Re: [PATCH 01/10] cifs: add function to get length of NULL termination in bytes

On Wed, Apr 29, 2009 at 9:12 AM, Jeff Layton <[email protected]> wrote:
> On Wed, 29 Apr 2009 08:58:22 -0500
> Shirish Pargaonkar <[email protected]> wrote:
>
>> On Wed, Apr 29, 2009 at 8:29 AM, Jeff Layton <[email protected]> wrote:
>> > It's possible to have the null terminator for a charset be a single or
>> > multiple character. Add a function to tell us how long it should be.
>> >
>> > Signed-off-by: Jeff Layton <[email protected]>
>> > ---
>> >  fs/cifs/cifs_unicode.h |   19 +++++++++++++++++++
>> >  1 files changed, 19 insertions(+), 0 deletions(-)
>> >
>> > diff --git a/fs/cifs/cifs_unicode.h b/fs/cifs/cifs_unicode.h
>> > index 14eb9a2..6bffab5 100644
>> > --- a/fs/cifs/cifs_unicode.h
>> > +++ b/fs/cifs/cifs_unicode.h
>> > @@ -64,6 +64,25 @@ int cifs_strtoUCS(__le16 *, const char *, int, const struct nls_table *);
>> >  #endif
>> >
>> >  /*
>> > + * null_charlen - return length of null character for codepage
>> > + * @codepage - codepage for which to return length of NULL terminator
>> > + *
>> > + * Since we can't guarantee that the null terminator will be a particular
>> > + * length, we have to check against the codepage. If there's a problem
>> > + * determining it, assume a single-byte NULL terminator.
>> > + */
>> > +static inline int
>> > +null_charlen(const struct nls_table *codepage)
>> > +{
>> > +       int charlen;
>> > +       char tmp[NLS_MAX_CHARSET_SIZE];
>> > +
>> > +       charlen = codepage->uni2char(0, tmp, NLS_MAX_CHARSET_SIZE);
>> > +
>> > +       return charlen > 0 ? charlen : 1;
>> > +}
>> > +
>> > +/*
>> >  * UniStrcat:  Concatenate the second string to the first
>> >  *
>> >  * Returns:
>> > --
>> > 1.6.0.6
>> >
>> > _______________________________________________
>> > linux-cifs-client mailing list
>> > [email protected]
>> > https://lists.samba.org/mailman/listinfo/linux-cifs-client
>> >
>>
>> For some of the charsets I looked at under fs/nls, it looks like uni2char
>> always returns 1, I think to indicate the function succeeded as opposed
>> to sending an error.
>> Are there any charsets that you might have looked at whose
>> uni2char function returns more than 1 byte as size of the null character?
>
> No, I haven't see any, but I didn't do an exhaustive search. Given the
> number of problems we've had in this area, I'm leery of making any
> assumptions about these lengths. It's also possible that at some point
> in the future we could have an in-kernel version of UTF-16 or UTF-32.
> In the event of that we'll need to deal with multibyte null termination.
>
> So I think it makes sense to use a helper function for determining this
> rather than sprinkling "+1" to lengths all over the code. The overhead
> looks pretty minimal anyway.
>
> --
> Jeff Layton <[email protected]>
>

Jeff, I do not think uni2char returns the lenght of a character is bytes.
But what you are saying as I understand is, in the future null_charlen may
call some other function than uni2char to get the size of a null character
to get an accurate value, so interface will remain same, just the functionility
(of null_charlen) may change.