tools/xl: fix autoballoon regex

This regex is used for auto-balloon mode detection based on Xen command line.

The case of specifying a negative size was handled incorrectly.
>From misc/xen-command-line documentation:

    dom0_mem (x86)
    = List of ( min:<sz> | max:<sz> | <sz> )

    If a size is positive, it represents an absolute value.
    If a size is negative, it is subtracted from the total available memory.

Also add support for [tT] granularity suffix.
Also add support for memory fractions (i.e. '50%' or '1G+25%').

Signed-off-by: Dmitry Isaykin <isaikin-dmitry@yandex.ru>
Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>

tools/xl/xl.c

@@ -80,14 +80,20 @@ static int auto_autoballoon(void)
     if (!info)
         return 1; /* default to on */
 
+#define SIZE_PATTERN "-?[0-9]+[bBkKmMgGtT]?"
+
     ret = regcomp(&regex,
-                  "(^| )dom0_mem=((|min:|max:)[0-9]+[bBkKmMgG]?,?)+($| )",
+                  "(^| )dom0_mem=((|min:|max:)(" SIZE_PATTERN "|(" SIZE_PATTERN "\\+)?[0-9]{1,2}%),?)+($| )",
                   REG_NOSUB | REG_EXTENDED);
+
+#undef SIZE_PATTERN
+
     if (ret)
         return 1;
 
     ret = regexec(&regex, info->commandline, 0, NULL, 0);
     regfree(&regex);
+
     return ret == REG_NOMATCH;
 }