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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v4] displif: add ABI for para-virtual display
Hey!
I only had minor comments - and if you are OK with them I can also
put them in the patch when checking them in (or if you want you can
repost it right away and I will check in the new version).
>
> ---
> Changes since v3:
> * add clarification on buffer's size/depth/format and
> connector's resolution
> * move be_alloc feature into domain's configuration
> to allow more use-cases and freedom (e.g. for 1:1
> mapped domains there may be no need to request backend
> to allocate buffers, while for the rest it may make more
> sense)
> * rename XenStore entries:
> ctrl-ring-ref -> req-ring-ref
> ctrl-channel -> req-event-channel
> event-ring-ref -> evt-ring-ref
> event-channel -> evt-event-channel
> * have 2 separate sections for req/resp and evt transport
> parameters
> * fix and extend recovery flow description
> * reserve request codes for future fbif integration if need be
> (request codes [0; 15] are reserved)
> * error on attempt to create multiple buffers with same cookie(s)
> * clarification of page directory usage for be_alloc feature
> * add editor's block
>
> Changes since v2:
> * updated XenStore configuration template/pattern
> * added "Recovery flow" to state diagram description
> * renamed gref_directory_start to gref_directory
> * added missing "versions" and "version" string constants
>
> Changes since v1:
> * fixed xendispl_event_page padding size
> * added versioning support
> * explicitly define value types for XenStore fields
> * text decoration re-work
> * added offsets to ASCII box notation
>
> Changes since initial:
> * DRM changed to DISPL, protocol made generic
> * major re-work addressing issues raised for sndif
>
> Signed-off-by: Oleksandr Grytsov <oleksandr_grytsov@xxxxxxxx>
> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
> ---
> xen/include/public/io/displif.h | 847
> ++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 847 insertions(+)
> create mode 100644 xen/include/public/io/displif.h
>
> diff --git a/xen/include/public/io/displif.h b/xen/include/public/io/displif.h
> new file mode 100644
> index 000000000000..ac55c4fe8bbe
> --- /dev/null
> +++ b/xen/include/public/io/displif.h
> @@ -0,0 +1,847 @@
> +/******************************************************************************
> + * displif.h
> + *
> + * Unified display device I/O interface for Xen guest OSes.
> + *
> + * Permission is hereby granted, free of charge, to any person obtaining a
> copy
> + * of this software and associated documentation files (the "Software"), to
> + * deal in the Software without restriction, including without limitation the
> + * rights to use, copy, modify, merge, publish, distribute, sublicense,
> and/or
> + * sell copies of the Software, and to permit persons to whom the Software is
> + * furnished to do so, subject to the following conditions:
> + *
> + * The above copyright notice and this permission notice shall be included in
> + * all copies or substantial portions of the Software.
> + *
> + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
> + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
> + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
> THE
> + * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
> + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
> + * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
> + * DEALINGS IN THE SOFTWARE.
> + *
> + * Copyright (C) 2016-2017 EPAM Systems Inc.
> + *
> + * Authors: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
> + * Oleksandr Grytsov <oleksandr_grytsov@xxxxxxxx>
> + */
> +
> +#ifndef __XEN_PUBLIC_IO_DISPLIF_H__
> +#define __XEN_PUBLIC_IO_DISPLIF_H__
> +
> +#include "ring.h"
> +#include "../grant_table.h"
> +
> +/*
> +
> ******************************************************************************
> + * Main features provided by the protocol
> +
> ******************************************************************************
> + * This protocol aims to provide a unified protocol which fits more
> + * sophisticated use-cases than a framebuffer device can handle. At the
> + * moment basic functionality is supported with the intention to be extended:
> + * o multiple dynamically allocated/destroyed framebuffers
> + * o buffers of arbitrary sizes
> + * o buffer allocation at either back or front end
> + * o better configuration options including multiple display support
> + *
> + * Note: existing fbif can be used together with displif running at the
> + * same time, e.g. on Linux one provides framebuffer and another DRM/KMS
> + *
> + * Note: display resolution (XenStore's "resolution" property) defines
> + * visible area of the virtual display. At the same time resolution of
> + * the display and frame buffers may differ: buffers can be smaller, equal
> + * or bigger than the visible area. This is to enable use-cases, where
> backend
> + * may do some post-processing of the display and frame buffers supplied,
> + * e.g. those buffers can be just a part of the final composition.
