_llseek(2) System Calls Manual _llseek(2)

_llseek - reposition read/write file offset

Standard C library (libc, -lc)

#include <sys/syscall.h>      /* Definition of SYS_* constants */
#include <unistd.h>
int syscall(SYS__llseek, unsigned int fd, unsigned long offset_high,
            unsigned long offset_low, loff_t *result,
            unsigned int whence);

Note: glibc provides no wrapper for _llseek(), necessitating the use of syscall(2).

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.

Upon successful completion, _llseek() returns 0. Otherwise, a value of -1 is returned and errno is set to indicate the error.

fd is not an open file descriptor.
Problem with copying results to user space.
whence is invalid.

You probably want to use the lseek(2) wrapper function instead.


lseek(2), open(2), lseek64(3)

2024-05-02 Linux man-pages 6.9.1