On Mon, Feb 20, 2017 at 11:54:31AM +0800, Qu Wenruo wrote:
>
>
> At 02/18/2017 09:28 AM, Liu Bo wrote:
> > Since DISCARD is not as important as an operation like write, we don't
> > copy it to target device during replace, and it makes __btrfs_map_block
> > less complex.
>
> Makes sense to me.
>
> >
> > Signed-off-by: Liu Bo <[email protected]>
> > ---
> > fs/btrfs/volumes.c | 306
> > +++++++++++++++++++++++++++++++++--------------------
> > 1 file changed, 192 insertions(+), 114 deletions(-)
> >
> > diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> > index c52b0fe..96228f3 100644
> > --- a/fs/btrfs/volumes.c
> > +++ b/fs/btrfs/volumes.c
> > @@ -5294,6 +5294,175 @@ void btrfs_put_bbio(struct btrfs_bio *bbio)
> > kfree(bbio);
> > }
> >
> > +/* can REQ_OP_DISCARD be sent with other REQ like REQ_OP_WRITE? */
> > +/*
> > + * Please note that, discard won't be sent to target device of device
> > + * replace.
> > + */
> > +static int __btrfs_map_block_for_discard(struct btrfs_fs_info *fs_info,
> > + u64 logical, u64 length,
> > + struct btrfs_bio **bbio_ret)
> > +{
> > + struct extent_map_tree *em_tree = &fs_info->mapping_tree.map_tree;
> > + struct extent_map *em;
> > + struct map_lookup *map;
> > + struct btrfs_bio *bbio;
> > + u64 offset;
> > + u64 stripe_nr;
> > + u64 stripe_nr_end;
> > + u64 stripe_end_offset;
> > + u64 stripe_cnt;
> > + u64 stripe_len;
> > + u64 stripe_offset;
> > + u64 num_stripes;
> > + u32 stripe_index;
> > + u32 factor = 0;
> > + u32 sub_stripes = 0;
> > + u64 stripes_per_dev = 0;
> > + u32 remaining_stripes = 0;
> > + u32 last_stripe = 0;
> > + int ret = 0;
> > + int i;
> > +
> > + /* discard always return a bbio */
> > + ASSERT(bbio_ret);
> > +
> > + read_lock(&em_tree->lock);
> > + em = lookup_extent_mapping(em_tree, logical, length);
> > + read_unlock(&em_tree->lock);
>
> It seems that get_chunk_map() in previous patch can replace such searching
> and error message.
>
Yeah, I forgot to update with it.
> > +
> > + if (!em) {
> > + btrfs_crit(fs_info, "unable to find logical %llu len %llu",
> > + logical, length);
> > + return -EINVAL;
> > + }
> > +
> > + if (em->start > logical || em->start + em->len < logical) {
> > + btrfs_crit(fs_info,
> > + "found a bad mapping, wanted %Lu, found %Lu-%Lu",
> > + logical, em->start, em->start + em->len);
> > + free_extent_map(em);
> > + return -EINVAL;
> > + }
> > +
> > + map = em->map_lookup;
> > + /* we don't discard raid56 yet */
> > + if (map->type & BTRFS_BLOCK_GROUP_RAID56_MASK) {
> > + ret = -EOPNOTSUPP;
> > + goto out;
> > + }
> > +
> > + offset = logical - em->start;
> > + length = min_t(u64, em->len - offset, length);
> > +
> > + stripe_len = map->stripe_len;
> > + /*
> > + * stripe_nr counts the total number of stripes we have to stride
> > + * to get to this block
> > + */
> > + stripe_nr = div64_u64(offset, stripe_len);
> > + stripe_offset = stripe_nr * stripe_len;
> > + ASSERT(offset >= stripe_offset);
>
> What about a DIV_ROUND_DOWN helper?
> Surprisingly we only have DIR_ROUND_UP, not not DIV_ROUND_DOWN.
>
> And if we're only going to support 64K stripe len, then round_down() is good
> for current usage.
>
> > +
> > + /* stripe_offset is the offset of this block in its stripe */
> > + stripe_offset = offset - stripe_offset;
>
> This is a little confusing.
> What about using another variable called @stripe_start instead of using the
> same variable @stripe_offset to temporarily store stripe start bytenr.
>
> I prefer to do it in one run without resuing @stripe_offset variable to
> avoid confusion.
Right, I was trying to keep the check of (offset >= stripe_offset), but it's not
necessary.
>
> > +
> > + stripe_nr_end = ALIGN(offset + length, map->stripe_len);
>
> round_up() causes less confusion.
>
> And IIRC, ALIGN/round_up can only handle power of 2, this implies the
> stripe_len must be power of 2, which is OK for now.
> If using ALIGN here, we can also use round_down() in previous stripe_nr.
>
Good point.
Thanks,
-liubo
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