Content-type: text/html Man page of dat_ep_post_rdma_read


Section: Direct Access Transport Library Functions (3DAT)
Updated: 16 Jul 2004
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dat_ep_post_rdma_read - transfer all data to the local data buffer  


cc [ flag... ] file... -ldat [ library... ] 
#include <dat/udat.h>

    dat_ep_post_rdma_read (
    IN    DAT_EP_HANDLE        ep_handle,
    IN    DAT_COUNT            num_segments,
    IN    DAT_LMR_TRIPLET      *local_iov,
    IN    DAT_DTO_COOKIE       user_cookie,
    IN    DAT_RMR_TRIPLET      *remote_buffer,
    IN    DAT_COMPLETION_FLAGS completion_flags


ep_handle Handle for an instance of the Endpoint.

num_segments Number of lmr_triplets in local_iov.

local_iov I/O Vector that specifies the local buffer to fill.

user_cookie User-provided cookie that is returned to the Consumer at the completion of the RDMA Read. Can be NULL.

remote_buffer A pointer to an RMR Triplet that specifies the remote buffer from which the data is read.

completion_flags Flags for posted RDMA Read. The default DAT_COMPLETION_DEFAULT_FLAG is 0x00. Other values are as follows:

Completion Suppression


0x01 Suppress successful Completion.

Notification of Completion


0x04 Non-notification completion. Local Endpoint must be configured for Notification Suppression.

Barrier Fence


0x08 Request for Barrier Fence.



The dat_ep_post_rdma_read() function requests the transfer of all the data specified by the remote_buffer over the connection of the ep_handle Endpoint into the local_iov.

The num_segments parameter specifies the number of segments in the local_iov. The local_iov segments are filled in the I/O Vector order until the whole message is received. This ensures that all the "front" segments of the local_iov I/O Vector are completely filled, only one segment is partially filled, if needed, and all segments that follow it are not filled at all.

The user_cookie allows Consumers to have unique identifiers for each DTO. These identifiers are completely under user control and are opaque to the Provider. There is no requirement on the Consumer that the value user_cookie should be unique for each DTO. The user_cookie is returned to the Consumer in the Completion event for the posted RDMA Read.

A Consumer must not modify the local_iov or its content until the DTO is completed. When a Consumer does not adhere to this rule, the behavior of the Provider and the underlying Transport is not defined. Providers that allow Consumers to get ownership of the local_iov but not the memory it specifies back after the dat_ep_post_rdma_read() returns should document this behavior and also specify its support in Provider attributes. This behavior allows Consumers full control of the local_iov after dat_ep_post_rdma_read() returns. Because this behavior is not guaranteed by all Providers, portable Consumers should not rely on this behavior. Consumers should not rely on the Provider copying local_iov information.

The completion of the posted RDMA Read is reported to the Consumer asynchronously through a DTO Completion event based on the specified completion_flags value. The value of DAT_COMPLETION_UNSIGNALLED_FLAG is only valid if the Endpoint Request Completion Flags DAT_COMPLETION_UNSIGNALLED_FLAG. Otherwise, DAT_INVALID_PARAMETER is returned.

The DAT_SUCCESS return of the dat_ep_post_rdma_read() is at least the equivalent of posting an RDMA Read operation directly by native Transport. Providers should avoid resource allocation as part of dat_ep_post_rdma_read() to ensure that this operation is nonblocking and thread safe for an UpCall.

The operation is valid for the Endpoint in the DAT_EP_STATE_CONNECTED and DAT_EP_STATE_DISCONNECTED states. If the operation returns successfully for the Endpoint in the DAT_EP_STATE_DISCONNECTED state, the posted RDMA Read is immediately flushed to request_evd_handle.  


DAT_SUCCESS The operation was successful.

DAT_INSUFFICIENT_RESOURCES The operation failed due to resource limitations.

DAT_INVALID_PARAMETER Invalid parameter. For example, one of the IOV segments pointed to a memory outside its LMR.

DAT_INVALID_HANDLE The ep_handle parameter is invalid.

DAT_INVALID_STATE A parameter is in an invalid state. Endpoint was not in the DAT_EP_STATE_CONNECTED or DAT_EP_STATE_DISCONNECTED state.

DAT_LENGTH_ERROR The size of the receiving buffer is too small for sending buffer data. The size of the local buffer is too small for the data of the remote buffer.

DAT_PROTECTION_VIOLATION Protection violation for local or remote memory access. Protection Zone mismatch between either an LMR of one of the local_iov segments and the local Endpoint or the rmr_context and the remote Endpoint.

DAT_PRIVILEGES_VIOLATION Privileges violation for local or remote memory access. Either one of the LMRs used in local_iov is invalid or does not have the local write privileges, or rmr_context does not have the remote read privileges.



For best RDMA Read operation performance, the Consumer should align each buffer segment of local_iov to the Optimal Buffer Alignment attribute of the Provider. For portable applications, the Consumer should align each buffer segment of local_iov to the DAT_OPTIMAL_ALIGNMENT.

If connection was established without outstanding RDMA Read attributes matching on Endpoints on both sides (outstanding RDMA Read outgoing on one end is larger than the outstanding RDMA Read incoming on the other end), connection is broken when the number of incoming RDMA Read exceeds the outstanding RDMA Read incoming attribute of the Endpoint. The Consumer can use its own flow control to ensure that it does not post more RDMA Reads then the remote EP outstanding RDMA Read incoming attribute is. Thus, they do not rely on the underlying Transport enforcing it.  


See attributes(5) for descriptions of the following attributes:

Interface StabilityStandard: uDAPL, 1.1, 1.2



libdat(3LIB), attributes(5)




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Time: 02:40:01 GMT, October 02, 2010