Re: [Qemu-devel] [PATCH] xen_disk: support cache backend option

[Anthony Liguori <anthony@codemonkey.ws>]

Stefano Stabellini <stefano.stabellini@eu.citrix.com> writes:

> Support a backend option "cache" that specifies the cache mode that
> should be used to open the disk file or device.
>
> See: http://marc.info/?l=xen-devel&m=137226872905057
>
> Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

Is the guest setting this or a management tool?  I thought we were
moving to having the Xen management tools use QMP and the command line
instead of putting this stuff in XenStore...

Regards,

Anthony Liguori

>
> diff --git a/hw/xen_disk.c b/hw/xen_disk.c
> index f484404..092aa6b 100644
> --- a/hw/block/xen_disk.c
> +++ b/hw/block/xen_disk.c
> @@ -94,6 +94,7 @@ struct XenBlkDev {
>      char                *type;
>      char                *dev;
>      char                *devtype;
> +    char                *cache;
>      const char          *fileproto;
>      const char          *filename;
>      int                 ring_ref;
> @@ -734,6 +735,12 @@ static int blk_init(struct XenDevice *xendev)
>      if (blkdev->devtype == NULL) {
>          blkdev->devtype = xenstore_read_be_str(&blkdev->xendev, "device-type");
>      }
> +    if (blkdev->cache == NULL) {
> +        blkdev->cache = xenstore_read_be_str(&blkdev->xendev, "cache");
> +    }
> +    if (blkdev->cache == NULL) {
> +        blkdev->cache = g_strdup("writeback");
> +    }
>  
>      /* do we have all we need? */
>      if (blkdev->params == NULL ||
> @@ -774,6 +781,8 @@ out_error:
>      blkdev->dev = NULL;
>      g_free(blkdev->devtype);
>      blkdev->devtype = NULL;
> +    g_free(blkdev->cache);
> +    blkdev->cache = NULL;
>      return -1;
>  }
>  
> @@ -782,8 +791,14 @@ static int blk_connect(struct XenDevice *xendev)
>      struct XenBlkDev *blkdev = container_of(xendev, struct XenBlkDev, xendev);
>      int pers, index, qflags;
>  
> -    /* read-only ? */
> -    qflags = BDRV_O_CACHE_WB | BDRV_O_NATIVE_AIO;
> +    if (!strcmp(blkdev->cache, "none")) {
> +        qflags = BDRV_O_NATIVE_AIO | BDRV_O_NOCACHE;
> +    } else if (!strcmp(blkdev->cache, "writethrough")) {
> +        qflags = 0;
> +    } else {
> +        /* default to writeback */
> +        qflags = BDRV_O_NATIVE_AIO | BDRV_O_CACHE_WB;
> +    }
>      if (strcmp(blkdev->mode, "w") == 0) {
>          qflags |= BDRV_O_RDWR;
>      }
> @@ -950,6 +965,7 @@ static int blk_free(struct XenDevice *xendev)
>      g_free(blkdev->type);
>      g_free(blkdev->dev);
>      g_free(blkdev->devtype);
> +    g_free(blkdev->cache);
>      qemu_bh_delete(blkdev->bh);
>      return 0;
>  }