On 07/13/2015 12:52 PM, Geert Uytterhoeven wrote:
> From: Arnd Bergmann <arnd@xxxxxxxx>
>
> 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
> We already have a list of architectures that are known to be incompatible,
> but the list is missing ARC and SH at the moment. Further, blackfin and
> c6x also lack support for this function, but are already excluded because
> they do not support MMU-based kernels.
>
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> Reported-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
> [Geert: s/SH/SUPERH/, as reported by Paul Bolle <pebolle@xxxxxxxxxx>]
> Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
> ---
> fs/Kconfig | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/Kconfig b/fs/Kconfig
> index 011f43365d7b1e53..53326a50a3ce3830 100644
> --- a/fs/Kconfig
> +++ b/fs/Kconfig
> @@ -37,7 +37,7 @@ source "fs/f2fs/Kconfig"
> config FS_DAX
> bool "Direct Access (DAX) support"
> depends on MMU
> - depends on !(ARM || MIPS || SPARC)
> + depends on !(ARC || ARM || MIPS || SPARC || SUPERH)
> help
> Direct Access (DAX) can be used on memory-backed block devices.
> If the block device supports DAX and the filesystem supports DAX,
>
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