# vkGetValidationCacheDataEXT(3) Manual Page

## Name

vkGetValidationCacheDataEXT - Get the data store from a validation cache

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## C Specification

Data can be retrieved from a validation cache object using the command:

    // Provided by VK_EXT_validation_cache
    VkResult vkGetValidationCacheDataEXT(
        VkDevice                                    device,
        VkValidationCacheEXT                        validationCache,
        size_t*                                     pDataSize,
        void*                                       pData);

## Parameters

- `device` is the logical device that owns the validation cache.

- `validationCache` is the validation cache to retrieve data from.

- `pDataSize` is a pointer to a value related to the amount of data in the validation cache, as described below.

- `pData` is either `NULL` or a pointer to a buffer.

## Description

If `pData` is `NULL`, then the maximum size of the data that can be retrieved from the validation cache, in bytes, is returned in `pDataSize`. Otherwise, `pDataSize` must point to a variable set by the application to the size of the buffer, in bytes, pointed to by `pData`, and on return the variable is overwritten with the amount of data actually written to `pData`. If `pDataSize` is less than the maximum size that can be retrieved by the validation cache, at most `pDataSize` bytes will be written to `pData`, and `vkGetValidationCacheDataEXT` will return `VK_INCOMPLETE` instead of `VK_SUCCESS`, to indicate that not all of the validation cache was returned.

Any data written to `pData` is valid and can be provided as the `pInitialData` member of the VkValidationCacheCreateInfoEXT structure passed to `vkCreateValidationCacheEXT`.

Two calls to `vkGetValidationCacheDataEXT` with the same parameters must retrieve the same data unless a command that modifies the contents of the cache is called between them.

Applications can store the data retrieved from the validation cache, and use these data, possibly in a future run of the application, to populate new validation cache objects. The results of validation, however, may depend on the vendor ID, device ID, driver version, and other details of the device. To enable applications to detect when previously retrieved data is incompatible with the device, the initial bytes written to `pData` must be a header consisting of the following members:

Table 1. Layout for Validation Cache Header Version `VK_VALIDATION_CACHE_HEADER_VERSION_ONE_EXT`
Offset | Size | Meaning
--- | --- | ---
0 | 4 | length in bytes of the entire validation cache header written as a stream of bytes, with the least significant byte first
4 | 4 | a VkValidationCacheHeaderVersionEXT value written as a stream of bytes, with the least significant byte first
8 | `VK_UUID_SIZE` | a layer commit ID expressed as a UUID, which uniquely identifies the version of the validation layers used to generate these validation results

The first four bytes encode the length of the entire validation cache header, in bytes. This value includes all fields in the header including the validation cache version field and the size of the length field.

The next four bytes encode the validation cache version, as described for VkValidationCacheHeaderVersionEXT. A consumer of the validation cache should use the cache version to interpret the remainder of the cache header.

If `pDataSize` is less than what is necessary to store this header, nothing will be written to `pData` and zero will be written to `pDataSize`.

Valid Usage (Implicit)

- VUID-vkGetValidationCacheDataEXT-device-parameter
  `device` must be a valid VkDevice handle

- VUID-vkGetValidationCacheDataEXT-validationCache-parameter
  `validationCache` must be a valid VkValidationCacheEXT handle

- VUID-vkGetValidationCacheDataEXT-pDataSize-parameter
  `pDataSize` must be a valid pointer to a `size_t` value

- VUID-vkGetValidationCacheDataEXT-pData-parameter
  If the value referenced by `pDataSize` is not `0`, and `pData` is not `NULL`, `pData` must be a valid pointer to an array of `pDataSize` bytes

- VUID-vkGetValidationCacheDataEXT-validationCache-parent
  `validationCache` must have been created, allocated, or retrieved from `device`

Return Codes

On success, this command returns

  - `VK_SUCCESS`

  - `VK_INCOMPLETE`

On failure, this command returns

  - `VK_ERROR_OUT_OF_HOST_MEMORY`

  - `VK_ERROR_OUT_OF_DEVICE_MEMORY`

## See Also

VK_EXT_validation_cache, VkDevice, VkValidationCacheEXT

## Document Notes

For more information, see the Vulkan Specification

This page is extracted from the Vulkan Specification. Fixes and changes should be made to the Specification, not directly.

## Copyright

Copyright 2014-2024 The Khronos Group Inc.

SPDX-License-Identifier: CC-BY-4.0