(PECL eio >= 0.0.1dev)
eio_fallocate — Allows the caller to directly manipulate the allocated disk space for a file
$fd,$mode,$offset,$length,$pri = EIO_PRI_DEFAULT,$callback = NULL,$data = NULL
eio_fallocate() allows the caller to directly manipulate the allocated disk space for the
file specified by fd file descriptor for the byte
range starting at offset and continuing for
length bytes.
注意: File should be opened for writing
EIO_O_CREATshould be logically OR'd withEIO_O_WRONLY, orEIO_O_RDWR
fdStream, Socket resource, or numeric file descriptor, e.g. returned by eio_open().
modeCurrently only one flag is supported for mode:
EIO_FALLOC_FL_KEEP_SIZE (the same as POSIX constant
FALLOC_FL_KEEP_SIZE).
offsetSpecifies start of the byte range.
lengthSpecifies length the byte range.
pri请求的优先级：EIO_PRI_DEFAULT，EIO_PRI_MIN，EIO_PRI_MAX 或 null。如果是
null，pri 将设为
EIO_PRI_DEFAULT。
callback
callback
函数在请求完成时被调用。其应匹配一下原型：
void callback(mixed $data, int $result[, resource $req]);data传递给请求的用户数据。
result针对请求的结果的值。通常是相应的系统调用返回的值。
req可选的请求资源，可被 eio_get_last_error() 之类的函数使用。
data
Arbitrary variable passed to callback.
eio_fallocate() returns request resource on success, 或者在失败时返回 false.