6.1 Where are the read and write attributes of an open file descriptor stored?
6.2 Why is the close-on-exec bit located in the per-process descriptor table instead of in the system file table?
6.3 Why are the file-table entries reference counted?
6.4 What three shortcomings of lock files are addressed by the FreeBSD descriptor-locking facilities?
6.5 What two problems are raised by mandatory locks?
6.6 Why is the implementation of select split between the descriptor-management code and the lower-level routines?
6.7 Describe how the process selecting flag is used in the implementation of select.
6.8 The syncer daemon starts as part of system boot. Once every second, it does an fsync on any vnodes that it finds that have been dirty for 30 seconds. What problem could arise if this daemon were not run?
6.9 When is a vnode placed on the free list?
6.10 Why must the lookup routine call through the vnode interface once for each component in a pathname?
6.11 Give three reasons for revoking access to a vnode.
6.12 Why are the buffer headers allocated separately from the memory that holds the contents of the buffer?
6.13 Asynchronous I/O is provided through the aio_read and aio_write systems calls rather than through the traditional read and write system calls. What problems arise with providing asynchronous I/O in the existing read-write interface?
*6.14 Why are there both a CLEAN list and a DIRTY list instead of all buffers being managed on one list?
*6.15 If a process reads a large file, the blocks of the file will fill the virtual memory cache completely, flushing out all other contents. All other processes in the system then will have to go to disk for all their filesystem accesses. Write an algorithm to control the purging of the buffer cache.
*6.16 Vnode operation parameters are passed between layers in structures. What alternatives are there to this approach? Explain why your approach is more or less efficient, compared to the current approach, when there are less than five layers in the stack. Also compare the efficiency of your solution when there are more than five layers in the stack.
