linux-kernel - [PATCH] fs: ufs: Remove switch statement from ufs_set_de

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Date:   Wed, 17 Oct 2018 13:34:26 +0100
From:   Phillip Potter <phil@...lpotter.co.uk>
To:     dushistov@...l.ru, David.Laight@...lab.com
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: [PATCH] fs: ufs: Remove switch statement from ufs_set_de_type
 function

Remove switch statement from ufs_set_de_type function in fs/ufs/util.h
header and replace with simple assignment. For each case, S_IFx >> 12
is equal to DT_x, so in valid cases (mode & S_IFMT) >> 12 should give
us the correct file type. This is verified at compile-time with
BUILD_BUG_ON macro calls. For invalid cases, upper layer validation
catches this anyway, so this improves readability and arguably
performance by assigning (mode & S_IFMT) >> 12 directly.

Signed-off-by: Phillip Potter <phil@...lpotter.co.uk>
---
 fs/ufs/util.h | 39 +++++++++++----------------------------
 1 file changed, 11 insertions(+), 28 deletions(-)

diff --git a/fs/ufs/util.h b/fs/ufs/util.h
index 1fd3011ea623..dcf86829edc2 100644
--- a/fs/ufs/util.h
+++ b/fs/ufs/util.h
@@ -16,6 +16,7 @@
  * some useful macros
  */
 #define in_range(b,first,len)	((b)>=(first)&&(b)<(first)+(len))
+#define S_SHIFT			12
 
 /*
  * functions used for retyping
@@ -158,34 +159,16 @@ ufs_set_de_type(struct super_block *sb, struct ufs_dir_entry *de, int mode)
 	if ((UFS_SB(sb)->s_flags & UFS_DE_MASK) != UFS_DE_44BSD)
 		return;
 
-	/*
-	 * TODO turn this into a table lookup
-	 */
-	switch (mode & S_IFMT) {
-	case S_IFSOCK:
-		de->d_u.d_44.d_type = DT_SOCK;
-		break;
-	case S_IFLNK:
-		de->d_u.d_44.d_type = DT_LNK;
-		break;
-	case S_IFREG:
-		de->d_u.d_44.d_type = DT_REG;
-		break;
-	case S_IFBLK:
-		de->d_u.d_44.d_type = DT_BLK;
-		break;
-	case S_IFDIR:
-		de->d_u.d_44.d_type = DT_DIR;
-		break;
-	case S_IFCHR:
-		de->d_u.d_44.d_type = DT_CHR;
-		break;
-	case S_IFIFO:
-		de->d_u.d_44.d_type = DT_FIFO;
-		break;
-	default:
-		de->d_u.d_44.d_type = DT_UNKNOWN;
-	}
+	/* Compile-time assertions that S_IFx >> S_SHIFT == DT_x */
+	BUILD_BUG_ON(S_IFIFO >> S_SHIFT != DT_FIFO);
+	BUILD_BUG_ON(S_IFCHR >> S_SHIFT != DT_CHR);
+	BUILD_BUG_ON(S_IFDIR >> S_SHIFT != DT_DIR);
+	BUILD_BUG_ON(S_IFBLK >> S_SHIFT != DT_BLK);
+	BUILD_BUG_ON(S_IFREG >> S_SHIFT != DT_REG);
+	BUILD_BUG_ON(S_IFLNK >> S_SHIFT != DT_LNK);
+	BUILD_BUG_ON(S_IFSOCK >> S_SHIFT != DT_SOCK);
+
+	de->d_u.d_44.d_type = (mode & S_IFMT) >> S_SHIFT;
 }
 
 static inline u32
-- 
2.17.2