> + *
> +
> ******************************************************************************
> + * Direction of improvements
> +
> ******************************************************************************
> + * Future extensions to the existing protocol may include:
> + * o display/connector cloning
> + * o allocation of objects other than display buffers
> + * o plane/overlay support
> + * o scaling support
> + * o rotation support
> + *
> +
> ******************************************************************************
> + * Feature and Parameter Negotiation
> +
> ******************************************************************************
> + *
> + * Front->back notifications: when enqueuing a new request, sending a
> + * notification can be made conditional on xendispl_req (i.e., the generic
> + * hold-off mechanism provided by the ring macros). Backends must set
> + * xendispl_req appropriately (e.g., using RING_FINAL_CHECK_FOR_REQUESTS()).
> + *
> + * Back->front notifications: when enqueuing a new response, sending a
> + * notification can be made conditional on xendispl_resp (i.e., the generic
> + * hold-off mechanism provided by the ring macros). Frontends must set
> + * xendispl_resp appropriately (e.g., using
> RING_FINAL_CHECK_FOR_RESPONSES()).
> + *
> + * The two halves of a para-virtual display driver utilize nodes within
> + * XenStore to communicate capabilities and to negotiate operating
> parameters.
> + * This section enumerates these nodes which reside in the respective front
> and
> + * backend portions of XenStore, following the XenBus convention.
> + *
> + * All data in XenStore is stored as strings. Nodes specifying numeric
> + * values are encoded in decimal. Integer value ranges listed below are
> + * expressed as fixed sized integer types capable of storing the conversion
> + * of a properly formated node string, without loss of information.
> + *
> +
> ******************************************************************************
> + * Example configuration
> +
> ******************************************************************************
> + *
> + * Note: depending on the use-case backend can expose more display connectors
> + * than the underlying HW physically has by employing SW graphics compositors
> + *
> + * This is an example of backend and frontend configuration:
> + *
> + *--------------------------------- Backend
> -----------------------------------
> + *
> + * /local/domain/0/backend/vdispl/1/0/frontend-id = "1"
> + * /local/domain/0/backend/vdispl/1/0/frontend =
> "/local/domain/1/device/vdispl/0"
> + * /local/domain/0/backend/vdispl/1/0/state = "4"
> + * /local/domain/0/backend/vdispl/1/0/versions = "1,2"
> + *
> + *--------------------------------- Frontend
> ----------------------------------
> + *
> + * /local/domain/1/device/vdispl/0/backend-id = "0"
> + * /local/domain/1/device/vdispl/0/backend =
> "/local/domain/0/backend/vdispl/1/0"
> + * /local/domain/1/device/vdispl/0/state = "4"
> + * /local/domain/1/device/vdispl/0/version = "1"
> + * /local/domain/1/device/vdispl/0/be_alloc = "1"
This could be changed to '-'. As in "be-alloc" instead of "be_alloc"
> + *
> + *-------------------------- Connector 0 configuration
> ------------------------
> + *
> + * /local/domain/1/device/vdispl/0/0/resolution = "1920x1080"
> + * /local/domain/1/device/vdispl/0/0/req-ring-ref = "2832"
> + * /local/domain/1/device/vdispl/0/0/req-event-channel = "15"
> + * /local/domain/1/device/vdispl/0/0/evt-ring-ref = "387"
> + * /local/domain/1/device/vdispl/0/0/evt-event-channel = "16"
> + *
> + *-------------------------- Connector 1 configuration
> ------------------------
> + *
> + * /local/domain/1/device/vdispl/0/1/resolution = "800x600"
> + * /local/domain/1/device/vdispl/0/1/req-ring-ref = "2833"
> + * /local/domain/1/device/vdispl/0/1/req-event-channel = "17"
> + * /local/domain/1/device/vdispl/0/1/evt-ring-ref = "388"
> + * /local/domain/1/device/vdispl/0/1/evt-event-channel = "18"
> + *
> +
> ******************************************************************************
> + * Backend XenBus Nodes
> +
> ******************************************************************************
> + *
> + *----------------------------- Protocol version
> ------------------------------
> + *
> + * versions
> + * Values: <string>
> + *
> + * List of XENDISPL_LIST_SEPARATOR separated protocol versions supported
> + * by the backend. For example "1,2,3".
