[v2] cmdline: treat hyphens and underscores the same
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Message ID 63d1bdfc-9000-7471-f4f2-7c7f2e931bfe@suse.com
State New
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  • [v2] cmdline: treat hyphens and underscores the same
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Commit Message

Jan Beulich Jan. 23, 2020, 11:42 a.m. UTC
In order to avoid permanently having to ask that no new command line
options using underscores be introduced (albeit I'm likely to still make
remarks), and in order to also allow extending the use of hyphens to
pre-existing ones, introduce custom comparison functions treating both
characters as matching.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
---
v2: Rename to opt_str{,n}cmp(). Don't use the new function for comapring
    against "no-" in parse_params(). Add comment to cdiff().

Comments

Durrant, Paul Jan. 23, 2020, 12:11 p.m. UTC | #1
> -----Original Message-----
> From: Xen-devel <xen-devel-bounces@lists.xenproject.org> On Behalf Of Jan
> Beulich
> Sent: 23 January 2020 11:43
> To: xen-devel@lists.xenproject.org
> Cc: Stefano Stabellini <sstabellini@kernel.org>; Julien Grall
> <julien@xen.org>; Wei Liu <wl@xen.org>; Konrad Wilk
> <konrad.wilk@oracle.com>; George Dunlap <George.Dunlap@eu.citrix.com>;
> Andrew Cooper <andrew.cooper3@citrix.com>; Ian Jackson
> <ian.jackson@citrix.com>
> Subject: [Xen-devel] [PATCH v2] cmdline: treat hyphens and underscores the
> same
> 
> In order to avoid permanently having to ask that no new command line
> options using underscores be introduced (albeit I'm likely to still make
> remarks), and in order to also allow extending the use of hyphens to
> pre-existing ones, introduce custom comparison functions treating both
> characters as matching.
> 
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> ---
> v2: Rename to opt_str{,n}cmp(). Don't use the new function for comapring
>     against "no-" in parse_params(). Add comment to cdiff().
> 
> --- a/docs/misc/xen-command-line.pandoc
> +++ b/docs/misc/xen-command-line.pandoc
> @@ -72,6 +72,11 @@ Some options take a comma separated list
>  Some parameters act as combinations of the above, most commonly a mix
>  of Boolean and String.  These are noted in the relevant sections.
> 
> +### Spelling
> +
> +Parameter names may include hyphens or underscores.  These are
> +generally being treated as matching one another by the parsing logic.
> +
>  ## Parameter details
> 
>  ### acpi
> --- a/xen/common/kernel.c
> +++ b/xen/common/kernel.c
> @@ -23,6 +23,53 @@ enum system_state system_state = SYS_STA
>  xen_commandline_t saved_cmdline;
>  static const char __initconst opt_builtin_cmdline[] = CONFIG_CMDLINE;
> 
> +/*
> + * Calculate the difference between two characters for command line
> parsing
> + * purposes, i.e. treating '-' and '_' the same.
> + */
> +static int cdiff(unsigned char c1, unsigned char c2)
> +{
> +    int res = c1 - c2;
> +
> +    if ( res && (c1 ^ c2) == ('-' ^ '_') &&
> +         (c1 == '-' || c1 == '_') )
> +        res = 0;
> +

Wow! That makes my head hurt. How about:

static int cdiff(unsigned char c1, unsigned char c2)
{
    if ( c1 == '-' )
        c1 = '_';

    if ( c2 == '-' )
        c2 = '_';

    return c1 - c2;
}

?

  Paul
Jan Beulich Jan. 23, 2020, 1:27 p.m. UTC | #2
On 23.01.2020 13:11, Durrant, Paul wrote:
>> -----Original Message-----
>> From: Xen-devel <xen-devel-bounces@lists.xenproject.org> On Behalf Of Jan
>> Beulich
>> Sent: 23 January 2020 11:43
>> To: xen-devel@lists.xenproject.org
>> Cc: Stefano Stabellini <sstabellini@kernel.org>; Julien Grall
>> <julien@xen.org>; Wei Liu <wl@xen.org>; Konrad Wilk
>> <konrad.wilk@oracle.com>; George Dunlap <George.Dunlap@eu.citrix.com>;
>> Andrew Cooper <andrew.cooper3@citrix.com>; Ian Jackson
>> <ian.jackson@citrix.com>
>> Subject: [Xen-devel] [PATCH v2] cmdline: treat hyphens and underscores the
>> same
>>
>> In order to avoid permanently having to ask that no new command line
>> options using underscores be introduced (albeit I'm likely to still make
>> remarks), and in order to also allow extending the use of hyphens to
>> pre-existing ones, introduce custom comparison functions treating both
>> characters as matching.
>>
>> Signed-off-by: Jan Beulich <jbeulich@suse.com>
>> ---
>> v2: Rename to opt_str{,n}cmp(). Don't use the new function for comapring
>>     against "no-" in parse_params(). Add comment to cdiff().
>>
>> --- a/docs/misc/xen-command-line.pandoc
>> +++ b/docs/misc/xen-command-line.pandoc
>> @@ -72,6 +72,11 @@ Some options take a comma separated list
>>  Some parameters act as combinations of the above, most commonly a mix
>>  of Boolean and String.  These are noted in the relevant sections.
>>
>> +### Spelling
>> +
>> +Parameter names may include hyphens or underscores.  These are
>> +generally being treated as matching one another by the parsing logic.
>> +
>>  ## Parameter details
>>
>>  ### acpi
>> --- a/xen/common/kernel.c
>> +++ b/xen/common/kernel.c
>> @@ -23,6 +23,53 @@ enum system_state system_state = SYS_STA
>>  xen_commandline_t saved_cmdline;
>>  static const char __initconst opt_builtin_cmdline[] = CONFIG_CMDLINE;
>>
>> +/*
>> + * Calculate the difference between two characters for command line
>> parsing
>> + * purposes, i.e. treating '-' and '_' the same.
>> + */
>> +static int cdiff(unsigned char c1, unsigned char c2)
>> +{
>> +    int res = c1 - c2;
>> +
>> +    if ( res && (c1 ^ c2) == ('-' ^ '_') &&
>> +         (c1 == '-' || c1 == '_') )
>> +        res = 0;
>> +
> 
> Wow! That makes my head hurt. How about:
> 
> static int cdiff(unsigned char c1, unsigned char c2)
> {
>     if ( c1 == '-' )
>         c1 = '_';
> 
>     if ( c2 == '-' )
>         c2 = '_';
> 
>     return c1 - c2;
> }
> 
> ?

