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Top Forums UNIX for Advanced & Expert Users System Call Wrapper of 'open' Post 302328913 by fpmurphy on Thursday 25th of June 2009 12:35:59 PM
Old 06-25-2009
Perhaps the following will help you. Assuming you are using a 32-bit X86 2.6 Linux kernel .....

0x80 is the value of the software interrupt (INT) which performs the transfer to kernel mode via system_call(). See ../arch/x84/kernel/entry_32.S for the system_call() source.

The syscall interface for open() is defined in ../include/linux/syscalls.h
Code:
asmlinkage long sys_open(const char __user *filename, int flags, int mode);

The system call number for open is defined in ../arch/include/asm/unistd_32.h
Code:
#define __NR_open 5

 

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LLSEEK(2)						     Linux Programmer's Manual							 LLSEEK(2)

NAME
_llseek - reposition read/write file offset SYNOPSIS
#include <sys/types.h> #include <unistd.h> int _llseek(unsigned int fd, unsigned long offset_high, unsigned long offset_low, loff_t *result, unsigned int whence); Note: There is no glibc wrapper for this system call; see NOTES. DESCRIPTION
The _llseek() system call repositions the offset of the open file description associated with the file descriptor fd to (offset_high<<32) | offset_low bytes relative to the beginning of the file, the current file offset, or the end of the file, depending on whether whence is SEEK_SET, SEEK_CUR, or SEEK_END, respectively. It returns the resulting file position in the argument result. This system call exists on various 32-bit platforms to support seeking to large file offsets. RETURN VALUE
Upon successful completion, _llseek() returns 0. Otherwise, a value of -1 is returned and errno is set to indicate the error. ERRORS
EBADF fd is not an open file descriptor. EFAULT Problem with copying results to user space. EINVAL whence is invalid. CONFORMING TO
This function is Linux-specific, and should not be used in programs intended to be portable. NOTES
Glibc does not provide a wrapper for this system call. To invoke it directly, use syscall(2). However, you probably want to use the lseek(2) wrapper function instead. SEE ALSO
lseek(2), open(2), lseek64(3) COLOPHON
This page is part of release 4.15 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/. Linux 2017-09-15 LLSEEK(2)
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