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

On Wed, Jul 29, 2026 at 11:03 AM Sergey Senozhatsky
<[email protected]> wrote:
>
> On (26/07/28 17:29), Haoqin Huang wrote:
> [..]
> > diff --git a/include/linux/zstd_lib.h b/include/linux/zstd_lib.h
> > index e295d4125dde..f4b26844e53a 100644
> > --- a/include/linux/zstd_lib.h
> > +++ b/include/linux/zstd_lib.h
> > @@ -1241,6 +1241,7 @@ ZSTDLIB_API size_t ZSTD_sizeof_DDict(const ZSTD_DDict* ddict);
> >  #define ZSTD_SEARCHLOG_MIN        1
> >  #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?