Re: [PATCH]Fix for map_private_extent_buffer to handle extent which is not page alignment

["Liu Hui" <onlyflyer@gmail.com>]

There is a little problem with the first ASCII figure, here is the new one.
   |-extent1-|
+-----++-----+
|page1||page2|
+-----++-----+

Thanks,
Liu Hui

2008/12/4 Liu Hui <onlyflyer@gmail.com>:
> Hi,
> Now, BTRFS only supports page alignment extent. But in
> map_private_extent(), there are already some codes to handle the
> extent which is not page alignment. For example,
> map_private_extent_buffer also wants to handle a extent which is 7K
> length properly. The problem is the codes are not enough, e.g. in the
> following figure, map_private_extent_buffer can handle extent1, but it
> can't take the right behavior to handle extent2. This patch fixs it.
>
> PS:Please use the mono font to view the ASCII figures, thanks.
>
>   |-extent1-|
> +-----++-----+
> |page1||page2|
> +-----++-----+
>
> |-extent2-|
> +-----++-----+
> |page1||page2|
> +-----++-----+
>
> --
> Thanks & Best Regards
> Liu Hui
> --
>
> diff --git a/extent_io.c b/extent_io.c
> index c3dfe2a..cac47d1 100644
> --- a/extent_io.c
> +++ b/extent_io.c
> @@ -3426,9 +3426,11 @@ int map_private_extent_buffer(struct
> extent_buffer *eb, unsigned long start,
>        char *kaddr;
>        struct page *p;
>        size_t start_offset = eb->start & ((u64)PAGE_CACHE_SIZE - 1);
> +       size_t last_offset;
>        unsigned long i = (start_offset + start) >> PAGE_CACHE_SHIFT;
>        unsigned long end_i = (start_offset + start + min_len - 1) >>
>                PAGE_CACHE_SHIFT;
> +       unsigned long last_i = (start_offset + eb->len - 1) >> PAGE_CACHE_SHIFT;
>
>        if (i != end_i)
>                return -EINVAL;
> @@ -3440,8 +3442,16 @@ int map_private_extent_buffer(struct
> extent_buffer *eb, unsigned long start,
>                offset = 0;
>                *map_start = ((u64)i << PAGE_CACHE_SHIFT) - start_offset;
>        }
> +
> +       if (i == last_i)
> +               last_offset = ((u64)(i + 1) << PAGE_CACHE_SHIFT) - start_offset
> +                             - eb->len;
> +       else
> +               last_offset = 0;
> +
>        if (start + min_len > eb->len) {
> -printk("bad mapping eb start %Lu len %lu, wanted %lu %lu\n",
> eb->start, eb->len, start, min_len);
> +               printk("bad mapping eb start %Lu len %lu, wanted %lu %lu\n",
> +                      eb->start, eb->len, start, min_len);
>                WARN_ON(1);
>        }
>
> @@ -3449,7 +3459,7 @@ printk("bad mapping eb start %Lu len %lu, wanted
> %lu %lu\n", eb->start, eb->len,
>        kaddr = kmap_atomic(p, km);
>        *token = kaddr;
>        *map = kaddr + offset;
> -       *map_len = PAGE_CACHE_SIZE - offset;
> +       *map_len = PAGE_CACHE_SIZE - offset - last_offset;
>        return 0;
>  }
>  EXPORT_SYMBOL(map_private_extent_buffer);
>

-- 
Thanks & Best Regards
Liu Hui
--