clCreateSubBuffer

Creates a new buffer object (referred to as a sub-buffer object) from an existing buffer object.

`cl_mem clCreateSubBuffer (`	cl_mem `buffer`,
	cl_mem_flags `flags`,
	cl_buffer_create_type `buffer_create_type`,
	const void `*buffer_create_info`,
	cl_int `*errcode_ret)`

Parameters

buffer

A valid buffer object and cannot be a sub-buffer object.

flags

A bit-field that is used to specify allocation and usage information about the sub-buffer memory object being created and is described in the table below. If the CL_MEM_READ_WRITE, CL_MEM_READ_ONLY or CL_MEM_WRITE_ONLY values are not specified in flags, they are inherited from the corresponding memory access qualifers associated with buffer. The CL_MEM_USE_HOST_PTR, CL_MEM_ALLOC_HOST_PTR and CL_MEM_COPY_HOST_PTR values cannot be specified in flags but are inherited from the corresponding memory access qualifiers associated with buffer. If CL_MEM_COPY_HOST_PTR is specified in the memory access qualifier values associated with buffer it does not imply any additional copies when the sub-buffer is created from buffer. If the CL_MEM_HOST_WRITE_ONLY, CL_MEM_HOST_READ_ONLY or CL_MEM_HOST_NO_ACCESS values are not specified in flags, they are inherited from the corresponding memory access qualifiers associated with buffer.

cl_mem_flags	Description
`CL_MEM_READ_WRITE`	This flag specifies that the memory object will be read and written by a kernel. This is the default.
`CL_MEM_WRITE_ONLY`	This flag specifies that the memory object will be written but not read by a kernel. Reading from a buffer or image object created with `CL_MEM_WRITE_ONLY` inside a kernel is undefined. `CL_MEM_READ_WRITE` and `CL_MEM_WRITE_ONLY` are mutually exclusive.
`CL_MEM_READ_ONLY`	This flag specifies that the memory object is a read-only memory object when used inside a kernel. Writing to a buffer or image object created with `CL_MEM_READ_ONLY` inside a kernel is undefined. `CL_MEM_READ_WRITE` or `CL_MEM_WRITE_ONLY` and `CL_MEM_READ_ONLY` are mutually exclusive.
`CL_MEM_USE_HOST_PTR`	This flag is valid only if `host_ptr` is not NULL. If specified, it indicates that the application wants the OpenCL implementation to use memory referenced by `host_ptr` as the storage bits for the memory object. OpenCL implementations are allowed to cache the buffer contents pointed to by `host_ptr` in device memory. This cached copy can be used when kernels are executed on a device. The result of OpenCL commands that operate on multiple buffer objects created with the same `host_ptr` or overlapping host regions is considered to be undefined. Refer to the description of the alignment rules for `host_ptr` for memory objects (buffer and images) created using `CL_MEM_USE_HOST_PTR`.
`CL_MEM_ALLOC_HOST_PTR`	This flag specifies that the application wants the OpenCL implementation to allocate memory from host accessible memory. `CL_MEM_ALLOC_HOST_PTR` and `CL_MEM_USE_HOST_PTR` are mutually exclusive.
`CL_MEM_COPY_HOST_PTR`	This flag is valid only if `host_ptr` is not NULL. If specified, it indicates that the application wants the OpenCL implementation to allocate memory for the memory object and copy the data from memory referenced by `host_ptr`. `CL_MEM_COPY_HOST_PTR` and `CL_MEM_USE_HOST_PTR` are mutually exclusive. `CL_MEM_COPY_HOST_PTR` can be used with `CL_MEM_ALLOC_HOST_PTR` to initialize the contents of the cl_mem object allocated using host-accessible (e.g. PCIe) memory.
`CL_MEM_HOST_WRITE_ONLY`	This flag specifies that the host will only write to the memory object (using OpenCL APIs that enqueue a write or a map for write). This can be used to optimize write access from the host (e.g. enable write-combined allocations for memory objects for devices that communicate with the host over a system bus such as PCIe).
`CL_MEM_HOST_READ_ONLY`	This flag specifies that the host will only read the memory object (using OpenCL APIs that enqueue a read or a map for read). `CL_MEM_HOST_WRITE_ONLY` and `CL_MEM_HOST_READ_ONLY` are mutually exclusive.
`CL_MEM_HOST_NO_ACCESS`	This flag specifies that the host will not read or write the memory object. `CL_MEM_HOST_WRITE_ONLY` or `CL_MEM_HOST_READ_ONLY` and `CL_MEM_HOST_NO_ACCESS` are mutually exclusive.

