Re: [PATCH RFC 3/8] libxl: add backend_features to libxl_device_disk

[Joao Martins <joao.m.martins@oracle.com>]

On 11/07/2017 11:28 AM, Oleksandr Grytsov wrote:
> On Thu, Nov 2, 2017 at 8:06 PM, Joao Martins <joao.m.martins@oracle.com
> <mailto:joao.m.martins@oracle.com>> wrote:
> 
>     The function libxl__device_generic_add will have an additional
>     argument whereby it adds a second set of entries visible to the
>     backend only. These entries will then be used for devices
>     thus overriding backend maximum feature set with this user-defined ones.
> 
>     libxl_device_disk.backend_features are a key value store storing:
>      <feature-name> = <feature-value>
> 
>     xl|libxl are stateless with respect to feature names therefore is up to the
>     admin to carefully select those. If backend isn't supported therefore the
>     features won't be overwritten.
> 
>     Signed-off-by: Joao Martins <joao.m.martins@oracle.com
>     <mailto:joao.m.martins@oracle.com>>
>     ---
>      tools/libxl/libxl.h          |  8 ++++++++
>      tools/libxl/libxl_console.c  |  5 +++--
>      tools/libxl/libxl_device.c   | 37 +++++++++++++++++++++++++++++++++----
>      tools/libxl/libxl_disk.c     | 17 +++++++++++++++--
>      tools/libxl/libxl_internal.h |  4 +++-
>      tools/libxl/libxl_pci.c      |  2 +-
>      tools/libxl/libxl_types.idl  |  1 +
>      tools/libxl/libxl_usb.c      |  2 +-
>      8 files changed, 65 insertions(+), 11 deletions(-)
> 
> 
> No need to extend libxl__device_generic_add with additional parameter (brents).
> You can add nested entry in libxl__set_xenstore_<device> as following:
> 
> flexarray_append(back, "require/feature-persistent", "0");

Right, although entries on "back" array will have readonly permission to the
frontend. And these newly added "require" directory in this RFC was meant to be
only visible to the backend, hence only having XS_PERM_NONE permission set.

Joao

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