> + *
> +
> ******************************************************************************
> + * Frontend XenBus Nodes
> +
> ******************************************************************************
> + *
> + *-------------------------------- Addressing
> ---------------------------------
> + *
> + * dom-id
> + * Values: <uint16_t>
> + *
> + * Domain identifier.
> + *
> + * dev-id
> + * Values: <uint16_t>
> + *
> + * Device identifier.
> + *
> + * conn-idx
> + * Values: <uint8_t>
> + *
> + * Zero based contigous index of the connector.
> + * /local/domain/<dom-id>/device/vdispl/<dev-id>/<conn-idx>/...
> + *
> + *----------------------------- Protocol version
> ------------------------------
> + *
> + * version
> + * Values: <string>
> + *
> + * Protocol version, chosen among the ones supported by the backend.
> + *
> + *------------------------- Backend buffer allocation
> -------------------------
> + *
> + * be_alloc
> + * Values: "0", "1"
> + *
> + * If value is set to "1", then backend can be a buffer
> provider/allocator
> + * for this domain during XENDISPL_OP_DBUF_CREATE operation (see below
> + * for negotiation).
> + * If value is not "1" or omitted frontend must allocate buffers itself.
> + *
> + *----------------------------- Connector settings
> ----------------------------
> + *
> + * resolution
> + * Values: <width, uint32_t>x<height, uint32_t>
> + *
> + * Width and height of the connector in pixels separated by
> + * XENDISPL_RESOLUTION_SEPARATOR. This defines visible area of the
> + * display.
> + *
> + *------------------ Connector Request Transport Parameters
> -------------------
> + *
> + * This communication path is used to deliver requests from frontend to
> backend
> + * and get the corresponding responses from backend to frontend,
> + * set up per connector.
> + *
> + * req-event-channel
> + * Values: <uint32_t>
> + *
> + * The identifier of the Xen connector's control event channel
> + * used to signal activity in the ring buffer.
> + *
> + * req-ring-ref
> + * Values: <uint32_t>
> + *
> + * The Xen grant reference granting permission for the backend to map
> + * a sole page in a single page sized connector's control ring buffer.
Perhaps s/in a single page sized/of/ ?
> + *
> + *------------------- Connector Event Transport Parameters
> --------------------
> + *
> + * This communication path is used to deliver asynchronous events from
> backend
> + * to frontend, set up per connector.
> + *
> + * evt-event-channel
> + * Values: <uint32_t>
> + *
> + * The identifier of the Xen connector's event channel
> + * used to signal activity in the ring buffer.
> + *
> + * evt-ring-ref
> + * Values: <uint32_t>
> + *
> + * The Xen grant reference granting permission for the backend to map
> + * a sole page in a single page sized connector's event ring buffer.
The same here? s/in a single page sized/of/
> + */
> +
> +/*
> +
> ******************************************************************************
> + * STATE DIAGRAMS
> +
> ******************************************************************************
> + *
> + * Tool stack creates front and back state nodes with initial state
> + * XenbusStateInitialising.
> + * Tool stack creates and sets up frontend display configuration
> + * nodes per domain.
> + *
> + *-------------------------------- Normal flow
> --------------------------------
> + *
> + * Front Back
> + * ================================= =====================================
> + * XenbusStateInitialising XenbusStateInitialising
> + * o Query backend device
> identification
> + * data.
> + * o Open and validate backend device.
> + * |
> + * |
> + * V
> + * XenbusStateInitWait
> + *
> + * o Query frontend configuration
> + * o Allocate and initialize
> + * event channels per configured
> + * connector.
