SUNRPC: support abstract unix socket addresses

An "abtract" address for an AF_UNIX socket start with a nul and can
contain any bytes for the given length, but traditionally doesn't
contain other nuls.  When reported, the leading nul is replaced by '@'.

sunrpc currently rejects connections to these addresses and reports them
as an empty string.  To provide support for future use of these
addresses, allow them for outgoing connections and report them more
usefully.
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

net/sunrpc/clnt.c

@@ -565,8 +565,12 @@ struct rpc_clnt *rpc_create(struct rpc_create_args *args)
 		servername[0] = '\0';
 		switch (args->address->sa_family) {
 		case AF_LOCAL:
-			snprintf(servername, sizeof(servername), "%s",
-				 sun->sun_path);
+			if (sun->sun_path[0])
+				snprintf(servername, sizeof(servername), "%s",
+					 sun->sun_path);
+			else
+				snprintf(servername, sizeof(servername), "@%s",
+					 sun->sun_path+1);
 			break;
 		case AF_INET:
 			snprintf(servername, sizeof(servername), "%pI4",

net/sunrpc/xprtsock.c

@@ -253,7 +253,12 @@ static void xs_format_common_peer_addresses(struct rpc_xprt *xprt)
 	switch (sap->sa_family) {
 	case AF_LOCAL:
 		sun = xs_addr_un(xprt);
-		strscpy(buf, sun->sun_path, sizeof(buf));
+		if (sun->sun_path[0]) {
+			strscpy(buf, sun->sun_path, sizeof(buf));
+		} else {
+			buf[0] = '@';
+			strscpy(buf+1, sun->sun_path+1, sizeof(buf)-1);
+		}
 		xprt->address_strings[RPC_DISPLAY_ADDR] =
 						kstrdup(buf, GFP_KERNEL);
 		break;
@@ -2858,7 +2863,7 @@ static struct rpc_xprt *xs_setup_local(struct xprt_create *args)
 
 	switch (sun->sun_family) {
 	case AF_LOCAL:
-		if (sun->sun_path[0] != '/') {
+		if (sun->sun_path[0] != '/' && sun->sun_path[0] != '\0') {
 			dprintk("RPC:       bad AF_LOCAL address: %s\n",
 					sun->sun_path);
 			ret = ERR_PTR(-EINVAL);