COP 4600 Operating Systems Fall 2010 Dan C
- Slides: 6
COP 4600 Operating Systems Fall 2010 Dan C. Marinescu Office: HEC 439 B Office hours: Tu-Th 3: 30 -4: 30 PM
Lecture 14 – Thursday October 7, 2010 n Last time: n n Today: n n ¨ Presentation of the RPC paper by Birell. Domain Name Service (DNS) Peer-to-peer systems Remote Procedure Calls NFS (Network File System) Virtualization: Threads, Virtual memory, Bounded buffers. Virtual Links Next time n Threads Lecture 14 2
Why file handles and not path names ----------------- Example 1 ------------------------ Program 1 on client 1 Program 2 on client 2 CHDIR (‘dir 1’) fd OPEN(“f”, READONLY) RENAME(‘dir 1’, ’dir 2) RENAME(‘dir 3’, ’dir 1’) READ(fd, buf, n) To follow the UNIX specification if both clients would be on the same system client 1 would read from dir 2. f. If the inode number allows the client 1 to follw the same semantics rather than read from dir 1/f ------------------ Example 2 -----------------------fd OPEN(“file 1”, READONLY) UNLINK(“f”) fd OPEN(“f”, CREATE) READ(fd, buf, n) 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 3
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Virtualization – relating physical with virtual objects n Virtualization simulating the interface to a physical object by: 1. 2. 3. 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 Resource Multiplexing processor thread real memory virtual memory communication channel virtual circuit processor server (e. g. , Web server) disk RAID core multi-core processor disk RAM disk system (e. g. Macintosh) virtual machine (e. g. , Virtual PC) real memory + disk virtual memory with paging communication channel + processor TCP protocol Aggregation Emulation Multiplexing + Emulation Lecture 14 6
