cifs: add a "nosharesock" mount option to force new sockets to server to be created

Some servers set max_vcs to 1 and actually do enforce that limit. Add a
new mount option to work around this behavior that forces a mount
request to open a new socket to the server instead of reusing an
existing one.

I'd prefer to come up with a solution that doesn't require this, so
consider this a debug patch that you can use to determine whether this
is the real problem.

Cc: Jim McDonough <jmcd@samba.org>
Cc: Steve French <smfrench@gmail.com>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

fs/cifs/cifsglob.h

@@ -441,6 +441,7 @@ struct smb_vol {
 	bool mfsymlinks:1; /* use Minshall+French Symlinks */
 	bool multiuser:1;
 	bool rwpidforward:1; /* pid forward for read/write operations */
+	bool nosharesock;
 	unsigned int rsize;
 	unsigned int wsize;
 	bool sockopt_tcp_nodelay:1;

fs/cifs/connect.c

@@ -85,7 +85,7 @@ enum {
 	Opt_acl, Opt_noacl, Opt_locallease,
 	Opt_sign, Opt_seal, Opt_noac,
 	Opt_fsc, Opt_mfsymlinks,
-	Opt_multiuser, Opt_sloppy,
+	Opt_multiuser, Opt_sloppy, Opt_nosharesock,
 
 	/* Mount options which take numeric value */
 	Opt_backupuid, Opt_backupgid, Opt_uid,
@@ -165,6 +165,7 @@ static const match_table_t cifs_mount_option_tokens = {
 	{ Opt_mfsymlinks, "mfsymlinks" },
 	{ Opt_multiuser, "multiuser" },
 	{ Opt_sloppy, "sloppy" },
+	{ Opt_nosharesock, "nosharesock" },
 
 	{ Opt_backupuid, "backupuid=%s" },
 	{ Opt_backupgid, "backupgid=%s" },
@@ -1455,6 +1456,9 @@ cifs_parse_mount_options(const char *mountdata, const char *devname,
 		case Opt_sloppy:
 			sloppy = true;
 			break;
+		case Opt_nosharesock:
+			vol->nosharesock = true;
+			break;
 
 		/* Numeric Values */
 		case Opt_backupuid:
@@ -2027,6 +2031,9 @@ static int match_server(struct TCP_Server_Info *server, struct smb_vol *vol)
 {
 	struct sockaddr *addr = (struct sockaddr *)&vol->dstaddr;
 
+	if (vol->nosharesock)
+		return 0;
+
 	if ((server->vals != vol->vals) || (server->ops != vol->ops))
 		return 0;