llseek (2) - Linux Manuals

llseek: reposition read/write file offset

Command to display llseek manual in Linux: $ man 2 llseek

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

Note: for information about the llseek(3) library function, see lseek64(3).

The _llseek() system call repositions the offset of the open file description associated with the file descriptor fd to the value

: (offset_high << 32) | offset_low

This new offset is a byte offset 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.

The new file offset is returned in the argument result. The type loff_t is a 64-bit signed type.

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.

COLOPHON

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