NFS: Fix the ustat() regression

Since 2.6.18, the superblock sb->s_root has been a dummy dentry with a
dummy inode. This breaks ustat(), which actually uses sb->s_root in a
vfstat() call.

Fix this by making the s_root a dummy alias to the directory inode that was
used when creating the superblock.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 27 insertions, 54 deletions

diff --git a/fs/nfs/getroot.c b/fs/nfs/getroot.c
index 522e5ad4d8ad..0ee43843f4ec 100644
--- a/fs/nfs/getroot.c
+++ b/fs/nfs/getroot.c
@@ -43,6 +43,25 @@
 #define NFSDBG_FACILITY         NFSDBG_CLIENT
 
 /*
+ * Set the superblock root dentry.
+ * Note that this function frees the inode in case of error.
+ */
+static int nfs_superblock_set_dummy_root(struct super_block *sb, struct inode *inode)
+{
+        /* The mntroot acts as the dummy root dentry for this superblock */
+        if (sb->s_root == NULL) {
+                sb->s_root = d_alloc_root(inode);
+                if (sb->s_root == NULL) {
+                        iput(inode);
+                        return -ENOMEM;
+                }
+                /* Circumvent igrab(): we know the inode is not being freed */
+                atomic_inc(&inode->i_count);
+        }
+        return 0;
+}
+
+/*
  * get an NFS2/NFS3 root dentry from the root filehandle
  */
 struct dentry *nfs_get_root(struct super_block *sb, struct nfs_fh *mntfh)
@@ -54,33 +73,6 @@ struct dentry *nfs_get_root(struct super_block *sb, struct nfs_fh *mntfh)
         struct inode *inode;
         int error;
 
-        /* create a dummy root dentry with dummy inode for this superblock */
-        if (!sb->s_root) {
-                struct nfs_fh dummyfh;
-                struct dentry *root;
-                struct inode *iroot;
-
-                memset(&dummyfh, 0, sizeof(dummyfh));
-                memset(&fattr, 0, sizeof(fattr));
-                nfs_fattr_init(&fattr);
-                fattr.valid = NFS_ATTR_FATTR;
-                fattr.type = NFDIR;
-                fattr.mode = S_IFDIR | S_IRUSR | S_IWUSR;
-                fattr.nlink = 2;
-
-                iroot = nfs_fhget(sb, &dummyfh, &fattr);
-                if (IS_ERR(iroot))
-                        return ERR_PTR(PTR_ERR(iroot));
-
-                root = d_alloc_root(iroot);
-                if (!root) {
-                        iput(iroot);
-                        return ERR_PTR(-ENOMEM);
-                }
-
-                sb->s_root = root;
-        }
-
         /* get the actual root for this mount */
         fsinfo.fattr = &fattr;
 
@@ -96,6 +88,10 @@ struct dentry *nfs_get_root(struct super_block *sb, struct nfs_fh *mntfh)
                 return ERR_PTR(PTR_ERR(inode));
         }
 
+        error = nfs_superblock_set_dummy_root(sb, inode);
+        if (error != 0)
+                return ERR_PTR(error);
+
         /* root dentries normally start off anonymous and get spliced in later
          * if the dentry tree reaches them; however if the dentry already
          * exists, we'll pick it up at this point and use it as the root
@@ -241,33 +237,6 @@ struct dentry *nfs4_get_root(struct super_block *sb, struct nfs_fh *mntfh)
 
         dprintk("--> nfs4_get_root()\n");
 
-        /* create a dummy root dentry with dummy inode for this superblock */
-        if (!sb->s_root) {
-                struct nfs_fh dummyfh;
-                struct dentry *root;
-                struct inode *iroot;
-
-                memset(&dummyfh, 0, sizeof(dummyfh));
-                memset(&fattr, 0, sizeof(fattr));
-                nfs_fattr_init(&fattr);
-                fattr.valid = NFS_ATTR_FATTR;
-                fattr.type = NFDIR;
-                fattr.mode = S_IFDIR | S_IRUSR | S_IWUSR;
-                fattr.nlink = 2;
-
-                iroot = nfs_fhget(sb, &dummyfh, &fattr);
-                if (IS_ERR(iroot))
-                        return ERR_PTR(PTR_ERR(iroot));
-
-                root = d_alloc_root(iroot);
-                if (!root) {
-                        iput(iroot);
-                        return ERR_PTR(-ENOMEM);
-                }
-
-                sb->s_root = root;
-        }
-
         /* get the info about the server and filesystem */
         error = nfs4_server_capabilities(server, mntfh);
         if (error < 0) {
@@ -289,6 +258,10 @@ struct dentry *nfs4_get_root(struct super_block *sb, struct nfs_fh *mntfh)
                 return ERR_PTR(PTR_ERR(inode));
         }
 
+        error = nfs_superblock_set_dummy_root(sb, inode);
+        if (error != 0)
+                return ERR_PTR(error);
+
         /* root dentries normally start off anonymous and get spliced in later
          * if the dentry tree reaches them; however if the dentry already
          * exists, we'll pick it up at this point and use it as the root