Re: [Xen-devel] [PATCH v4 4/4] libxl: fix cd-eject

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Roger Pau Monne writes ("[PATCH v4 4/4] libxl: fix cd-eject"):
> Current libxl__device_disk_set_backend implementation tried to guess the
> backend of devices with format LIBXL_DISK_FORMAT_EMPTY, which is of course
> doomed to fail since the disk is empty. Instead just return early from the
> function if an empty disk is detected.
> 
> This fixes cd ejection.

DYK when this was broken ?  Or, to put it another way, how did this
ever work ?

...looking at the code...

AFAICT disk_try_backend should succeed for both LIBXL_DISK_BACKEND_PHY
and LIBXL_DISK_BACKEND_QDISK.  So even before your patch:

>          }
> -        memset(&a.stab, 0, sizeof(a.stab));
> +        /* Disk is empty, so it's useless to try to guess the backend type. 
> */
> +        return 0;
>      } else if ((disk->backend == LIBXL_DISK_BACKEND_UNKNOWN ||

libxl__device_disk_set_backend should work.

Worse, this change seems to leave disk->backend unset on return from
libxl__device_disk_set_backend, which seems quite wrong to me.

Ian.

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