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Date:	Fri, 19 Sep 2014 14:39:10 -0400
From:	Trond Myklebust <trond.myklebust@...marydata.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Linux NFS Mailing List <linux-nfs@...r.kernel.org>,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH][linux-next] pnfs/blocklayout: Use do_div for 64 bit
 divide operations

Hi Steven,

On Fri, Sep 19, 2014 at 1:30 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
>
> Commit 5c83746a0cf2 "pnfs/blocklayout: in-kernel GETDEVICEINFO XDR parsing"
> added some open coded 64 bit divisions which caused the following
> error on 32 bit builds:
>
> fs/built-in.o: In function `bl_map_stripe':
> fs/nfs/blocklayout/dev.c:153: undefined reference to `__udivdi3'
> fs/nfs/blocklayout/dev.c:154: undefined reference to `__umoddi3'
> fs/nfs/blocklayout/dev.c:168: undefined reference to `__udivdi3'
>
> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
> ---
>  fs/nfs/blocklayout/dev.c | 16 +++++++++++++---
>  1 file changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/fs/nfs/blocklayout/dev.c b/fs/nfs/blocklayout/dev.c
> index 00f159da06ee..05d32e2175db 100644
> --- a/fs/nfs/blocklayout/dev.c
> +++ b/fs/nfs/blocklayout/dev.c
> @@ -150,10 +150,18 @@ static bool bl_map_stripe(struct pnfs_block_dev *dev, u64 offset,
>                 struct pnfs_block_dev_map *map)
>  {
>         struct pnfs_block_dev *child;
> -       u64 chunk = (offset / dev->chunk_size);
> -       int chunk_idx = chunk % dev->nr_children;
> +       u64 chunk;
> +       u64 chunk_tmp;
> +       int chunk_idx;
>         u64 disk_offset;
>
> +       chunk = offset;
> +       /* chunk = offset / dev->chunk_size */
> +       do_div(chunk, dev->chunk_size);
> +       chunk_tmp = chunk;
> +       /* chunk_idx = chunk % dev->nr_children) */
> +       chunk_idx = do_div(chunk_tmp, dev->nr_children);
> +
>         if (chunk_idx > dev->nr_children) {
>                 dprintk("%s: invalid chunk idx %d (%lld/%lld)\n",
>                         __func__, chunk_idx, offset, dev->chunk_size);
> @@ -165,7 +173,9 @@ static bool bl_map_stripe(struct pnfs_block_dev *dev, u64 offset,
>         offset = chunk * dev->chunk_size;
>
>         /* disk offset of the stripe */
> -       disk_offset = offset / dev->nr_children;
> +       disk_offset = offset;
> +       /* disk_offset = offset / dev->nr_children */
> +       do_div(disk_offset, dev->nr_children);
>
>         child = &dev->children[chunk_idx];
>         child->map(child, disk_offset, map);
> --
> 1.8.1.4
>

Thanks. I posted a similar bugfix on the linux-nfs mailing list
yesterday. That hasn't been pushed to linux-next yet because Christoph
wanted to run it through some QA tests first.

Cheers
  Trond

-- 
Trond Myklebust

Linux NFS client maintainer, PrimaryData

trond.myklebust@...marydata.com
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