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>

diff --git a/fs/nfs/getroot.c b/fs/nfs/getroot.c
index 522e5ad4d8ad9b3946e201926c7f799ddf0f2e36..0ee43843f4ec40c79f1516fb869a5eb720cb355c 100644 (file)
--- a/fs/nfs/getroot.c
+++ b/fs/nfs/getroot.c
@@ -42,6 +42,25 @@
 
 #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
  */
@@ -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