fi_endpoint(3) Libfabric v1.15.1 fi_endpoint(3) NAME fi_endpoint - Fabric endpoint operations fi_endpoint / fi_scalable_ep / fi_passive_ep / fi_close Allocate or close an endpoint. fi_ep_bind Associate an endpoint with hardware resources, such as event queues, completion queues, counters, address vectors, or shared transmit/re- ceive contexts. fi_scalable_ep_bind Associate a scalable endpoint with an address vector fi_pep_bind Associate a passive endpoint with an event queue fi_enable Transitions an active endpoint into an enabled state. fi_cancel Cancel a pending asynchronous data transfer fi_ep_alias Create an alias to the endpoint fi_control Control endpoint operation. fi_getopt / fi_setopt Get or set endpoint options. fi_rx_context / fi_tx_context / fi_srx_context / fi_stx_context Open a transmit or receive context. fi_tc_dscp_set / fi_tc_dscp_get Convert between a DSCP value and a network traffic class fi_rx_size_left / fi_tx_size_left (DEPRECATED) Query the lower bound on how many RX/TX operations may be posted without an operation returning -FI_EAGAIN. This functions have been deprecated and will be removed in a future version of the library. SYNOPSIS #include <rdma/fabric.h> #include <rdma/fi_endpoint.h> int fi_endpoint(struct fid_domain *domain, struct fi_info *info, struct fid_ep **ep, void *context); int fi_scalable_ep(struct fid_domain *domain, struct fi_info *info, struct fid_ep **sep, void *context); int fi_passive_ep(struct fi_fabric *fabric, struct fi_info *info, struct fid_pep **pep, void *context); int fi_tx_context(struct fid_ep *sep, int index, struct fi_tx_attr *attr, struct fid_ep **tx_ep, void *context); int fi_rx_context(struct fid_ep *sep, int index, struct fi_rx_attr *attr, struct fid_ep **rx_ep, void *context); int fi_stx_context(struct fid_domain *domain, struct fi_tx_attr *attr, struct fid_stx **stx, void *context); int fi_srx_context(struct fid_domain *domain, struct fi_rx_attr *attr, struct fid_ep **rx_ep, void *context); int fi_close(struct fid *ep); int fi_ep_bind(struct fid_ep *ep, struct fid *fid, uint64_t flags); int fi_scalable_ep_bind(struct fid_ep *sep, struct fid *fid, uint64_t flags); int fi_pep_bind(struct fid_pep *pep, struct fid *fid, uint64_t flags); int fi_enable(struct fid_ep *ep); int fi_cancel(struct fid_ep *ep, void *context); int fi_ep_alias(struct fid_ep *ep, struct fid_ep **alias_ep, uint64_t flags); int fi_control(struct fid *ep, int command, void *arg); int fi_getopt(struct fid *ep, int level, int optname, void *optval, size_t *optlen); int fi_setopt(struct fid *ep, int level, int optname, const void *optval, size_t optlen); uint32_t fi_tc_dscp_set(uint8_t dscp); uint8_t fi_tc_dscp_get(uint32_t tclass); DEPRECATED ssize_t fi_rx_size_left(struct fid_ep *ep); DEPRECATED ssize_t fi_tx_size_left(struct fid_ep *ep); ARGUMENTS fid On creation, specifies a fabric or access domain. On bind, identi- fies the event queue, completion queue, counter, or address vector to bind to the endpoint. In other cases, it's a fabric identifier of an associated resource. info Details about the fabric interface endpoint to be opened, obtained from fi_getinfo. ep A fabric endpoint. sep A scalable fabric endpoint. pep A passive fabric endpoint. context Context associated with the endpoint or asynchronous operation. index Index to retrieve a specific transmit/receive context. attr Transmit or receive context attributes. flags Additional flags to apply to the operation. command Command of control operation to perform on endpoint. arg Optional control argument. level Protocol level at which the desired option resides. optname The protocol option to read or set. optval The option value that was read or to set. optlen The size of the optval buffer. DESCRIPTION Endpoints are transport level communication portals. There are two types of endpoints: active and passive. Passive endpoints belong to a fabric do- main and are most often used to listen for incoming connection requests. However, a passive endpoint may be used to reserve a fabric address that can be granted to an active endpoint. Active endpoints belong to access domains and can perform data transfers. Active endpoints may be connection-oriented or connectionless, and may pro- vide data reliability. The data transfer interfaces - messages (fi_msg), tagged messages (fi_tagged), RMA (fi_rma), and atomics (fi_atomic) - are associated with active endpoints. In basic configurations, an active end- point has transmit and receive queues. In general, operations that gener- ate traffic on the fabric are posted to the transmit queue. This includes all RMA and atomic operations, along with sent messages and sent tagged messages. Operations that post buffers for receiving incoming data are submitted to the receive queue. Active endpoints are created in the disabled state. They must transition into an enabled state before accepting data transfer operations, including posting of receive buffers. The fi_enable call is used to transition an active endpoint into an enabled state. The fi_connect and fi_accept calls will also transition an endpoint into the enabled state, if it is not al- ready active. In order to transition an endpoint into an enabled state, it must be bound to one or more fabric resources. An endpoint that will generate asynchro- nous completions, either through data transfer operations or communication establishment events, must be bound to the appropriate completion queues or event queues, respectively, before being enabled. Additionally, endpoints that use manual progress must be associated with relevant completion queues or event queues in order to drive progress. For endpoints that are only used as the target of RMA or atomic operations, this means binding the end- point to a completion queue associated with receive processing. Connec- tionless endpoints must be bound to an address vector. Once an endpoint has been activated, it