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A high-level overview of the Linux kernel's system call interface, which handles communication between its various components and the userspace. In computing, a system call (commonly abbreviated to syscall) is the programmatic way in which a computer program requests a service from the operating system [a] on which it is executed.
For a process to start the execution of a different program, it first forks to create a copy of itself. Then, the copy, called the "child process", calls the exec system call to overlay itself with the other program: it ceases execution of its former program in favor of the other. The fork operation creates a separate address space for the ...
The putmsg and getmsg system calls were originally called send and recv, [5] but were renamed to avoid namespace conflict. [6] In System V Release 4, STREAMS was extended and used for the terminal I/O framework and pipes, providing useful new functionality like bidirectional pipes and file descriptor passing. [3] A port for UNICOS was also ...
A system call usually takes the form of a "system call vector", in which the desired system call is indicated with an index number. For instance, exit() might be system call number 1, and write() number 4. The system call vector is then used to find the desired kernel function for the request.
In Version 7, the number of system calls was only around 50, although later Unix and Unix-like systems would add many more: [23] Version 7 of the Research UNIX System provided about 50 system calls, 4.4BSD provided about 110, and SVR4 had around 120. The exact number of system calls varies depending on the operating system version.
In the Linux kernel, various subsystems, such as the Direct Rendering Manager (DRM), define their own system calls, all of which are part of the system call interface. Various issues with the organization of the Linux kernel system calls are being publicly discussed. Issues have been pointed out by Andy Lutomirski, Michael Kerrisk and others.
The number of system calls in Version 7 was only around 50, while later Unix and Unix-like systems continued to add many more: [5] Version 7 of the Research UNIX System provided about 50 system calls, 4.4BSD provided about 110, and SVR4 had around 120. The exact number of system calls varies depending on the operating system version.
select is a system call and application programming interface (API) in Unix-like and POSIX-compliant operating systems for examining the status of file descriptors of open input/output channels. [1] The select system call is similar to the poll facility introduced in UNIX System V and later