Re: [PATCH 2/3] writeback: fix incorrect return value type of bdi_dirty_limit

[Marco Stornelli <marco.stornelli@xxxxxxxxx>]

Il 19/08/2012 12:23, Marco Stornelli ha scritto:
> Il 19/08/2012 04:17, Fengguang Wu ha scritto:
> > On Sat, Aug 18, 2012 at 05:49:21AM -0400, Namjae Jeon wrote:
> > > unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned
> > > long dirty)
> > >
> > > Above function return type is unsigned long, but return value is
> > > kept in "u64 bdi_dirty".
> > > It can return incorrect value by type casting.
> >
> > I don't see how the cast can return wrong value.
> > The u64 is necessary for the intermediate calculations.
> >
> > Thanks,
> > Fengguang
>
> We are sure u64 is 8byte long, but unsigned long is 4byte long on 32-bit
> machine, so if bdi_dirty can assume values bigger than 2^32 there is an
> implicit truncate of its value, isn't it?
>
> Marco

Sorry but I didn't see the code, it seems not possible so the wrong 
situation can't happen. Maybe we can simply add a comment, nothing more.

Marco
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