[PATCH] triple_down in fs.h

["Per Persson" <per.persson@gnosjo.pp.se>]

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First, I'd like to send a thank to the Linux community from my father who
passed away this morning. He was very impressed by Linux and other free or
semi-free software like Samba, MySQL, GIMP and StarOffice.


Now to the patch:
I've made a couple of minor (but important?) changes in my patch of
{double,triple}_down in include/linux/fs.h.

Changes:

1) Added #undef's of my macros.
   Thanks to Mitchell Blank Jr who proposed this change.
   Also thanks to Yaroslav Popovitch who told me he had got an error caused
by the lack of #undef's.

2) Changed the names of the macros to further minimize the risk for name
collision; exch -> exch_vars,  sort -> sort_vars.


Per Persson
per.persson@gnosjo.pp.se

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--- include/linux/fs.h.orig	Sat Sep 29 22:10:21 2001
+++ include/linux/fs.h	Mon Oct  8 13:03:24 2001
@@ -1476,14 +1476,27 @@
 /*
  * Whee.. Deadlock country. Happily there are only two VFS
  * operations that does this..
+ *
+ * {double,triple}_down modified by Per Persson in September, 2001
  */
+
+#define exch_vars(x,y)				\
+do {						\
+	typeof(x) __tmp__ = (x);		\
+	(x) = (y);				\
+	(y) = __tmp__;				\
+						\
+	(void)(&(x) == &(y))  /* typecheck */	\
+} while(0)
+
+#define sort_vars(x,y)			\
+if((x) > (y))				\
+	exch_vars((x), (y))
+
 static inline void double_down(struct semaphore *s1, struct semaphore *s2)
 {
 	if (s1 != s2) {
-		if ((unsigned long) s1 < (unsigned long) s2) {
-			struct semaphore *tmp = s2;
-			s2 = s1; s1 = tmp;
-		}
+		sort_vars((ulong) s2, (ulong) s1);	// s2 < s1
 		down(s1);
 	}
 	down(s2);
@@ -1493,9 +1506,11 @@
  * Ewwwwwwww... _triple_ lock. We are guaranteed that the 3rd argument is
  * not equal to 1st and not equal to 2nd - the first case (target is parent of
  * source) would be already caught, the second is plain impossible (target is
- * its own parent and that case would be caught even earlier). Very messy.
- * I _think_ that it works, but no warranties - please, look it through.
- * Pox on bloody lusers who mandated overwriting rename() for directories...
+ * its own parent and that case would be caught even earlier).
+ *
+ * Hopefully it does the same thing as the old code,
+ * but in a cleaner and more efficient way.
+ *     /Per
  */
 
 static inline void triple_down(struct semaphore *s1,
@@ -1503,33 +1518,17 @@
 			       struct semaphore *s3)
 {
 	if (s1 != s2) {
-		if ((unsigned long) s1 < (unsigned long) s2) {
-			if ((unsigned long) s1 < (unsigned long) s3) {
-				struct semaphore *tmp = s3;
-				s3 = s1; s1 = tmp;
-			}
-			if ((unsigned long) s1 < (unsigned long) s2) {
-				struct semaphore *tmp = s2;
-				s2 = s1; s1 = tmp;
-			}
-		} else {
-			if ((unsigned long) s1 < (unsigned long) s3) {
-				struct semaphore *tmp = s3;
-				s3 = s1; s1 = tmp;
-			}
-			if ((unsigned long) s2 < (unsigned long) s3) {
-				struct semaphore *tmp = s3;
-				s3 = s2; s2 = tmp;
-			}
-		}
+		sort_vars((ulong) s2, (ulong) s1);	// s2 < s1
+		sort_vars((ulong) s3, (ulong) s1);	// s3 < s1
 		down(s1);
-	} else if ((unsigned long) s2 < (unsigned long) s3) {
-		struct semaphore *tmp = s3;
-		s3 = s2; s2 = tmp;
 	}
+	sort_vars((ulong) s3, (ulong) s2);		// s2 > s3
 	down(s2);
 	down(s3);
 }
+
+#undef exch_vars
+#undef sort_vars
 
 static inline void double_up(struct semaphore *s1, struct semaphore *s2)
 {