pre-lib9p servers: fix incorrect Tversion handling

version(5) says:

	If the server does not understand the client's version
	string, it should respond with an Rversion message (not
	Rerror) with the version string the 7 characters
	``unknown''.

Pre-lib9p file servers -- all except cwfs(4) -- do return Rerror.

lib9p(2) follows the above spec, although ignoring the next part
concerning comparison after period-stripping.  It assumes an
Fcall.version starting with "9P" is correctly formed and returns
the only supported version of the protocol, which seems alright.

This patch brings pre-lib9p servers in accordance with the spec.

1 files changed, 3 insertions, 7 deletions

diff --git a/sys/src/cmd/exportfs/exportsrv.c b/sys/src/cmd/exportfs/exportsrv.c
index e5be53017..a413ed0dc 100644
--- a/sys/src/cmd/exportfs/exportsrv.c
+++ b/sys/src/cmd/exportfs/exportsrv.c
@@ -15,7 +15,6 @@ char Exmnt[] = "Cannot .. past mount point";
 char Emip[] = "Mount in progress";
 char Enopsmt[] = "Out of pseudo mount points";
 char Enomem[] = "No memory";
-char Eversion[] = "Bad 9P2000 version";
 char Ereadonly[] = "File system read only";
 char Enoprocs[] = "Out of processes";
 
@@ -35,13 +34,10 @@ Xversion(Fsrpc *t)
 	if(t->work.msize > messagesize)
 		t->work.msize = messagesize;
 	messagesize = t->work.msize;
-	if(strncmp(t->work.version, "9P2000", 6) != 0){
-		reply(&t->work, &rhdr, Eversion);
-		putsbuf(t);
-		return;
-	}
-	rhdr.version = "9P2000";
 	rhdr.msize = t->work.msize;
+	rhdr.version = "9P2000";
+	if(strncmp(t->work.version, "9P", 2) != 0)
+		rhdr.version = "unknown";
 	reply(&t->work, &rhdr, 0);
 	putsbuf(t);
 }