> + * o Publish transport parameters
> + * that will be in effect during
> + * this connection.
> + * |
> + * |
> + * V
> + * XenbusStateInitialised
> + *
> + * o Query frontend transport
> parameters.
> + * o Connect to the event channels.
> + * |
> + * |
> + * V
> + * XenbusStateConnected
> + *
> + * o Create and initialize OS
> + * virtual display connectors
> + * as per configuration.
> + * |
> + * |
> + * V
> + * XenbusStateConnected
> + *
> + * XenbusStateUnknown
> + * XenbusStateClosed
> + * XenbusStateClosing
> + * o Remove virtual display device
> + * o Remove event channels
> + * |
> + * |
> + * V
> + * XenbusStateClosed
> + *
> + *------------------------------- Recovery flow
> -------------------------------
> + *
> + * In case of frontend unrecoverable errors backend handles that as
> + * if frontend goes into the XenbusStateClosed state.
> + *
> + * In case of backend unrecoverable errors frontend tries removing
> + * the virtualized device. If this is possible at the moment of error,
> + * then frontend goes into the XenbusStateInitialising state and is ready for
> + * new connection with backend. If the virtualized device is still in use and
> + * cannot be removed, then frontend goes into the XenbusStateReconfiguring
> state
> + * until either the virtualized device removed or backend initiates a new
s/removed/is removed/
> + * connection. On the virtualized device removal frontend goes into the
> + * XenbusStateInitialising state.
> + *
> + * Note on XenbusStateReconfiguring state of the frontend: if backend has
> + * unrecoverable errors then frontend cannot send requests to the backend
> + * and thus cannot provide functionality of the virtualized device anymore.
> + * After backend is back to normal the virtualized device may still hold some
> + * state: configuration in use, allocated buffers, client application state
> etc.
> + * So, in most cases, this will require frontend to implement complex
> recovery
s/So, in/In/
> + * reconnect logic. Instead, by going into XenbusStateReconfiguring state,
> + * frontend will make sure no new clients of the virtualized device are
> + * accepted, allow existing client(s) to exit gracefully by signaling error
> + * state etc.
> + * Once all the clients are gone frontend can reinitialize the virtualized
> + * device and get into XenbusStateInitialising state again signaling the
> + * backend that a new connection can be made.
> + *
> + * There are multiple conditions possible under which frontend will go from
> + * XenbusStateReconfiguring into XenbusStateInitialising, some of them are OS
> + * specific. For example:
> + * 1. The underlying OS framework may provide callbacks to signal that the
> last
> + * client of the virtualized device has gone and the device can be removed
> + * 2. Frontend can schedule a deferred work (timer/tasklet/workqueue)
> + * to periodically check if this is the right time to re-try removal of
> + * the virtualized device.
> + * 3. By any other means.
> + *
> +
> ******************************************************************************
> + * REQUEST CODES
> +
> ******************************************************************************
> + * Request codes [0; 15] are reserved and must not be used
> + */
> +
> +#define XENDISPL_OP_DBUF_CREATE 0x10
> +#define XENDISPL_OP_DBUF_DESTROY 0x11
> +#define XENDISPL_OP_FB_ATTACH 0x12
> +#define XENDISPL_OP_FB_DETACH 0x13
> +#define XENDISPL_OP_SET_CONFIG 0x14
> +#define XENDISPL_OP_PG_FLIP 0x15
> +
> +/*
> +
> ******************************************************************************
> + * EVENT CODES
> +
> ******************************************************************************
> + */
> +#define XENDISPL_EVT_PG_FLIP 0x00
> +
> +/*
> +
> ******************************************************************************
> + * XENSTORE FIELD AND PATH NAME STRINGS, HELPERS
> +
> ******************************************************************************
> + */
> +#define XENDISPL_DRIVER_NAME "vdispl"
> +
> +#define XENDISPL_LIST_SEPARATOR ","
> +#define XENDISPL_RESOLUTION_SEPARATOR "x"
> +
> +#define XENDISPL_FIELD_BE_VERSIONS "versions"
> +#define XENDISPL_FIELD_FE_VERSION "version"
> +#define XENDISPL_FIELD_REQ_RING_REF "req-ring-ref"
> +#define XENDISPL_FIELD_REQ_CHANNEL "req-event-channel"
> +#define XENDISPL_FIELD_EVT_RING_REF "evt-ring-ref"
> +#define XENDISPL_FIELD_EVT_CHANNEL "evt-event-channel"
> +#define XENDISPL_FIELD_RESOLUTION "resolution"
> +#define XENDISPL_FIELD_BE_ALLOC "be_alloc"
s/be_alloc/be-alloc/ ?
