Revert "Introduce and use sleeplocks instead of BUSY flags"

My changes have a race with re-used bufs and the code doesn't seem to get shorter
Keep the changes that fixed ip->off race

This reverts commit 3a5fa7ed9020eaf8ab843a16d26db7393b2ec072.

Conflicts:

	defs.h
	file.c
	file.h

1 files changed, 22 insertions, 23 deletions

diff --git a/bio.c b/bio.c
index f11328d..6a3968b 100644
--- a/bio.c
+++ b/bio.c
@@ -13,7 +13,9 @@
 // * Only one process at a time can use a buffer,
 //     so do not keep them longer than necessary.
 // 
-// The implementation uses two state flags internally:
+// The implementation uses three state flags internally:
+// * B_BUSY: the block has been returned from bread
+//     and has not been passed back to brelse.  
 // * B_VALID: the buffer data has been initialized
 //     with the associated disk block contents.
 // * B_DIRTY: the buffer data has been modified
@@ -49,8 +51,6 @@ binit(void)
     b->next = bcache.head.next;
     b->prev = &bcache.head;
     b->dev = -1;
-    initlock(&b->lock, "buf");
-    initsleeplock(&b->sleeplock);
     bcache.head.next->prev = b;
     bcache.head.next = b;
   }
@@ -58,43 +58,42 @@ binit(void)
 
 // Look through buffer cache for sector on device dev.
 // If not found, allocate fresh block.
-// In either case, return sleep-locked buffer.
+// In either case, return locked buffer.
 static struct buf*
 bget(uint dev, uint sector)
 {
   struct buf *b;
 
   acquire(&bcache.lock);
+
+ loop:
   // Try for cached block.
   for(b = bcache.head.next; b != &bcache.head; b = b->next){
-    acquire(&b->lock);
     if(b->dev == dev && b->sector == sector){
-      release(&bcache.lock);
-      acquire_sleeplock(&b->sleeplock, &b->lock);
-      release(&b->lock);
-      return b;
+      if(!(b->flags & B_BUSY)){
+        b->flags |= B_BUSY;
+        release(&bcache.lock);
+        return b;
+      }
+      sleep(b, &bcache.lock);
+      goto loop;
     }
-    release(&b->lock);
   }
 
   // Allocate fresh block.
   for(b = bcache.head.prev; b != &bcache.head; b = b->prev){
-    acquire(&b->lock);
-    if (!acquired_sleeplock(&b->sleeplock)) {
-      release(&bcache.lock);
+    if((b->flags & B_BUSY) == 0){
       b->dev = dev;
       b->sector = sector;
-      b->flags = 0;
-      acquire_sleeplock(&b->sleeplock, &b->lock);
-      release(&b->lock);
+      b->flags = B_BUSY;
+      release(&bcache.lock);
       return b;
     }
-    release(&b->lock);
   }
   panic("bget: no buffers");
 }
 
-// Return a locked buf with the contents of the indicated disk sector.
+// Return a B_BUSY buf with the contents of the indicated disk sector.
 struct buf*
 bread(uint dev, uint sector)
 {
@@ -110,7 +109,7 @@ bread(uint dev, uint sector)
 void
 bwrite(struct buf *b)
 {
-  if(!acquired_sleeplock(&b->sleeplock))
+  if((b->flags & B_BUSY) == 0)
     panic("bwrite");
   b->flags |= B_DIRTY;
   iderw(b);
@@ -120,11 +119,11 @@ bwrite(struct buf *b)
 void
 brelse(struct buf *b)
 {
-  if(!acquired_sleeplock(&b->sleeplock))
+  if((b->flags & B_BUSY) == 0)
     panic("brelse");
 
   acquire(&bcache.lock);
-  acquire(&b->lock);
+
   b->next->prev = b->prev;
   b->prev->next = b->next;
   b->next = bcache.head.next;
@@ -132,8 +131,8 @@ brelse(struct buf *b)
   bcache.head.next->prev = b;
   bcache.head.next = b;
 
-  release_sleeplock(&b->sleeplock);
-  release(&b->lock);
+  b->flags &= ~B_BUSY;
+  wakeup(b);
 
   release(&bcache.lock);
 }