[PATCH 2/3] xen/cmdline: Extend parse_boolean() to signal a name match

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

This will help parsing a sub-option which has boolean and non-boolean options
available.

First, rework 'int val' into 'bool has_neg_prefix'.  This inverts it's value,
but the resulting logic is far easier to follow.

Second, reject anything of the form 'no-$FOO=' which excludes ambiguous
constructs such as 'no-$foo=yes' which have never been valid.

This just leaves the case where everything is otherwise fine, but parse_bool()
can't interpret the provided string.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
CC: Julien Grall <julien@xxxxxxx>
CC: Juergen Gross <jgross@xxxxxxxx>
---
 xen/common/kernel.c   | 20 ++++++++++++++++----
 xen/include/xen/lib.h |  3 ++-
 2 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/xen/common/kernel.c b/xen/common/kernel.c
index adff2d2c77f3..74dbaf31ea70 100644
--- a/xen/common/kernel.c
+++ b/xen/common/kernel.c
@@ -272,9 +272,9 @@ int parse_bool(const char *s, const char *e)
 int parse_boolean(const char *name, const char *s, const char *e)
 {
     size_t slen, nlen;
-    int val = !!strncmp(s, "no-", 3);
+    bool has_neg_prefix = !strncmp(s, "no-", 3);
 
-    if ( !val )
+    if ( has_neg_prefix )
         s += 3;
 
     slen = e ? ({ ASSERT(e >= s); e - s; }) : strlen(s);
@@ -286,11 +286,23 @@ int parse_boolean(const char *name, const char *s, const 
char *e)
 
     /* Exact, unadorned name?  Result depends on the 'no-' prefix. */
     if ( slen == nlen )
-        return val;
+        return !has_neg_prefix;
+
+    /* Inexact match with a 'no-' prefix?  Not valid. */
+    if ( has_neg_prefix )
+        return -1;
 
     /* =$SOMETHING?  Defer to the regular boolean parsing. */
     if ( s[nlen] == '=' )
-        return parse_bool(&s[nlen + 1], e);
+    {
+        int b = parse_bool(&s[nlen + 1], e);
+
+        if ( b >= 0 )
+            return b;
+
+        /* Not a boolean, but the name matched.  Signal specially. */
+        return -2;
+    }
 
     /* Unrecognised.  Give up. */
     return -1;
diff --git a/xen/include/xen/lib.h b/xen/include/xen/lib.h
index aab1fc7c4a69..05ee1e18af6b 100644
--- a/xen/include/xen/lib.h
+++ b/xen/include/xen/lib.h
@@ -89,7 +89,8 @@ int parse_bool(const char *s, const char *e);
 /**
  * Given a specific name, parses a string of the form:
  *   [no-]$NAME[=...]
- * returning 0 or 1 for a recognised boolean, or -1 for an error.
+ * returning 0 or 1 for a recognised boolean.  Returns -1 for general errors,
+ * and -2 for "not a boolean, but $NAME= matches".
  */
 int parse_boolean(const char *name, const char *s, const char *e);
 
-- 
2.11.0