On Tue, 2015-05-12 at 17:24 +0800, Yang Hongyang wrote: > > On 05/12/2015 04:19 PM, Ian Campbell wrote: > > On Tue, 2015-05-12 at 15:18 +0800, Yang Hongyang wrote: > >> > >> On 05/11/2015 07:53 PM, Ian Campbell wrote: > >>> On Fri, 2015-05-08 at 17:33 +0800, Yang Hongyang wrote: > >>>> Define a user pointer that can access the hypercall buffer data > >>>> Useful when you only need to access the hypercall buffer data > >>> > >>> Can you expand on this please, I think the context is a hypercall buffer > >>> passed as an argument or as a member of a struct. Please describe why > >>> DECLARE_HYPERCALL_BUFFER_ARGUMENT and/or DECLARE_HYPERCALL_BUFFER_SHADOW > >>> are not usable here. > >> > >> There are cases that we only need to use the hypercall buffer data, and do > >> not use the xc_hypercall_buffer_t struct. > >> > >> DECLARE_HYPERCALL_BUFFER_ARGUMENT will only define a xc_hypercall_buffer_t, > >> while DECLARE_HYPERCALL_BUFFER_SHADOW do define a user pointer that can > >> allow > >> us to access the hypercall buffer data but it also define a > >> xc_hypercall_buffer_t that we don't use, the compiler will report arg > >> unused > >> error. > >> > >> The cases for example: > >> In send_all_pages(), we only need to use the haypercall buffer data which > >> is a > >> dirty bitmap, we set the dirty bitmap to all dirty and call > >> send_dirty_pages, > >> we will not use the xc_hypercall_buffer_t and hypercall to retrive the > >> dirty > >> bitmap. > >> In send_some_pages(), we will also only need to use the dirty_bitmap. the > >> retrive dirty bitmap hypercall are done by the caller. > > > > Thanks. Please include the bulk of this description in the commit > > message. > > > > However, perhaps we should just mark the xc_hypercall_buffer_t as > > potentially unused, by tagging it with __attribute__((unused)), in some > > or all of the DECLARE_HYPERCALL_* variants. Then I think you could use > > DECLARE_HYPERCALL_BUFFER_SHADOW as is? > > If __attribute__((unused)) won't cause other problems here, I also prefer > to add this to DECLARE_HYPERCALL_BUFFER_SHADOW instead of create another > macro, I think only DECLARE_HYPERCALL_BUFFER_SHADOW may need to set this > attribute because this is a shadow, we might not use the xc_hypercall_buffer_t > which already allocated.
We can certainly start from there and consider other such additions as the need arises. Ian. _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel
