linux-ext4 - [PATCH] ext4: Modify the rec_len helpers to accommodate future cases

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Date:   Mon,  7 Aug 2023 09:26:54 +0800
From:   zhangshida <starzhangzsd@...il.com>
To:     tytso@....edu, adilger.kernel@...ger.ca
Cc:     linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
        zhangshida@...inos.cn, starzhangzsd@...il.com,
        Andreas Dilger <adilger@...ger.ca>
Subject: [PATCH] ext4: Modify the rec_len helpers to accommodate future cases

From: Shida Zhang <zhangshida@...inos.cn>

Following Andreas' suggestion, it is time to adapt these helpers
to handle larger records during runtime, especially in preparation
for the eventual support of ext4 with a block size greater than
PAGE_SIZE.

Suggested-by: Andreas Dilger <adilger@...ger.ca>
Signed-off-by: Shida Zhang <zhangshida@...inos.cn>
Link: https://lore.kernel.org/lkml/A9ECDF14-95A1-4B1E-A815-4B6ABF4916C6@dilger.ca/
---
 fs/ext4/ext4.h | 34 ++++++++++++++++++----------------
 1 file changed, 18 insertions(+), 16 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 0a2d55faa095..87cdf4d56da1 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -2386,39 +2386,41 @@ static inline unsigned int ext4_dir_rec_len(__u8 name_len,
 }
 
 /*
- * If we ever get support for fs block sizes > page_size, we'll need
- * to remove the #if statements in the next two functions...
+ * The next two helpers facilitate the conversion between the encoded
+ * and plain forms of rec_len. Try to access rec_len through these helpers
+ * rather than accessing it directly.
  */
-static inline unsigned int
-ext4_rec_len_from_disk(__le16 dlen, unsigned blocksize)
+static inline
+unsigned int ext4_rec_len_from_disk(__le16 dlen, unsigned blocksize)
 {
 	unsigned len = le16_to_cpu(dlen);
 
-#if (PAGE_SIZE >= 65536)
+	if (blocksize < 65536)
+		return len;
+
 	if (len == EXT4_MAX_REC_LEN || len == 0)
 		return blocksize;
+
 	return (len & 65532) | ((len & 3) << 16);
-#else
-	return len;
-#endif
 }
 
 static inline __le16 ext4_rec_len_to_disk(unsigned len, unsigned blocksize)
 {
-	BUG_ON((len > blocksize) || (blocksize > (1 << 18)) || (len & 3));
-#if (PAGE_SIZE >= 65536)
-	if (len < 65536)
+	BUG_ON(len > blocksize);
+	BUG_ON(blocksize > (1 << 18));
+	BUG_ON(len & 3);
+
+	if (len < 65536) /* always true for blocksize < 65536 */
 		return cpu_to_le16(len);
+
 	if (len == blocksize) {
 		if (blocksize == 65536)
 			return cpu_to_le16(EXT4_MAX_REC_LEN);
-		else
-			return cpu_to_le16(0);
+
+		return cpu_to_le16(0);
 	}
+
 	return cpu_to_le16((len & 65532) | ((len >> 16) & 3));
-#else
-	return cpu_to_le16(len);
-#endif
 }
 
 /*
-- 
2.27.0