may be associated with an address vector. Receive buffers may be posted to it and calls may be made to con- nection establishment routines. Connectionless endpoints may also perform data transfers. The behavior of an endpoint may be adjusted by setting its control data and protocol options. This allows the underlying provider to redirect function calls to implementations optimized to meet the desired application behav- ior. If an endpoint experiences a critical error, it will transition back into a disabled state. Critical errors are reported through the event queue asso- ciated with the EP. In certain cases, a disabled endpoint may be re-en- abled. The ability to transition back into an enabled state is provider specific and depends on the type of error that the endpoint experienced. When an endpoint is disabled as a result of a critical error, all pending operations are discarded. fi_endpoint / fi_passive_ep / fi_scalable_ep fi_endpoint allocates a new active endpoint. fi_passive_ep allocates a new passive endpoint. fi_scalable_ep allocates a scalable endpoint. The prop- erties and behavior of the endpoint are defined based on the provided struct fi_info. See fi_getinfo for additional details on fi_info. fi_info flags that control the operation of an endpoint are defined below. See section SCALABLE ENDPOINTS. If an active endpoint is allocated in order to accept a connection request, the fi_info parameter must be the same as the fi_info structure provided with the connection request (FI_CONNREQ) event. An active endpoint may acquire the properties of a passive endpoint by set- ting the fi_info handle field to the passive endpoint fabric descriptor. This is useful for applications that need to reserve the fabric address of an endpoint prior to knowing if the endpoint will be used on the active or passive side of a connection. For example, this feature is useful for sim- ulating socket semantics. Once an active endpoint acquires the properties of a passive endpoint, the passive endpoint is no longer bound to any fab- ric resources and must no longer be used. The user is expected to close the passive endpoint after opening the active endpoint in order to free up any lingering resources that had been used. fi_close Closes an endpoint and release all resources associated with it. When closing a scalable endpoint, there must be no opened transmit con- texts, or receive contexts associated with the scalable endpoint. If re- sources are still associated with the scalable endpoint when attempting to close, the call will return -FI_EBUSY. Outstanding operations posted to the endpoint when fi_close is called will be discarded. Discarded operations will silently be dropped, with no com- pletions reported. Additionally, a provider may discard previously com- pleted operations from the associated completion queue(s). The behavior to discard completed operations is provider specific. fi_ep_bind fi_ep_bind is used to associate an endpoint with other allocated resources, such as completion queues, counters, address vectors, event queues, shared contexts, and memory regions. The type of objects that must be bound with an endpoint depend on the endpoint type and its configuration. Passive endpoints must be bound with an EQ that supports connection manage- ment events. Connectionless endpoints must be bound to a single address vector. If an endpoint is using a shared transmit and/or receive context, the shared contexts must be bound to the endpoint. CQs, counters, AV, and shared contexts must be bound to endpoints before they are enabled either explicitly or implicitly. An endpoint must be bound with CQs capable of reporting completions for any asynchronous operation initiated on the endpoint. For example, if the end- point supports any outbound transfers (sends, RMA, atomics, etc.), then it must be bound to a completion queue that can report transmit completions. This is true even if the endpoint is configured to suppress successful com- pletions, in order that operations that complete in error may be reported to the user. An active endpoint may direct asynchronous completions to different CQs, based on the type of operation. This is specified using fi_ep_bind flags. The following flags may be OR'ed together when binding an endpoint to a completion domain CQ. FI_RECV Directs the notification of inbound data transfers to the specified completion queue. This includes received messages. This binding automatically includes FI_REMOTE_WRITE, if applicable to the end- point. FI_SELECTIVE_COMPLETION By default, data transfer operations write CQ completion entries into the associated completion queue after they have successfully completed. Applications can use this bind flag to selectively en- able when completions are generated. If FI_SELECTIVE_COMPLETION is specified, data transfer operations will not generate CQ entries for successful completions unless FI_COMPLETION is set as an operational flag for the given operation. Operations that fail asynchronously will still generate completions, even if a completion is not re- quested. FI_SELECTIVE_COMPLETION must be OR'ed with FI_TRANSMIT and/or FI_RECV flags. When FI_SELECTIVE_COMPLETION is set, the user must determine when a request that does NOT have FI_COMPLETION set has completed indirectly, usually based on the completion of a subsequent operation or by using completion counters. Use of this flag may improve performance by allowing the provider to avoid writing a CQ completion entry for every operation. See Notes section below for additional information on how this flag inter- acts with the FI_CONTEXT and FI_CONTEXT2 mode bits. FI_TRANSMIT Directs the completion of outbound data transfer requests to the specified completion queue. This includes send message, RMA, and atomic operations. An endpoint may optionally be bound to a completion counter. Associating an endpoint with a counter is