question about configure warning

[Michael S. Fischer]

On Jan 6, 2009, at 7:42 AM, Marcus Smith wrote:
> "The build system will automatically detect the availability of  
> epoll()
> and build the corresponding cache_acceptor. It will also automatically
> detect the availability of sendfile(), though its use is discouraged
> (and disabled by default) due to a variety of non-Linux-specific  
> issues."
>
> (http://varnish.projects.linpro.no/wiki/Porting/Linux/2.6)

What are these "non-Linux-specific issues" to which the document refers?

--Michael