> This PR begs a question:
> 
> 	should every system call manual page list every possible
> 	error that can be returned by that call?
> 
> For example, this means that any system call dealing with a 
> descriptor (file, socket, whatever) would need to list all filesystem 
> error codes, plus all socket (network) error codes, and so on. It 
> would be a fairly exhaustive list.

Not exactly.  "read" will never return EROFS or EPROTONOSUPPORT unless
a driver is playing games with us..

> If we decide "yes" then we need to go through section 2 pretty thoroughly.
> 
> The alternative is to list the error codes in one place, and give a 
> general description of when to expect them, with pointers to the 
> right subset from each system call man page.

we certainly shouldn't rip out the errno descriptions from the
existing manual pages -- EINVAL means different things for different
syscalls.  What's there already should not be removed.  Maybe a
semi-boilerplate "additional error codes may be returned, see
driver/filesystem/protocol-family-specific man page for details".

> Or we could just say UTSL with a pointer to /usr/include/errno.h

uhh, no.