On 03.12.2020 09:47, Jürgen Groß wrote: > On 02.12.20 16:36, Jan Beulich wrote: >> On 01.12.2020 09:21, Juergen Gross wrote: >>> static int hypfs_write(struct hypfs_entry *entry, >>> XEN_GUEST_HANDLE_PARAM(void) uaddr, unsigned long >>> ulen) >> >> As a tangent, is there a reason these write functions don't take >> handles of "const void"? (I realize this likely is nothing that >> wants addressing right here.) > > Uh, this is harder than I thought. > > guest_handle_cast() doesn't handle const guest handle types currently: > > hypfs.c:447:58: error: unknown type name ‘const_void’; did you mean ‘const’? > ret = hypfs_write(entry, guest_handle_cast(arg3, const_void), > arg4); > ^ > /home/gross/xen/unstable/xen/include/xen/guest_access.h:26:5: note: in > definition of macro ‘guest_handle_cast’ > type *_x = (hnd).p; \ > ^~~~ > > Currently my ideas would be to either: > > - add a new macro for constifying a guest handle (type -> const_type) > - add a new macro for casting a guest handle to a const_type > - add typedefs for the const_* types (typedef const x const_x) > - open code the cast > > Or am I missing an existing variant?
I don't think you are. Both of your first two suggestions look good to me - ultimately we may want to have both anyway, eventually. For its (presumed) type safety I may have a slight preference for option 1, albeit afaics guest_handle_cast() doesn't allow conversion between arbitrary types either (only to/from void). It's quite unfortunate that this requires an explicit cast in the first place, but what do you do. Jan
