linux-kernel - [PATCH v2] ubifs: remove unnecessary check in ubifs_log_start

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Date:   Fri, 24 Aug 2018 09:15:45 +0800
From:   Liu Song <liu.song11@....com.cn>
To:     richard@....at, dedekind1@...il.com, adrian.hunter@...el.com
Cc:     linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
        liu.song11@....com.cn, jiang.biao2@....com.cn,
        zhong.weidong@....com.cn
Subject: [PATCH v2] ubifs: remove unnecessary check in ubifs_log_start_commit

In ubifs_log_start_commit, the value of c->lhead_offs is zero or set
to zero by code bellow.

	/* Switch to the next log LEB */
	if (c->lhead_offs) {
		c->lhead_lnum = ubifs_next_log_lnum(c, c->lhead_lnum);
		ubifs_assert(c->lhead_lnum != c->ltail_lnum);
		c->lhead_offs = 0;
	}

The value of 'len' can not exceed 'max_len' which assigned value by
code bellow.

	max_len = UBIFS_CS_NODE_SZ + c->jhead_cnt * UBIFS_REF_NODE_SZ;

The value of c->lhead_offs changed by code bellow and cannot exceed
'max_len'.

	c->lhead_offs += len;
	if (c->lhead_offs == c->leb_size) {
		c->lhead_lnum = ubifs_next_log_lnum(c, c->lhead_lnum);
		c->lhead_offs = 0;
	}

Usually, the size of PEB is between 64KB and 256KB. So the value of
c->lhead_offs is far less than c->leb_size. The check 
'if (c->lhead_offs == c->leb_size)' could never to be true.

Signed-off-by: Liu Song <liu.song11@....com.cn>
Reviewed-by: Jiang Biao <jiang.biao2@....com.cn>
---
v2: Improve description and code as suggestted by Richard.

 fs/ubifs/log.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/fs/ubifs/log.c b/fs/ubifs/log.c
index 7cffa12..78afb78 100644
--- a/fs/ubifs/log.c
+++ b/fs/ubifs/log.c
@@ -427,10 +427,7 @@ int ubifs_log_start_commit(struct ubifs_info *c, int *ltail_lnum)
 	*ltail_lnum = c->lhead_lnum;
 
 	c->lhead_offs += len;
-	if (c->lhead_offs == c->leb_size) {
-		c->lhead_lnum = ubifs_next_log_lnum(c, c->lhead_lnum);
-		c->lhead_offs = 0;
-	}
+	ubifs_assert(c->lhead_offs < c->leb_size);
 
 	remove_buds(c);
 
-- 
2.1.0.GIT