[PATCH v2 3/7] jffs2: write verify: add byte-by-byte comparison on mismatch

jffs2_verify_write() uses memcmp() to compare the write buffer
against data read back from flash. On mismatch, the current code
dumps the entire source and read-back data, which will become
impractical once the verify path is extended to NOR flash where
a single write can span PAGE_SIZE.

Add a byte-by-byte comparison after the memcmp() mismatch path
to locate the exact mismatch offset, reporting the first
differing offset and dumping up to 128 bytes of both the source
and read-back data. memcmp() remains on the hotpath for
successful writes, and the byte-by-byte loop only runs when an
error is actually detected.

Signed-off-by: zhouminqiang <[email protected]>
---
 fs/jffs2/wbuf.c | 46 ++++++++++++++++++++++++++++------------------
 1 file changed, 28 insertions(+), 18 deletions(-)

diff --git a/fs/jffs2/wbuf.c b/fs/jffs2/wbuf.c
index f10be57c5543..74e169dedab7 100644
--- a/fs/jffs2/wbuf.c
+++ b/fs/jffs2/wbuf.c
@@ -231,7 +231,7 @@ static int jffs2_verify_write(struct jffs2_sb_info *c, unsigned char *buf,
 			      uint32_t ofs)
 {
 	int ret;
-	size_t retlen;
+	size_t retlen, i;
 	char *eccstr;
 	void *verify_buf;
 
@@ -246,10 +246,10 @@ static int jffs2_verify_write(struct jffs2_sb_info *c, unsigned char *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;
@@ -259,24 +259,34 @@ static int jffs2_verify_write(struct jffs2_sb_info *c, unsigned char *buf,
 		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";
 
-	kfree(verify_buf);
-	return -EIO;
+		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;
+	}
 
 out_free:
 	kfree(verify_buf);
-- 
2.52.0