a design for OVFS. First, describe changes to ?lesystem naming required to support #7 without causing undue interference to users' abilities to name ?les normally Second, describe how to perform a snapshot to store old ?le versions. Keep in mind that other ?le activity may be taking place, and consider whether you can provide a coherent snapshot of the entire ?lesystem at an exact moment in time or something more approximate.
Third, present a default policy for removing old ?le versions and argue why it is an appropriate default.
Finally, describe one performance or storage optimization that you can implement in OVFS to either reduce the disk activity or storage overhead of ?le versioning compared with the simplest approach