[PATCH] erofs: fix compacted_2b if compacted_4b_initial > totalidx

[Yue Hu <zbestahu@gmail.com>]

From: Yue Hu <huyue2@yulong.com>

Currently, the whole indexes will only be compacted 4B if
compacted_4b_initial > totalidx. So, the calculated compacted_2b
is worthless for that case. It may waste CPU resources.

No need to update compacted_4b_initial as mkfs since it's used to
fulfill the alignment of the 1st compacted_2b pack and would handle
the case above.

We also need to clarify compacted_4b_end here. It's used for the
last lclusters which aren't fitted in the previous compacted_2b
packs.

Some messages are from Xiang.

Signed-off-by: Yue Hu <huyue2@yulong.com>
---
 fs/erofs/zmap.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/erofs/zmap.c b/fs/erofs/zmap.c
index 9fb98d8..aeed404 100644
--- a/fs/erofs/zmap.c
+++ b/fs/erofs/zmap.c
@@ -369,7 +369,8 @@ static int compacted_load_cluster_from_disk(struct z_erofs_maprecorder *m,
 	if (compacted_4b_initial == 32 / 4)
 		compacted_4b_initial = 0;
 
-	if (vi->z_advise & Z_EROFS_ADVISE_COMPACTED_2B)
+	if ((vi->z_advise & Z_EROFS_ADVISE_COMPACTED_2B) &&
+	    compacted_4b_initial <= totalidx) {
 		compacted_2b = rounddown(totalidx - compacted_4b_initial, 16);
 	else
 		compacted_2b = 0;
-- 
1.9.1