[TUHS] fstat(2) on pipes?

[Warren Toomey]

All, sorry this is slightly off-topic. I'm trying to
find out what fstat(2) returns when the file descriptor
is a pipe. The POSIX/Open Group documentation doesn't
really specify what should be returned. Does anybody have
any pointers?

Thanks, Warren

P.S. Why? xv6 has fstat() but returns an error if the
file descriptor isn't associated with an i-node. I'm
trying to work out if/how to fix it.