buffer_create_type and buffer_create_info

Describes the type of buffer object to be created. The list of supported values for buffer_create_type and corresponding descriptor that buffer_create_info points to is described below.

cl_buffer_create_type Description

cl_buffer_create_type	Description
`CL_BUFFER_CREATE_TYPE_REGION`	Create a buffer object that represents a specific region in `buffer`. `buffer_create_info` is a pointer to the following structure: typedef struct _cl_buffer_region { size_t origin; size_t size; } cl_buffer_region; (`origin, size`) defines the offset and size in bytes in `buffer`. If `buffer` is created with `CL_MEM_USE_HOST_PTR`, the `host_ptr` associated with the buffer object returned is `host_ptr` + `origin`. The buffer object returned references the data store allocated for `buffer` and points to a specific region given by (`origin, size`) in this data store. `CL_INVALID_VALUE` is returned in `errcode_ret` if the region specified by (`origin, size`) is out of bounds in `buffer`. `CL_INVALID_BUFFER_SIZE` if `size` is 0. `CL_MISALIGNED_SUB_BUFFER_OFFSET` is returned in `errcode_ret` if there are no devices in context associated with `buffer` for which the `origin` value is aligned to the `CL_DEVICE_MEM_BASE_ADDR_ALIGN` value.

CL_BUFFER_CREATE_TYPE_REGION

Create a buffer object that represents a specific region in buffer.

buffer_create_info is a pointer to the following structure:

typedef struct _cl_buffer_region {
    size_t origin;
    size_t size;
} cl_buffer_region;

(origin, size) defines the offset and size in bytes in buffer.

If buffer is created with CL_MEM_USE_HOST_PTR, the host_ptr associated with the buffer object returned is host_ptr + origin.

The buffer object returned references the data store allocated for buffer and points to a specific region given by (origin, size) in this data store.

CL_INVALID_VALUE is returned in errcode_ret if the region specified by (origin, size) is out of bounds in buffer.

CL_INVALID_BUFFER_SIZE if size is 0.

CL_MISALIGNED_SUB_BUFFER_OFFSET is returned in errcode_ret if there are no devices in context associated with buffer for which the origin value is aligned to the CL_DEVICE_MEM_BASE_ADDR_ALIGN value.

Notes

Concurrent reading from, writing to and copying between both a buffer object and its sub-buffer object(s) is undefined. Concurrent reading from, writing to and copying between overlapping sub-buffer objects created with the same buffer object is undefined. Only reading from both a buffer object and its sub-buffer objects or reading from multiple overlapping sub-buffer objects is defined.

Errors

Returns CL_SUCCESS if the function is executed successfully. Otherwise, it returns one of the following errors in errcode_ret

CL_INVALID_MEM_OBJECT if buffer is not a valid buffer object or is a sub-buffer object.
CL_INVALID_VALUE if buffer was created with CL_MEM_WRITE_ONLY and flags specifies CL_MEM_READ_WRITE or CL_MEM_READ_ONLY, or if buffer was created with CL_MEM_READ_ONLY and flags specifies CL_MEM_READ_WRITE or CL_MEM_WRITE_ONLY, or if flags specifies CL_MEM_USE_HOST_PTR or CL_MEM_ALLOC_HOST_PTR or CL_MEM_COPY_HOST_PTR.
CL_INVALID_VALUE if buffer was created with CL_MEM_HOST_WRITE_ONLY and flags specifies CL_MEM_HOST_READ_ONLY or if buffer was created with CL_MEM_HOST_READ_ONLY and flags specifies CL_MEM_HOST_WRITE_ONLY, or if buffer was created with CL_MEM_HOST_NO_ACCESS and flags specifies CL_MEM_HOST_READ_ONLY or CL_MEM_HOST_WRITE_ONLY.
CL_INVALID_VALUE if value specified in buffer_create_type is not valid.
CL_INVALID_VALUE if value(s) specified in buffer_create_info (for a given buffer_create_type) is not valid or if buffer_create_info is NULL.
CL_INVALID_BUFFER_SIZE if size is 0.
CL_MEM_OBJECT_ALLOCATION_FAILURE if there is a failure to allocate memory for sub-buffer object.
CL_OUT_OF_RESOURCES if there is a failure to allocate resources required by the OpenCL implementation on the device.
CL_OUT_OF_HOST_MEMORY if there is a failure to allocate resources required by the OpenCL implementation on the host.

Specification

OpenCL Specification

Also see

clCreateBuffer, clEnqueueReadBuffer, clEnqueueWriteBuffer, clEnqueueCopyBuffer

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