Re: [Xen-devel] [PATCH v2 1/1] public/io/netif.h: add gref mapping control messages

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Joao Martins [mailto:joao.m.martins@xxxxxxxxxx]
> Sent: 01 September 2017 15:51
> To: Xen-devel <xen-devel@xxxxxxxxxxxxx>
> Cc: Wei Liu <wei.liu2@xxxxxxxxxx>; Paul Durrant <Paul.Durrant@xxxxxxxxxx>;
> Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>; Joao Martins
> <joao.m.martins@xxxxxxxxxx>
> Subject: [PATCH v2 1/1] public/io/netif.h: add gref mapping control messages
> 
> Adds 3 messages to allow guest to let backend keep grants mapped,
> such that 1) guests allowing fast recycling of pages can avoid doing
> grant ops for those cases, or otherwise 2) preferring copies over
> grants and 3) always using a fixed set of pages for network I/O.
> 
> The three control ring messages added are:
>  - Add grefs to be mapped by backend
>  - Remove grefs mappings (If they are not in use)
>  - Get maximum amount of grefs kept mapped.
> 
> Signed-off-by: Joao Martins <joao.m.martins@xxxxxxxxxx>
> ---
>  xen/include/public/io/netif.h | 114
> ++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 114 insertions(+)
> 
> diff --git a/xen/include/public/io/netif.h b/xen/include/public/io/netif.h
> index ca0061410d..264c317471 100644
> --- a/xen/include/public/io/netif.h
> +++ b/xen/include/public/io/netif.h
> @@ -353,6 +353,9 @@ struct xen_netif_ctrl_request {
>  #define XEN_NETIF_CTRL_TYPE_SET_HASH_MAPPING_SIZE 5
>  #define XEN_NETIF_CTRL_TYPE_SET_HASH_MAPPING      6
>  #define XEN_NETIF_CTRL_TYPE_SET_HASH_ALGORITHM    7
> +#define XEN_NETIF_CTRL_TYPE_GET_GREF_MAPPING_SIZE 8
> +#define XEN_NETIF_CTRL_TYPE_ADD_GREF_MAPPING      9
> +#define XEN_NETIF_CTRL_TYPE_PUT_GREF_MAPPING     10
> 
>      uint32_t data[3];
>  };
> @@ -391,6 +394,41 @@ struct xen_netif_ctrl_response {
>  };
> 
>  /*
> + * Static Grants (struct xen_netif_gref_alloc)
> + * ===========================================
> + *
> + * A frontend may provide a fixed set of grant references to be mapped on
> + * the backend. The message of type
> XEN_NETIF_CTRL_TYPE_ADD_GREF_MAPPING
> + * prior its usage in the command ring allows for creation of these mappings.
> + * The backend will maintain a fixed amount of these mappings.
> + *
> + * XEN_NETIF_CTRL_TYPE_GET_GREF_MAPPING_SIZE lets a frontend
> query how many
> + * of these mappings can be kept.
> + *
> + * Each entry in the XEN_NETIF_CTRL_TYPE_{ADD,PUT}_GREF_MAPPING
> input table has

ADD and PUT are slightly odd choices for opposites. Normally you'd have 'get' 
and 'put' or 'add' and 'remove' (or 'delete').

> + * the following format:
> + *
> + *    0     1     2     3     4     5     6     7  octet
> + * +-----+-----+-----+-----+-----+-----+-----+-----+
> + * | grant ref             |  flags    |  padding  |
> + * +-----+-----+-----+-----+-----+-----+-----+-----+
> + *
> + * grant ref: grant reference
> + * flags: flags describing the control operation
> + *
> + */
> +
> +struct xen_netif_gref_alloc {

Is 'alloc' really desirable here? What's being allocated?

