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, 45 insertions, 2 deletions

diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
index 9c6d95ffca97..12875d55c5a9 100644
--- a/fs/cifs/smb2ops.c
+++ b/fs/cifs/smb2ops.c
@@ -322,6 +322,40 @@ SMB3_request_interfaces(const unsigned int xid, struct cifs_tcon *tcon)
 }
 #endif /* STATS2 */
 
+/*
+ * Open the directory at the root of a share
+ */
+int open_shroot(unsigned int xid, struct cifs_tcon *tcon, struct cifs_fid *pfid)
+{
+	struct cifs_open_parms oparams;
+	int rc;
+	__le16 srch_path = 0; /* Null - since an open of top of share */
+	u8 oplock = SMB2_OPLOCK_LEVEL_NONE;
+
+	mutex_lock(&tcon->prfid_mutex);
+	if (tcon->valid_root_fid) {
+		cifs_dbg(FYI, "found a cached root file handle\n");
+		memcpy(pfid, tcon->prfid, sizeof(struct cifs_fid));
+		mutex_unlock(&tcon->prfid_mutex);
+		return 0;
+	}
+
+	oparams.tcon = tcon;
+	oparams.create_options = 0;
+	oparams.desired_access = FILE_READ_ATTRIBUTES;
+	oparams.disposition = FILE_OPEN;
+	oparams.fid = pfid;
+	oparams.reconnect = false;
+
+	rc = SMB2_open(xid, &oparams, &srch_path, &oplock, NULL, NULL);
+	if (rc == 0) {
+		memcpy(tcon->prfid, pfid, sizeof(struct cifs_fid));
+		tcon->valid_root_fid = true;
+	}
+	mutex_unlock(&tcon->prfid_mutex);
+	return rc;
+}
+
 static void
 smb3_qfs_tcon(const unsigned int xid, struct cifs_tcon *tcon)
 {
@@ -330,6 +364,7 @@ smb3_qfs_tcon(const unsigned int xid, struct cifs_tcon *tcon)
 	u8 oplock = SMB2_OPLOCK_LEVEL_NONE;
 	struct cifs_open_parms oparms;
 	struct cifs_fid fid;
+	bool no_cached_open = tcon->nohandlecache;
 
 	oparms.tcon = tcon;
 	oparms.desired_access = FILE_READ_ATTRIBUTES;
@@ -338,7 +373,11 @@ smb3_qfs_tcon(const unsigned int xid, struct cifs_tcon *tcon)
 	oparms.fid = &fid;
 	oparms.reconnect = false;
 
-	rc = SMB2_open(xid, &oparms, &srch_path, &oplock, NULL, NULL);
+	if (no_cached_open)
+		rc = SMB2_open(xid, &oparms, &srch_path, &oplock, NULL, NULL);
+	else
+		rc = open_shroot(xid, tcon, &fid);
+
 	if (rc)
 		return;
 
@@ -352,7 +391,8 @@ smb3_qfs_tcon(const unsigned int xid, struct cifs_tcon *tcon)
 			FS_DEVICE_INFORMATION);
 	SMB2_QFS_attr(xid, tcon, fid.persistent_fid, fid.volatile_fid,
 			FS_SECTOR_SIZE_INFORMATION); /* SMB3 specific */
-	SMB2_close(xid, tcon, fid.persistent_fid, fid.volatile_fid);
+	if (no_cached_open)
+		SMB2_close(xid, tcon, fid.persistent_fid, fid.volatile_fid);
 	return;
 }
 
@@ -394,6 +434,9 @@ smb2_is_path_accessible(const unsigned int xid, struct cifs_tcon *tcon,
 	struct cifs_open_parms oparms;
 	struct cifs_fid fid;
 
+	if ((*full_path == 0) && tcon->valid_root_fid)
+		return 0;
+
 	utf16_path = cifs_convert_path_to_utf16(full_path, cifs_sb);
 	if (!utf16_path)
 		return -ENOMEM;