svcadm(8)을 검색하려면 섹션에서 8 을 선택하고, 맨 페이지 이름에 svcadm을 입력하고 검색을 누른다.
lseek(2)
lseek(2) System Calls lseek(2)
NAME
lseek, llseek - move read/write file pointer
SYNOPSIS
#include <sys/types.h>
#include <unistd.h>
off_t lseek(int fildes, off_t offset, int whence);
offset_t llseek(int fildes, offset_t offset, int whence);
DESCRIPTION
The lseek() function sets the file pointer associated with the open
file descriptor specified by fildes as follows:
o If whence is SEEK_SET, the pointer is set to offset bytes.
o If whence is SEEK_CUR, the pointer is set to its current lo‐
cation plus offset.
o If whence is SEEK_END, the pointer is set to the size of the
file plus offset.
o If whence is SEEK_HOLE, the offset of the start of the next
hole greater than or equal to the supplied offset is re‐
turned. The definition of a hole is provided near the end of
the DESCRIPTION.
o 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 supplied offset.
The symbolic constants SEEK_SET, SEEK_CUR, SEEK_END, SEEK_HOLE, and
SEEK_DATA are defined in the header <unistd.h>.
Some devices are incapable of seeking. The value of the file pointer
associated with such a device is undefined.
The lseek() function allows the file pointer to be set beyond the ex‐
isting data in the file. If data are later written at this point, sub‐
sequent reads in the gap between the previous end of data and the newly
written data will return bytes of value 0 until data are written into
the gap.
If fildes is a remote file descriptor and offset is negative, lseek()
returns the file pointer even if it is negative. The lseek() function
will not, by itself, extend the size of a file.
If fildes refers to a shared memory object, lseek() behaves as if
fildes referred to a regular file.
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.
Applications should use fpathconf(_PC_MIN_HOLE_SIZE) or path‐
conf(_PC_MIN_HOLE_SIZE) to determine if a filesystem supports
SEEK_HOLE. See fpathconf(2).
For filesystems that do not supply information about holes, the file
will be represented as one entire data region.
The llseek() function operates similarly to the lseek() function, ex‐
cept that in 32-bit processes it sets the 64-bit extended file pointer
associated with the open file descriptor specified by fildes, instead
of a 32-bit file pointer. In 64-bit processes, the two functions oper‐
ate identically.
RETURN VALUES
Upon successful completion, the resulting offset, as measured in bytes
from the beginning of the file, is returned. Remote file descriptors
are the only ones that allow negative file pointers. Otherwise, −1 is
returned, the file offset remains unchanged, and errno is set to indi‐
cate the error.
ERRORS
The lseek() and llseek() functions will fail if:
EBADF The fildes argument is not an open file descriptor.
EINVAL The whence argument is not SEEK_SET, SEEK_CUR, SEEK_END,
SEEK_DATA, or SEEK_HOLE; or the fildes argument is not a re‐
mote file descriptor and the resulting file pointer would be
negative.
ENXIO For SEEK_DATA, there are no more data regions past the sup‐
plied offset. For SEEK_HOLE, there are no more holes past the
supplied offset.
ESPIPE The fildes argument is associated with a pipe, a FIFO, a
socket, or a STREAMS device.
The lseek() function will fail if:
EOVERFLOW The resulting file offset would be a value which cannot be
represented correctly in an object of type off_t for regu‐
lar files.
USAGE
The lseek() function has a transitional interface for 64-bit file off‐
sets. See lf64(7).
In multithreaded applications, using lseek() in conjunction with a
read(2) or write(2) call on a file descriptor shared by more than one
thread is not an atomic operation. To ensure atomicity, use pread() or
pwrite().
ATTRIBUTES
See attributes(7) for descriptions of the following attributes:
tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) ATTRIBUTE TYPEAT‐
TRIBUTE VALUE _ Interface StabilityCommitted _ MT-LevelAsync-Signal-
Safe _ StandardSee standards(7).
SEE ALSO
creat(2), dup(2), fcntl(2), fpathconf(2), open(2), read(2), write(2),
attributes(7), lf64(7), standards(7)
HISTORY
The SEEK_DATA and SEEK_HOLE operations were added to Solaris in the So‐
laris 10 6/06 (Update 2) release.
The llseek() function was added to Solaris in the Solaris 2.4 release.
The lseek() function and the SEEK_SET, SEEK_CUR, and SEEK_END opera‐
tions have been included in all Sun and Oracle releases of Solaris.
Oracle Solaris 11.4 30 Jan 2023 lseek(2)