NFSv4.1 support for NFS4_RESULT_PRESERVER_UNLINKED

In 4.1+, the server is allowed to set a flag
NFS4_RESULT_PRESERVE_UNLINKED in reply to the OPEN, that tells
the client that it does not need to do a silly rename of an
opened file when it's being removed.
Signed-off-by: Olga Kornievskaia <kolga@netapp.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/dir.c

@@ -1419,7 +1419,12 @@ int nfs_lookup_verify_inode(struct inode *inode, unsigned int flags)
 	if (flags & LOOKUP_REVAL)
 		goto out_force;
 out:
-	return (inode->i_nlink == 0) ? -ESTALE : 0;
+	if (inode->i_nlink > 0 ||
+	    (inode->i_nlink == 0 &&
+	     test_bit(NFS_INO_PRESERVE_UNLINKED, &NFS_I(inode)->flags)))
+		return 0;
+	else
+		return -ESTALE;
 out_force:
 	if (flags & LOOKUP_RCU)
 		return -ECHILD;
@@ -2330,7 +2335,8 @@ int nfs_unlink(struct inode *dir, struct dentry *dentry)
 
 	trace_nfs_unlink_enter(dir, dentry);
 	spin_lock(&dentry->d_lock);
-	if (d_count(dentry) > 1) {
+	if (d_count(dentry) > 1 && !test_bit(NFS_INO_PRESERVE_UNLINKED,
+					     &NFS_I(d_inode(dentry))->flags)) {
 		spin_unlock(&dentry->d_lock);
 		/* Start asynchronous writeout of the inode */
 		write_inode_now(d_inode(dentry), 0);

fs/nfs/nfs4proc.c

@@ -3050,6 +3050,8 @@ static int _nfs4_open_and_get_state(struct nfs4_opendata *opendata,
 		set_bit(NFS_STATE_POSIX_LOCKS, &state->flags);
 	if (opendata->o_res.rflags & NFS4_OPEN_RESULT_MAY_NOTIFY_LOCK)
 		set_bit(NFS_STATE_MAY_NOTIFY_LOCK, &state->flags);
+	if (opendata->o_res.rflags & NFS4_OPEN_RESULT_PRESERVE_UNLINKED)
+		set_bit(NFS_INO_PRESERVE_UNLINKED, &NFS_I(state->inode)->flags);
 
 	dentry = opendata->dentry;
 	if (d_really_is_negative(dentry)) {

include/linux/nfs_fs.h

@@ -277,6 +277,7 @@ struct nfs4_copy_state {
 #define NFS_INO_STALE		(1)		/* possible stale inode */
 #define NFS_INO_ACL_LRU_SET	(2)		/* Inode is on the LRU list */
 #define NFS_INO_INVALIDATING	(3)		/* inode is being invalidated */
+#define NFS_INO_PRESERVE_UNLINKED (4)		/* preserve file if removed while open */
 #define NFS_INO_FSCACHE		(5)		/* inode can be cached by FS-Cache */
 #define NFS_INO_FORCE_READDIR	(7)		/* force readdirplus */
 #define NFS_INO_LAYOUTCOMMIT	(9)		/* layoutcommit required */

include/uapi/linux/nfs4.h

@@ -45,6 +45,7 @@
 
 #define NFS4_OPEN_RESULT_CONFIRM		0x0002
 #define NFS4_OPEN_RESULT_LOCKTYPE_POSIX		0x0004
+#define NFS4_OPEN_RESULT_PRESERVE_UNLINKED	0x0008
 #define NFS4_OPEN_RESULT_MAY_NOTIFY_LOCK	0x0020
 
 #define NFS4_SHARE_ACCESS_MASK	0x000F