Re: [PATCH] nfs: fix a couple of minor portability issues

From: Chris Metcalf
Date: Thu Aug 11 2011 - 09:26:40 EST

On 8/10/2011 6:02 PM, Boaz Harrosh wrote:
> On 08/10/2011 10:56 AM, Chris Metcalf wrote:
>> Building on tilepro revealed two minor portability issues: the
>> blocklayout.c file used prefetchw() without #include <linux/prefetch.h>,
>> and the nfs4filelayout.c file used do_div() on an s64 not a u64.
>> This change fixes those two issues so the NFS code builds on tilepro.
>> [...]
>> diff --git a/fs/nfs/nfs4filelayout.c b/fs/nfs/nfs4filelayout.c
>> index e8915d4..6976a72 100644
>> --- a/fs/nfs/nfs4filelayout.c
>> +++ b/fs/nfs/nfs4filelayout.c
>> @@ -48,13 +48,13 @@ filelayout_get_dense_offset(struct nfs4_filelayout_segment *flseg,
>> loff_t offset)
>> {
>> u32 stripe_width = flseg->stripe_unit * flseg->dsaddr->stripe_count;
>> - u64 tmp;
>> + u64 tmp, uoff;
>> offset -= flseg->pattern_offset;
>> - tmp = offset;
>> + tmp = uoff = offset;
>> do_div(tmp, stripe_width);
>> - return tmp * flseg->stripe_unit + do_div(offset, flseg->stripe_unit);
>> + return tmp * flseg->stripe_unit + do_div(uoff, flseg->stripe_unit);
> For proper u64 divisions it is best to use the div_u64 (and div64_u64) and not
> use do_div. (And please don't add an unnecessary variable, just use a cast)

You can't use a cast with do_div() or you get errors about non-lvalues.

And the context here is that we want the remainder, not the divided result,
so we'd need a temporary variable anyway if we were going to use a routine
from math64.h, presumably div_u64_rem(). But that's just an inline wrapper
around do_div() anyway, so it's no more efficient, and not obviously any
less "cluttered" in the source code here. The original code author (who
I'm adding belatedly to this email) may have a stronger opinion.

I'm not the author or maintainer of this code, I just want it to compile
without warning on 32-bit architectures :-)

Chris Metcalf, Tilera Corp.

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