SMB3: parsing for new snapshot timestamp mount parm

New mount option "snapshot=<time>" to allow mounting an earlier
version of the remote volume (if such a snapshot exists on
the server).

Note that eventually specifying a snapshot time of 1 will allow
the user to mount the oldest snapshot. A subsequent patch
add the processing for that and another for actually specifying
the "time warp" create context on SMB2/SMB3 open.

Check to make sure SMB2 negotiated, and ensure that
we use a different tcon if mount same share twice
but with different snaphshot times

Signed-off-by: Steve French <smfrench@gmail.com>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>

fs/cifs/cifsglob.h

@@ -525,6 +525,7 @@ struct smb_vol {
 	struct sockaddr_storage srcaddr; /* allow binding to a local IP */
 	struct nls_table *local_nls;
 	unsigned int echo_interval; /* echo interval in secs */
+	__u64 snapshot_time; /* needed for timewarp tokens */
 	unsigned int max_credits; /* smb3 max_credits 10 < credits < 60000 */
 };
 
@@ -932,6 +933,7 @@ struct cifs_tcon {
 	__u32 maximal_access;
 	__u32 vol_serial_number;
 	__le64 vol_create_time;
+	__u64 snapshot_time; /* for timewarp tokens - timestamp of snapshot */
 	__u32 ss_flags;		/* sector size flags */
 	__u32 perf_sector_size; /* best sector size for perf */
 	__u32 max_chunks;

fs/cifs/connect.c

@@ -95,6 +95,7 @@ enum {
 	Opt_dirmode, Opt_port,
 	Opt_rsize, Opt_wsize, Opt_actimeo,
 	Opt_echo_interval, Opt_max_credits,
+	Opt_snapshot,
 
 	/* Mount options which take string value */
 	Opt_user, Opt_pass, Opt_ip,
@@ -191,6 +192,7 @@ static const match_table_t cifs_mount_option_tokens = {
 	{ Opt_actimeo, "actimeo=%s" },
 	{ Opt_echo_interval, "echo_interval=%s" },
 	{ Opt_max_credits, "max_credits=%s" },
+	{ Opt_snapshot, "snapshot=%s" },
 
 	{ Opt_blank_user, "user=" },
 	{ Opt_blank_user, "username=" },
@@ -1601,6 +1603,14 @@ cifs_parse_mount_options(const char *mountdata, const char *devname,
 			}
 			vol->echo_interval = option;
 			break;
+		case Opt_snapshot:
+			if (get_option_ul(args, &option)) {
+				cifs_dbg(VFS, "%s: Invalid snapshot time\n",
+					 __func__);
+				goto cifs_parse_mount_err;
+			}
+			vol->snapshot_time = option;
+			break;
 		case Opt_max_credits:
 			if (get_option_ul(args, &option) || (option < 20) ||
 			    (option > 60000)) {
@@ -2586,7 +2596,7 @@ static int match_tcon(struct cifs_tcon *tcon, const char *unc)
 }
 
 static struct cifs_tcon *
-cifs_find_tcon(struct cifs_ses *ses, const char *unc)
+cifs_find_tcon(struct cifs_ses *ses, struct smb_vol *volume_info)
 {
 	struct list_head *tmp;
 	struct cifs_tcon *tcon;
@@ -2594,8 +2604,14 @@ cifs_find_tcon(struct cifs_ses *ses, const char *unc)
 	spin_lock(&cifs_tcp_ses_lock);
 	list_for_each(tmp, &ses->tcon_list) {
 		tcon = list_entry(tmp, struct cifs_tcon, tcon_list);
-		if (!match_tcon(tcon, unc))
+		if (!match_tcon(tcon, volume_info->UNC))
 			continue;
+
+#ifdef CONFIG_CIFS_SMB2
+		if (tcon->snapshot_time != volume_info->snapshot_time)
+			continue;
+#endif /* CONFIG_CIFS_SMB2 */
+
 		++tcon->tc_count;
 		spin_unlock(&cifs_tcp_ses_lock);
 		return tcon;
@@ -2636,7 +2652,7 @@ cifs_get_tcon(struct cifs_ses *ses, struct smb_vol *volume_info)
 	int rc, xid;
 	struct cifs_tcon *tcon;
 
-	tcon = cifs_find_tcon(ses, volume_info->UNC);
+	tcon = cifs_find_tcon(ses, volume_info);
 	if (tcon) {
 		cifs_dbg(FYI, "Found match on UNC path\n");
 		/* existing tcon already has a reference */
@@ -2657,6 +2673,22 @@ cifs_get_tcon(struct cifs_ses *ses, struct smb_vol *volume_info)
 		goto out_fail;
 	}
 
+	if (volume_info->snapshot_time) {
+#ifdef CONFIG_CIFS_SMB2
+		if (ses->server->vals->protocol_id == 0) {
+			cifs_dbg(VFS,
+			     "Use SMB2 or later for snapshot mount option\n");
+			rc = -EOPNOTSUPP;
+			goto out_fail;
+		} else
+			tcon->snapshot_time = volume_info->snapshot_time;
+#else
+		cifs_dbg(VFS, "Snapshot mount option requires SMB2 support\n");
+		rc = -EOPNOTSUPP;
+		goto out_fail;
+#endif /* CONFIG_CIFS_SMB2 */
+	}
+
 	tcon->ses = ses;
 	if (volume_info->password) {
 		tcon->password = kstrdup(volume_info->password, GFP_KERNEL);