[Toybox] Small issue with mount option syntax: "mount -a -t noblah, blah"

[Andy Hu via Toybox]

# toybox mount -a -t nomsdos,smbfs
returns error "bad typelist". Toybox seems to expect
# toybox mount -a -t nomsdos,nosmbfs
as commented in lib/portability.c:134
// If one -t starts with "no", the rest must too

Most manuals and implementations of mount have, quote:
              More than one type may be specified in a comma-separated list,
              for the -t option as well as in an /etc/fstab entry.  The list
              of filesystem types for the -t option can be prefixed with no
              to specify the filesystem types on which no action should be
              taken.  The prefix no has no effect when specified in an
              /etc/fstab entry.
              The prefix no can be meaningful with the -a option.  For
              example, the command

                     mount -a -t nomsdos,smbfs

              mounts all filesystems except those of type msdos and smbfs.
------ end quote ------
I couldn't find specifications on how prefixing no with each type, or some
types should be handled. Suggest making a patch for the time being:
1. leading "no" in whole string negates all types
2. skip prefix "no" if leading "no" (in case there are people using the
syntax mount -a -t nomsdos,nosmbfs).

From cd1f2fb53ab91b93a113a0372b9a9296014bcfed Mon Sep 17 00:00:00 2001
From: andyhu <and...@google.com>
Date: Tue, 15 Dec 2020 12:02:42 -0800
Subject: [PATCH] mount -a -t "no" negates all listed types

---
 lib/portability.c | 14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/lib/portability.c b/lib/portability.c
index 91c01900..50f17c2c 100644
--- a/lib/portability.c
+++ b/lib/portability.c
@@ -130,16 +130,12 @@ int mountlist_istype(struct mtab_list *ml, char *typelist)
 
   for (;;) {
     if (!(t = comma_iterate(&typelist, &len))) break;
+    // If first item starts with "no", ignore no for the rest
     if (!skip) {
-      // If one -t starts with "no", the rest must too
-      if (strncmp(t, "no", 2)) error_exit("bad typelist");
-      if (!strncmp(t+2, ml->type, len-2)) {
-        skip = 1;
-        break;
-      }
-    } else if (!strncmp(t, ml->type, len) && !ml->type[len]) {
-      skip = 0;
-      break;
+      if (strncmp(t, "no", 2)) t+=2;
+    }
+    if (!strncmp(t, ml->type, len) && !ml->type[len]){
+      skip = (!skip);
     }
   }
 
-- 
2.29.2.684.gfbc64c5ab5-goog


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