in addition to binding the EP with a CQ. When binding an endpoint to a counter, the following flags may be speci- fied. FI_READ Increments the specified counter whenever an RMA read, atomic fetch, or atomic compare operation initiated from the endpoint has com- pleted successfully or in error. FI_RECV Increments the specified counter whenever a message is received over the endpoint. Received messages include both tagged and normal mes- sage operations. FI_REMOTE_READ Increments the specified counter whenever an RMA read, atomic fetch, or atomic compare operation is initiated from a remote endpoint that targets the given endpoint. Use of this flag requires that the end- point be created using FI_RMA_EVENT. FI_REMOTE_WRITE Increments the specified counter whenever an RMA write or base atomic operation is initiated from a remote endpoint that targets the given endpoint. Use of this flag requires that the endpoint be created using FI_RMA_EVENT. FI_SEND Increments the specified counter whenever a message transfer initi- ated over the endpoint has completed successfully or in error. Sent messages include both tagged and normal message operations. FI_WRITE Increments the specified counter whenever an RMA write or base atomic operation initiated from the endpoint has completed success- fully or in error. An endpoint may only be bound to a single CQ or counter for a given type of operation. For example, a EP may not bind to two counters both using FI_WRITE. Furthermore, providers may limit CQ and counter bindings to end- points of the same endpoint type (DGRAM, MSG, RDM, etc.). fi_scalable_ep_bind fi_scalable_ep_bind is used to associate a scalable endpoint with an ad- dress vector. See section on SCALABLE ENDPOINTS. A scalable endpoint has a single transport level address and can support multiple transmit and re- ceive contexts. The transmit and receive contexts share the trans- port-level address. Address vectors that are bound to scalable endpoints are implicitly bound to any transmit or receive contexts created using the scalable endpoint. fi_enable This call transitions the endpoint into an enabled state. An endpoint must be enabled before it may be used to perform data transfers. Enabling an endpoint typically results in hardware resources being assigned to it. Endpoints making use of completion queues, counters, event queues, and/or address vectors must be bound to them before being enabled. Calling connect or accept on an endpoint will implicitly enable an endpoint if it has not already been enabled. fi_enable may also be used to re-enable an endpoint that has been disabled as a result of experiencing a critical error. Applications should check the return value from fi_enable to see if a disabled endpoint has success- fully be re-enabled. fi_cancel fi_cancel attempts to cancel an outstanding asynchronous operation. Can- celing an operation causes the fabric provider to search for the operation and, if it is still pending, complete it as having been canceled. An error queue entry will be available in the associated error queue with error code FI_ECANCELED. On the other hand, if the operation completed before the call to fi_cancel, then the completion status of that operation will be available in the associated completion queue. No specific entry related to fi_cancel itself will be posted. Cancel uses the context parameter associated with an operation to identify the request to cancel. Operations posted without a valid context parameter - either no context parameter is specified or the context value was ignored by the provider - cannot be canceled. If multiple outstanding operations match the context parameter, only one will be canceled. In this case, the operation which is canceled is provider specific. The cancel operation is asynchronous, but will complete within a bounded period of time. fi_ep_alias This call creates an alias to the specified endpoint. Conceptually, an endpoint alias provides an alternate software path from the application to the underlying provider hardware. An alias EP differs from its parent end- point only by its default data transfer flags. For example, an alias EP may be configured to use a different completion mode. By default, an alias EP inherits the same data transfer flags as the parent endpoint. An appli- cation can use fi_control to modify the alias EP operational flags. When allocating an alias, an application may configure either the transmit or receive operational flags. This avoids needing a separate call to fi_control to set those flags. The flags passed to fi_ep_alias must in- clude FI_TRANSMIT or FI_RECV (not both) with other operational flags OR'ed in. This will override the transmit or receive flags, respectively, for operations posted through the alias endpoint. All allocated aliases must be closed for the underlying endpoint to be released. fi_control The control operation is used to adjust the default behavior of an end- point. It allows the underlying provider to redirect function calls to im- plementations optimized to meet the desired application behavior. As a re- sult, calls to fi_ep_control must be serialized against all other calls to an endpoint. The base operation of an endpoint is selected during creation using struct fi_info. The following control commands and arguments may be assigned to an endpoint. **FI_BACKLOG - int *value** This option only applies to passive endpoints. It is used to set the connection request backlog for listening endpoints. **FI_GETOPSFLAG - uint64_t *flags** Used to retrieve the current value of flags associated with the data transfer operations initiated on the endpoint. The control argument must include FI_TRANSMIT or FI_RECV (not both) flags to indicate the type of data transfer flags to be returned. See below for a list of control flags. FI_GETWAIT - void ** This command allows the user to retrieve the file descriptor associ- ated