Merge branch 'riscv-bcache' into riscv

5 files changed, 43 insertions, 31 deletions

diff --git a/kernel/bio.c b/kernel/bio.c
index a08884b..a1074f2 100644
--- a/kernel/bio.c
+++ b/kernel/bio.c
@@ -12,11 +12,7 @@
 // * Do not use the buffer after calling brelse.
 // * 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:
-// * B_VALID: the buffer data has been read from the disk.
-// * B_DIRTY: the buffer data has been modified
-//     and needs to be written to disk.
+
 
 #include "types.h"
 #include "param.h"
@@ -76,13 +72,11 @@ bget(uint dev, uint blockno)
   }
 
   // Not cached; recycle an unused buffer.
-  // Even if refcnt==0, B_DIRTY indicates a buffer is in use
-  // because log.c has modified it but not yet committed it.
   for(b = bcache.head.prev; b != &bcache.head; b = b->prev){
-    if(b->refcnt == 0 && (b->flags & B_DIRTY) == 0) {
+    if(b->refcnt == 0) {
       b->dev = dev;
       b->blockno = blockno;
-      b->flags = 0;
+      b->valid = 0;
       b->refcnt = 1;
       release(&bcache.lock);
       acquiresleep(&b->lock);
@@ -99,8 +93,9 @@ bread(uint dev, uint blockno)
   struct buf *b;
 
   b = bget(dev, blockno);
-  if((b->flags & B_VALID) == 0) {
-    virtio_disk_rw(b);
+  if(!b->valid) {
+    virtio_disk_rw(b, 0);
+    b->valid = 1;
   }
   return b;
 }
@@ -111,8 +106,7 @@ bwrite(struct buf *b)
 {
   if(!holdingsleep(&b->lock))
     panic("bwrite");
-  b->flags |= B_DIRTY;
-  virtio_disk_rw(b);
+  virtio_disk_rw(b, 1);
 }
 
 // Release a locked buffer.
@@ -139,3 +133,19 @@ brelse(struct buf *b)
   
   release(&bcache.lock);
 }
+
+void
+bpin(struct buf *b) {
+  acquire(&bcache.lock);
+  b->refcnt++;
+  release(&bcache.lock);
+}
+
+void
+bunpin(struct buf *b) {
+  acquire(&bcache.lock);
+  b->refcnt--;
+  release(&bcache.lock);
+}
+
+
diff --git a/kernel/buf.h b/kernel/buf.h
index 3266495..4a3a39d 100644
--- a/kernel/buf.h
+++ b/kernel/buf.h
@@ -1,5 +1,6 @@
 struct buf {
-  int flags;
+  int valid;   // has data been read from disk?
+  int disk;    // does disk "own" buf?
   uint dev;
   uint blockno;
   struct sleeplock lock;
@@ -9,6 +10,4 @@ struct buf {
   struct buf *qnext; // disk queue
   uchar data[BSIZE];
 };
-#define B_VALID 0x2  // buffer has been read from disk
-#define B_DIRTY 0x4  // buffer needs to be written to disk
 
diff --git a/kernel/defs.h b/kernel/defs.h
index de4acfd..2689bed 100644
--- a/kernel/defs.h
+++ b/kernel/defs.h
@@ -14,6 +14,8 @@ void            binit(void);
 struct buf*     bread(uint, uint);
 void            brelse(struct buf*);
 void            bwrite(struct buf*);
+void            bpin(struct buf*);
+void            bunpin(struct buf*);
 
 // console.c
 void            consoleinit(void);
@@ -177,7 +179,7 @@ void            plic_complete(int);
 
 // virtio_disk.c
 void            virtio_disk_init(void);
-void            virtio_disk_rw(struct buf *);
+void            virtio_disk_rw(struct buf *, int);
 void            virtio_disk_intr();
 
 // number of elements in fixed-size array
diff --git a/kernel/log.c b/kernel/log.c
index c8f7e62..59984db 100644
--- a/kernel/log.c
+++ b/kernel/log.c
@@ -77,6 +77,7 @@ install_trans(void)
     struct buf *dbuf = bread(log.dev, log.lh.block[tail]); // read dst
     memmove(dbuf->data, lbuf->data, BSIZE);  // copy block to dst
     bwrite(dbuf);  // write dst to disk
+    bunpin(dbuf);
     brelse(lbuf);
     brelse(dbuf);
   }
@@ -203,7 +204,7 @@ commit()
 }
 
 // Caller has modified b->data and is done with the buffer.
-// Record the block number and pin in the cache with B_DIRTY.
+// Record the block number and pin in the cache by increasing refcnt.
 // commit()/write_log() will do the disk write.
 //
 // log_write() replaces bwrite(); a typical use is:
@@ -227,9 +228,10 @@ log_write(struct buf *b)
       break;
   }
   log.lh.block[i] = b->blockno;
-  if (i == log.lh.n)
+  if (i == log.lh.n) {  // Add new block to log?
+    bpin(b);
     log.lh.n++;
-  b->flags |= B_DIRTY; // prevent eviction
+  }
   release(&log.lock);
 }
 
diff --git a/kernel/virtio_disk.c b/kernel/virtio_disk.c
index 3ace5ef..14c718d 100644
--- a/kernel/virtio_disk.c
+++ b/kernel/virtio_disk.c
@@ -164,7 +164,7 @@ alloc3_desc(int *idx)
 }
 
 void
-virtio_disk_rw(struct buf *b)
+virtio_disk_rw(struct buf *b, int write)
 {
   uint64 sector = b->blockno * (BSIZE / 512);
 
@@ -192,7 +192,7 @@ virtio_disk_rw(struct buf *b)
     uint64 sector;
   } buf0;
 
-  if(b->flags & B_DIRTY)
+  if(write)
     buf0.type = VIRTIO_BLK_T_OUT; // write the disk
   else
     buf0.type = VIRTIO_BLK_T_IN; // read the disk
@@ -208,7 +208,7 @@ virtio_disk_rw(struct buf *b)
 
   desc[idx[1]].addr = (uint64) b->data;
   desc[idx[1]].len = BSIZE;
-  if(b->flags & B_DIRTY)
+  if(write)
     desc[idx[1]].flags = 0; // device reads b->data
   else
     desc[idx[1]].flags = VRING_DESC_F_WRITE; // device writes b->data
@@ -222,6 +222,7 @@ virtio_disk_rw(struct buf *b)
   desc[idx[2]].next = 0;
 
   // record struct buf for virtio_disk_intr().
+  b->disk = 1;
   info[idx[0]].b = b;
 
   // avail[0] is flags
@@ -235,10 +236,13 @@ virtio_disk_rw(struct buf *b)
   *R(VIRTIO_MMIO_QUEUE_NOTIFY) = 0; // value is queue number
 
   // Wait for virtio_disk_intr() to say request has finished.
-  while((b->flags & (B_VALID|B_DIRTY)) != B_VALID){
+  while(b->disk == 1) {
     sleep(b, &vdisk_lock);
   }
 
+  info[idx[0]].b = 0;
+  free_chain(idx[0]);
+
   release(&vdisk_lock);
 }
 
@@ -252,15 +256,10 @@ virtio_disk_intr()
 
     if(info[id].status != 0)
       panic("virtio_disk_intr status");
-
-    info[id].b->flags |= B_VALID;
-    info[id].b->flags &= ~B_DIRTY;
-
+    
+    info[id].b->disk = 0;   // disk is done with buf
     wakeup(info[id].b);
 
-    info[id].b = 0;
-    free_chain(id);
-
     used_idx = (used_idx + 1) % NUM;
   }