smb3: fix redundant opens on root

In SMB2/SMB3 unlike in cifs we unnecessarily open the root of the share
over and over again in various places during mount and path revalidation
and also in statfs.  This patch cuts redundant traffic (opens and closes)
by simply keeping the directory handle for the root around (and reopening
it as needed on reconnect), so query calls don't require three round
trips to copmlete - just one, and eases load on network, client and
server (on mount alone, cuts network traffic by more than a third).

Also add a new cifs mount parm "nohandlecache" to allow users whose
servers might have resource constraints (eg in case they have a server
with so many users connecting to it that this extra handle per mount
could possibly be a resource concern).

Signed-off-by: Steve French <smfrench@gmail.com>
Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/fs/cifs/cifs_fs_sb.h b/fs/cifs/cifs_fs_sb.h
index 350fa55a1bf7..9731d0d891e7 100644
--- a/fs/cifs/cifs_fs_sb.h
+++ b/fs/cifs/cifs_fs_sb.h
@@ -50,6 +50,7 @@
 					      * root mountable
 					      */
 #define CIFS_MOUNT_UID_FROM_ACL 0x2000000 /* try to get UID via special SID */
+#define CIFS_MOUNT_NO_HANDLE_CACHE 0x4000000 /* disable caching dir handles */
 
 struct cifs_sb_info {
 	struct rb_root tlink_tree;