linux-kernel - Re: [PATCH] scsi: bfa: Avoid implicit enum conversion in bfad_im_post_vendor

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Date:   Thu, 27 Sep 2018 16:35:37 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     anil.gurumurthy@...gic.com, sudarsana.kalluru@...gic.com,
        "James E.J. Bottomley" <jejb@...ux.vnet.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        linux-scsi@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] scsi: bfa: Avoid implicit enum conversion in bfad_im_post_vendor_event

On Tue, Sep 25, 2018 at 9:58 PM Nathan Chancellor
<natechancellor@...il.com> wrote:
>
> Clang warns when one enumerated type is implicitly converted to another.
>
> drivers/scsi/bfa/bfa_fcs_lport.c:379:26: warning: implicit conversion
> from enumeration type 'enum bfa_lport_aen_event' to different
> enumeration type 'enum bfa_ioc_aen_event' [-Wenum-conversion]
>                                   BFA_AEN_CAT_LPORT, event);
>                                                      ^~~~~
>
> The root cause of these warnings is the bfad_im_post_vendor_event
> function, which expects a value from enum bfa_ioc_aen_event but there
> are multiple instances of values from enums bfa_port_aen_event,
> bfa_audit_aen_event, and bfa_lport_aen_event being used in this
> function.

Indeed, it seems that bfad_im_post_vendor_event() assigns this parameter to
161         entry->aen_type = evt;

which is defined as:

1456         u32                     aen_type;

so already we know that aen_type is meant to be a grab bag of enum
values.  bfad_im_post_vendor_event() is already passed many different
types of enums, as you mention.  Does changing aen_type to an `int`
produce further warnings, because it would be nice to have that change
in this one, too.  AFAICT, it's only ever saved away in a containing
struct.

>
> Given that this doesn't appear to be a problem since cat helps with
> differentiating the events, just change evt's type to int so that no
> conversion needs to happen and Clang won't warn.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/147
> Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> ---
>
> The alternate way of fixing these warnings is to explicitly cast the
> conversion when calling the function but since there are about 8-10 of
> these warnings, it seems logical to just change the function definiton
> which is cleaner in my opinion.
>
> See commits 3eb95feac113 ("mm/zsmalloc.c: change stat type parameter to
> int") and 04fecbf51b3c ("mm: memcontrol: use int for event/state
> parameter in several functions") for similar fixes.
>
>  drivers/scsi/bfa/bfad_im.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/scsi/bfa/bfad_im.h b/drivers/scsi/bfa/bfad_im.h
> index e61ed8dad0b4..bd4ac187fd8e 100644
> --- a/drivers/scsi/bfa/bfad_im.h
> +++ b/drivers/scsi/bfa/bfad_im.h
> @@ -143,7 +143,7 @@ struct bfad_im_s {
>  static inline void bfad_im_post_vendor_event(struct bfa_aen_entry_s *entry,
>                                              struct bfad_s *drv, int cnt,
>                                              enum bfa_aen_category cat,
> -                                            enum bfa_ioc_aen_event evt)
> +                                            int evt)
>  {
>         struct timespec64 ts;
>
> --
> 2.19.0
>


-- 
Thanks,
~Nick Desaulniers