[PATCH] erofs-utils: fix battach on full buffer block

[Hu Weiwen <sehuww@mail.scut.edu.cn>]

When __erofs_battach() is called on an buffer block of which
(bb->buffers.off % EROFS_BLKSIZ == 0), `tail_blkaddr' will not be
updated correctly. This bug can be reproduced by:

mkdir bug-repo
head -c 4032 /dev/urandom > bug-repo/1
head -c 4095 /dev/urandom > bug-repo/2
head -c 12345 /dev/urandom > bug-repo/3  # arbitrary size
mkfs.erofs -Eforce-inode-compact bug-repo.erofs.img bug-repo

Then mount this image and see that file `3' in the image is different
from `bug-repo/3'.

This patch fix this by:

* Don't inline tail-end data in this case, since the tail-end data will
be in a different block from inode.
* Correctly handle `battach' in this case.

Signed-off-by: Hu Weiwen <sehuww@mail.scut.edu.cn>
---
 lib/cache.c | 4 ++--
 lib/inode.c | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/lib/cache.c b/lib/cache.c
index 9e65429..464a43c 100644
--- a/lib/cache.c
+++ b/lib/cache.c
@@ -102,7 +102,7 @@ static int __erofs_battach(struct erofs_buffer_block *bb,
 			   bool dryrun)
 {
 	const erofs_off_t alignedoffset = roundup(bb->buffers.off, alignsize);
-	const int oob = cmpsgn(roundup(bb->buffers.off % EROFS_BLKSIZ,
+	const int oob = cmpsgn(roundup((bb->buffers.off - 1) % EROFS_BLKSIZ + 1,
 				       alignsize) + incr + extrasize,
 			       EROFS_BLKSIZ);
 	bool tailupdate = false;
@@ -134,7 +134,7 @@ static int __erofs_battach(struct erofs_buffer_block *bb,
 			tail_blkaddr = blkaddr + BLK_ROUND_UP(bb->buffers.off);
 		erofs_bupdate_mapped(bb);
 	}
-	return (alignedoffset + incr) % EROFS_BLKSIZ;
+	return (alignedoffset + incr - 1) % EROFS_BLKSIZ + 1;
 }
 
 int erofs_bh_balloon(struct erofs_buffer_head *bh, erofs_off_t incr)
diff --git a/lib/inode.c b/lib/inode.c
index 4ed6aed..d6a64cc 100644
--- a/lib/inode.c
+++ b/lib/inode.c
@@ -531,7 +531,7 @@ int erofs_prepare_tail_block(struct erofs_inode *inode)
 	}
 	/* expend a block as the tail block (should be successful) */
 	ret = erofs_bh_balloon(bh, EROFS_BLKSIZ);
-	DBG_BUGON(ret);
+	DBG_BUGON(ret < 0);
 	return 0;
 }
 
-- 
2.30.0