with a socket endpoint. The fi_control arg parameter should be an address where a pointer to the returned file descriptor will be written. See fi_eq.3 for addition details using fi_control with FI_GETWAIT. The file descriptor may be used for notification that the endpoint is ready to send or receive data. **FI_SETOPSFLAG - uint64_t *flags** Used to change the data transfer operation flags associated with an endpoint. The control argument must include FI_TRANSMIT or FI_RECV (not both) to indicate the type of data transfer that the flags should apply to, with other flags OR'ed in. The given flags will override the previous transmit and receive attributes that were set when the endpoint was created. Valid control flags are defined be- low. fi_getopt / fi_setopt Endpoint protocol operations may be retrieved using fi_getopt or set using fi_setopt. Applications specify the level that a desired option exists, identify the option, and provide input/output buffers to get or set the op- tion. fi_setopt provides an application a way to adjust low-level protocol and implementation specific details of an endpoint. The following option levels and option names and parameters are defined. FI_OPT_ENDPOINT * .RS 2 FI_OPT_BUFFERED_LIMIT - size_t Defines the maximum size of a buffered message that will be reported to users as part of a receive completion when the FI_BUFFERED_RECV mode is enabled on an endpoint. fi_getopt() will return the currently configured threshold, or the provider's default threshold if one has not be set by the application. fi_setopt() allows an application to configure the threshold. If the provider cannot support the requested threshold, it will fail the fi_se- topt() call with FI_EMSGSIZE. Calling fi_setopt() with the threshold set to SIZE_MAX will set the threshold to the maximum supported by the provider. fi_getopt() can then be used to retrieve the set size. In most cases, the sending and receiving endpoints must be configured to use the same threshold value, and the threshold must be set prior to en- abling the endpoint. * .RS 2 FI_OPT_BUFFERED_MIN - size_t Defines the minimum size of a buffered message that will be re- ported. Applications would set this to a size that's big enough to decide whether to discard or claim a buffered receive or when to claim a buffered receive on getting a buffered receive completion. The value is typically used by a provider when sending a rendezvous protocol request where it would send at least FI_OPT_BUFFERED_MIN bytes of application data along with it. A smaller sized rendezvous protocol message usually results in better latency for the overall transfer of a large message. * .RS 2 FI_OPT_CM_DATA_SIZE - size_t Defines the size of available space in CM messages for user-defined data. This value limits the amount of data that applications can exchange between peer endpoints using the fi_connect, fi_accept, and fi_reject operations. The size returned is dependent upon the prop- erties of the endpoint, except in the case of passive endpoints, in which the size reflects the maximum size of the data that may be present as part of a connection request event. This option is read only. * .RS 2 FI_OPT_MIN_MULTI_RECV - size_t Defines the minimum receive buffer space available when the receive buffer is released by the provider (see FI_MULTI_RECV). Modifying this value is only guaranteed to set the minimum buffer space needed on receives posted after the value has been changed. It is recom- mended that applications that want to override the default MIN_MULTI_RECV value set this option before enabling the correspond- ing endpoint. * .RS 2 FI_OPT_FI_HMEM_P2P - int Defines how the provider should handle peer to peer FI_HMEM trans- fers for this endpoint. By default, the provider will chose whether to use peer to peer support based on the type of transfer (FI_HMEM_P2P_ENABLED). Valid values defined in fi_endpoint.h are: * FI_HMEM_P2P_ENABLED: Peer to peer support may be used by the provider to handle FI_HMEM transfers, and which transfers are ini- tiated using peer to peer is subject to the provider implementa- tion. * FI_HMEM_P2P_REQUIRED: Peer to peer support must be used for trans- fers, transfers that cannot be performed using p2p will be re- ported as failing. * FI_HMEM_P2P_PREFERRED: Peer to peer support should be used by the provider for all transfers if available, but the provider may choose to copy the data to initiate the transfer if peer to peer support is unavailable. * FI_HMEM_P2P_DISABLED: Peer to peer support should not be used. fi_setopt() will return -FI_EOPNOTSUPP if the mode requested cannot be sup- ported by the provider. The FI_HMEM_DISABLE_P2P environment variable dis- cussed in fi_mr(3) takes precedence over this setopt option. * .RS 2 FI_OPT_XPU_TRIGGER - struct fi_trigger_xpu * This option only applies to the fi_getopt() call. It is used to query the maximum number of variables required to support XPU trig- gered operations, along with the size of each variable. The user provides a filled out struct fi_trigger_xpu on input. The iface and device fields should reference an HMEM domain. If the provider does not support XPU triggered operations from the given device, fi_getopt() will return -FI_EOPNOTSUPP. On input, var should reference an array of struct fi_trigger_var data structures, with count set to the size of the referenced array. If count is 0, the var field will be ignored, and the provider will return the number of fi_trigger_var structures needed. If count is > 0, the provider will set count to the needed value, and for each fi_trigger_var available, set the datatype and count of the variable used for the trigger. fi_tc_dscp_set This call converts a DSCP defined value into a libfabric traffic class value. It should be used when assigning a DSCP value when setting the tclass field in either domain or endpoint attributes fi_tc_dscp_get This call returns the