[PATCH 2/2] cifs: Correct comment about domainname length

Chen Gang gang.chen at asianux.com
Mon Jul 29 18:09:58 MDT 2013

On 07/30/2013 05:10 AM, Scott Lovenberg wrote:
> On Mon, Jul 29, 2013 at 4:17 PM, Jeff Layton <jlayton at redhat.com> wrote:
>>>>> Still, how can we have a FQDN that's 256 characters long when the host
>>>>> name length can be 1024 characters long?
>>>> Excuse me, I am not quite familiar about cifs, so can not provide
>>>> additional more information (I found it only by reading code).
>>>> But I feel, it really need additional discussion and check by the
>>>> related experts (related members who are familiar with cifs).
>>>> Welcome any members' suggestions and completions.
>>>> Thanks.
>>> Come on guys, enough already. As per here:
>>> https://en.wikipedia.org/wiki/Domain_Name_System
>>> and a comment above the max len of the fully qualified domain name (FQDN) is
>>> 63 octets per label and 255 bytes per FQDN. This maximum includes 254
>>> bytes for the FQDN and one byte for the ending dot.
>> Ok, I think I knew that at one point and paged it out. It does make one
>> wonder why NI_MAXHOST is so big though -- is that for some
>> internationalization scheme?
>> --
>> Jeff Layton <jlayton at redhat.com>
> I guess it works if you're storing as UTF-32 or wchar_t at 4 bytes per
> character. 256 characters * 4 bytes/char + 1 byte for NULL.  Microsoft
> seems to use the same value for NI_MAXHOST ref:
> http://msdn.microsoft.com/en-us/library/windows/desktop/ms738532(v=vs.85).aspx
> .

As far as I know, the kernel implementation wants to use 255 + 1 as
character count, not bytes count for FQDN (256 bytes for 8-bit, 512
bytes for 16-bit, ...), it can be translated into uni-code or other
format within 255 + 1 character count.

May it be useful for our discussion ?

(BTW: if kernel really wants to do, I also suggest to check the kernel
implementation for it whether correct or not).

Chen Gang

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