linux-kernel - [RFC PATCH v1 10/57] fs/ext4: Remove PAGE_SIZE compile-time constant assumption

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Message-ID: <20241014105912.3207374-10-ryan.roberts@arm.com>
Date: Mon, 14 Oct 2024 11:58:17 +0100
From: Ryan Roberts <ryan.roberts@....com>
To: "Theodore Ts'o" <tytso@....edu>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Anshuman Khandual <anshuman.khandual@....com>,
	Ard Biesheuvel <ardb@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	David Hildenbrand <david@...hat.com>,
	Greg Marsden <greg.marsden@...cle.com>,
	Ivan Ivanov <ivan.ivanov@...e.com>,
	Kalesh Singh <kaleshsingh@...gle.com>,
	Marc Zyngier <maz@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Matthias Brugger <mbrugger@...e.com>,
	Miroslav Benes <mbenes@...e.cz>,
	Will Deacon <will@...nel.org>
Cc: Ryan Roberts <ryan.roberts@....com>,
	linux-arm-kernel@...ts.infradead.org,
	linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: [RFC PATCH v1 10/57] fs/ext4: Remove PAGE_SIZE compile-time constant assumption

To prepare for supporting boot-time page size selection, refactor code
to remove assumptions about PAGE_SIZE being compile-time constant. Code
intended to be equivalent when compile-time page size is active.

Convert CPP PAGE_SIZE conditionals to C if/else. For compile-time page
size, the compiler will strip the dead part, and for boot-time page
size, the condition will be evaluated at run time.

Signed-off-by: Ryan Roberts <ryan.roberts@....com>
---

***NOTE***
Any confused maintainers may want to read the cover note here for context:
https://lore.kernel.org/all/20241014105514.3206191-1-ryan.roberts@arm.com/

 fs/ext4/ext4.h | 36 ++++++++++++++++++------------------
 1 file changed, 18 insertions(+), 18 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 08acd152261ed..1a6dbd925024a 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -2415,31 +2415,31 @@ ext4_rec_len_from_disk(__le16 dlen, unsigned blocksize)
 {
 	unsigned len = le16_to_cpu(dlen);
 
-#if (PAGE_SIZE >= 65536)
-	if (len == EXT4_MAX_REC_LEN || len == 0)
-		return blocksize;
-	return (len & 65532) | ((len & 3) << 16);
-#else
-	return len;
-#endif
+	if (PAGE_SIZE >= 65536) {
+		if (len == EXT4_MAX_REC_LEN || len == 0)
+			return blocksize;
+		return (len & 65532) | ((len & 3) << 16);
+	} else {
+		return len;
+	}
 }
 
 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)
+	if (PAGE_SIZE >= 65536) {
+		if (len < 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((len & 65532) | ((len >> 16) & 3));
+	} else {
 		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((len & 65532) | ((len >> 16) & 3));
-#else
-	return cpu_to_le16(len);
-#endif
 }
 
 /*
-- 
2.43.0