DSCP value associated with the tclass field for the domain or endpoint attributes. fi_rx_size_left (DEPRECATED) This function has been deprecated and will be removed in a future version of the library. It may not be supported by all providers. The fi_rx_size_left call returns a lower bound on the number of receive op- erations that may be posted to the given endpoint without that operation returning -FI_EAGAIN. Depending on the specific details of the subse- quently posted receive operations (e.g., number of iov entries, which re- ceive function is called, etc.), it may be possible to post more receive operations than originally indicated by fi_rx_size_left. fi_tx_size_left (DEPRECATED) This function has been deprecated and will be removed in a future version of the library. It may not be supported by all providers. The fi_tx_size_left call returns a lower bound on the number of transmit operations that may be posted to the given endpoint without that operation returning -FI_EAGAIN. Depending on the specific details of the subse- quently posted transmit operations (e.g., number of iov entries, which transmit function is called, etc.), it may be possible to post more trans- mit operations than originally indicated by fi_tx_size_left. ENDPOINT ATTRIBUTES The fi_ep_attr structure defines the set of attributes associated with an endpoint. Endpoint attributes may be further refined using the transmit and receive context attributes as shown below. struct fi_ep_attr { enum fi_ep_type type; uint32_t protocol; uint32_t protocol_version; size_t max_msg_size; size_t msg_prefix_size; size_t max_order_raw_size; size_t max_order_war_size; size_t max_order_waw_size; uint64_t mem_tag_format; size_t tx_ctx_cnt; size_t rx_ctx_cnt; size_t auth_key_size; uint8_t *auth_key; }; type - Endpoint Type If specified, indicates the type of fabric interface communication desired. Supported types are: FI_EP_DGRAM Supports a connectionless, unreliable datagram communication. Mes- sage boundaries are maintained, but the maximum message size may be limited to the fabric MTU. Flow control is not guaranteed. FI_EP_MSG Provides a reliable, connection-oriented data transfer service with flow control that maintains message boundaries. FI_EP_RDM Reliable datagram message. Provides a reliable, connectionless data transfer service with flow control that maintains message bound- aries. FI_EP_SOCK_DGRAM A connectionless, unreliable datagram endpoint with UDP socket-like semantics. FI_EP_SOCK_DGRAM is most useful for applications de- signed around using UDP sockets. See the SOCKET ENDPOINT section for additional details and restrictions that apply to datagram socket endpoints. FI_EP_SOCK_STREAM Data streaming endpoint with TCP socket-like semantics. Provides a reliable, connection-oriented data transfer service that does not maintain message boundaries. FI_EP_SOCK_STREAM is most useful for applications designed around using TCP sockets. See the SOCKET END- POINT section for additional details and restrictions that apply to stream endpoints. FI_EP_UNSPEC The type of endpoint is not specified. This is usually provided as input, with other attributes of the endpoint or the provider select- ing the type. Protocol Specifies the low-level end to end protocol employed by the provider. A matching protocol must be used by communicating endpoints to ensure inter- operability. The following protocol values are defined. Provider specific protocols are also allowed. Provider specific protocols will be indicated by having the upper bit of the protocol value set to one. FI_PROTO_GNI Protocol runs over Cray GNI low-level interface. FI_PROTO_IB_RDM Reliable-datagram protocol implemented over InfiniBand reliable-con- nected queue pairs. FI_PROTO_IB_UD The protocol runs over Infiniband unreliable datagram queue pairs. FI_PROTO_IWARP The protocol runs over the Internet wide area RDMA protocol trans- port. FI_PROTO_IWARP_RDM Reliable-datagram protocol implemented over iWarp reliable-connected queue pairs. FI_PROTO_NETWORKDIRECT Protocol runs over Microsoft NetworkDirect service provider inter- face. This adds reliable-datagram semantics over the NetworkDirect connection- oriented endpoint semantics. FI_PROTO_PSMX The protocol is based on an Intel proprietary protocol known as PSM, performance scaled messaging. PSMX is an extended version of the PSM protocol to support the libfabric interfaces. FI_PROTO_PSMX2 The protocol is based on an Intel proprietary protocol known as PSM2, performance scaled messaging version 2. PSMX2 is an extended version of the PSM2 protocol to support the libfabric interfaces. FI_PROTO_PSMX3 The protocol is Intel's protocol known as PSM3, performance scaled messaging version 3. PSMX3 is implemented over RoCEv2 and verbs. FI_PROTO_RDMA_CM_IB_RC The protocol runs over Infiniband reliable-connected queue pairs, using the RDMA CM protocol for connection establishment. FI_PROTO_RXD Reliable-datagram protocol implemented over datagram endpoints. RXD is a libfabric utility component that adds RDM endpoint semantics over DGRAM endpoint semantics. FI_PROTO_RXM Reliable-datagram protocol implemented over message endpoints. RXM is a libfabric utility component that adds RDM endpoint semantics over MSG endpoint semantics. FI_PROTO_SOCK_TCP The protocol is layered over TCP packets. FI_PROTO_UDP The protocol sends and receives UDP datagrams. For example, an end- point using FI_PROTO_UDP will be able to communicate with a remote peer that is using Berkeley SOCK_DGRAM sockets using IPPROTO_UDP. FI_PROTO_UNSPEC The protocol is not specified. This is usually provided as input, with other attributes of the socket or the provider selecting the actual protocol. protocol_version - Protocol Version Identifies which version of the protocol is employed by the provider. The protocol version allows providers to extend an existing protocol, by adding support for additional features