[xen stable-4.14] xen/cmdline: Extend parse_boolean() to signal a name match

[patchbot@xxxxxxx]

commit 2d316660e542fb843f8ac394cc0f961787d19301
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Tue Jul 5 19:19:01 2022 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Tue Jul 12 16:31:49 2022 +0100

    xen/cmdline: Extend parse_boolean() to signal a name match
    
    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>
    Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    (cherry picked from commit 382326cac528dd1eb0d04efd5c05363c453e29f4)
---
 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 c3a943f077..f07ff41d88 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 076bcfb67d..900c0ce3e4 100644
--- a/xen/include/xen/lib.h
+++ b/xen/include/xen/lib.h
@@ -82,7 +82,8 @@ 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);
 
--
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