Re: [Qemu-devel] [PATCH v2 3/3] xen-hvm: try to use xenforeignmemory_map_resource() to map ioreq pages

[Eric Blake]

On 05/15/2018 11:16 AM, Anthony PERARD wrote:

> > > > +    errno = EOPNOTSUPP;
> > >
> > > I think ENOSYS would be better. EOPNOTSUPP seems to be for sockets.
> >
> > No, EOPNOTSUPP is more general than that and is convention for unimplemented 
> > API operations elsewhere. ENOSYS is supposed to strictly mean 'system call not 
> > implemented' but we use it for hypercalls in Xen, leading to occasional fun 
> > with Linux checkpatch.pl.
>
> In man errno, I have:
> ENOTSUP         Operation not supported (POSIX.1-2001)
> EOPNOTSUPP      Operation not supported on socket (POSIX.1-2001).

POSIX allows (and Linux exploits) ENOTSUP and EOPNOTSUPP to be synonyms 
for the same error value.  I somewhat prefer the ENOTSUP spelling; and 
it's probably a bit nicer between the two when porting to platforms 
where the two spellings are not synonyms.

> ENOSYS          Function not implemented (POSIX.1-2001).
>
> But I guess any of these would work.

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org