NFSv4: Follow a referral

Respond to a moved error on NFS lookup by setting up the referral.
Note: We don't actually follow the referral during lookup/getattr, but
later when we detect fsid mismatch in inode revalidation (similar to the
processing done for cloning submounts). Referrals will have fake attributes
until they are actually followed or traversed.

Signed-off-by: Manoj Naik <manoj@almaden.ibm.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

3 files changed, 58 insertions, 2 deletions

diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c
index 0d8302e59d69..ee13cb01b56e 100644
--- a/fs/nfs/inode.c
+++ b/fs/nfs/inode.c
@@ -888,7 +888,10 @@ nfs_fhget(struct super_block *sb, struct nfs_fh *fh, struct nfs_fattr *fattr)
                                 set_bit(NFS_INO_ADVISE_RDPLUS, &NFS_FLAGS(inode));
                         /* Deal with crossing mountpoints */
                         if (!nfs_fsid_equal(&NFS_SB(sb)->fsid, &fattr->fsid)) {
-                                inode->i_op = &nfs_mountpoint_inode_operations;
+                                if (fattr->valid & NFS_ATTR_FATTR_V4_REFERRAL)
+                                        inode->i_op = &nfs_referral_inode_operations;
+                                else
+                                        inode->i_op = &nfs_mountpoint_inode_operations;
                                 inode->i_fop = NULL;
                         }
                 } else if (S_ISLNK(inode->i_mode))
diff --git a/fs/nfs/namespace.c b/fs/nfs/namespace.c
index e426516c1116..8ca44b7b25c3 100644
--- a/fs/nfs/namespace.c
+++ b/fs/nfs/namespace.c
@@ -58,7 +58,10 @@ static void * nfs_follow_mountpoint(struct dentry *dentry, struct nameidata *nd)
         if (err != 0)
                 goto out_err;
 
-        mnt = nfs_do_submount(nd->mnt, nd->dentry, &fh, &fattr);
+        if (fattr.valid & NFS_ATTR_FATTR_V4_REFERRAL)
+                mnt = nfs_do_refmount(nd->mnt, nd->dentry);
+        else
+                mnt = nfs_do_submount(nd->mnt, nd->dentry, &fh, &fattr);
         err = PTR_ERR(mnt);
         if (IS_ERR(mnt))
                 goto out_err;
@@ -94,6 +97,10 @@ struct inode_operations nfs_mountpoint_inode_operations = {
         .getattr        = nfs_getattr,
 };
 
+struct inode_operations nfs_referral_inode_operations = {
+        .follow_link    = nfs_follow_mountpoint,
+};
+
 static void nfs_expire_automounts(void *data)
 {
         struct list_head *list = (struct list_head *)data;
diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index 90ee21a07b3e..3300e35d74ad 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -1462,6 +1462,50 @@ out:
         return nfs4_map_errors(status);
 }
 
+/*
+ * Get locations and (maybe) other attributes of a referral.
+ * Note that we'll actually follow the referral later when
+ * we detect fsid mismatch in inode revalidation
+ */
+static int nfs4_get_referral(struct inode *dir, struct qstr *name, struct nfs_fattr *fattr, struct nfs_fh *fhandle)
+{
+        int status = -ENOMEM;
+        struct page *page = NULL;
+        struct nfs4_fs_locations *locations = NULL;
+        struct dentry dentry = {};
+
+        page = alloc_page(GFP_KERNEL);
+        if (page == NULL)
+                goto out;
+        locations = kmalloc(sizeof(struct nfs4_fs_locations), GFP_KERNEL);
+        if (locations == NULL)
+                goto out;
+
+        dentry.d_name.name = name->name;
+        dentry.d_name.len = name->len;
+        status = nfs4_proc_fs_locations(dir, &dentry, locations, page);
+        if (status != 0)
+                goto out;
+        /* Make sure server returned a different fsid for the referral */
+        if (nfs_fsid_equal(&NFS_SERVER(dir)->fsid, &locations->fattr.fsid)) {
+                dprintk("%s: server did not return a different fsid for a referral at %s\n", __FUNCTION__, name->name);
+                status = -EIO;
+                goto out;
+        }
+
+        memcpy(fattr, &locations->fattr, sizeof(struct nfs_fattr));
+        fattr->valid |= NFS_ATTR_FATTR_V4_REFERRAL;
+        if (!fattr->mode)
+                fattr->mode = S_IFDIR;
+        memset(fhandle, 0, sizeof(struct nfs_fh));
+out:
+        if (page)
+                __free_page(page);
+        if (locations)
+                kfree(locations);
+        return status;
+}
+
 static int _nfs4_proc_getattr(struct nfs_server *server, struct nfs_fh *fhandle, struct nfs_fattr *fattr)
 {
         struct nfs4_getattr_arg args = {
@@ -1566,6 +1610,8 @@ static int _nfs4_proc_lookup(struct inode *dir, struct qstr *name,
         
         dprintk("NFS call  lookup %s\n", name->name);
         status = rpc_call_sync(NFS_CLIENT(dir), &msg, 0);
+        if (status == -NFS4ERR_MOVED)
+                status = nfs4_get_referral(dir, name, fattr, fhandle);
         dprintk("NFS reply lookup: %d\n", status);
         return status;
 }