Start of a fix for bug#71477

* src/filelock.c (integer_prefixed): New static function.
(VALID_PROCESS_ID): New macro.
(current_lock_owner): Use them to allow negative process IDs
on some Microsoft platforms.

(cherry picked from commit ac14d56a4d749661a9c52941e6511a0c300d35e4)

diff --git a/src/filelock.c b/src/filelock.c
index 050cac565c9c9454a4d93b45c739274b378c622c..d4a4747955a031a6f5c2ef624d95b2d68c133c46 100644 (file)
--- a/src/filelock.c
+++ b/src/filelock.c
@@ -342,6 +342,22 @@ read_lock_data (char *lfname, char lfinfo[MAX_LFINFO + 1])
   return nbytes;
 }
 
+/* Whether the string S starts with a decimal integer, optionally
+   negative.  */
+static bool
+integer_prefixed (char const *s)
+{
+  /* Doing it this way avoids a conditional branch on most platforms.  */
+  return c_isdigit (s[s[0] == '-']);
+}
+
+/* Whether the integer P could identify an individual process.  On most
+   platforms this simply checks for positive pid_t, but on some
+   Microsoft ports our headers #define it to to some other test.  */
+#ifndef VALID_PROCESS_ID
+# define VALID_PROCESS_ID(p) (0 < (p) && (p) <= TYPE_MAXIMUM (pid_t))
+#endif
+
 /* True if errno values are negative.  Although the C standard
    requires them to be positive, they are negative in Haiku.  */
 enum { NEGATIVE_ERRNO = EDOM < 0 };
@@ -393,7 +409,7 @@ current_lock_owner (lock_info_type *owner, Lisp_Object lfname)
     return EINVAL;
 
   /* The PID is everything from the last '.' to the ':' or equivalent.  */
-  if (! c_isdigit (dot[1]))
+  if (! integer_prefixed (dot + 1))
     return EINVAL;
   errno = 0;
   pid = strtoimax (dot + 1, &owner->colon, 10);
@@ -419,9 +435,7 @@ current_lock_owner (lock_info_type *owner, Lisp_Object lfname)
       boot += 2;
       FALLTHROUGH;
     case ':':
-      if (!(c_isdigit (boot[0])
-           /* A negative number.  */
-           || (boot[0] == '-' && c_isdigit (boot[1]))))
+      if (! integer_prefixed (boot))
        return EINVAL;
       boot_time = strtoimax (boot, &lfinfo_end, 10);
       break;
@@ -451,7 +465,7 @@ current_lock_owner (lock_info_type *owner, Lisp_Object lfname)
     {
       if (pid == getpid ())
         return I_OWN_IT;
-      else if (0 < pid && pid <= TYPE_MAXIMUM (pid_t)
+      else if (VALID_PROCESS_ID (pid)
                && (kill (pid, 0) >= 0 || errno == EPERM)
               && (boot_time == 0
                   || (boot_time <= TYPE_MAXIMUM (time_t)