commit f4f42cd328771f335ec1dc15884f2bf337bdf36a
from: Omar Polo <op@omarpolo.com>
date: Sun Jan 09 09:39:22 2022 UTC

fix cd

Walk can be successful in various conditions where cd has to fail.
For instance, we may have reached a file or we couldn't walk all the
required components.  In these "soft-fail" cases, the walk has mutated
the fids, so to abort the cd we have to do a walk using a second fid
and then clunk the old or new one depending on if it was _completely_
successful or not.

Another option may be to track the number of walked path and attempt
to walk '..' the right amount of times, this would saves a Tclunk in
the case the walk succeeded and require a slightly bigger 9P packet to
be sent in the failure case.  It would complicate the walk_path API
though, so I've not chosen this option.

commit - 63b9781e99a5b7519106753eb93d50fb568d4d4c
commit + f4f42cd328771f335ec1dc15884f2bf337bdf36a
blob - 00de21321efa7a139f236cbb2e24eb7ee0ee00ee
blob + 0a94e51e387e1d2ef71134435d01043769fe9216
--- ftp.c
+++ ftp.c
@@ -708,15 +708,22 @@ static void
 cmd_cd(int argc, const char **argv)
 {
 	struct qid qid;
+	int nfid;
 
 	if (argc != 1) {
 		printf("usage: cd remote-path\n");
 		return;
 	}
 
-	if (walk_path(pwdfid, pwdfid, argv[0], &qid) == -1 ||
-	    !(qid.type & QTDIR))
+	nfid = pwdfid+1;
+	if (walk_path(pwdfid, nfid, argv[0], &qid) == -1 ||
+	    !(qid.type & QTDIR)) {
 		printf("can't cd %s\n", argv[0]);
+		do_clunk(nfid);
+	} else {
+		do_clunk(pwdfid);
+		pwdfid = nfid;
+	}
 }
 
 static void