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Re: [PATCH v2 09/17] xen/hypfs: move per-node function pointers into a dedicated struct
On 03.12.20 10:12, Jan Beulich wrote:
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.
Right.
I'm going with variant 2, as variant 1 is not really easy to achieve
without specifying the basic type as a macro parameter - which will
basically be variant 2.
Juergen
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