Re: [PATCH 4/7] pc-bios: s390x: Rework data initialization

[Thomas Huth <thuth@redhat.com>]

On 15/07/2020 11.40, Janosch Frank wrote:
> Sometimes a memset is nicer to read than multiple struct->data = 0;
> 
> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
> Reviewed-by: Pierre Morel <pmorel@linux.ibm.com>
> ---
>  pc-bios/s390-ccw/dasd-ipl.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/pc-bios/s390-ccw/dasd-ipl.c b/pc-bios/s390-ccw/dasd-ipl.c
> index e8f2846740..0543334ed4 100644
> --- a/pc-bios/s390-ccw/dasd-ipl.c
> +++ b/pc-bios/s390-ccw/dasd-ipl.c
> @@ -167,16 +167,13 @@ static void ipl1_fixup(void)
>      ccwSeek->cda = ptr2u32(seekData);
>      ccwSeek->chain = 1;
>      ccwSeek->count = sizeof(*seekData);
> -    seekData->reserved = 0x00;
> -    seekData->cyl = 0x00;
> -    seekData->head = 0x00;
> +    memset(seekData, 0, sizeof(*seekData));

Sounds ok for me if the whole struct gets cleared (though I wonder
whether this is really worth the effort)...

>      ccwSearchID->cmd_code = CCW_CMD_DASD_SEARCH_ID_EQ;
>      ccwSearchID->cda = ptr2u32(searchData);
>      ccwSearchID->chain = 1;
>      ccwSearchID->count = sizeof(*searchData);
> -    searchData->cyl = 0;
> -    searchData->head = 0;
> +    memset(searchData, 0, sizeof(*searchData));
>      searchData->record = 2;

... but that looks rather worse to me, and the generated code will
likely also be slightly worse (since ->record is cleared first and then
set to 2 again).

Maybe rather drop this patch?

 Thomas