nfs: don't open in ->d_revalidate

NFSv4 can't do reliable opens in d_revalidate, since it cannot know whether a
mount needs to be followed or not.  It does check d_mountpoint() on the dentry,
which can result in a weird error if the VFS found that the mount does not in
fact need to be followed, e.g.:

  # mount --bind /mnt/nfs /mnt/nfs-clone
  # echo something > /mnt/nfs/tmp/bar
  # echo x > /tmp/file
  # mount --bind /tmp/file /mnt/nfs-clone/tmp/bar
  # cat  /mnt/nfs/tmp/bar
  cat: /mnt/nfs/tmp/bar: Not a directory

Which should, by any sane filesystem, result in "something" being printed.

So instead do the open in f_op->open() and in the unlikely case that the cached
dentry turned out to be invalid, drop the dentry and return EOPENSTALE to let
the VFS retry.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
CC: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 73 insertions, 4 deletions

diff --git a/fs/nfs/file.c b/fs/nfs/file.c
index 56311ca5f9f8..a6708e6b438d 100644
--- a/fs/nfs/file.c
+++ b/fs/nfs/file.c
@@ -879,12 +879,81 @@ const struct file_operations nfs_file_operations = {
 static int
 nfs4_file_open(struct inode *inode, struct file *filp)
 {
+        struct nfs_open_context *ctx;
+        struct dentry *dentry = filp->f_path.dentry;
+        struct dentry *parent = NULL;
+        struct inode *dir;
+        unsigned openflags = filp->f_flags;
+        struct iattr attr;
+        int err;
+
+        BUG_ON(inode != dentry->d_inode);
         /*
-         * NFSv4 opens are handled in d_lookup and d_revalidate. If we get to
-         * this point, then something is very wrong
+         * If no cached dentry exists or if it's negative, NFSv4 handled the
+         * opens in ->lookup() or ->create().
+         *
+         * We only get this far for a cached positive dentry.  We skipped
+         * revalidation, so handle it here by dropping the dentry and returning
+         * -EOPENSTALE.  The VFS will retry the lookup/create/open.
          */
-        dprintk("NFS: %s called! inode=%p filp=%p\n", __func__, inode, filp);
-        return -ENOTDIR;
+
+        dprintk("NFS: open file(%s/%s)\n",
+                dentry->d_parent->d_name.name,
+                dentry->d_name.name);
+
+        if ((openflags & O_ACCMODE) == 3)
+                openflags--;
+
+        /* We can't create new files here */
+        openflags &= ~(O_CREAT|O_EXCL);
+
+        parent = dget_parent(dentry);
+        dir = parent->d_inode;
+
+        ctx = alloc_nfs_open_context(filp->f_path.dentry, filp->f_mode);
+        err = PTR_ERR(ctx);
+        if (IS_ERR(ctx))
+                goto out;
+
+        attr.ia_valid = ATTR_OPEN;
+        if (openflags & O_TRUNC) {
+                attr.ia_valid |= ATTR_SIZE;
+                attr.ia_size = 0;
+                nfs_wb_all(inode);
+        }
+
+        inode = NFS_PROTO(dir)->open_context(dir, ctx, openflags, &attr);
+        if (IS_ERR(inode)) {
+                err = PTR_ERR(inode);
+                switch (err) {
+                case -EPERM:
+                case -EACCES:
+                case -EDQUOT:
+                case -ENOSPC:
+                case -EROFS:
+                        goto out_put_ctx;
+                default:
+                        goto out_drop;
+                }
+        }
+        iput(inode);
+        if (inode != dentry->d_inode)
+                goto out_drop;
+
+        nfs_set_verifier(dentry, nfs_save_change_attribute(dir));
+        nfs_file_set_open_context(filp, ctx);
+        err = 0;
+
+out_put_ctx:
+        put_nfs_open_context(ctx);
+out:
+        dput(parent);
+        return err;
+
+out_drop:
+        d_drop(dentry);
+        err = -EOPENSTALE;
+        goto out_put_ctx;
 }
 
 const struct file_operations nfs4_file_operations = {