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SubjectRe: [PATCH 2/3] devmem: introduce size_inside_page()
On Fri, 11 Sep 2009 10:23:35 +0800
Wu Fengguang <fengguang.wu@intel.com> wrote:

> Introduce size_inside_page() to replace duplicate /dev/mem code.
>
> Also apply it to /dev/kmem, whose alignment logic was buggy.
>
>
> CC: Marcelo Tosatti <mtosatti@redhat.com>
> CC: Greg Kroah-Hartman <gregkh@suse.de>
> CC: Mark Brown <broonie@opensource.wolfsonmicro.com>
> CC: Johannes Berg <johannes@sipsolutions.net>
> CC: Avi Kivity <avi@qumranet.com>
> Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
> ---
> drivers/char/mem.c | 60 +++++++++++++------------------------------
> 1 file changed, 19 insertions(+), 41 deletions(-)
>
> --- linux.orig/drivers/char/mem.c
> +++ linux/drivers/char/mem.c
> @@ -35,6 +35,19 @@
> # include <linux/efi.h>
> #endif
>
> +static inline unsigned long size_inside_page(unsigned long start,
> + unsigned long size)
> +{
> + unsigned long sz;
> +
> + if (-start & (PAGE_SIZE - 1))
> + sz = -start & (PAGE_SIZE - 1);

What on earth is this doing? Negating an unsigned number?

Can we get rid of these party tricks and use something more
conventional here? In a separate patch I guess.

> + else
> + sz = PAGE_SIZE;
> +
> + return min_t(unsigned long, sz, size);

Can use min() here.

> +}

Please have a think about the types. Should we be using unsigned long,
or size_t? Which makes more sense? Which maps better onto reality?

I suspect that the min_t which you inherited was added somewhere
because someone didn't get the types right: int-vs-size_t or something.
If we actually get the types right, this sort of thing goes away.


> @@ -462,10 +451,8 @@ static ssize_t read_kmem(struct file *fi
> if (!kbuf)
> return -ENOMEM;
> while (count > 0) {
> - int len = count;
> + int len = size_inside_page(p, count);

int?




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