[PATCH 2/6] jffs2: write verify: replace memcmp with byte-by-byte comparison

jffs2_verify_write() uses memcmp() to compare the write buffer
against data read back from flash. While memcmp() compares byte
by byte internally, it only reports equal or not-equal without
identifying the mismatch offset.

To pinpoint the exact mismatch offset, replace this with the
approach used by UBI's self_check_write(): compare byte by byte
and, on mismatch, report the first differing offset and dump up
to 128 bytes of both the source and read-back data.

Signed-off-by: zhouminqiang <[email protected]>
---
 fs/jffs2/wbuf.c | 53 +++++++++++++++++++++++++++++--------------------
 1 file changed, 31 insertions(+), 22 deletions(-)

diff --git a/fs/jffs2/wbuf.c b/fs/jffs2/wbuf.c
index 7e4608b43a4e..da6da813a4ef 100644
--- a/fs/jffs2/wbuf.c
+++ b/fs/jffs2/wbuf.c
@@ -231,8 +231,8 @@ static struct jffs2_raw_node_ref **jffs2_incore_replace_raw(struct jffs2_sb_info
 static int jffs2_verify_write(struct jffs2_sb_info *c, unsigned char *buf,
 			      uint32_t ofs)
 {
-	int ret;
-	size_t retlen;
+	int ret = 0;
+	size_t retlen, i;
 	char *eccstr;
 	void *verify_buf;
 
@@ -246,37 +246,46 @@ static int jffs2_verify_write(struct jffs2_sb_info *c, unsigned char *buf,
 	ret = mtd_read(c->mtd, ofs, c->wbuf_pagesize, &retlen, verify_buf);
 	if (ret && ret != -EUCLEAN && ret != -EBADMSG) {
 		pr_warn("%s(): Read back of page at %08x failed: %d\n",
-			__func__, c->wbuf_ofs, ret);
+			__func__, ofs, ret);
 		goto out_free;
 	} else if (retlen != c->wbuf_pagesize) {
-		pr_warn("%s(): Read back of page at %08x gave short read: %zd not %d\n",
+		pr_warn("%s(): Read back of page at %08x gave short read: %zu not %d\n",
 			__func__, ofs, retlen, c->wbuf_pagesize);
 		ret = -EIO;
 		goto out_free;
 	}
-	if (!memcmp(buf, verify_buf, c->wbuf_pagesize)) {
-		ret = 0;
-		goto out_free;
-	}
 
-	if (ret == -EUCLEAN)
-		eccstr = "corrected";
-	else if (ret == -EBADMSG)
-		eccstr = "correction failed";
-	else
-		eccstr = "OK or unused";
+	for (i = 0; i < c->wbuf_pagesize; i++) {
+		uint8_t c1 = ((uint8_t *)buf)[i];
+		uint8_t c2 = ((uint8_t *)verify_buf)[i];
+		int dump_len;
 
-	pr_warn("Write verify error (ECC %s) at %08x. Wrote:\n",
-		eccstr, c->wbuf_ofs);
-	print_hex_dump(KERN_WARNING, "", DUMP_PREFIX_OFFSET, 16, 1,
-		       c->wbuf, c->wbuf_pagesize, 0);
+		if (c1 == c2)
+			continue;
 
-	pr_warn("Read back:\n");
-	print_hex_dump(KERN_WARNING, "", DUMP_PREFIX_OFFSET, 16, 1,
-		       verify_buf, c->wbuf_pagesize, 0);
+		if (ret == -EUCLEAN)
+			eccstr = "corrected";
+		else if (ret == -EBADMSG)
+			eccstr = "correction failed";
+		else
+			eccstr = "OK or unused";
+
+		dump_len = min_t(int, 128, c->wbuf_pagesize - i);
+		pr_warn("Write verify error (ECC %s) at %08x (+%zu/%d). Wrote:\n",
+			eccstr, ofs, i, c->wbuf_pagesize);
+		print_hex_dump(KERN_WARNING, "", DUMP_PREFIX_OFFSET, 16, 1,
+			       buf + i, dump_len, 0);
+
+		pr_warn("Read back:\n");
+		print_hex_dump(KERN_WARNING, "", DUMP_PREFIX_OFFSET, 16, 1,
+			       verify_buf + i, dump_len, 0);
+
+		ret = -EIO;
+		goto out_free;
+	}
 
 	vfree(verify_buf);
-	return -EIO;
+	return 0;
 
 out_free:
 	vfree(verify_buf);
-- 
2.52.0