On 07/13/2015 12:52 PM, Geert Uytterhoeven wrote:

From: Arnd Bergmann <arnd@arndb.de>

The DAX implementation relies on the architecture to provide a working
copy_user_page() function, as reported by Michael Ellerman's kisskb
build bot:

fs/dax.c: error: implicit declaration of function 'copy_user_page' [-Werror=implicit-function-declaration]:  => 266:2

static int copy_user_bh(struct page *to, struct buffer_head *bh,
			unsigned blkbits, unsigned long vaddr)
{
	void *vfrom, *vto;
	if (dax_get_addr(bh, &vfrom, blkbits) < 0)
		return -EIO;
	vto = kmap_atomic(to);
	copy_user_page(vto, vfrom, vaddr, to);
	kunmap_atomic(vto);
	return 0;
}

I do not understand why we need to call copy_user_page here at all?
the destination is kmap_atomic() so it must be there right? also the
destination is the cow-to page so surly it is not yet mapped to user-space
mapping.

the from is pmem which is just there.

From what I understand copy_user_page means:
    On these ARCHs that each user-mapping has its own VM cache, please invalidate
    the other VM caches.
Like on arm64 (arch/arm64/mm/copypage.c):
	copy_page(kto, kfrom);
	__flush_dcache_area(kto, PAGE_SIZE);

So what I do not understand is why copy_user_page does not have a default
implementation for those ARCHs that don't override it.

But again I think the above copy_user_page use is not at all needed.

And of course what do I know?

Thanks
Boaz