or functionality for example, in a backward compatible manner. Providers that support different versions of the same protocol should inter-operate, but only when using the capabilities defined for the lesser version. max_msg_size - Max Message Size Defines the maximum size for an application data transfer as a single oper- ation. msg_prefix_size - Message Prefix Size Specifies the size of any required message prefix buffer space. This field will be 0 unless the FI_MSG_PREFIX mode is enabled. If msg_prefix_size is > 0 the specified value will be a multiple of 8-bytes. Max RMA Ordered Size The maximum ordered size specifies the delivery order of transport data into target memory for RMA and atomic operations. Data ordering is sepa- rate, but dependent on message ordering (defined below). Data ordering is unspecified where message order is not defined. Data ordering refers to the access of the same target memory by subsequent operations. When back to back RMA read or write operations access the same registered memory location, data ordering indicates whether the second op- eration reads or writes the target memory after the first operation has completed. For example, will an RMA read that follows an RMA write read back the data that was written? Similarly, will an RMA write that follows an RMA read update the target buffer after the read has transferred the original data? Data ordering answers these questions, even in the presence of errors, such as the need to resend data because of lost or corrupted network traffic. RMA ordering applies between two operations, and not within a single data transfer. Therefore, ordering is defined per byte-addressable memory loca- tion. I.e. ordering specifies whether location X is accessed by the sec- ond operation after the first operation. Nothing is implied about the com- pletion of the first operation before the second operation is initiated. For example, if the first operation updates locations X and Y, but the sec- ond operation only accesses location X, there are no guarantees defined relative to location Y and the second operation. In order to support large data transfers being broken into multiple packets and sent using multiple paths through the fabric, data ordering may be lim- ited to transfers of a specific size or less. Providers specify when data ordering is maintained through the following values. Note that even if data ordering is not maintained, message ordering may be. max_order_raw_size Read after write size. If set, an RMA or atomic read operation is- sued after an RMA or atomic write operation, both of which are smaller than the size, will be ordered. Where the target memory lo- cations overlap, the RMA or atomic read operation will see the re- sults of the previous RMA or atomic write. max_order_war_size Write after read size. If set, an RMA or atomic write operation is- sued after an RMA or atomic read operation, both of which are smaller than the size, will be ordered. The RMA or atomic read op- eration will see the initial value of the target memory location be- fore a subsequent RMA or atomic write updates the value. max_order_waw_size Write after write size. If set, an RMA or atomic write operation issued after an RMA or atomic write operation, both of which are smaller than the size, will be ordered. The target memory location will reflect the results of the second RMA or atomic write. An order size value of 0 indicates that ordering is not guaranteed. A value of -1 guarantees ordering for any data size. mem_tag_format - Memory Tag Format The memory tag format is a bit array used to convey the number of tagged bits supported by a provider. Additionally, it may be used to divide the bit array into separate fields. The mem_tag_format optionally begins with a series of bits set to 0, to signify bits which are ignored by the provider. Following the initial prefix of ignored bits, the array will consist of alternating groups of bits set to all 1's or all 0's. Each group of bits corresponds to a tagged field. The implication of defining a tagged field is that when a mask is applied to the tagged bit array, all bits belonging to a single field will either be set to 1 or 0, collec- tively. For example, a mem_tag_format of 0x30FF indicates support for 14 tagged bits, separated into 3 fields. The first field consists of 2-bits, the second field 4-bits, and the final field 8-bits. Valid masks for such a tagged field would be a bitwise OR'ing of zero or more of the following values: 0x3000, 0x0F00, and 0x00FF. The provider may not validate the mask provided by the application for performance reasons. By identifying fields within a tag, a provider may be able to optimize their search routines. An application which requests tag fields must pro- vide tag masks that either set all mask bits corresponding to a field to all 0 or all 1. When negotiating tag fields, an application can request a specific number of fields of a given size. A provider must return a tag format that supports the requested number of fields, with each field being at least the size requested, or fail the request. A provider may increase the size of the fields. When reporting completions (see FI_CQ_FOR- MAT_TAGGED), it is not guaranteed that the provider would clear out any un- supported tag bits in the tag field of the completion entry. It is recommended that field sizes be ordered from smallest to largest. A generic, unstructured tag and mask can be achieved by requesting a bit ar- ray consisting of alternating 1's and 0's. tx_ctx_cnt - Transmit Context Count Number of transmit contexts to associate with the endpoint. If not speci- fied (0), 1 context will be assigned if the endpoint supports outbound transfers. Transmit contexts are independent transmit queues that may be separately configured. Each transmit context may be bound to a separate CQ, and no ordering is defined between