Re: match_token weird behavior

[Steve French]

Looking at more examples, some of which are much larger match tables
maybe it has to do with how the final entry is defined.  In this
example the NULL match is explicitly stated.

static const match_table_t cifs_secflavor_tokens = {
    { Opt_sec_krb5, "krb5" },
    { Opt_sec_krb5i, "krb5i" },
    { Opt_sec_krb5p, "krb5p" },
    { Opt_sec_ntlmsspi, "ntlmsspi" },
    { Opt_sec_ntlmssp, "ntlmssp" },
    { Opt_ntlm, "ntlm" },
    { Opt_sec_ntlmi, "ntlmi" },
    { Opt_sec_ntlmv2, "nontlm" },
    { Opt_sec_ntlmv2, "ntlmv2" },
    { Opt_sec_ntlmv2i, "ntlmv2i" },
    { Opt_sec_lanman, "lanman" },
    { Opt_sec_none, "none" },

    { Opt_sec_err, NULL }
};

On Wed, Sep 17, 2014 at 3:53 PM, Steve French <smfrench@xxxxxxxxx> wrote:
> For additional information the strings that are being matched against are:
>
> #define SMB1_VERSION_STRING    "1.0"
> #define SMB20_VERSION_STRING    "2.0"
> #define SMB21_VERSION_STRING    "2.1"
> #define SMB30_VERSION_STRING    "3.0"
> #define SMB302_VERSION_STRING    "3.02"
> #define SMB31_VERSION_STRING    "3.1"
>
>
> The matching works as expected, e,g. specifying 3.0 gets matched to
> Smb_30, before and/after adding the sixth element to the match_table_t
> - except that unmatched items (picking a dialect that doesn't exist
> like "5.1") matches to Smb_21 where it used to fall through to the
> default (error) case.
>
> It got me a little worried that there MAX_OPT_ARGS is 3 and I am
> getting the third element in the case of the error.
>
> Looking at other examples in the kernel were strange e.g. ext4/super.c has this
>
>         /*
>          * Initialize args struct so we know whether arg was
>          * found; some options take optional arguments.
>          */
>         args[0].to = args[0].from = NULL;
>         token = match_token(p, tokens, args);
>         (and then passes args down to a large helper function handle_mount_opt)
>
> Initializing args didn't seem to help in the cifs case
>
> On Wed, Sep 17, 2014 at 3:36 PM, Randy Dunlap <rdunlap@xxxxxxxxxxxxx> wrote:
>> On 09/17/14 13:33, Randy Dunlap wrote:
>>> On 09/17/14 11:20, Steve French wrote:
>>>> Noticing something very strange with match_token.   I had five strings
>>>> I need to compare a version string (protocol dialect eg. "2.1" or
>>>> "3.0") against, to find which it matches (if any), but adding one to
>>>> the list (now checking for one of six strings instead of five) causes
>>>> the error case to always default to element 3 (in my example looks as
>>>> if it matched to the 2.1 string) instead of the error case.
>>>>
>>>> enum smb_version {
>>>>     Smb_1 = 1,
>>>>     Smb_20,
>>>>     Smb_21,
>>>>     Smb_30,
>>>>     Smb_302,
>>>> };
>>>>
>>>> static const match_table_t cifs_smb_version_tokens = {
>>>>     { Smb_1, SMB1_VERSION_STRING },
>>>>     { Smb_20, SMB20_VERSION_STRING},
>>>>     { Smb_21, SMB21_VERSION_STRING },
>>>>     { Smb_30, SMB30_VERSION_STRING },
>>>>     { Smb_302, SMB302_VERSION_STRING },
>>>> };
>>>>
>>>
>>> You don't tell us what the actual string values are, but I'm guessing that
>>> SMB302_VERSION_STRING is a subset (same in first N characters) of SMB30_VERSION_STRING. ??
>>>
>>> In that case I think that match_token() will return a ptr to SMB_30 instead of to
>>> SMB_302 when the input is "3.02" (matches "3.0" due to the kernel's implementation
>>> of strcmp() stopping at the end of string1 (where string1 is "3.0" in this case).
>>
>> Oops, it seems that I got the strcmp() parameters reversed.  Sorry about that.
>> Feel free to disregard my ramblings.
>>
>>>
>>> If that is all correct, then could your return value be off by 1?
>>>
>>>>
>>>> When I add one entry to the lists above (going from 5 to 6 elements),
>>>> and then add one additional case for it to the switch statement, an
>>>> attempt to provide an unrecognized string (e.g. if I specify an illegal
>>>> dialect string like "9" instead of "3.0" or "2.1" etc) will now match the
>>>> third element (Smb_21) instead of "default" in the code snippet below.
>>>> Is match_token broken? Can match token only handle tables with 5
>>>> elements or fewer? Is there a replacement for it for this kind of thing
>>>> (matching a string versus which from among a list of valid strings)
>>>> other than match_token?  Is match_token just broken?
>>>>
>>>>     substring_t args[MAX_OPT_ARGS];
>>>>
>>>>     switch (match_token(value, cifs_smb_version_tokens, args)) {
>>>>     case Smb_1:
>>>>         vol->ops = &smb1_operations;
>>>>         vol->vals = &smb1_values;
>>>>         break;
>>>>     case Smb_20:
>>>>         vol->ops = &smb20_operations;
>>>>         vol->vals = &smb20_values;
>>>>         break;
>>>>     case Smb_21:
>>>>         vol->ops = &smb21_operations;
>>>>         vol->vals = &smb21_values;
>>>>         break;
>>>>     case Smb_30:
>>>>         vol->ops = &smb30_operations;
>>>>         vol->vals = &smb30_values;
>>>>         break;
>>>>     case Smb_302:
>>>>         vol->ops = &smb30_operations; /* currently identical with 3.0 */
>>>>         vol->vals = &smb302_values;
>>>>         break;
>>>>     default:
>>>>         cifs_dbg(VFS, "Unknown vers= option specified: %s\n", value);
>>>>         return 1;
>>>>
>>>
>>>
>>
>>
>> --
>> ~Randy
>
>
>
> --
> Thanks,
>
> Steve



-- 
Thanks,

Steve
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