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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>
hifive-unleashed-5.1
Li Zefan 2011-12-01 14:06:42 +08:00
parent de11cc12df
commit ec9ef7a13b
1 changed files with 32 additions and 65 deletions
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97
fs/btrfs/volumes.c
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@ -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;
if ((i / sub_stripes + 1) %
sub_stripes == remaining_stripes)
bbio->stripes[i].length -=
stripe_end_offset;
if (i == sub_stripes - 1)
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)) {
bbio->stripes[i].length -=
stripe_end_offset;
}
} else
bbio->stripes[i].length = *length;