posix_fallocate Subroutine

Purpose

Reserve storage space for a given file descriptor.

Syntax

 #include <fcntl.h>
int posix_fallocate (int fd, off_t offset, off_t len);

Description

This function reserves adequate space on the file system for the file data range beginning at the value specified by the offset parameter and continuing for the number of bytes specified by the len parameter. Upon successful return, subsequent writes to this file data range will not fail due to lack of free space on the file system media. Space allocated by the posix_fallocate subroutine can be freed by a successful call to the creat subroutine or open subroutine, or by the ftruncate subroutine, which truncates the file size to a size smaller than the sum of the offset parameter and the len parameter.

Note: Incase of return error code EFBIG and ENOSPC, the posix_fallocate subroutine might do partial allocation based on maximum file size or free space available on the file system.

Parameters

Item	Description
fd	File descriptor of the file toreserve
offset	Represents the beginning of the address range
len	Determines the length of the address range

Return Values

Upon successful completion, the posix_fallocate subroutine returns 0. Otherwise, one of the following error codes will be returned.

Error Codes

Item	Description
EBADF	The fd parameter is not a valid file descriptor
EBADF	The fd parameter references a file that was opened without write permission.
EFBIG	The value of the offset parameter plus the len parameter is greater than the maximum file size
EINTR	A signal was caught during execution
EIO	An I/O error occurred while reading from or writing to a file system
ENODEV	The fd parameter does not refer to a regular file.
EINVAL	The value of the advice parameter is invalid.
ENOSPC	There is insufficient free space remaining on the file system storage media
ESPIPE	The fd parameter is associated with a pipe of FIFO
ENOTSUP	The underlying file system is not supported