This is a nonportable, Linux-specific system call.
For the portable, POSIX.1-specified method of ensuring that space
is allocated for a file, see
allows the caller to directly manipulate the allocated disk space
for the file referred to by
for the byte range starting at
and continuing for
argument determines the operation to be performed on the given range.
Currently only one flag is supported for
This flag allocates and initializes to zero the disk space
within the range specified by
After a successful call, subsequent writes into this range
are guaranteed not to fail because of lack of disk space.
Preallocating zeroed blocks beyond the end of the file
is useful for optimizing append workloads.
Preallocating blocks does not change
the file size (as reported by
even if it is less than
flag is not specified in
the default behavior is almost same as when this flag is specified.
The only difference is that on success,
the file size will be changed if
offset + len
is greater than the file size.
This default behavior closely resembles the behavior of the
and is intended as a method of optimally implementing that function.
Because allocation is done in block size chunks,
may allocate a larger range than that which was specified.
returns zero on success, and -1 on failure.
is not a valid file descriptor, or is not opened for writing.
exceeds the maximum file size.
A signal was caught during execution.
was less than 0, or
was less than or equal to 0.
An I/O error occurred while reading from or writing to a file system.
does not refer to a regular file or a directory.
is a pipe or FIFO, a different error results.)
There is not enough space left on the device containing the file
referred to by
The file system containing the file referred to by
does not support this operation.
is not supported by the file system containing the file referred to by
is available on Linux since kernel 2.6.23.
Support is provided by glibc since version 2.10.