Btrfs: Invalidate dcache entry after creating snapshot and

We need to invalidate an existing dcache entry after creating a new
snapshot or subvolume, because a negative dache entry will stop us from
accessing the new snapshot or subvolume.

---
  ctree.h       |   23 +++++++++++++++++++++++
  inode.c       |    4 ++++
  transaction.c |    4 ++++
  3 files changed, 31 insertions(+)

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 29 insertions, 0 deletions

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 1569fb864515..31aa4ba06fce 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -2642,6 +2642,31 @@ static void btrfs_truncate(struct inode *inode)
         btrfs_throttle(root);
 }
 
+/*
+ * Invalidate a single dcache entry at the root of the filesystem.
+ * Needed after creation of snapshot or subvolume.
+ */
+void btrfs_invalidate_dcache_root(struct btrfs_root *root, char *name,
+                                  int namelen)
+{
+        struct dentry *alias, *entry;
+        struct qstr qstr;
+
+        alias = d_find_alias(root->fs_info->sb->s_root->d_inode);
+        if (alias) {
+                qstr.name = name;
+                qstr.len = namelen;
+                /* change me if btrfs ever gets a d_hash operation */
+                qstr.hash = full_name_hash(qstr.name, qstr.len);
+                entry = d_lookup(alias, &qstr);
+                dput(alias);
+                if (entry) {
+                        d_invalidate(entry);
+                        dput(entry);
+                }
+        }
+}
+
 static int noinline create_subvol(struct btrfs_root *root, char *name,
                                   int namelen)
 {
@@ -2761,6 +2786,10 @@ static int noinline create_subvol(struct btrfs_root *root, char *name,
         ret = btrfs_update_inode(trans, new_root, inode);
         if (ret)
                 goto fail;
+
+        /* Invalidate existing dcache entry for new subvolume. */
+        btrfs_invalidate_dcache_root(root, name, namelen);
+
 fail:
         nr = trans->blocks_used;
         err = btrfs_commit_transaction(trans, new_root);