int posix_fallocate(int fd, off_toffset,
The posix_fallocate() function shall ensure that any required
storage for regular file data starting at offset and
continuing for len bytes is allocated on the file system storage
media. If posix_fallocate() returns successfully,
subsequent writes to the specified file data shall not fail due to
the lack of free space on the file system storage media.
If the offset+ len is beyond the current file size, then
posix_fallocate() shall adjust the file size to
offset+ len. Otherwise, the file size shall not be changed.
It is implementation-defined whether a previous posix_fadvise()
influences allocation strategy.
Space allocated via posix_fallocate() shall be freed by a successful
call to creat() or open() that truncates the size of the
file. Space allocated via posix_fallocate() may be freed by
a successful call to ftruncate() that reduces the file size
to a size smaller than offset+
Upon successful completion, posix_fallocate() shall return zero;
otherwise, an error number shall be returned to indicate
The posix_fallocate() function shall fail if:
The fd argument is not a valid file descriptor.
The fd argument references a file that was opened without write
The value of offset+ len is greater than the maximum file
A signal was caught during execution.
The len argument was zero or the offset argument was less
An I/O error occurred while reading from or writing to a file system.
The fd argument does not refer to a regular file.
There is insufficient free space remaining on the file system storage
The fd argument is associated with a pipe or FIFO.
The following sections are informative.
The posix_fallocate() function is part of the Advisory Information
option and need not be provided on all
creat() , ftruncate() , open() , unlink()
, the Base Definitions volume of
IEEE Std 1003.1-2001, <fcntl.h>
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at