easy way to determine if a stream or fd is seekable

[perryh at pluto.rain.com]

Alexander Best <arundel at freebsd.org> wrote:

> since i've never worked with tape: what file type does it identify
> as?  character special file, or block special file, or ...?

IIUC all devices are now character, block devices having been
dropped from FreeBSD some time ago.  Come to think of it, it
would not be altogether surprising if that turned out to be
the point at which the ability to seek a device went away.