text stringlengths 139 4.06k | source stringlengths 16 26 |
|---|---|
42 INTRODUCTION CHAP. 1 nice, clean abstract model of device-independent files. System calls are obviously needed to create files, remove files, read files, and write files. Before a file can be read, it must be located on the disk and opened, and after being read it should be closed, so calls are provided to do these ... | OS_Page_42_Chunk42 |
SEC. 1.5 OPERATING SYSTEM CONCEPTS 43 access a child process, but mechanisms nearly always exist to allow files and direc- tories to be read by a wider group than just the owner. Every file within the directory hierarchy can be specified by giving its path name from the top of the directory hierarchy, the root director... | OS_Page_43_Chunk43 |
44 INTRODUCTION CHAP. 1 Root CD-ROM a b c d c d a b x y x y (a) (b) Figure 1-15. (a) Before mounting, the files on the CD-ROM are not accessible. (b) After mounting, they are part of the file hierarchy. Another important concept in UNIX is the special file. Special files are pro- vided in order to make I/O devices look... | OS_Page_44_Chunk44 |
SEC. 1.5 OPERATING SYSTEM CONCEPTS 45 1.5.4 Input/Output All computers have physical devices for acquiring input and producing output. After all, what good would a computer be if the users could not tell it what to do and could not get the results after it did the work requested? Many kinds of input and output devices ... | OS_Page_45_Chunk45 |
46 INTRODUCTION CHAP. 1 between a user sitting at his terminal and the operating system, unless the user is using a graphical user interface. Many shells exist, including sh, csh, ksh, and bash. All of them support the functionality described below, which derives from the orig- inal shell (sh). When any user logs in, a... | OS_Page_46_Chunk46 |
SEC. 1.5 OPERATING SYSTEM CONCEPTS 47 1.5.7 Ontogeny Recapitulates Phylogeny After Charles Darwin’s book On the Origin of the Species was published, the German zoologist Ernst Haeckel stated that ‘‘ontogeny recapitulates phylogeny.’’ By this he meant that the development of an embryo (ontogeny) repeats (i.e., reca- pit... | OS_Page_47_Chunk47 |
48 INTRODUCTION CHAP. 1 is not always crucial because network delays are so great that they tend to domi- nate. Thus the pendulum has already swung several cycles between direct execu- tion and interpretation and may yet swing again in the future. Large Memories Let us now examine some historical developments in hardwa... | OS_Page_48_Chunk48 |
SEC. 1.5 OPERATING SYSTEM CONCEPTS 49 hardware was added and multiprogramming became possible. Until this day, many embedded systems have no protection hardware and run just a single program. Now let us look at operating systems. The first mainframes initially had no protection hardware and no support for multiprogramm... | OS_Page_49_Chunk49 |
50 INTRODUCTION CHAP. 1 40 cm in diameter and 5 cm high. But it, too, had a single-level directory initially. When microcomputers came out, CP/M was initially the dominant operating sys- tem, and it, too, supported just one directory on the (floppy) disk. Virtual Memory Virtual memory (discussed in Chap. 3) gives the a... | OS_Page_50_Chunk50 |
SEC. 1.6 SYSTEM CALLS 51 mechanics of issuing a system call are highly machine dependent and often must be expressed in assembly code, a procedure library is provided to make it possible to make system calls from C programs and often from other languages as well. It is useful to keep the following in mind. Any single-C... | OS_Page_51_Chunk51 |
52 INTRODUCTION CHAP. 1 Return to caller 4 10 6 0 9 7 8 3 2 1 11 Dispatch Sys call handler Address 0xFFFFFFFF User space Kernel space (Operating system) Library procedure read User program calling read Trap to the kernel Put code for read in register Increment SP Call read Push fd Push &buffer Push nbytes 5 Figure 1-17... | OS_Page_52_Chunk52 |
SEC. 1.6 SYSTEM CALLS 53 does, the compiled code increments the stack pointer exactly enough to remove the parameters pushed before the call to read. The program is now free to do whatever it wants to do next. In step 9 above, we said ‘‘may be returned to the user-space library procedure’’ for good reason. The system c... | OS_Page_53_Chunk53 |
54 INTRODUCTION CHAP. 1 Process management Call Description pid = for k( ) Create a child process identical to the parent pid = waitpid(pid, &statloc, options) Wait for a child to terminate s = execve(name, argv, environp) Replace a process’ core image exit(status) Ter minate process execution and return status File ma... | OS_Page_54_Chunk54 |
SEC. 1.6 SYSTEM CALLS 55 the parent executes a waitpid system call, which just waits until the child terminates (any child if more than one exists). Waitpid can wait for a specific child, or for any old child by setting the first parameter to −1. When waitpid completes, the address pointed to by the second parameter, s... | OS_Page_55_Chunk55 |
56 INTRODUCTION CHAP. 1 The main program of cp (and main program of most other C programs) con- tains the declaration main(argc, argv, envp) where argc is a count of the number of items on the command line, including the program name. For the example above, argc is 3. The second parameter, argv, is a pointer to an arra... | OS_Page_56_Chunk56 |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.