Introduce and use sleeplocks instead of BUSY flags

Remove I_BUSY, B_BUSY, and intrans defs and usages
One spinlock per buf to avoid ugly loop in bget
fix race in filewrite (don't update f->off after releasing lock)

1 files changed, 38 insertions, 4 deletions

diff --git a/spinlock.c b/spinlock.c
index a16621c..c1f6a96 100644
--- a/spinlock.c
+++ b/spinlock.c
@@ -17,10 +17,9 @@ initlock(struct spinlock *lk, char *name)
   lk->cpu = 0;
 }
 
-// Acquire the lock.
-// Loops (spins) until the lock is acquired.
-// Holding a lock for a long time may cause
-// other CPUs to waste time spinning to acquire it.
+// Acquire a spin lock. Loops (spins) until the lock is acquired.
+// Holding a lock for a long time may cause other CPUs to waste time spinning to acquire it.
+// Spinlocks shouldn't be held across sleep(); for those cases, use sleeplocks.
 void
 acquire(struct spinlock *lk)
 {
@@ -115,3 +114,38 @@ popcli(void)
     sti();
 }
 
+void
+initsleeplock(struct sleeplock *l)
+{
+  l->locked = 0;
+}
+
+// Grab the sleeplock that is protected by spinl. Sleeplocks allow a process to lock
+// a data structure for long times, including across sleeps.  Other processes that try
+// to acquire a sleeplock will be put to sleep when another process hold the sleeplock.
+// To update status of the sleeplock atomically, the caller must hold spinl
+void
+acquire_sleeplock(struct sleeplock *sleepl, struct spinlock *spinl)
+{
+  while (sleepl->locked) {
+    sleep(sleepl, spinl);
+  }
+  sleepl->locked = 1;
+}
+
+// Release the sleeplock that is protected by a spin lock
+// Caller must hold the spinlock that protects the sleeplock
+void
+release_sleeplock(struct sleeplock *sleepl)
+{
+  sleepl->locked = 0;
+  wakeup(sleepl);
+}
+
+// Is the sleeplock acquired?
+// Caller must hold the spinlock that protects the sleeplock
+int
+acquired_sleeplock(struct sleeplock *sleepl)
+{
+  return sleepl->locked;
+}