> +
> +/*
> +
> ******************************************************************************
> + * STATUS RETURN CODES
> +
> ******************************************************************************
> + *
> + * Status return code is zero on success and -XEN_EXX on failure.
> + *
> +
> ******************************************************************************
> + * Assumptions
> +
> ******************************************************************************
> + * o usage of grant reference 0 as invalid grant reference:
> + * grant reference 0 is valid, but never exposed to a PV driver,
> + * because of the fact it is already in use/reserved by the PV console.
> + * o all references in this document to page sizes must be treated
> + * as pages of size XEN_PAGE_SIZE unless otherwise noted.
> + *
> +
> ******************************************************************************
> + * Description of the protocol between frontend and backend driver
> +
> ******************************************************************************
> + *
> + * The two halves of a Para-virtual display driver communicate with
> + * each other using shared pages and event channels.
> + * Shared page contains a ring with request/response packets.
> + *
> + * All reserved fields in the structures below must be 0.
> + * Display buffers's cookie of value 0 treated as invalid.
s/treated/is treated/
> + * Framebuffer's cookie of value 0 treated as invalid.
s/treated/is treated/
> + *
> + * For all request/response/event packets that use cookies:
> + * dbuf_cookie - uint64_t, unique to guest domain value used by the backend
> + * to map remote display buffer to its local one
> + * fb_cookie - uint64_t, unique to guest domain value used by the backend
> + * to map remote framebuffer to its local one
> + *
> + *---------------------------------- Requests
> ---------------------------------
> + *
> + * All requests/responses, which are not connector specific, must be sent
> over
> + * control ring of the connector with index 0.
s/with index 0/which has the index value of 0/ ?
[and for the four other places]. The 'with index 0' got me thinking that the
structure has to have some index 0. But you mean that it should go over:
/local/domain/<dom-id>/device/vdispl/<dev-id>/0/req-ring-ref
Perhaps include that? Like:
"
control ring of the connector which has the index value of 0:
/local/domain/<dom-id>/device/vdispl/<dev-id>/0/req-ring-ref
"?
> + *
> + * All request packets have the same length (64 octets)
> + * All request packets have common header:
> + * 0 1 2 3 octet
> + * +----------------+----------------+----------------+----------------+
> + * | id | operation | reserved | 4
> + * +----------------+----------------+----------------+----------------+
> + * | reserved | 8
> + * +----------------+----------------+----------------+----------------+
> + * id - uint16_t, private guest value, echoed in response
> + * operation - uint8_t, operation code, XENDISPL_OP_???
> + *
> + * Request dbuf creation - request creation of a display buffer.
> + * 0 1 2 3 octet
> + * +----------------+----------------+----------------+----------------+
> + * | id |_OP_DBUF_CREATE | reserved | 4
> + * +----------------+----------------+----------------+----------------+
> + * | reserved | 8
> + * +----------------+----------------+----------------+----------------+
> + * | dbuf_cookie low 32-bit | 12
> + * +----------------+----------------+----------------+----------------+
> + * | dbuf_cookie high 32-bit | 16
> + * +----------------+----------------+----------------+----------------+
> + * | width | 20
> + * +----------------+----------------+----------------+----------------+
> + * | height | 24
> + * +----------------+----------------+----------------+----------------+
> + * | bpp | 28
> + * +----------------+----------------+----------------+----------------+
> + * | buffer_sz | 32
> + * +----------------+----------------+----------------+----------------+
> + * | flags | 36
> + * +----------------+----------------+----------------+----------------+
> + * | gref_directory | 40
> + * +----------------+----------------+----------------+----------------+
> + * | reserved | 44
> + * +----------------+----------------+----------------+----------------+
> + * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
> + * +----------------+----------------+----------------+----------------+
> + * | reserved | 64
> + * +----------------+----------------+----------------+----------------+
> + *
> + * Must be sent over control ring of the connector with index 0.
