create doesn't touch parent director references

04f26a8d · Silas Boyd-Wickizer · 11771df4 · 04f26a8d · 04f26a8d · 04f26a8d
--- a/include/kernel.hh
+++ b/include/kernel.hh
@@ -89,6 +89,7 @@ struct inode*   dirlookup(struct inode*, char*);
 struct inode*   ialloc(u32, short);
 struct inode*   namei(inode *cwd, const char*);
 void            iput(struct inode*);
+void            iput(inode* ip, bool haveref);
 struct inode*   iget(u32 dev, u32 inum);
 void            ilock(struct inode*, int writer);
 void            iunlockput(struct inode*);

--- a/kernel/fs.cc
+++ b/kernel/fs.cc
@@ -476,6 +476,13 @@ iunlock(struct inode *ip)
  release(&ip->lock);
 }

+void
+iput(inode* ip, bool haveref)
+{
+  if (haveref)
+    iput(ip);
+}
+
 // Caller holds reference to unlocked ip.  Drop reference.
 void
 iput(struct inode *ip)

--- a/kernel/sysfile.cc
+++ b/kernel/sysfile.cc
@@ -224,53 +224,65 @@ create(inode *cwd, const char *path, short type, short major, short minor)
 {
  struct inode *ip, *dp;
  char name[DIRSIZ];
+  bool haveref = false;
+
  mt_ascope ascope("%s(%d.%d,%s,%d,%d,%d)",
                   __func__, cwd->dev, cwd->inum,
                   path, type, major, minor);

 retry:
-  if((dp = nameiparent(cwd, path, name)) == 0)
-    return 0;
-  if(dp->type != T_DIR)
-    panic("create");
-
-  if((ip = dirlookup(dp, name)) != 0){
-    iput(dp);
-    ilock(ip, 1);
-    if(type == T_FILE && ip->type == T_FILE)
-      return ip;
-    iunlockput(ip);
-    return nullptr;
-  }
-
-  if((ip = ialloc(dp->dev, type)) == nullptr)
-    return nullptr;
-
-  ip->major = major;
-  ip->minor = minor;
-  ip->link();
-  iupdate(ip);
-
-  mtwriteavar("inode:%x.%x", ip->dev, ip->inum);
-
-  if(type == T_DIR){  // Create . and .. entries.
-    dp->link(); // for ".."
-    iupdate(dp);
-    // No ip->nlink++ for ".": avoid cyclic ref count.
-    if(dirlink(ip, ".", ip->inum) < 0 || dirlink(ip, "..", dp->inum) < 0)
-      panic("create dots");
-  }
+  {
+    scoped_gc_epoch e;
+    if((dp = __nameiparent(cwd, path, name, &haveref)) == 0)
+      return 0;
+
+    if(dp->type != T_DIR)
+      panic("create");
+
+    if((ip = dirlookup(dp, name)) != 0){
+      iput(dp, haveref);
+      ilock(ip, 1);
+      if(type == T_FILE && ip->type == T_FILE)
+        return ip;
+      iunlockput(ip);
+      return nullptr;
+    }
+    
+    if((ip = ialloc(dp->dev, type)) == nullptr)
+      return nullptr;
+    
+    ip->major = major;
+    ip->minor = minor;
+    ip->link();
+    iupdate(ip);
+    
+    mtwriteavar("inode:%x.%x", ip->dev, ip->inum);
+    
+    if(type == T_DIR){  // Create . and .. entries.
+      dp->link(); // for ".."
+      iupdate(dp);
+      // No ip->nlink++ for ".": avoid cyclic ref count.
+      if(dirlink(ip, ".", ip->inum) < 0 || dirlink(ip, "..", dp->inum) < 0)
+        panic("create dots");
+    }
+    
+    if(dirlink(dp, name, ip->inum) < 0) {
+      // create race
+      ip->unlink();
+      iunlockput(ip);
+      iput(dp, haveref);
+      goto retry;
+    }

-  if(dirlink(dp, name, ip->inum) < 0) {
-    // create race
-    ip->unlink();
-    iunlockput(ip);
-    iput(dp);
-    goto retry;
+    if (!dp->valid()) {
+      // XXX(sbw) we need to undo everything we just did
+      // (at least all the modifications to dp) and retry.
+      panic("create: race");
+    }
  }

  //nc_insert(dp, name, ip);
-  iput(dp);
+  iput(dp, haveref);
  return ip;
 }