44 Conversion Of A Path Name To An Inode
The initial access to a file is by its path name, as in the open, chdir change directory , or link system calls. Because the kernel works internally with inodes rather than with path names, it converts the path names to inodes to access files. The algorithm namei parses the path name one component at a time, converting each component into an inode based on its name and the directory being searched, and eventually returns the inode of the input path name Figure 4.11 . Recall from Chapter 2 that...
I Mvg
caller will increment region reference count with subsequent attachreg call return input region pointer allocate new region algorithm allocreg set up auxiliary memory management structures, as currently exists in input region allocate physical memory for region contents copy region contents from input region to newly allocated region return pointer to allocated region The fork system call requires that the kernel duplicate the regions of a process. If a region is shared shared text or shared...
I Yiw
if there are no buffers on free list scenario 4 sleep event any buffer becomes free continue back to while loop if buffer marked for delayed write scenario 3 asynchronous write buffer to disk continue back to while loop scenario 2 found a free buffer remove buffer from old hash queue put buffer onto new hash queue return buffer Figure 3.4. Algorithm for Buffer Allocation b Remove Block 4 from Free List Figure 3.5. Scenario 1 in Finding a Buffer Buffer on Hash Queue algorithm brelse input locked...
122 Solution With Master And Slave Processors
Goble implemented a system on a pair of modified VAX 11 780 machines where one processor, called the master, can execute in kernel mode and the other processor, called 'he slave, executes only in user mode see Goble 81 . Although Gobles implementation contained two machines, the technique extends to systems with one master and several slaves. The master processor is responsible for handling all system calls and interrupts. . Slave processors execute processes in user mode and inform the master...
32 Structure Of The Buffer Pool
The kernel caches data in the buffer pool according to a least recently used algorithm after it allocates a buffer to a disk block, it cannot use the buffer for another block until all other buffers have been used more recently. The kernel maintains a free list of buffers that preserves the least recently used order. The free list is a doubly linked circular list of buffers with a dummy buffer header that marks its beginning and end Figure 3.2 . Every buffer is put on the free list when the...
516 Unlink
The unlink system call removes a directory entry for a file. The syntax for the unlink call is where pathname identifies the name of the file to be unlinked from the directory hierarchy. If a process unlinks, a given file, no file is accessible by that name until another directory entry with that name is created. In the following code fragment, for example, fd open myfile, O RDONLY the open call should fail, because the current directory no longer contains a file called myfile. If the file...
V Leu
V semaphore operation, 372, 389, 396-403, Valid bit, 287, 296-298. 301, 303, 304, 306, 307, 310 software, 306, 307 Valid page, 294 Validity fault, 286, 296, 298, 300, 301, 304 Validity fault handler, 293, 298, 299, 301, 305, 309 interaction with protection fault handler, 306 VAX, 171, 189, 205, 206, 306, 307, 310, 321, 393 Version 6, 282 Version 7, 144 Vfault, algorithm, See Validity fault handler Vfork, 291, 292, 309 Vhand, See Page stealer Virtual address, 18, 158, 189, 278, 298 Virtual...
78 The Shell
This chapter has covered enough material to explain how the shell works. The shell is more complex than described here, but the process relationships are illustrative of the real program. Figure 7.28 shows the main loop of the shell and demonstrates asynchronous execution, redirection of output, and pipes. The shell reads a command line from its standard input and interprets it according to a fixed set of rules. The standard input and standard output file descriptors for the login shell are...
I Fuq
Figure 5.37. A Ha If-Baked Directory 15. Write a program that prints the owner, file type, access permissions, and access times of files supplied as parameters. If a file parameter is a directory, the program should read the directory and print the above information for all files in the directory. 16. Suppose a directory has read permission for a user but not execute permission. What happens when the directory is used as a parameter to Is with the i option What about the ' option Explain the...
n I
if read fd, buf, sizeof buf gt 0 printf read at n d n, n n else no data read returns due to nor-delay n It is sometimes convenient to poll a device, that is, to read it if there is data present but to continue regular processing otherwise. The program in Figure 10.18 illustrates this case By opening the terminal with the no delay option, subsequent reads will not sleep if there is no data present but will return immediately refer to algorithm terminal_read, Figure 10.15 . Such a method also...
12 System Structure
Figure 1.1 depicts the high-level architecture of the UNIX system. The hardware at the center of the diagram provides the operating system with basic services that will be described in Section 1.5, The operating system interacts directly3 with the hardware, providing common services to programs and insulating them from hardware idiosyncrasies. Viewing the system as a set of layers, the operating system is commonly called the system kernel, or just the kernel, emphasizing its 3. In some...
31 Buffer Headers
During system initialization, the kernel allocates space for a number of buffers, configurable according to memory size and system performance constraints. A buffer consists of two parts a memory array that contains data from the disk and a buffer header that identifies the buffer. Because there is a one to one mapping of buffer headers to data arrays, the ensuing text will frequently refer to both parts as a buffer, and the context should make clear which part is being discussed. The data in a...
33 Scenarios For Retrieval Of A Buffer
As seen in Figure 2.1, high-level kernel algorithms in the file subsystem invoke the algorithms for managing the buffer cache. The high-level algorithms determine the logical device number and block number that they wish to access when they attempt to retrieve a block. For example, if a process wants to read data from a file, the kernel determines which file system contains the file and which block in the file system contains the data, as will be seen in Chapter 4. When about to read data from...
Info Ecj
external to a process. Exceptions happen in the middle of the execution of an instruction, and the system attempts to restart the instruction after handling the exception interrupts are considered to happen between the execution of two instructions, and the system continues with the next instruction after servicing the interrupt. The UNIX system uses one mechanism to handle interrupts and exception conditions. The kernel must sometimes prevent the occurrence of interrupts during critical...