From: Ian Kent <raven@themaw.net>

For a long time now I have had a problem with not being able to return a
lookup failure on an existsing directory.  In autofs this corresponds to a
mount failure on a autofs managed mount entry that is browsable (and so the
mount point directory exists).

While this problem has been present for a long time I've avoided resolving
it because it was not very visible.  But now that autofs v5 has "mount and
expire on demand" of nested multiple mounts, such as is found when mounting
an export list from a server, solving the problem cannot be avoided any
longer.

I've tried very hard to find a way to do this entirely within the autofs4
module but have not been able to find a satisfactory way to achieve it.

So, I need to propose a change to the VFS.

Signed-off-by: Ian Kent <raven@themaw.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---

 fs/autofs4/root.c |   38 ++++++++++++++++++++++++++-------
 fs/namei.c        |   50 ++++++++++++++++++++++++++++++--------------
 linux/dcache.h    |    0 
 3 files changed, 65 insertions(+), 23 deletions(-)

diff -puN fs/autofs4/root.c~autofs4-needs-to-force-fail-return-revalidate fs/autofs4/root.c
--- a/fs/autofs4/root.c~autofs4-needs-to-force-fail-return-revalidate
+++ a/fs/autofs4/root.c
@@ -137,7 +137,9 @@ static int autofs4_dir_open(struct inode
 		nd.flags = LOOKUP_DIRECTORY;
 		ret = (dentry->d_op->d_revalidate)(dentry, &nd);
 
-		if (!ret) {
+		if (ret <= 0) {
+			if (ret < 0)
+				status = ret;
 			dcache_dir_close(inode, file);
 			goto out;
 		}
@@ -400,13 +402,23 @@ static int autofs4_revalidate(struct den
 	struct autofs_sb_info *sbi = autofs4_sbi(dir->i_sb);
 	int oz_mode = autofs4_oz_mode(sbi);
 	int flags = nd ? nd->flags : 0;
-	int status = 0;
+	int status = 1;
 
 	/* Pending dentry */
 	if (autofs4_ispending(dentry)) {
-		if (!oz_mode)
-			status = try_to_fill_dentry(dentry, flags);
-		return !status;
+		/* The daemon never causes a mount to trigger */
+		if (oz_mode)
+			return 1;
+
+		/*
+		 * A zero status is success otherwise we have a
+		 * negative error code.
+		 */
+		status = try_to_fill_dentry(dentry, flags);
+		if (status == 0)
+				return 1;
+
+		return status;
 	}
 
 	/* Negative dentry.. invalidate if "old" */
@@ -421,9 +433,19 @@ static int autofs4_revalidate(struct den
 		DPRINTK("dentry=%p %.*s, emptydir",
 			 dentry, dentry->d_name.len, dentry->d_name.name);
 		spin_unlock(&dcache_lock);
-		if (!oz_mode)
-			status = try_to_fill_dentry(dentry, flags);
-		return !status;
+		/* The daemon never causes a mount to trigger */
+		if (oz_mode)
+			return 1;
+
+		/*
+		 * A zero status is success otherwise we have a
+		 * negative error code.
+		 */
+		status = try_to_fill_dentry(dentry, flags);
+		if (status == 0)
+			return 1;
+
+		return status;
 	}
 	spin_unlock(&dcache_lock);
 
diff -puN fs/namei.c~autofs4-needs-to-force-fail-return-revalidate fs/namei.c
--- a/fs/namei.c~autofs4-needs-to-force-fail-return-revalidate
+++ a/fs/namei.c
@@ -365,6 +365,30 @@ void release_open_intent(struct nameidat
 		fput(nd->intent.open.file);
 }
 
+static inline struct dentry *
+do_revalidate(struct dentry *dentry, struct nameidata *nd)
+{
+	int status = dentry->d_op->d_revalidate(dentry, nd);
+	if (unlikely(status <= 0)) {
+		/*
+		 * The dentry failed validation.
+		 * If d_revalidate returned 0 attempt to invalidate
+		 * the dentry otherwise d_revalidate is asking us
+		 * to return a fail status.
+		 */
+		if (!status) {
+			if (!d_invalidate(dentry)) {
+				dput(dentry);
+				dentry = NULL;
+			}
+		} else {
+			dput(dentry);
+			dentry = ERR_PTR(status);
+		}
+	}
+	return dentry;
+}
+
 /*
  * Internal lookup() using the new generic dcache.
  * SMP-safe
@@ -379,12 +403,9 @@ static struct dentry * cached_lookup(str
 	if (!dentry)
 		dentry = d_lookup(parent, name);
 
-	if (dentry && dentry->d_op && dentry->d_op->d_revalidate) {
-		if (!dentry->d_op->d_revalidate(dentry, nd) && !d_invalidate(dentry)) {
-			dput(dentry);
-			dentry = NULL;
-		}
-	}
+	if (dentry && dentry->d_op && dentry->d_op->d_revalidate)
+		dentry = do_revalidate(dentry, nd);
+
 	return dentry;
 }
 
@@ -477,10 +498,9 @@ static struct dentry * real_lookup(struc
 	 */
 	mutex_unlock(&dir->i_mutex);
 	if (result->d_op && result->d_op->d_revalidate) {
-		if (!result->d_op->d_revalidate(result, nd) && !d_invalidate(result)) {
-			dput(result);
+		result = do_revalidate(result, nd);
+		if (!result)
 			result = ERR_PTR(-ENOENT);
-		}
 	}
 	return result;
 }
@@ -760,12 +780,12 @@ need_lookup:
 	goto done;
 
 need_revalidate:
-	if (dentry->d_op->d_revalidate(dentry, nd))
-		goto done;
-	if (d_invalidate(dentry))
-		goto done;
-	dput(dentry);
-	goto need_lookup;
+	dentry = do_revalidate(dentry, nd);
+	if (!dentry)
+		goto need_lookup;
+	if (IS_ERR(dentry))
+		goto fail;
+	goto done;
 
 fail:
 	return PTR_ERR(dentry);
diff -puN include/linux/dcache.h~autofs4-needs-to-force-fail-return-revalidate include/linux/dcache.h
_