[PATCH] nfs: when attempting to open a directory, fall back on normal lookup (try #2)

[Jeff Layton <jlayton@redhat.com>]

commit d953126 changed how nfs_atomic_lookup handles an -EISDIR return
from an OPEN call. Prior to that patch, that caused the client to fall
back to doing a normal lookup. When that patch went in, the code began
returning that error to userspace. The d_revalidate codepath however
never had the corresponding change, so it was still possible to end up
with a NULL ctx->state pointer after that.

That patch caused a regression. When we attempt to open a directory that
does not have a cached dentry, that open now errors out with EISDIR. If
you attempt the same open with a cached dentry, it will succeed.

Fix this by reverting the change in nfs_atomic_lookup and allowing
attempts to open directories to fall back to a normal lookup

Also, add a NFSv4-specific f_ops->open routine that just returns
-ENOTDIR.  This should never be called if things are working properly.
If it ever is, we can use the WARN() in that function to recognize it
and perhaps troubleshoot it.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
---
 fs/nfs/dir.c           |    2 +-
 fs/nfs/file.c          |   31 +++++++++++++++++++++++++++++++
 fs/nfs/inode.c         |    5 ++++-
 include/linux/nfs_fs.h |    1 +
 4 files changed, 37 insertions(+), 2 deletions(-)

diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index b238d95..ac28990 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -1468,12 +1468,12 @@ static struct dentry *nfs_atomic_lookup(struct inode *dir, struct dentry *dentry
 				res = NULL;
 				goto out;
 			/* This turned out not to be a regular file */
+			case -EISDIR:
 			case -ENOTDIR:
 				goto no_open;
 			case -ELOOP:
 				if (!(nd->intent.open.flags & O_NOFOLLOW))
 					goto no_open;
-			/* case -EISDIR: */
 			/* case -EINVAL: */
 			default:
 				res = ERR_CAST(inode);
diff --git a/fs/nfs/file.c b/fs/nfs/file.c
index 28b8c3f..9a5cab5 100644
--- a/fs/nfs/file.c
+++ b/fs/nfs/file.c
@@ -41,6 +41,7 @@
 #define NFSDBG_FACILITY		NFSDBG_FILE
 
 static int nfs_file_open(struct inode *, struct file *);
+static int nfs4_file_open(struct inode *, struct file *);
 static int nfs_file_release(struct inode *, struct file *);
 static loff_t nfs_file_llseek(struct file *file, loff_t offset, int origin);
 static int  nfs_file_mmap(struct file *, struct vm_area_struct *);
@@ -63,6 +64,25 @@ static int nfs_setlease(struct file *file, long arg, struct file_lock **fl);
 
 static const struct vm_operations_struct nfs_file_vm_ops;
 
+const struct file_operations nfs4_file_operations = {
+	.llseek		= nfs_file_llseek,
+	.read		= do_sync_read,
+	.write		= do_sync_write,
+	.aio_read	= nfs_file_read,
+	.aio_write	= nfs_file_write,
+	.mmap		= nfs_file_mmap,
+	.open		= nfs4_file_open,
+	.flush		= nfs_file_flush,
+	.release	= nfs_file_release,
+	.fsync		= nfs_file_fsync,
+	.lock		= nfs_lock,
+	.flock		= nfs_flock,
+	.splice_read	= nfs_file_splice_read,
+	.splice_write	= nfs_file_splice_write,
+	.check_flags	= nfs_check_flags,
+	.setlease	= nfs_setlease,
+};
+
 const struct file_operations nfs_file_operations = {
 	.llseek		= nfs_file_llseek,
 	.read		= do_sync_read,
@@ -135,6 +155,17 @@ nfs_file_open(struct inode *inode, struct file *filp)
 }
 
 static int
+nfs4_file_open(struct inode *inode, struct file *filp)
+{
+	/*
+	 * NFSv4 opens are handled in d_lookup and d_revalidate. If we get to
+	 * this point, then something is very wrong
+	 */
+	dprintk("NFS: %s called! inode=%p filp=%p\n", __func__, inode, filp);
+	return -ENOTDIR;
+}
+
+static int
 nfs_file_release(struct inode *inode, struct file *filp)
 {
 	struct dentry *dentry = filp->f_path.dentry;
diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c
index b7c4301..3389f46 100644
--- a/fs/nfs/inode.c
+++ b/fs/nfs/inode.c
@@ -293,7 +293,10 @@ nfs_fhget(struct super_block *sb, struct nfs_fh *fh, struct nfs_fattr *fattr)
 		 */
 		inode->i_op = NFS_SB(sb)->nfs_client->rpc_ops->file_inode_ops;
 		if (S_ISREG(inode->i_mode)) {
-			inode->i_fop = &nfs_file_operations;
+			if (NFS_SB(sb)->nfs_client->rpc_ops->version == 4)
+				inode->i_fop = &nfs4_file_operations;
+			else
+				inode->i_fop = &nfs_file_operations;
 			inode->i_data.a_ops = &nfs_file_aops;
 			inode->i_data.backing_dev_info = &NFS_SB(sb)->backing_dev_info;
 		} else if (S_ISDIR(inode->i_mode)) {
diff --git a/include/linux/nfs_fs.h b/include/linux/nfs_fs.h
index eaac770..81072b0 100644
--- a/include/linux/nfs_fs.h
+++ b/include/linux/nfs_fs.h
@@ -410,6 +410,7 @@ extern const struct inode_operations nfs_file_inode_operations;
 extern const struct inode_operations nfs3_file_inode_operations;
 #endif /* CONFIG_NFS_V3 */
 extern const struct file_operations nfs_file_operations;
+extern const struct file_operations nfs4_file_operations;
 extern const struct address_space_operations nfs_file_aops;
 extern const struct address_space_operations nfs_dir_aops;
 
-- 
1.7.6.4