Re: [RFC PATCH V2 02/11] hw/block/nvme: open code for volatile write cache

[Sai Pavan Boddu]

Hi Minwoo,

On Sun, Jan 17, 2021 at 11:53:32PM +0900, Minwoo Im wrote:
> Volatile Write Cache(VWC) feature is set in nvme_ns_setup() in the
> initial time.  This feature is related to block device backed,  but this
> feature is controlled in controller level via Set/Get Features command.
> 
> This patch removed dependency between nvme and nvme-ns to manage the VWC
> flag value.  Also, it open coded the Get Features for VWC to check all
> namespaces attached to the controller, and if false detected, return
> directly false.
> 
> Signed-off-by: Minwoo Im <minwoo.im.dev@gmail.com>
> ---
>  hw/block/nvme-ns.c |  4 ----
>  hw/block/nvme.c    | 15 ++++++++++++---
>  hw/block/nvme.h    |  1 -
>  3 files changed, 12 insertions(+), 8 deletions(-)
> 
> diff --git a/hw/block/nvme-ns.c b/hw/block/nvme-ns.c
> index 32662230130b..c403cd36b6bd 100644
> --- a/hw/block/nvme-ns.c
> +++ b/hw/block/nvme-ns.c
> @@ -89,10 +89,6 @@ static int nvme_ns_init_blk(NvmeCtrl *n, NvmeNamespace 
> *ns, Error **errp)
>          return -1;
>      }
>  
> -    if (blk_enable_write_cache(ns->blkconf.blk)) {
> -        n->features.vwc = 0x1;
> -    }
> -
>      return 0;
>  }
>  
> diff --git a/hw/block/nvme.c b/hw/block/nvme.c
> index cf0fe28fe6eb..b2a9c48a9d81 100644
> --- a/hw/block/nvme.c
> +++ b/hw/block/nvme.c
> @@ -3033,6 +3033,7 @@ static uint16_t nvme_get_feature(NvmeCtrl *n, 
> NvmeRequest *req)
>      NvmeGetFeatureSelect sel = NVME_GETFEAT_SELECT(dw10);
>      uint16_t iv;
>      NvmeNamespace *ns;
> +    int i;
>  
>      static const uint32_t nvme_feature_default[NVME_FID_MAX] = {
>          [NVME_ARBITRATION] = NVME_ARB_AB_NOLIMIT,
> @@ -3108,7 +3109,17 @@ static uint16_t nvme_get_feature(NvmeCtrl *n, 
> NvmeRequest *req)
>          result = ns->features.err_rec;
>          goto out;
>      case NVME_VOLATILE_WRITE_CACHE:
> -        result = n->features.vwc;
>
> This change breaks the build on ubuntu 16.04, gcc is detecting error
> as below
> ../hw/block/nvme.c: In function ‘nvme_process_sq’:
> ../hw/block/nvme.c:3242:9: error: ‘result’ may be used uninitialized
> in this function [-Werror=maybe-uninitialized]
>          trace_pci_nvme_getfeat_vwcache(result ? "enabled" :
>          "disabled");
>                   ^
>                   ../hw/block/nvme.c:3150:14: note: ‘result’ was
>                   declared here
>                        uint32_t result;
>                                      ^
>GCC version  5.4.0.
>Tested initilizing result variable, build looks good then.
>
>Regards,
>Sai Pavan
>
> +        for (i = 1; i <= n->num_namespaces; i++) {
> +            ns = nvme_ns(n, i);
> +            if (!ns) {
> +                continue;
> +            }
> +
> +            result = blk_enable_write_cache(ns->blkconf.blk);
> +            if (!result) {
> +                break;
> +            }
> +        }
>          trace_pci_nvme_getfeat_vwcache(result ? "enabled" : "disabled");
>          goto out;
>      case NVME_ASYNCHRONOUS_EVENT_CONF:
> @@ -3271,8 +3282,6 @@ static uint16_t nvme_set_feature(NvmeCtrl *n, 
> NvmeRequest *req)
>          ns->features.err_rec = dw11;
>          break;
>      case NVME_VOLATILE_WRITE_CACHE:
> -        n->features.vwc = dw11 & 0x1;
> -
>          for (i = 1; i <= n->num_namespaces; i++) {
>              ns = nvme_ns(n, i);
>              if (!ns) {
> diff --git a/hw/block/nvme.h b/hw/block/nvme.h
> index b7fbcca39d9f..5ba83ee77841 100644
> --- a/hw/block/nvme.h
> +++ b/hw/block/nvme.h
> @@ -117,7 +117,6 @@ typedef struct NvmeFeatureVal {
>          uint16_t temp_thresh_low;
>      };
>      uint32_t    async_config;
> -    uint32_t    vwc;
>  } NvmeFeatureVal;
>  
>  typedef struct NvmeCtrl {
> -- 
> 2.17.1
> 
>