Re: [PATCH v2 3/5] zstd: move ZSTD_MAX_CLEVEL to zstd_lib.h

[Sergey Senozhatsky <senozhatsky@chromium.org>]

On (26/07/29 12:16), haoqin huang wrote:
> > On (26/07/28 17:29), Haoqin Huang wrote:
> > [..]
> > >  #define ZSTD_MINMATCH_MAX         7   /* only for ZSTD_fast, other strategies are limited to 6 */
> > >  #define ZSTD_MINMATCH_MIN         3   /* only for ZSTD_btopt+, faster strategies are limited to 4 */
> > > +#define ZSTD_MAX_CLEVEL              22
> > >  #define ZSTD_TARGETLENGTH_MAX    ZSTD_BLOCKSIZE_MAX
> > >  #define ZSTD_TARGETLENGTH_MIN     0   /* note : comparing this constant to an unsigned results in a tautological test */
> > >  #define ZSTD_STRATEGY_MIN        ZSTD_fast
> > > diff --git a/lib/zstd/compress/clevels.h b/lib/zstd/compress/clevels.h
> > > index 6ab8be6532ef..06565e064456 100644
> > > --- a/lib/zstd/compress/clevels.h
> > > +++ b/lib/zstd/compress/clevels.h
> > > @@ -17,8 +17,6 @@
> > >
> > >  /*-=====  Pre-defined compression levels  =====-*/
> > >
> > > -#define ZSTD_MAX_CLEVEL     22
> > > -
> > >  __attribute__((__unused__))
> >
> > Sashiko made a good point.  Can we use zstd_max_clevel() instead?
> 
> Good point, I'll drop this patch and use zstd_max_clevel() instead
> in v3.
> 
> Since it's a runtime function and can't be used for static struct
> initialization, I plan to set backend_zstd's level_max to -1 as a
> sentinel value, and query the actual maximum in
> zcomp_validate_params():
> 
>     s32 max = backend->level_max;
>     if (max < 0)
>         max = zstd_max_clevel();
> 
> Do you think this approach is feasible?

Hmm, no, that doesn't look good. zcomp should not include
zstd.h or any other libs directly.  Should params validation
be a per-backend callback then?