On Sat, 29 Dec 2018, Arnd Bergmann wrote: > On Wed, Dec 26, 2018 at 1:43 AM Finn Thain <fth...@telegraphics.com.au> wrote: > > > +static ssize_t ppc_nvram_get_size(void) > > +{ > > + if (ppc_md.nvram_size) > > + return ppc_md.nvram_size(); > > + return -ENODEV; > > +} > > > +const struct nvram_ops arch_nvram_ops = { > > + .read = ppc_nvram_read, > > + .write = ppc_nvram_write, > > + .get_size = ppc_nvram_get_size, > > + .sync = ppc_nvram_sync, > > +}; > > Coming back to this after my comment on the m68k side, I notice that > there is now a double indirection through function pointers. Have you > considered completely removing the operations from ppc_md instead by > having multiple copies of nvram_ops? >
I considered a few alternatives. I figured that it was refactoring that could be deferred, as it would be confined to arch/powerpc. I was more interested in the cross-platform API. > With the current method, it does seem odd to have a single > per-architecture instance of the exported structure containing function > pointers. This doesn't give us the flexibility of having multiple copies > in the kernel the way that ppc_md does, but it adds overhead compared to > simply exporting the functions directly. > You're right, there is overhead here. With a bit of auditing, wrappers like the one you quoted (which merely checks whether or not a ppc_md method is implemented) could surely be avoided. The arch_nvram_ops methods are supposed to optional (that is, they are allowed to be NULL). We could call exactly the same function pointers though either ppc_md or arch_nvram_ops. That would avoid the double indirection. -- > Arnd >