Re: [PATCH 5/5] hw/scsi/spapr_vscsi: Do not mix SRP IU size with DMA buffer size

[David Gibson <david@gibson.dropbear.id.au>]

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On Wed, Mar 04, 2020 at 04:33:11PM +0100, Philippe Mathieu-Daudé wrote:
> The 'union srp_iu' is meant as a pointer to any SRP Information
> Unit type, it is not related to the size of a VIO DMA buffer.
> 
> Use a plain buffer for the VIO DMA read/write calls.
> We can remove the reserved buffer from the 'union srp_iu'.
> 
> This issue was noticed when replacing the zero-length arrays
> from hw/scsi/srp.h with flexible array member,
> 'clang -fsanitize=undefined' reported:
> 
>   hw/scsi/spapr_vscsi.c:69:29: error: field 'iu' with variable sized type 'union viosrp_iu' not at the end of a struct or class is a GNU extension [-Werror,-Wgnu-variable-sized-type-not-at-end]
>        union viosrp_iu         iu;
>                                ^
> 
> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> ---
>  hw/scsi/viosrp.h      |  2 +-
>  hw/scsi/spapr_vscsi.c | 10 +++++-----
>  2 files changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/hw/scsi/viosrp.h b/hw/scsi/viosrp.h
> index 25676c2383..aba3203028 100644
> --- a/hw/scsi/viosrp.h
> +++ b/hw/scsi/viosrp.h
> @@ -49,8 +49,8 @@ union srp_iu {
>      struct srp_tsk_mgmt tsk_mgmt;
>      struct srp_cmd cmd;
>      struct srp_rsp rsp;
> -    uint8_t reserved[SRP_MAX_IU_LEN];
>  };
> +_Static_assert(sizeof(union srp_iu) <= SRP_MAX_IU_LEN, "srp_iu size incorrect");

Hrm.  Given that srp_iu will be a variably sized type, is this
assertion actually testing anything meaningful?


Otherwise, LGTM.

>  
>  enum viosrp_crq_formats {
>      VIOSRP_SRP_FORMAT = 0x01,
> diff --git a/hw/scsi/spapr_vscsi.c b/hw/scsi/spapr_vscsi.c
> index f1a0bbdc31..f9be68e44e 100644
> --- a/hw/scsi/spapr_vscsi.c
> +++ b/hw/scsi/spapr_vscsi.c
> @@ -66,7 +66,7 @@ typedef union vscsi_crq {
>  
>  typedef struct vscsi_req {
>      vscsi_crq               crq;
> -    union viosrp_iu         iu;
> +    uint8_t                 viosrp_iu_buf[SRP_MAX_IU_LEN];
>  
>      /* SCSI request tracking */
>      SCSIRequest             *sreq;
> @@ -99,7 +99,7 @@ typedef struct {
>  
>  static union viosrp_iu *req_iu(vscsi_req *req)
>  {
> -    return (union viosrp_iu *)req->iu.srp.reserved;
> +    return (union viosrp_iu *)req->viosrp_iu_buf;
>  }
>  
>  
> @@ -184,7 +184,7 @@ static int vscsi_send_iu(VSCSIState *s, vscsi_req *req,
>  
>      /* First copy the SRP */
>      rc = spapr_vio_dma_write(&s->vdev, req->crq.s.IU_data_ptr,
> -                             &req->iu, length);
> +                             &req->viosrp_iu_buf, length);
>      if (rc) {
>          fprintf(stderr, "vscsi_send_iu: DMA write failure !\n");
>      }
> @@ -603,7 +603,7 @@ static const VMStateDescription vmstate_spapr_vscsi_req = {
>      .minimum_version_id = 1,
>      .fields = (VMStateField[]) {
>          VMSTATE_BUFFER(crq.raw, vscsi_req),
> -        VMSTATE_BUFFER(iu.srp.reserved, vscsi_req),
> +        VMSTATE_BUFFER(viosrp_iu_buf, vscsi_req),
>          VMSTATE_UINT32(qtag, vscsi_req),
>          VMSTATE_BOOL(active, vscsi_req),
>          VMSTATE_UINT32(data_len, vscsi_req),
> @@ -1104,7 +1104,7 @@ static void vscsi_got_payload(VSCSIState *s, vscsi_crq *crq)
>      }
>  
>      /* XXX Handle failure differently ? */
> -    if (spapr_vio_dma_read(&s->vdev, crq->s.IU_data_ptr, &req->iu,
> +    if (spapr_vio_dma_read(&s->vdev, crq->s.IU_data_ptr, &req->viosrp_iu_buf,
>                             crq->s.IU_length)) {
>          fprintf(stderr, "vscsi_got_payload: DMA read failure !\n");
>          vscsi_put_req(req);

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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