> + * All unused bits in flags field must be set to 0.
> + *
> + * An attempt to create multiple display buffers with the same dbuf_cookie is
> + * an error. dbuf_cookie can be re-used after destroying the corresponding
> + * display buffer.
> + *
> + * Width and height of the display buffers can be smaller, equal or bigger
> + * than the connector's resolution. Depth/pixel format of the individual
> + * buffers can differ as well.
> + *
> + * width - uint32_t, width in pixels
> + * height - uint32_t, height in pixels
> + * bpp - uint32_t, bits per pixel
> + * buffer_sz - uint32_t, buffer size to be allocated, octets
> + * flags - uint32_t, flags of the operation
> + * o XENDISPL_DBUF_FLG_REQ_ALLOC - if set, then backend is requested
> + * to allocate the buffer with the parameters provided in this request.
> + * Page directory is handled as follows:
> + * Frontend on request:
> + * o allocates pages for the directory (gref_directory,
> + * gref_dir_next_page(s)
> + * o grants permissions for the pages of the directory
.. to the backend.
> + * o sets gref_dir_next_page fields
> + * Backend on response:
> + * o grants permissions for the pages of the buffer allocated
.. to the frontend
> + * o fills in page directory with grant references
> + * (gref[] in struct xendispl_page_directorygref)
s/directorygref/xendispl_page_directory
> + * gref_directory - grant_ref_t, a reference to the first shared page
> + * describing shared buffer references. At least one page exists. If shared
> + * buffer size (buffer_sz) exceeds what can be addressed by this single
> page,
> + * then reference to the next page must be supplied (see gref_dir_next_page
> + * below)
> + */
> +
.. snip..
> +
> ******************************************************************************
> + * Back to front events delivery
> +
> ******************************************************************************
> + * In order to deliver asynchronous events from back to front a shared page
> is
> + * allocated by front and its granted reference propagated to back via
> + * XenStore entries (event-XXX).
s/event-XXXX/.. the right name?/
> + * This page has a common header used by both front and back to synchronize
> + * access and control event's ring buffer, while back being a producer of the
> + * events and front being a consumer. The rest of the page after the header
> + * is used for event packets.
> + *
> + * Upon reception of an event(s) front may confirm its reception
> + * for either each event, group of events or none.
> + */
> +
> +struct xendispl_event_page {
> + uint32_t in_cons;
> + uint32_t in_prod;
> + uint8_t reserved[56];
> +};
> +
> +#define XENDISPL_EVENT_PAGE_SIZE 4096
> +#define XENDISPL_IN_RING_OFFS (sizeof(struct xendispl_event_page))
> +#define XENDISPL_IN_RING_SIZE (XENDISPL_EVENT_PAGE_SIZE -
> XENDISPL_IN_RING_OFFS)
> +#define XENDISPL_IN_RING_LEN (XENDISPL_IN_RING_SIZE / sizeof(struct
> xendispl_evt))
> +#define XENDISPL_IN_RING(page) \
> + ((struct xendispl_evt *)((char *)(page) + XENDISPL_IN_RING_OFFS))
> +#define XENDISPL_IN_RING_REF(page, idx) \
> + (XENDISPL_IN_RING((page))[(idx) % XENDISPL_IN_RING_LEN])
> +
> +#endif /* __XEN_PUBLIC_IO_DISPLIF_H__ */
> +
> +/*
> + * Local variables:
> + * mode: C
> + * c-file-style: "BSD"
> + * c-basic-offset: 4
> + * tab-width: 4
> + * indent-tabs-mode: nil
> + * End:
> + */
> --
> 2.7.4
>
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