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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.
The write is one of the most basic routines provided by a Unix-like operating system kernel. It writes data from a buffer declared by the user to a given device, such as a file. This is the primary way to output data from a program by directly using a system call. The destination is identified by a numeric code.
The exec calls named ending with an e alter the environment for the new process image by passing a list of environment settings through the envp argument. This argument is an array of character pointers; each element (except for the final element) points to a null-terminated string defining an environment variable .
stat() is a Unix system call that returns file attributes about an inode. The semantics of stat() vary between operating systems. As an example, Unix command ls uses this system call to retrieve information on files that includes: atime: time of last access (ls -lu) mtime: time of last modification (ls -l) ctime: time of last status change (ls -lc)
The GNU C Library is a wrapper around the Linux kernel system call interface. A C standard library for Linux includes wrappers around the system calls of the Linux kernel; the combination of the Linux kernel system call interface and a C standard library is what builds the Linux API. Some popular implementations of the C standard library are glibc
Examples of this are the x86 calling conventions. Adhering to an ABI (which may or may not be officially standardized) is usually the job of a compiler, operating system, or library author. However, an application programmer may have to deal with an ABI directly when writing a program in a mix of programming languages, or even compiling a ...
For example, on 32-bit Windows, operating system calls have the stdcall calling convention, whereas many C programs that run there use the cdecl calling convention. To accommodate these differences in calling convention, compilers often permit keywords that specify the calling convention for a given function.
For most file systems, a program initializes access to a file in a file system using the open system call. This allocates resources associated to the file (the file descriptor), and returns a handle that the process will use to refer to that file. In some cases the open is performed by the first access.