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>

1 files changed, 31 insertions, 64 deletions

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 540fdd25fb5e..563ef650850e 100644
--- 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;