Btrfs: simplfy calculation of stripe length for discard operation

For btrfs raid, while discarding a range of space, we'll need to know
the start offset and length to discard for each device, and it's done
in btrfs_map_block().

However the calculation is a bit complex for raid0 and raid10, so I
reimplement it based on a fact that:

        dev1          dev2           dev3    (raid0)
        -----------------------------------
        s0 s3 s6      s1 s4 s7       s2 s5

Each device has (total_stripes / nr_dev) stripes, or plus one.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 540fdd2..563ef65 100644 (file)
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -3024,80 +3024,47 @@ static int __btrfs_map_block(struct btrfs_mapping_tree *map_tree, int rw,
        atomic_set(&bbio->error, 0);
 
        if (rw & REQ_DISCARD) {
+               int factor = 0;
+               int sub_stripes = 0;
+               u64 stripes_per_dev = 0;
+               u32 remaining_stripes = 0;
+
+               if (map->type &
+                   (BTRFS_BLOCK_GROUP_RAID0 | BTRFS_BLOCK_GROUP_RAID10)) {
+                       if (map->type & BTRFS_BLOCK_GROUP_RAID0)
+                               sub_stripes = 1;
+                       else
+                               sub_stripes = map->sub_stripes;
+
+                       factor = map->num_stripes / sub_stripes;
+                       stripes_per_dev = div_u64_rem(stripe_nr_end -
+                                                     stripe_nr_orig,
+                                                     factor,
+                                                     &remaining_stripes);
+               }
+
                for (i = 0; i < num_stripes; i++) {
                        bbio->stripes[i].physical =
                                map->stripes[stripe_index].physical +
                                stripe_offset + stripe_nr * map->stripe_len;
                        bbio->stripes[i].dev = map->stripes[stripe_index].dev;
 
-                       if (map->type & BTRFS_BLOCK_GROUP_RAID0) {
-                               u64 stripes;
-                               u32 last_stripe = 0;
-                               int j;
-
-                               div_u64_rem(stripe_nr_end - 1,
-                                           map->num_stripes,
-                                           &last_stripe);
-
-                               for (j = 0; j < map->num_stripes; j++) {
-                                       u32 test;
-
-                                       div_u64_rem(stripe_nr_end - 1 - j,
-                                                   map->num_stripes, &test);
-                                       if (test == stripe_index)
-                                               break;
-                               }
-                               stripes = stripe_nr_end - 1 - j;
-                               do_div(stripes, map->num_stripes);
-                               bbio->stripes[i].length = map->stripe_len *
-                                       (stripes - stripe_nr + 1);
-
-                               if (i == 0) {
+                       if (map->type & (BTRFS_BLOCK_GROUP_RAID0 |
+                                        BTRFS_BLOCK_GROUP_RAID10)) {
+                               bbio->stripes[i].length = stripes_per_dev *
+                                                         map->stripe_len;
+                               if (i / sub_stripes < remaining_stripes)
+                                       bbio->stripes[i].length +=
+                                               map->stripe_len;
+                               if (i < sub_stripes)
                                        bbio->stripes[i].length -=
                                                stripe_offset;
-                                       stripe_offset = 0;
-                               }
-                               if (stripe_index == last_stripe)
-                                       bbio->stripes[i].length -=
-                                               stripe_end_offset;
-                       } else if (map->type & BTRFS_BLOCK_GROUP_RAID10) {
-                               u64 stripes;
-                               int j;
-                               int factor = map->num_stripes /
-                                            map->sub_stripes;
-                               u32 last_stripe = 0;
-
-                               div_u64_rem(stripe_nr_end - 1,
-                                           factor, &last_stripe);
-                               last_stripe *= map->sub_stripes;
-
-                               for (j = 0; j < factor; j++) {
-                                       u32 test;
-
-                                       div_u64_rem(stripe_nr_end - 1 - j,
-                                                   factor, &test);
-
-                                       if (test ==
-                                           stripe_index / map->sub_stripes)
-                                               break;
-                               }
-                               stripes = stripe_nr_end - 1 - j;
-                               do_div(stripes, factor);
-                               bbio->stripes[i].length = map->stripe_len *
-                                       (stripes - stripe_nr + 1);
-
-                               if (i < map->sub_stripes) {
-                                       bbio->stripes[i].length -=
-                                               stripe_offset;
-                                       if (i == map->sub_stripes - 1)
-                                               stripe_offset = 0;
-                               }
-                               if (stripe_index >= last_stripe &&
-                                   stripe_index <= (last_stripe +
-                                                    map->sub_stripes - 1)) {
+                               if ((i / sub_stripes + 1) %
+                                   sub_stripes == remaining_stripes)
                                        bbio->stripes[i].length -=
                                                stripe_end_offset;
-                               }
+                               if (i == sub_stripes - 1)
+                                       stripe_offset = 0;
                        } else
                                bbio->stripes[i].length = *length;