patch-2.4.20 linux-2.4.20/include/asm-i386/rwsem.h

• Lines: 59
• Date: Thu Nov 28 15:53:15 2002
• Orig file: linux-2.4.19/include/asm-i386/rwsem.h
• Orig date: Fri Aug 2 17:39:45 2002

diff -urN linux-2.4.19/include/asm-i386/rwsem.h linux-2.4.20/include/asm-i386/rwsem.h
@@ -4,6 +4,8 @@
  *
  * Derived from asm-i386/semaphore.h
  *
+ * Trylock by Brian Watson (Brian.J.Watson@compaq.com).
+ *
  *
  * The MSW of the count is the negated number of active writers and waiting
  * lockers, and the LSW is the total number of active locks
@@ -117,6 +119,29 @@
 }
 
 /*
+ * trylock for reading -- returns 1 if successful, 0 if contention
+ */
+static inline int __down_read_trylock(struct rw_semaphore *sem)
+{
+	__s32 result, tmp;
+	__asm__ __volatile__(
+		"# beginning __down_read_trylock\n\t"
+		"  movl      %0,%1\n\t"
+		"1:\n\t"
+		"  movl	     %1,%2\n\t"
+		"  addl      %3,%2\n\t"
+		"  jle	     2f\n\t"
+LOCK_PREFIX	"  cmpxchgl  %2,%0\n\t"
+		"  jnz	     1b\n\t"
+		"2:\n\t"
+		"# ending __down_read_trylock\n\t"
+		: "+m"(sem->count), "=&a"(result), "=&r"(tmp)
+		: "i"(RWSEM_ACTIVE_READ_BIAS)
+		: "memory", "cc");
+	return result>=0 ? 1 : 0;
+}
+
+/*
  * lock for writing
  */
 static inline void __down_write(struct rw_semaphore *sem)
@@ -144,6 +169,19 @@
 }
 
 /*
+ * trylock for writing -- returns 1 if successful, 0 if contention
+ */
+static inline int __down_write_trylock(struct rw_semaphore *sem)
+{
+	signed long ret = cmpxchg(&sem->count,
+				  RWSEM_UNLOCKED_VALUE, 
+				  RWSEM_ACTIVE_WRITE_BIAS);
+	if (ret == RWSEM_UNLOCKED_VALUE)
+		return 1;
+	return 0;
+}
+
+/*
  * unlock after reading
  */
 static inline void __up_read(struct rw_semaphore *sem)