exofs: groups support

* _calc_stripe_info() changes to accommodate for grouping
  calculations. Returns additional information

* old _prepare_pages() becomes _prepare_one_group()
  which stores pages belonging to one device group.

* New _prepare_for_striping iterates on all groups calling
  _prepare_one_group().

* Enable mounting of groups data_maps (group_width != 0)

[QUESTION]
what is faster A or B;
A.	x += stride;
	x = x % width + first_x;

B	x += stride
	if (x < last_x)
		x = first_x;

Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/fs/exofs/exofs.h b/fs/exofs/exofs.h
index acfebd36de83..59b8bf2825c7 100644
--- a/fs/exofs/exofs.h
+++ b/fs/exofs/exofs.h
@@ -63,6 +63,8 @@ struct exofs_layout {
         unsigned mirrors_p1;
 
         unsigned group_width;
+        u64      group_depth;
+        unsigned group_count;
 
         enum exofs_inode_layout_gen_functions lay_func;
 
@@ -132,6 +134,7 @@ struct exofs_io_state {
         struct page             **pages;
         unsigned                nr_pages;
         unsigned                pgbase;
+        unsigned                pages_consumed;
 
         /* Attributes */
         unsigned                in_attr_len;