On Sat, 29 Dec 2018, Arnd Bergmann wrote:
On Wed, Dec 26, 2018 at 1:43 AM Finn Thain <fthain@xxxxxxxxxxxxxxxxxxx> 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