contexts. Additionally, no synchro- nization is needed when accessing contexts in parallel. If the count is set to the value FI_SHARED_CONTEXT, the endpoint will be configured to use a shared transmit context, if supported by the provider. Providers that do not support shared transmit contexts will fail the re- quest. See the scalable endpoint and shared contexts sections for additional de- tails. rx_ctx_cnt - Receive Context Count Number of receive contexts to associate with the endpoint. If not speci- fied, 1 context will be assigned if the endpoint supports inbound trans- fers. Receive contexts are independent processing queues that may be sepa- rately configured. Each receive context may be bound to a separate CQ, and no ordering is defined between contexts. Additionally, no synchronization is needed when accessing contexts in parallel. If the count is set to the value FI_SHARED_CONTEXT, the endpoint will be configured to use a shared receive context, if supported by the provider. Providers that do not support shared receive contexts will fail the re- quest. See the scalable endpoint and shared contexts sections for additional de- tails. auth_key_size - Authorization Key Length The length of the authorization key in bytes. This field will be 0 if au- thorization keys are not available or used. This field is ignored unless the fabric is opened with API version 1.5 or greater. auth_key - Authorization Key If supported by the fabric, an authorization key (a.k.a. job key) to asso- ciate with the endpoint. An authorization key is used to limit communica- tion between endpoints. Only peer endpoints that are programmed to use the same authorization key may communicate. Authorization keys are often used to implement job keys, to ensure that processes running in different jobs do not accidentally cross traffic. The domain authorization key will be used if auth_key_size is set to 0. This field is ignored unless the fabric is opened with API version 1.5 or greater. TRANSMIT CONTEXT ATTRIBUTES Attributes specific to the transmit capabilities of an endpoint are speci- fied using struct fi_tx_attr. struct fi_tx_attr { uint64_t caps; uint64_t mode; uint64_t op_flags; uint64_t msg_order; uint64_t comp_order; size_t inject_size; size_t size; size_t iov_limit; size_t rma_iov_limit; uint32_t tclass; }; caps - Capabilities The requested capabilities of the context. The capabilities must be a sub- set of those requested of the associated endpoint. See the CAPABILITIES section of fi_getinfo(3) for capability details. If the caps field is 0 on input to fi_getinfo(3), the applicable capability bits from the fi_info structure will be used. The following capabilities apply to the transmit attributes: FI_MSG, FI_RMA, FI_TAGGED, FI_ATOMIC, FI_READ, FI_WRITE, FI_SEND, FI_HMEM, FI_TRIG- GER, FI_FENCE, FI_MULTICAST, FI_RMA_PMEM, FI_NAMED_RX_CTX, FI_COLLECTIVE, and FI_XPU. Many applications will be able to ignore this field and rely solely on the fi_info::caps field. Use of this field provides fine grained control over the transmit capabilities associated with an endpoint. It is useful when handling scalable endpoints, with multiple transmit contexts, for example, and allows configuring a specific transmit context with fewer capabilities than that supported by the endpoint or other transmit contexts. mode The operational mode bits of the context. The mode bits will be a subset of those associated with the endpoint. See the MODE section of fi_get- info(3) for details. A mode value of 0 will be ignored on input to fi_get- info(3), with the mode value of the fi_info structure used instead. On re- turn from fi_getinfo(3), the mode will be set only to those constraints specific to transmit operations. op_flags - Default transmit operation flags Flags that control the operation of operations submitted against the con- text. Applicable flags are listed in the Operation Flags section. msg_order - Message Ordering Message ordering refers to the order in which transport layer headers (as viewed by the application) are identified and processed. Relaxed message order enables data transfers to be sent and received out of order, which may improve performance by utilizing multiple paths through the fabric from the initiating endpoint to a target endpoint. Message order applies only between a single source and destination endpoint pair. Ordering between different target endpoints is not defined. Message order is determined using a set of ordering bits. Each set bit in- dicates that ordering is maintained between data transfers of the specified type. Message order is defined for [read | write | send] operations sub- mitted by an application after [read | write | send] operations. Message ordering only applies to the end to end transmission of transport headers. Message ordering is necessary, but does not guarantee, the order in which message data is sent or received by the transport layer. Message ordering requires matching ordering semantics on the receiving side of a data transfer operation in order to guarantee that ordering is met. FI_ORDER_ATOMIC_RAR Atomic read after read. If set, atomic fetch operations are trans- mitted in the order submitted relative to other atomic fetch opera- tions. If not set, atomic fetches may be transmitted out of order from their submission. FI_ORDER_ATOMIC_RAW Atomic read after write. If set, atomic fetch operations are trans- mitted in the order submitted relative to atomic update operations. If not set, atomic fetches may be transmitted ahead of atomic up- dates. FI_ORDER_ATOMIC_WAR RMA write after read. If set, atomic update operations are trans- mitted in the order submitted relative to atomic fetch operations. If not set, atomic updates may be transmitted ahead of atomic fetches. FI_ORDER_ATOMIC_WAW RMA write after write. If set, atomic update operations are trans- mitted in the order submitted relative to other atomic update