llseek(2) System Calls llseek(2)NAMEllseek - move extended read/write file pointer
SYNOPSIS
#include <sys/types.h>
#include <unistd.h>
offset_t llseek(int fildes, offset_t offset, int whence);
DESCRIPTION
The llseek() function sets the 64-bit extended file pointer associated
with the open file descriptor specified by fildes as follows:
· If whence is SEEK_SET, the pointer is set to offset bytes.
· If whence is SEEK_CUR, the pointer is set to its current location
plus offset.
· If whence is SEEK_END, the pointer is set to the size of the file
plus offset.
· If whence is SEEK_HOLE, the offset of the start of the next hole
greater than or equal to the supplied offset is returned. The def‐
inition of a hole immediately follows this list.
· If whence is SEEK_DATA, the file pointer is set to the start of
the next non-hole file region greater than or equal to the sup‐
plied offset.
A "hole" is defined as a contiguous range of bytes in a file, all hav‐
ing the value of zero, but not all zeros in a file are guaranteed to be
represented as holes returned with SEEK_HOLE. Filesystems are allowed
to expose ranges of zeros with SEEK_HOLE, but not required to. Applica‐
tions can use SEEK_HOLE to optimise their behavior for ranges of zeros,
but must not depend on it to find all such ranges in a file. The exis‐
tence of a hole at the end of every data region allows for easy pro‐
gramming and implies that a virtual hole exists at the end of the file.
For filesystems that do not supply information about holes, the file
will be represented as one entire data region.
Although each file has a 64-bit file pointer associated with it, some
existing file system types (such as tmpfs) do not support the full
range of 64-bit offsets. In particular, on such file systems, non-
device files remain limited to offsets of less than two gigabytes.
Device drivers may support offsets of up to 1024 gigabytes for device
special files.
Some devices are incapable of seeking. The value of the file pointer
associated with such a device is undefined.
RETURN VALUES
Upon successful completion, llseek() returns the resulting pointer
location as measured in bytes from the beginning of the file. Remote
file descriptors are the only ones that allow negative file pointers.
Otherwise, −1 is returned, the file pointer remains unchanged, and
errno is set to indicate the error.
ERRORS
The llseek() function will fail if:
EBADF The fildes argument is not an open file descriptor.
EINVAL The whence argument is not SEEK_SET, SEEK_CUR, or
SEEK_END; the offset argument is not a valid offset for
this file system type; or the fildes argument is not a
remote file descriptor and the resulting file pointer
would be negative.
ENXIO For SEEK_DATA, there are no more data regions past the
supplied offset. For SEEK_HOLE, there are no more holes
past the supplied offset.
ESPIPE The fildes argument is associated with a pipe or FIFO.
SEE ALSOcreat(2), dup(2), fcntl(2), lseek(2), open(2)SunOS 5.10 1 Apr 2005 llseek(2)
