A namex impl. that takes a ref. only for the inode it returns.

..next step is a namex that takes no refs.

A namex impl. that takes a ref. only for the inode it returns.
0aea01d8 · Silas Boyd-Wickizer · f51e9863 · 0aea01d8
--- a/kernel/fs.cc
+++ b/kernel/fs.cc
@@ -269,29 +269,29 @@ inode::~inode()
  destroycondvar(&cv);
 }

-struct inode*
-iget(u32 dev, u32 inum)
+static inode*
+__iget(u32 dev, u32 inum, bool* haveref)
 {
+  inode* ip;
+
+  // Assumes caller is holding a gc_epoch
+
 retry:
  // Try for cached inode.
-  {
-    scoped_gc_epoch e;
-    struct inode *ip = ins->lookup(make_pair(dev, inum));
+  ip = ins->lookup(make_pair(dev, inum));
  if (ip) {
-      if (ip->tryinc()) {
    if (!(ip->flags & I_VALID)) {
      acquire(&ip->lock);
      while((ip->flags & I_VALID) == 0)
        cv_sleep(&ip->cv, &ip->lock);
      release(&ip->lock);
    }
+    *haveref = false;
    return ip;
  }
-    }
-  }
  
  // Allocate fresh inode cache slot.
-  struct inode *ip = inode::alloc(dev, inum);
+  ip = inode::alloc(dev, inum);
  if (ip == nullptr)
    panic("igetnoref: should throw_bad_alloc()");
  
@@ -308,6 +308,22 @@ iget(u32 dev, u32 inum)
  ip->init();

  iunlock(ip);
+  *haveref = true;
+  return ip;
+}
+
+inode*
+iget(u32 dev, u32 inum)
+{
+  bool haveref;
+  inode* ip;
+
+  scoped_gc_epoch e;
+retry:
+  ip = __iget(dev, inum, &haveref);
+  if (!haveref)
+    if (!ip->tryinc())
+      goto retry;
  return ip;
 }

@@ -728,6 +744,20 @@ dir_flush(struct inode *dp)
 }

 // Look for a directory entry in a directory.
+static inode*
+__dirlookup(struct inode *dp, char *name, bool* haveref)
+{
+  // Assumes caller is holding a gc_epoch
+
+  dir_init(dp);
+
+  u32 inum = dp->dir.load()->lookup(strbuf<DIRSIZ>(name));
+  if (inum == 0)
+    return 0;
+  return __iget(dp->dev, inum, haveref);
+}
+
+// Look for a directory entry in a directory.
 struct inode*
 dirlookup(struct inode *dp, char *name)
 {
@@ -735,10 +765,8 @@ dirlookup(struct inode *dp, char *name)

  u32 inum = dp->dir.load()->lookup(strbuf<DIRSIZ>(name));

-  //cprintf("dirlookup: %x (%d): %s -> %d\n", dp, dp->inum, name, inum);
  if (inum == 0)
    return 0;
-
  return iget(dp->dev, inum);
 }

@@ -803,7 +831,7 @@ static struct inode*
 namex(inode *cwd, const char *path, int nameiparent, char *name)
 {
  struct inode *ip, *next;
-  bool drop_ref;
+  bool haveref;
  int r;

  scoped_gc_epoch e;
@@ -811,7 +839,7 @@ namex(inode *cwd, const char *path, int nameiparent, char *name)
    ip = the_root;
  else
    ip = cwd;
-  drop_ref = false;
+  haveref = false;

  while((r = skipelem(&path, name)) == 1){
    // XXX Doing this here requires some annoying reasoning about all
@@ -830,17 +858,18 @@ namex(inode *cwd, const char *path, int nameiparent, char *name)
      return 0;
    if(nameiparent && *path == '\0'){
      // Stop one level early.
-      if (!drop_ref)
+      if (!haveref)
        idup(ip);
      return ip;
    }

-    if((next = dirlookup(ip, name)) == 0)
+    bool nextref;
+    if((next = __dirlookup(ip, name, &nextref)) == 0)
      return 0;
-    if (drop_ref)
+    if (haveref)
      iput(ip);

-    drop_ref = true;
+    haveref = nextref;
    ip = next;
  }

@@ -854,7 +883,7 @@ namex(inode *cwd, const char *path, int nameiparent, char *name)
  // mtreadavar("inode:%x.%x", ip->dev, ip->inum);
  mtwriteavar("inode:%x.%x", ip->dev, ip->inum);

-  if (!drop_ref)
+  if (!haveref)
    idup(ip);
  return ip;
 }