tree 2791d81ab923fd046de7b8f944714b7079c72d97
parent bfca9a6d4b1322ba36235e8a652f05a9668ef59b
author Zhao Lei <zhaolei@cn.fujitsu.com> 1425386326 +0800
committer Chris Mason <clm@fb.com> 1453303336 -0800

btrfs: Use unified stripe_page's index calculation

We are using different index calculation method for stripe_page in
current code:
1: (rbio->stripe_len / PAGE_CACHE_SIZE) * stripe_index + page_index
2: DIV_ROUND_UP(rbio->stripe_len, PAGE_CACHE_SIZE) * stripe_index + page_index
3: DIV_ROUND_UP(rbio->stripe_len * stripe_index, PAGE_CACHE_SIZE) + page_index
...

They can get same result when stripe_len align to PAGE_CACHE_SIZE,
this is why current code can work, intruduce and use a common function
for calculation is a better choose.

Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: Chris Mason <clm@fb.com>