RE: [EXT] [PATCH v9 06/13] admin-cmds-resources: Add device resources admin commands

[Parav Pandit <parav@nvidia.com>]

> From: Satananda Burla <sburla@marvell.com>
> Sent: Monday, February 12, 2024 12:51 AM
> 
> Hi Parav
> > -----Original Message-----
> > From: Parav Pandit <parav@nvidia.com>
> > Sent: Tuesday, February 6, 2024 11:23 PM
> > To: virtio-comment@lists.oasis-open.org; mst@redhat.com;
> > cohuck@redhat.com
> > Cc: hengqi@linux.alibaba.com; Satananda Burla <sburla@marvell.com>;
> > shahafs@nvidia.com; si-wei.liu@oracle.com;
> > peter.hilber@opensynergy.com; jasowang@redhat.com;
> > xuanzhuo@linux.alibaba.com; Parav Pandit <parav@nvidia.com>
> > Subject: [EXT] [PATCH v9 06/13] admin-cmds-resources: Add device
> > resources admin commands
> >
> > External Email
> > +
> > +\paragraph{Device Resource Query Command}\label{par:Basic Facilities
> > +of
> > a Virtio Device / Device groups / Group
> > +administration commands / Device Resources / Device Resource Query
> > Command}
> > +
> > +This command reads the existing resource of \field{type} identified
> > +by \field{rid}, which is previously created using command
> > +VIRTIO_ADMIN_CMD_RESOURCE_CREATE.
> > +
> > +\begin{lstlisting}
> > +struct virtio_admin_cmd_resource_query_data {
> > +        struct virtio_admin_cmd_resource_cmd_hdr hdr; };
> > +\end{lstlisting}
> > +
> > +\begin{lstlisting}
> > +struct virtio_admin_cmd_resource_query_result {
> > +        le16 length;
> > +        le16 reserved[6];
> > +        struct virtio_admin_cmd_resource_attr attr; };
> > +\end{lstlisting}
> Since this is not fixed size, what happens when the write buffer allocated for
> this command result does not fit the result? Does device return specific error
> code?
It follows the standard admin infrastructure to allow device to truncated as I replied in previous email.
This continue the backward, forward compat design already in-place.

Returning error code would break the backward compat.
For example, old driver with size X bytes, and new device which is capable of X+Y bytes should not fail the command.

> > +
> > +For the command VIRTIO_ADMIN_CMD_RESOURCE_QUERY,
> \field{opcode} is
> > +set
> > to 0xc.
> > +
> > +\field{group_member_id} refers to the device itself to be accessed.
> > +\field{type} refers to the device resource type.
> > +\field{rid} identifies the existing resource of type \field{type}.
> > +\field{length} refers to the length of the \field{attr}.
> > +
> > +When the command completes successfully, the resource information is
> > returned
> > +to the driver in \field{attr}. When the optional fields of the
> > +\field{resource_specific_data} are valid, for each such field a
> > respective
> > +resource defined \field{fields_bmap} is set by the device.
> > +
> 
> Regards
> Satananda