[PATCH 1/5] btrfs-progs: check: Initialize extent_record::generation member

[Qu Wenruo <wqu@suse.com>]

[BUG]
When using `btrfs check --init-extent-tree`, there is a pretty high
chance that the result fs can't pass tree-checker:

  BTRFS critical (device dm-3): corrupt leaf: block=5390336 slot=149 extent bytenr=20115456 len=4096 invalid generation, have 16384 expect (0, 360]
  BTRFS error (device dm-3): block=5390336 read time tree block corruption detected
  BTRFS error (device dm-3): failed to read block groups: -5
  BTRFS error (device dm-3): open_ctree failed

[CAUSE]
The result fs has a pretty screwed up EXTENT_ITEMs for data extents:

        item 148 key (20111360 EXTENT_ITEM 4096) itemoff 8777 itemsize 53
                refs 1 gen 0 flags DATA
                extent data backref root FS_TREE objectid 841 offset 0 count 1
        item 149 key (20115456 EXTENT_ITEM 4096) itemoff 8724 itemsize 53
                refs 1 gen 16384 flags DATA
                extent data backref root FS_TREE objectid 906 offset 0 count 1

Kernel tree-checker will accept 0 generation, but that 16384 generation
is definitely going to trigger the alarm.

Looking into the code, it's add_extent_rec_nolookup() allocating a new
extent_rec, but not copying all members from parameter @tmpl, resulting
generation not properly initialized.

[FIX]
Just copy tmpl->generation in add_extent_rec_nolookup(). And since all
call sites have set all members of @tmpl to 0 before
add_extent_rec_nolookup(), we shouldn't get garbage values.

For the 0 generation problem, it will be solved in another patch.

Issue: 225 (Not the initial report, but extent tree rebuild result)
Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 check/main.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/check/main.c b/check/main.c
index 08dc9e66..2dbed091 100644
--- a/check/main.c
+++ b/check/main.c
@@ -4605,6 +4605,7 @@ static int add_extent_rec_nolookup(struct cache_tree *extent_cache,
 	rec->refs = tmpl->refs;
 	rec->extent_item_refs = tmpl->extent_item_refs;
 	rec->parent_generation = tmpl->parent_generation;
+	rec->generation = tmpl->generation;
 	INIT_LIST_HEAD(&rec->backrefs);
 	INIT_LIST_HEAD(&rec->dups);
 	INIT_LIST_HEAD(&rec->list);
-- 
2.24.1