This would work for the current uses where ultimately the
result is only evaluated for being (non-)zero, but wouldn't
be correct when used for actual collation.

Jan
Andrew Cooper Jan. 23, 2020, 4:19 p.m. UTC | #3
On 23/01/2020 11:42, Jan Beulich wrote:
> In order to avoid permanently having to ask that no new command line
> options using underscores be introduced (albeit I'm likely to still make
> remarks), and in order to also allow extending the use of hyphens to
> pre-existing ones, introduce custom comparison functions treating both
> characters as matching.
>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> ---
> v2: Rename to opt_str{,n}cmp(). Don't use the new function for comapring
>     against "no-" in parse_params(). Add comment to cdiff().

Personally, I think this is a bad idea and should not be continued.

Yes - it is irritating needing to remember whether an option is spelled
with hyphen or underscore, but that is nothing compared to the pain for
users, who will have less bleeding edge version of Xen where the
different really matters.

Having one consistent behaviour across all versions of Xen is of far
more value to people than trying to fix a few wonky corner cases for
developers benefit.

~Andrew

Patch
diff mbox series

--- a/docs/misc/xen-command-line.pandoc
+++ b/docs/misc/xen-command-line.pandoc
@@ -72,6 +72,11 @@  Some options take a comma separated list
 Some parameters act as combinations of the above, most commonly a mix
 of Boolean and String.  These are noted in the relevant sections.
 
+### Spelling
+
+Parameter names may include hyphens or underscores.  These are
+generally being treated as matching one another by the parsing logic.
+
 ## Parameter details
 
 ### acpi
--- a/xen/common/kernel.c
+++ b/xen/common/kernel.c
@@ -23,6 +23,53 @@  enum system_state system_state = SYS_STA
 xen_commandline_t saved_cmdline;
 static const char __initconst opt_builtin_cmdline[] = CONFIG_CMDLINE;
 
+/*
+ * Calculate the difference between two characters for command line parsing
+ * purposes, i.e. treating '-' and '_' the same.
+ */
+static int cdiff(unsigned char c1, unsigned char c2)
+{
+    int res = c1 - c2;
+
+    if ( res && (c1 ^ c2) == ('-' ^ '_') &&
+         (c1 == '-' || c1 == '_') )
+        res = 0;
+
+    return res;
+}
+
+/*
+ * String comparison functions mostly matching strcmp() / strncmp(),
+ * except that they treat '-' and '_' as matching one another.
+ */
+static int opt_strcmp(const char *s1, const char *s2)
+{
+    int res;
+
+    for ( ; ; ++s1, ++s2 )
+    {
+        res = cdiff(*s1, *s2);
+        if ( res || !*s1 )
+            break;
+    }
+
+    return res;
+}
+
+static int opt_strncmp(const char *s1, const char *s2, size_t n)
+{
+    int res = 0;
+
+    for ( ; n--; ++s1, ++s2 )
+    {
+        res = cdiff(*s1, *s2);
+        if ( res || !*s1 )
+            break;
+    }
+
+    return res;
+}
+
 static int assign_integer_param(const struct kernel_param *param, uint64_t val)
 {
     switch ( param->len )
@@ -94,7 +141,7 @@  static int parse_params(const char *cmdl
 
         /* Boolean parameters can be inverted with 'no-' prefix. */
         key = optkey;
-        bool_assert = !!strncmp("no-", optkey, 3);
+        bool_assert = !!opt_strncmp("no-", optkey, 3);
         if ( !bool_assert )
             optkey += 3;
 
@@ -105,11 +152,11 @@  static int parse_params(const char *cmdl
             int rctmp;
             const char *s;
 
-            if ( strcmp(param->name, optkey) )
+            if ( opt_strcmp(param->name, optkey) )
             {
                 if ( param->type == OPT_CUSTOM && q &&
                      strlen(param->name) == q + 1 - opt &&
-                     !strncmp(param->name, opt, q + 1 - opt) )
+                     !opt_strncmp(param->name, opt, q + 1 - opt) )
                 {
                     found = true;
                     optval[-1] = '=';
@@ -284,7 +331,7 @@  int parse_boolean(const char *name, cons
     nlen = strlen(name);
 
     /* Does s now start with name? */
-    if ( slen < nlen || strncmp(s, name, nlen) )
+    if ( slen < nlen || opt_strncmp(s, name, nlen) )
         return -1;
 
     /* Exact, unadorned name?  Result depends on the 'no-' prefix. */
@@ -304,7 +351,7 @@  int cmdline_strcmp(const char *frag, con
     for ( ; ; frag++, name++ )
     {
         unsigned char f = *frag, n = *name;
-        int res = f - n;
+        int res = cdiff(f, n);
 
         if ( res || n == '\0' )
         {