From: Peter Dinda <pdinda@northwestern.edu>
Date: Mon, 30 Jun 2014 19:22:07 +0000 (-0500)
Subject: Add shared-exclusive (readers-writer) locks
X-Git-Url: http://v3vee.org/palacios/gitweb/gitweb.cgi?p=palacios.git;a=commitdiff_plain;h=626494b00fd477070f7eb43693eb16c4dc45f66b

Add shared-exclusive (readers-writer) locks
---

diff --git a/palacios/include/palacios/vmm_lock.h b/palacios/include/palacios/vmm_lock.h
index 575bb81..5531aea 100644
--- a/palacios/include/palacios/vmm_lock.h
+++ b/palacios/include/palacios/vmm_lock.h
@@ -23,20 +23,50 @@
 #ifdef __V3VEE__
 #include <palacios/vmm_types.h>
 
+// Exclusive locks
+
 typedef addr_t v3_lock_t;
 
 int v3_lock_init(v3_lock_t * lock);
 void v3_lock_deinit(v3_lock_t * lock);
 
 
+// Interreupts unaffected
 void v3_lock(v3_lock_t lock);
 void v3_unlock(v3_lock_t lock);
 
-
+// Interrupts disabled
 addr_t v3_lock_irqsave(v3_lock_t lock);
 void v3_unlock_irqrestore(v3_lock_t lock, addr_t irq_state);
 
 
+// Reader-writer locks
+
+typedef struct v3_rw_lock {
+    v3_lock_t lock;
+    sint64_t  reader_count;
+} v3_rw_lock_t;
+
+int v3_rw_lock_init(v3_rw_lock_t *lock);
+void v3_rw_lock_deinit(v3_rw_lock_t *lock);
+
+// A read lock is not exclusive and does not
+// affect interrupts
+void v3_read_lock(v3_rw_lock_t *lock);
+void v3_read_unlock(v3_rw_lock_t *lock);
+
+// A write lock is exclusive and may affect
+// interrupts
+
+// leaves interrupt state alone
+void v3_write_lock(v3_rw_lock_t *lock);
+void v3_read_unlock(v3_rw_lock_t *lock);
+
+// turn interrupts off
+addr_t v3_write_lock_irqsave(v3_rw_lock_t *lock);
+void v3_write_unlock_irqrestore(v3_rw_lock_t *lock, addr_t irq_state);
+
+
 #endif
 
 #endif
diff --git a/palacios/src/palacios/vmm_lock.c b/palacios/src/palacios/vmm_lock.c
index 23569d2..7b3a091 100644
--- a/palacios/src/palacios/vmm_lock.c
+++ b/palacios/src/palacios/vmm_lock.c
@@ -57,3 +57,79 @@ addr_t v3_lock_irqsave(v3_lock_t lock) {
 void v3_unlock_irqrestore(v3_lock_t lock, addr_t irq_state) {
     os_hooks->mutex_unlock_irqrestore((void *)lock,(void*)irq_state);
 }
+
+
+int v3_rw_lock_init(v3_rw_lock_t *lock)
+{
+    lock->reader_count=0;
+    return v3_lock_init(&(lock->lock));
+}
+
+void v3_rw_lock_deinit(v3_rw_lock_t *lock)
+{
+    v3_lock_deinit(&(lock->lock));
+    lock->reader_count=0;
+}
+
+void v3_read_lock(v3_rw_lock_t *lock)
+{
+    addr_t flags;
+
+    flags=v3_lock_irqsave(lock->lock);
+    lock->reader_count++;
+    v3_unlock_irqrestore(lock->lock,flags);
+    // readers can come in after us, writers cannot
+}
+void v3_read_unlock(v3_rw_lock_t *lock)
+{
+    addr_t flags;
+
+    flags=v3_lock_irqsave(lock->lock);
+    lock->reader_count--;
+    v3_unlock_irqrestore(lock->lock,flags);
+    // readers can come in after us, and also writers if reader_count==0
+}
+
+void v3_write_lock(v3_rw_lock_t *lock)
+{
+    // a less hideous implementation is possible, of course...
+    while (1) { 
+	v3_lock(lock->lock);
+	if (!(lock->reader_count)) { 
+	    break;
+	}
+	v3_unlock(lock->lock);
+	V3_Yield();
+    }
+    // holding lock now - reader or writer cannot come in after us
+}
+
+addr_t v3_write_lock_irqsave(v3_rw_lock_t *lock)
+{
+    addr_t flags;
+
+    while (1) { 
+	flags=v3_lock_irqsave(lock->lock);
+	if (!(lock->reader_count)) { 
+	    break;
+	}
+	v3_unlock_irqrestore(lock->lock,flags);
+	V3_Yield();
+    }
+    // holding lock now with interrupts off - reader or writer canot come in after us
+    return flags;
+}
+
+void v3_write_unlock(v3_rw_lock_t *lock) 
+{
+    // I am already holding this lock
+    v3_unlock(lock->lock);
+    // readers/writers can now come in
+}
+
+void v3_write_unlock_irqrestore(v3_rw_lock_t *lock, addr_t irq_state)
+{
+    // I am already holding this lock with interrupts off
+    v3_unlock_irqrestore(lock->lock,irq_state);
+    // readers/writers can now come in
+}