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[PATCH] fs: dax: do not build on ARC or SH

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  [PATCH] fs: dax: do not build on ARC or SH Geert Uytterhoeven <geert+renesas@glider.be> - 2015-07-13 12:00 +0200
    Re: [PATCH] fs: dax: do not build on ARC or SH Boaz Harrosh <boaz@plexistor.com> - 2015-07-13 14:00 +0200

#1182668 — [PATCH] fs: dax: do not build on ARC or SH

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

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@arndb.de>
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
[Geert: s/SH/SUPERH/, as reported by Paul Bolle <pebolle@tiscali.nl>]
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
 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,
-- 
1.9.1

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#1182751

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

> 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@arndb.de>
> Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
> [Geert: s/SH/SUPERH/, as reported by Paul Bolle <pebolle@tiscali.nl>]
> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
> ---
>  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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