Re: [Xen-devel] libvirt, libxl and QDISKs

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Fri, 26 Apr 2013, Jim Fehlig wrote:
>     if (l_disk->driverName) {
>         if (STREQ(l_disk->driverName, "tap") ||
>             STREQ(l_disk->driverName, "tap2")) {
>             switch (l_disk->format) {
>             case VIR_STORAGE_FILE_QCOW:
>                 x_disk->format = LIBXL_DISK_FORMAT_QCOW;
>                 x_disk->backend = LIBXL_DISK_BACKEND_QDISK;
>                 break;
>             case VIR_STORAGE_FILE_QCOW2:
>                 x_disk->format = LIBXL_DISK_FORMAT_QCOW2;
>                 x_disk->backend = LIBXL_DISK_BACKEND_QDISK;
>                 break;
>             case VIR_STORAGE_FILE_VHD:
>                 x_disk->format = LIBXL_DISK_FORMAT_VHD;
>                 x_disk->backend = LIBXL_DISK_BACKEND_TAP;
>                 break;
>             case VIR_STORAGE_FILE_NONE:
>                 /* No subtype specified, default to raw/tap */
>             case VIR_STORAGE_FILE_RAW:
>                 x_disk->format = LIBXL_DISK_FORMAT_RAW;
>                 x_disk->backend = LIBXL_DISK_BACKEND_TAP;
>                 break;
>             default:
>                 virReportError(VIR_ERR_INTERNAL_ERROR,
>                                _("libxenlight does not support disk
> driver %s"),
>                               
> virStorageFileFormatTypeToString(l_disk->format));
>                 return -1;
>             }
>         } else if (STREQ(l_disk->driverName, "file")) {
>             x_disk->format = LIBXL_DISK_FORMAT_RAW;
>             x_disk->backend = LIBXL_DISK_BACKEND_TAP;
>         } else if (STREQ(l_disk->driverName, "phy")) {
>             x_disk->format = LIBXL_DISK_FORMAT_RAW;
>             x_disk->backend = LIBXL_DISK_BACKEND_PHY;
>         } else {
>             virReportError(VIR_ERR_INTERNAL_ERROR,
>                            _("libxenlight does not support disk driver %s"),
>                            l_disk->driverName);
>             return -1;
>         }
>     } else {
>         /*
>          * If driverName is not specified, default to raw as per
>          * xl-disk-configuration.txt in the xen documentation and let
>          * libxl pick a suitable backend.
>          */
>         x_disk->format = LIBXL_DISK_FORMAT_RAW;
>         x_disk->backend = LIBXL_DISK_BACKEND_UNKNOWN;
>     }

It looks like the defaults are the same of libxl.

However the mapping of RAW to TAP (libxl does the same) has always been
a bit dubious to me: now that upstream QEMU is used with HVM guests too
by libxl, there is no reason to use blktap over QEMU for raw files any
more.

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