GFS2: Add atomic_open support

I've restricted atomic_open to only operate on regular files, although
I still don't understand why atomic_open should not be possible also for
directories on GFS2. That can always be added in later though, if it
makes sense.

The ->atomic_open function can be passed negative dentries, which
in most cases means either ENOENT (->lookup) or a call to d_instantiate
(->create). In the GFS2 case though, we need to actually perform the
look up, since we do not know whether there has been a new inode created
on another node. The look up calls d_splice_alias which then tries to
rehash the dentry - so the solution here is to simply check for that
in d_splice_alias. The same issue is likely to affect any other cluster
filesystem implementing ->atomic_open

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: "J. Bruce Fields" <bfields fieldses org>
Cc: Jeff Layton <jlayton@redhat.com>

1 files changed, 9 insertions, 2 deletions

diff --git a/fs/dcache.c b/fs/dcache.c
index f09b9085f7d8..5a23073138df 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1612,6 +1612,10 @@ EXPORT_SYMBOL(d_obtain_alias);
  * If a dentry was found and moved, then it is returned.  Otherwise NULL
  * is returned.  This matches the expected return value of ->lookup.
  *
+ * Cluster filesystems may call this function with a negative, hashed dentry.
+ * In that case, we know that the inode will be a regular file, and also this
+ * will only occur during atomic_open. So we need to check for the dentry
+ * being already hashed only in the final case.
  */
 struct dentry *d_splice_alias(struct inode *inode, struct dentry *dentry)
 {
@@ -1636,8 +1640,11 @@ struct dentry *d_splice_alias(struct inode *inode, struct dentry *dentry)
 			security_d_instantiate(dentry, inode);
 			d_rehash(dentry);
 		}
-	} else
-		d_add(dentry, inode);
+	} else {
+		d_instantiate(dentry, inode);
+		if (d_unhashed(dentry))
+			d_rehash(dentry);
+	}
 	return new;
 }
 EXPORT_SYMBOL(d_splice_alias);