From 3a5fa7ed9020eaf8ab843a16d26db7393b2ec072 Mon Sep 17 00:00:00 2001
From: Frans Kaashoek <kaashoek@Frans-Kaashoeks-MacBook-Pro.local>
Date: Fri, 26 Aug 2011 10:08:29 -0400
Subject: 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)

---
 fs.c | 32 ++++++++++++++++----------------
 1 file changed, 16 insertions(+), 16 deletions(-)

(limited to 'fs.c')

diff --git a/fs.c b/fs.c
index b755c78..6bfe963 100644
--- a/fs.c
+++ b/fs.c
@@ -113,11 +113,8 @@ bfree(int dev, uint b)
 // It is an error to use an inode without holding a reference to it.
 //
 // Processes are only allowed to read and write inode
-// metadata and contents when holding the inode's lock,
-// represented by the I_BUSY flag in the in-memory copy.
-// Because inode locks are held during disk accesses, 
-// they are implemented using a flag rather than with
-// spin locks.  Callers are responsible for locking
+// metadata and contents when holding the inode's sleeplock.
+// Callers are responsible for locking
 // inodes before passing them to routines in this file; leaving
 // this responsibility with the caller makes it possible for them
 // to create arbitrarily-sized atomic operations.
@@ -216,6 +213,7 @@ iget(uint dev, uint inum)
   ip->inum = inum;
   ip->ref = 1;
   ip->flags = 0;
+  initsleeplock(&ip->sleeplock);
   release(&icache.lock);
 
   return ip;
@@ -232,7 +230,7 @@ idup(struct inode *ip)
   return ip;
 }
 
-// Lock the given inode.
+// Acquire the sleeplock for a given inode.
 void
 ilock(struct inode *ip)
 {
@@ -243,9 +241,7 @@ ilock(struct inode *ip)
     panic("ilock");
 
   acquire(&icache.lock);
-  while(ip->flags & I_BUSY)
-    sleep(ip, &icache.lock);
-  ip->flags |= I_BUSY;
+  acquire_sleeplock(&ip->sleeplock, &icache.lock);
   release(&icache.lock);
 
   if(!(ip->flags & I_VALID)){
@@ -268,12 +264,11 @@ ilock(struct inode *ip)
 void
 iunlock(struct inode *ip)
 {
-  if(ip == 0 || !(ip->flags & I_BUSY) || ip->ref < 1)
+  if(ip == 0 || !acquired_sleeplock(&ip->sleeplock) || ip->ref < 1)
     panic("iunlock");
 
   acquire(&icache.lock);
-  ip->flags &= ~I_BUSY;
-  wakeup(ip);
+  release_sleeplock(&ip->sleeplock);
   release(&icache.lock);
 }
 
@@ -284,14 +279,15 @@ iput(struct inode *ip)
   acquire(&icache.lock);
   if(ip->ref == 1 && (ip->flags & I_VALID) && ip->nlink == 0){
     // inode is no longer used: truncate and free inode.
-    if(ip->flags & I_BUSY)
+    if(acquired_sleeplock(&ip->sleeplock))
       panic("iput busy");
-    ip->flags |= I_BUSY;
+    acquire_sleeplock(&ip->sleeplock, &icache.lock);
     release(&icache.lock);
     itrunc(ip);
     ip->type = 0;
     iupdate(ip);
     acquire(&icache.lock);
+    release_sleeplock(&ip->sleeplock);
     ip->flags = 0;
     wakeup(ip);
   }
@@ -433,10 +429,14 @@ writei(struct inode *ip, char *src, uint off, uint n)
     return devsw[ip->major].write(ip, src, n);
   }
 
-  if(off > ip->size || off + n < off)
+  if(off > ip->size || off + n < off) {
+    panic("writei1");
     return -1;
-  if(off + n > MAXFILE*BSIZE)
+  }
+  if(off + n > MAXFILE*BSIZE) {
+    panic("writei2");
     return -1;
+  }
 
   for(tot=0; tot<n; tot+=m, off+=m, src+=m){
     bp = bread(ip->dev, bmap(ip, off/BSIZE));
-- 
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