Re: [Qemu-devel] [PATCH RFC v3] s390/css: handle CCW_FLAG_SKIP

[Eric Farman <farman@linux.ibm.com>]

On 5/8/19 5:12 AM, Cornelia Huck wrote:
> If a ccw has CCW_FLAG_SKIP set, and the command is of type
> read, read backwards, or sense, no data should be written
> to the guest for that command.
> 
> Signed-off-by: Cornelia Huck <cohuck@redhat.com>
> ---
> 
> v2 -> v3: fixed checks even more [Pierre]
> v1 -> v2: fixed checks for command type [Eric]
> 
> ---
>   hw/s390x/css.c         | 22 ++++++++++++++++++----
>   include/hw/s390x/css.h |  1 +
>   2 files changed, 19 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/s390x/css.c b/hw/s390x/css.c
> index 8fc9e35ba5d3..0fbaa233ffb5 100644
> --- a/hw/s390x/css.c
> +++ b/hw/s390x/css.c
> @@ -830,8 +830,12 @@ static int ccw_dstream_rw_noflags(CcwDataStream *cds, void *buff, int len,
>       if (op == CDS_OP_A) {
>           goto incr;
>       }
> -    ret = address_space_rw(&address_space_memory, cds->cda,
> -                           MEMTXATTRS_UNSPECIFIED, buff, len, op);
> +    if (!cds->do_skip) {
> +        ret = address_space_rw(&address_space_memory, cds->cda,
> +                               MEMTXATTRS_UNSPECIFIED, buff, len, op);
> +    } else {
> +        ret = 0;

Maybe set this to MEMTX_OK (defined as zero), just so it's clear based 
on the existing check below?

> +    }
>       if (ret != MEMTX_OK) {
>           cds->flags |= CDS_F_STREAM_BROKEN;
>           return -EINVAL;
> @@ -928,8 +932,13 @@ static int ccw_dstream_rw_ida(CcwDataStream *cds, void *buff, int len,
>       do {
>           iter_len = MIN(len, cont_left);
>           if (op != CDS_OP_A) {
> -            ret = address_space_rw(&address_space_memory, cds->cda,
> -                                   MEMTXATTRS_UNSPECIFIED, buff, iter_len, op);
> +            if (!cds->do_skip) {
> +                ret = address_space_rw(&address_space_memory, cds->cda,
> +                                       MEMTXATTRS_UNSPECIFIED, buff, iter_len,
> +                                       op);
> +            } else {
> +                ret = 0;

(here too)

Either way, this seems reasonable to me.

Reviewed-by: Eric Farman <farman@linux.ibm.com>

> +            }
>               if (ret != MEMTX_OK) {
>                   /* assume inaccessible address */
>                   ret = -EINVAL; /* channel program check */
> @@ -968,6 +977,11 @@ void ccw_dstream_init(CcwDataStream *cds, CCW1 const *ccw, ORB const *orb)
>   
>       cds->count = ccw->count;
>       cds->cda_orig = ccw->cda;
> +    /* skip is only effective for read, read backwards, or sense commands */
> +    cds->do_skip = (ccw->flags & CCW_FLAG_SKIP) &&
> +        ((ccw->cmd_code & 0x0f) == CCW_CMD_BASIC_SENSE ||
> +         (ccw->cmd_code & 0x03) == 0x02 /* read */ ||
> +         (ccw->cmd_code & 0x0f) == 0x0c /* read backwards */);
>       ccw_dstream_rewind(cds);
>       if (!(cds->flags & CDS_F_IDA)) {
>           cds->op_handler = ccw_dstream_rw_noflags;
> diff --git a/include/hw/s390x/css.h b/include/hw/s390x/css.h
> index aae19c427229..7cc183ef4366 100644
> --- a/include/hw/s390x/css.h
> +++ b/include/hw/s390x/css.h
> @@ -97,6 +97,7 @@ typedef struct CcwDataStream {
>       int (*op_handler)(struct CcwDataStream *cds, void *buff, int len,
>                         CcwDataStreamOp op);
>       hwaddr cda;
> +    bool do_skip;
>   } CcwDataStream;
>   
>   /*
>