1. COP 4600 Operating Systems Fall 2010
Dan C. Marinescu
Office: HEC 439 B
Office hours: Tu-Th 3:30-4:30 PM

2. Lecture 14 – Thursday October 7, 2010
Last time:
Presentation of the RPC paper by Birell.
Domain Name Service (DNS) Peer-to-peer systems
Remote Procedure Calls
Today:
NFS (Network File System)
Virtualization: Threads, Virtual memory, Bounded buffers.Virtual Links
Next time
Threads
Lecture 14

3. Why file handles and not path names
Example
Program 1 on client Program 2 on client 2
CHDIR (‘dir1’)
fd  OPEN(“f”, READONLY)
RENAME(‘dir1’,’dir2)
RENAME(‘dir3’,’dir1’)
READ(fd,buf,n)
To follow the UNIX specification if both clients would be on the same system client1 would read from dir2.f. If the inode number allows the client 1 to follw the same semantics rather than read from dir1/f
Example
fd  OPEN(“file1”, READONLY)
UNLINK(“f”)
fd  OPEN(“f”,CREATE)
If the NFS server reuses the inode of the old file then the RPC from client 2 will read from the new file created by client 1. The generation number allows the NSF server to distinguish between the old file opened by client 2 and the new one created by client 1.
Lecture 14

4. Lecture 14

5. Lecture 14

6. Virtualization – relating physical with virtual objects
Virtualization  simulating the interface to a physical object by:
Multiplexing  create multiple physical objects from one instance of a physical object.
Aggregation  create one virtual object from multiple physical objects
Emulation  construct a virtual object from a different type of a physical object. Emulation in software is slow.
Method
Physical
Resource
Virtual
Multiplexing
processor
thread
real memory
virtual memory
communication channel
virtual circuit
server (e.g., Web server)
Aggregation
disk
RAID
core
multi-core processor
Emulation
RAM disk
system (e.g. Macintosh)
virtual machine (e.g., Virtual PC)
Multiplexing + Emulation
real memory + disk
virtual memory with paging
communication channel +
TCP protocol
Lecture 14