Re: [virtio-comment] Re: [PATCH v9 08/10] admin: command list discovery

[Jason Wang <jasowang@redhat.com>]

å 2022/11/24 16:30, Michael S. Tsirkin åé:
> On Thu, Nov 24, 2022 at 02:40:15PM +0800, Jason Wang wrote:
> > On Thu, Nov 24, 2022 at 5:08 AM Michael S. Tsirkin <mst@redhat.com> wrote:
> > > Add commands to find out which commands does each group support,
> > > as well as enable their use by driver.
> > > This will be especially useful once we have multiple group types.
> > >
> > > An alternative is per-type VQs. This is possible but will
> > > require more per-transport work. Discovery through the vq
> > > helps keep things contained.
> > This seems to complicate the migration (compatibility) of the adminq
> > itself. We need check both features and command list.
> Yes. There's no way around this though - commands need to
> be per group and a pci device can host at least both
> SIOV and SRIOV children.
>
>
> > More below.
> >
> > > Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
> > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > > ---
> > >   admin.tex | 82 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-
> > >   1 file changed, 81 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/admin.tex b/admin.tex
> > > index eeccd2e..eec12a9 100644
> > > --- a/admin.tex
> > > +++ b/admin.tex
> > > @@ -91,7 +91,9 @@ \subsection{Group administration commands}\label{sec:Basic Facilities of a Virti
> > >   \hline
> > >   opcode & Name & Command Description \\
> > >   \hline \hline
> > > -0x0000 - 0x7FFF & - &  Group administration commands    \\
> > > +0x0000 & VIRTIO_ADMIN_CMD_LIST_QUERY & Provides to driver list of commands supported for this group type    \\
> > > +0x0001 & VIRTIO_ADMIN_CMD_LIST_USE & Provides to device list of commands used for this group type \\
> > > +0x0002 - 0x7FFF & - &  Group administration commands    \\
> > >   \hline
> > >   0x8000 - 0xFFFF & - & Reserved    \\
> > >   \hline
> > > @@ -142,6 +144,84 @@ \subsection{Group administration commands}\label{sec:Basic Facilities of a Virti
> > >   \hline
> > >   \end{tabular}
> > >
> > > +Before sending any administration commands to the device, the driver
> > > +needs to communicate to the device which commands it is going to
> > > +use. Initially (after reset), only two commands are assumed to be used:
> > > +VIRTIO_ADMIN_CMD_LIST_QUERY and VIRTIO_ADMIN_CMD_LIST_USE.
> > > +
> > > +Before sending any other commands for any member of a specific group to
> > > +the device, the driver queries the supported commands via
> > > +VIRTIO_ADMIN_CMD_LIST_QUERY and sends the commands it will use via
> > > +VIRTIO_ADMIN_CMD_LIST_USE.
> > > +
> > > +Commands VIRTIO_ADMIN_CMD_LIST_QUERY and
> > > +VIRTIO_ADMIN_CMD_LIST_USE
> > > +both use the following structure describing the
> > > +command opcodes:
> > > +
> > > +\begin{lstlisting}
> > > +struct virtio_admin_cmd_list {
> > > +       /* Indicates which of the below fields were returned
> > > +       le32 device_admin_cmds[];
> > > +};
> > > +\end{lstlisting}
> > > +
> > > +This structure is an array of 32 bit values in little-endian byte
> > > +order, in which a bit is set if the specific command opcode
> > > +is supported.
> > Is this simpler if we map group type instead of a single opcode? E.g
> > virtqueue transport will introduce 10+ commands, using a bit for a
> > specific opcode will complicate things.
> I think more flexibility is better, and bits are cheap.


So we may end up with something like:

If VIRTIO_F_TRANSPORT_VQ is supported, device MUST return the following 
opcodes via VIRTIO_ADMIN_CMD_LIST_QUERY

[opX, opY, ....]

Probably fine.



> > > +Thus, \field{device_admin_cmds[0]} refers to the first 32-bit value
> > > +in this array corresponding to opcodes 0 to 31,
> > > +\field{device_admin_cmds[1]} is the second 32-bit value
> > > +corresponding to opcodes 32 to 63, etc.
> > > +For example, the array of size 2 including
> > > +the values 0x3 in \field{device_admin_cmds[0]}
> > > +and 0x1 in \field{device_admin_cmds[1]} indicates that only opcodes 0, 1 and 32
> > > +are supported.
> > > +
> > > +Accordingly, bits 0 and 1 corresponding to opcode 0
> > > +(VIRTIO_ADMIN_CMD_LIST_QUERY) and 1
> > > +(VIRTIO_ADMIN_CMD_LIST_USE) are
> > > +always set in \field{device_admin_cmds[0]} returned by VIRTIO_ADMIN_CMD_LIST_QUERY.
> > > +
> > > +For the command VIRTIO_ADMIN_CMD_LIST_QUERY, \field{opcode} is set to 0x0.
> > > +The \field{group_member_id} is unused. It is set to zero by driver.
> > > +This command has no command specific data.
> > > +The device, upon success, returns a result in
> > > +\field{command_specific_result} in the format
> > > +\field{struct virtio_admin_cmd_list} describing the
> > > +list of administration commands supported for the given group.
> > > +
> > > +
> > > +For the command VIRTIO_ADMIN_CMD_LIST_USE, \field{opcode}
> > > +is set to 0x1.
> > > +The \field{group_member_id} is unused. It is set to zero by driver.
> > > +The \field{command_specific_data} is in the format
> > > +\field{struct virtio_admin_cmd_list} describing the
> > > +list of administration commands used by the driver.
> > > +This command has no command specific result.
> > > +
> > > +The driver issues the command VIRTIO_ADMIN_CMD_LIST_QUERY to
> > > +query the list of commands valid for this group and before sending
> > > +any commands for any member of a group.
> > > +
> > > +The driver then enables use of some of the opcodes by sending to
> > > +the device the command VIRTIO_ADMIN_CMD_LIST_USE with a subset
> > > +of the list returned by VIRTIO_ADMIN_CMD_LIST_QUERY that is
> > > +both understood and used by the driver.
> > Any reason we need to invent a negotiation process here? (This seems
> > only useful when some commands/opcodes are mutually exclusive)
> >
> > Thanks
> yes, features don't help because they are per owner.
> this is per group.
>
> imagine vq transport. SET_FEATURES commands sets the features
> for the child. we need something to negotiate with owner
> but still within the vq.


Should we document what happens if driver use a opcode that it doesn't 
negotiate? (It looks to me we don't document this for at leave 
virtio-net control virtqueue).

Thanks


> > > +
> > > +If the device supports the command list used by the driver, the
> > > +device completes the command with status VIRTIO_ADMIN_STATUS_OK.
> > > +If the device does not support the command list, the device
> > > +completes the command with status
> > > +VIRTIO_ADMIN_STATUS_INVALID_FIELD.
> > > +
> > > +Note: drivers are assumed not to set bits in device_admin_cmds
> > > +if they are not familiar with how the command opcode
> > > +is used, since devices could have dependencies between
> > > +command opcodes.
> > > +
> > > +It is assumed that all members in a group support and are used
> > > +with the same list of commands.
> > > +
> > >   \section{Administration Virtqueues}\label{sec:Basic Facilities of a Virtio Device / Administration Virtqueues}
> > >
> > >   An administration virtqueue of an owner device is used to submit
> > > --
> > > MST
>
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