> +       grant_ref_t ref;
> +       uint16_t flags;
> +
> +#define _XEN_NETIF_CTRLF_GREF_readonly    0
> +#define XEN_NETIF_CTRLF_GREF_readonly
> (1U<<_XEN_NETIF_CTRLF_GREF_readonly)
> +
> +       uint8_t pad[2];
> +};
> +
> +/*
>   * Control messages
>   * ================
>   *
> @@ -609,6 +647,82 @@ struct xen_netif_ctrl_response {
>   *       invalidate any table data outside that range.
>   *       The grant reference may be read-only and must remain valid until
>   *       the response has been processed.
> + *
> + * XEN_NETIF_CTRL_TYPE_GET_GREF_MAPPING_SIZE
> + * -----------------------------------------
> + *
> + * This is sent by the frontend to fetch the number of grefs that can be kept
> + * mapped in the backend.
> + *
> + * Request:
> + *
> + *  type    = XEN_NETIF_CTRL_TYPE_GET_GREF_MAPPING_SIZE
> + *  data[0] = queue index (assumed 0 for single queue)
> + *  data[1] = 0
> + *  data[2] = 0
> + *
> + * Response:
> + *
> + *  status = XEN_NETIF_CTRL_STATUS_NOT_SUPPORTED     - Operation not
> + *                                                     supported
> + *           XEN_NETIF_CTRL_STATUS_INVALID_PARAMETER - The queue index
> is
> + *                                                     out of range
> + *           XEN_NETIF_CTRL_STATUS_SUCCESS           - Operation successful
> + *  data   = maximum number of entries allowed in the gref mapping table
> + *           (if operation was successful) or zero if a mapping table is
> + *           not supported (i.e. hash mapping is done only by modular
> + *           arithmetic).

Too much cut'n'paste here methinks ;-)

> + *
> + * XEN_NETIF_CTRL_TYPE_ADD_GREF_MAPPING
> + * ------------------------------------
> + *
> + * This is sent by the frontend for backend to map a list of grant
> + * references.
> + *
> + * Request:
> + *
> + *  type    = XEN_NETIF_CTRL_TYPE_ADD_GREF_MAPPING
> + *  data[0] = queue index
> + *  data[1] = grant reference of page containing the mapping list
> + *            (assumed to start at beginning of grant)

Should then be 'assumed to start at beginning of *page*'?

> + *  data[2] = size of list in entries
> + *
> + * Response:
> + *
> + *  status = XEN_NETIF_CTRL_STATUS_NOT_SUPPORTED     - Operation not
> + *                                                     supported
> + *           XEN_NETIF_CTRL_STATUS_INVALID_PARAMETER - Operation failed
> + *           XEN_NETIF_CTRL_STATUS_SUCCESS           - Operation successful
> + *
> + * NOTE: Each entry in the input table has the format outlined
> + *       in struct xen_netif_gref_alloc.
> + *

What happens if the backend can successfully map some of the refs, but not all? 
Does the whole operation fail (the backend being required to unmap anything 
that it successfully mapped) or would it be better to have a per-ref status 
code in the structure, and allow partial success?

> + * XEN_NETIF_CTRL_TYPE_PUT_GREF_MAPPING
> + * ------------------------------------
> + *
> + * This is sent by the frontend for backend to unmap a list of grant
> +      * references.
> + *
> + * Request:
> + *
> + *  type    = XEN_NETIF_CTRL_TYPE_PUT_GREF_MAPPING
> + *  data[0] = queue index
> + *  data[1] = grant reference of page containing the mapping list
> + *            (assumed to start at beginning of page)
> + *  data[2] = size of list in entries
> + *
> + * Response:
> + *
> + *  status = XEN_NETIF_CTRL_STATUS_NOT_SUPPORTED     - Operation not
> + *                                                     supported
> + *           XEN_NETIF_CTRL_STATUS_INVALID_PARAMETER - Operation failed
> + *           XEN_NETIF_CTRL_STATUS_SUCCESS           - Operation successful
> + *
> + * NOTE: Each entry in the input table has the format outlined in
> + *       struct xen_netif_gref_alloc. The only valid entries are those
> + *    previously added with message
> XEN_NETIF_CTRL_TYPE_ADD_GREF_MAPPING
> + *    are valid. Additionally, entries in inflight will deliver an error.

Could you elaborate on what 'inflight' means?

Cheers,

  Paul

> + *
>   */
> 
>  DEFINE_RING_TYPES(xen_netif_ctrl,
> --
> 2.11.0


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel