On Mon, Nov 18, 2013 at 11:57 AM, Uwe Kleine-König
<u.kleine-koenig@xxxxxxxxxxxxxx> wrote:
> This patch makes mmapping the simple-framebuffer device work on a no-MMU
> ARM target. The code is mostly taken from
> arch/blackfin/kernel/sys_bfin.c.
>
> Note this is only tested on this no-MMU machine and I don't know enough
> about framebuffers and mm to decide if this patch is sane. Also I'm
> unsure about the size check because it triggers if userspace page aligns
> the len parameter. (I don't know how usual it is to do, I'd say it's
> wrong, but my test program (fbtest by Geert Uytterhoeven) does it.)
It's quite common: the granularity of mmap() is PAGE_SIZE, i.e. if you
try to map a partial page, you'll get access to the full page anyway
(with MMU; without MMU, you can access everything anyway).
Fbtest always mmap()s the full (page aligned) smem_len.
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
> ---
> drivers/video/fbmem.c | 22 +++++++++++++++++++---
> 1 file changed, 19 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/video/fbmem.c b/drivers/video/fbmem.c
> index dacaf74..70b328c 100644
> --- a/drivers/video/fbmem.c
> +++ b/drivers/video/fbmem.c
> @@ -1483,6 +1483,24 @@ __releases(&info->lock)
> return 0;
> }
>
> +#ifdef HAVE_ARCH_FB_UNMAPPED_AREA
> +#define fb_get_unmapped_area get_fb_unmapped_area
> +#else
> +unsigned long fb_get_unmapped_area(struct file *filp, unsigned long orig_addr,
> + unsigned long len, unsigned long pgoff, unsigned long flags)
> +{
> + struct fb_info * const info = filp->private_data;
> + unsigned long screen_size = info->screen_size ?: info->fix.smem_len;
Why restrict this to screen_size? Fbtest will map the whole frame buffer memory.
Typically screen_size is not a multiple of PAGE_SIZE, so this is another
reason why your size check fails.
> + if (len > screen_size) {
> + pr_info("%lu > %lu (%lu, %lu)\n", len, screen_size, info->screen_size, info->fix.smem_len);
> + return -EINVAL;
> + }
> +
> + return (unsigned long)info->screen_base;
Shouldn't you take into account pgoff?
> +}
> +#endif
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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