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.\"     @(#)open.2	8.2 (Berkeley) 11/16/93
.\" $FreeBSD$
.\"
.Dd November 4, 2017
.Dt POSIX_FALLOCATE 2
.Os
.Sh NAME
.Nm posix_fallocate
.Nd pre-allocate storage for a range in a file
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In fcntl.h
.Ft int
.Fn posix_fallocate "int fd" "off_t offset" "off_t len"
.Sh DESCRIPTION
Required storage for the range
.Fa offset
to
.Fa offset +
.Fa len
in the file referenced by
.Fa fd
is guaranteed to be allocated upon successful return.
That is, if
.Fn posix_fallocate
returns successfully, subsequent writes to the specified file data
will not fail due to lack of free space on the file system storage
media.
Any existing file data in the specified range is unmodified.
If
.Fa offset +
.Fa len
is beyond the current file size, then
.Fn posix_fallocate
will adjust the file size to
.Fa offset +
.Fa len .
Otherwise, the file size will not be changed.
.Pp
Space allocated by
.Fn posix_fallocate
will be freed by a successful call to
.Xr creat 2
or
.Xr open 2
that truncates the size of the file.
Space allocated via
.Fn posix_fallocate
may be freed by a successful call to
.Xr ftruncate 2
that reduces the file size to a size smaller than
.Fa offset +
.Fa len .
.Sh RETURN VALUES
If successful,
.Fn posix_fallocate
returns zero.
It returns an error on failure, without setting
.Va errno .
.Sh ERRORS
Possible failure conditions:
.Bl -tag -width Er
.It Bq Er EBADF
The
.Fa fd
argument is not a valid file descriptor.
.It Bq Er EBADF
The
.Fa fd
argument references a file that was opened without write permission.
.It Bq Er EFBIG
The value of
.Fa offset +
.Fa len
is greater than the maximum file size.
.It Bq Er EINTR
A signal was caught during execution.
.It Bq Er EINVAL
The
.Fa len
argument was less than or equal to zero, the
.Fa offset
argument was less than zero,
or the operation is not supported by the file system.
.It Bq Er EIO
An I/O error occurred while reading from or writing to a file system.
.It Bq Er ENODEV
The
.Fa fd
argument does not refer to a regular file.
.It Bq Er ENOSPC
There is insufficient free space remaining on the file system storage
media.
.It Bq Er ENOTCAPABLE
The file descriptor
.Fa fd
has insufficient rights.
.It Bq Er ESPIPE
The
.Fa fd
argument is associated with a pipe or FIFO.
.El
.Sh SEE ALSO
.Xr creat 2 ,
.Xr ftruncate 2 ,
.Xr open 2 ,
.Xr unlink 2
.Sh STANDARDS
The
.Fn posix_fallocate
system call conforms to
.St -p1003.1-2004 .
.Sh HISTORY
The
.Fn posix_fallocate
function appeared in
.Fx 9.0 .
.Sh AUTHORS
.Fn posix_fallocate
and this manual page were initially written by
.An Matthew Fleming Aq Mt mdf@FreeBSD.org .