opera- tions. If not atomic updates may be transmitted out of order from their submission. FI_ORDER_NONE No ordering is specified. This value may be used as input in order to obtain the default message order supported by the provider. FI_ORDER_NONE is an alias for the value 0. FI_ORDER_RAR Read after read. If set, RMA and atomic read operations are trans- mitted in the order submitted relative to other RMA and atomic read operations. If not set, RMA and atomic reads may be transmitted out of order from their submission. FI_ORDER_RAS Read after send. If set, RMA and atomic read operations are trans- mitted in the order submitted relative to message send operations, including tagged sends. If not set, RMA and atomic reads may be transmitted ahead of sends. FI_ORDER_RAW Read after write. If set, RMA and atomic read operations are trans- mitted in the order submitted relative to RMA and atomic write oper- ations. If not set, RMA and atomic reads may be transmitted ahead of RMA and atomic writes. FI_ORDER_RMA_RAR RMA read after read. If set, RMA read operations are transmitted in the order submitted relative to other RMA read operations. If not set, RMA reads may be transmitted out of order from their submis- sion. FI_ORDER_RMA_RAW RMA read after write. If set, RMA read operations are transmitted in the order submitted relative to RMA write operations. If not set, RMA reads may be transmitted ahead of RMA writes. FI_ORDER_RMA_WAR RMA write after read. If set, RMA write operations are transmitted in the order submitted relative to RMA read operations. If not set, RMA writes may be transmitted ahead of RMA reads. FI_ORDER_RMA_WAW RMA write after write. If set, RMA write operations are transmitted in the order submitted relative to other RMA write operations. If not set, RMA writes may be transmitted out of order from their sub- mission. FI_ORDER_SAR Send after read. If set, message send operations, including tagged sends, are transmitted in order submitted relative to RMA and atomic read operations. If not set, message sends may be transmitted ahead of RMA and atomic reads. FI_ORDER_SAS Send after send. If set, message send operations, including tagged sends, are transmitted in the order submitted relative to other mes- sage send. If not set, message sends may be transmitted out of or- der from their submission. FI_ORDER_SAW Send after write. If set, message send operations, including tagged sends, are transmitted in order submitted relative to RMA and atomic write operations. If not set, message sends may be transmitted ahead of RMA and atomic writes. FI_ORDER_WAR Write after read. If set, RMA and atomic write operations are transmitted in the order submitted relative to RMA and atomic read operations. If not set, RMA and atomic writes may be transmitted ahead of RMA and atomic reads. FI_ORDER_WAS Write after send. If set, RMA and atomic write operations are transmitted in the order submitted relative to message send opera- tions, including tagged sends. If not set, RMA and atomic writes may be transmitted ahead of sends. FI_ORDER_WAW Write after write. If set, RMA and atomic write operations are transmitted in the order submitted relative to other RMA and atomic write operations. If not set, RMA and atomic writes may be trans- mitted out of order from their submission. comp_order - Completion Ordering Completion ordering refers to the order in which completed requests are written into the completion queue. Completion ordering is similar to mes- sage order. Relaxed completion order may enable faster reporting of com- pleted transfers, allow acknowledgments to be sent over different fabric paths, and support more sophisticated retry mechanisms. This can result in lower-latency completions, particularly when using connectionless end- points. Strict completion ordering may require that providers queue com- pleted operations or limit available optimizations. For transmit requests, completion ordering depends on the endpoint communi- cation type. For unreliable communication, completion ordering applies to all data transfer requests submitted to an endpoint. For reliable communi- cation, completion ordering only applies to requests that target a single destination endpoint. Completion ordering of requests that target differ- ent endpoints over a reliable transport is not defined. Applications should specify the completion ordering that they support or require. Providers should return the completion order that they actually provide, with the constraint that the returned ordering is stricter than that specified by the application. Supported completion order values are: FI_ORDER_NONE No ordering is defined for completed operations. Requests submitted to the transmit context may complete in any order. FI_ORDER_STRICT Requests complete in the order in which they are submitted to the transmit context. inject_size The requested inject operation size (see the FI_INJECT flag) that the con- text will support. This is the maximum size data transfer that can be as- sociated with an inject operation (such as fi_inject) or may be used with the FI_INJECT data transfer flag. size The size of the transmit context. The mapping of the size value to re- sources is provider specific, but it is directly related to the number of command entries allocated for the endpoint. A smaller size value consumes fewer hardware and software resources, while a larger size allows queuing more transmit requests. While the size attribute guides the size of underlying endpoint transmit queue, there is not necessarily a one-to-one mapping between a transmit op- eration and a queue entry. A single transmit operation may consume multi- ple queue entries; for example, one per scatter-gather entry. Addition- ally, the size field is intended to guide the allocation of the endpoint's transmit context. Specifically, for connectionless endpoints, there may be lower-level queues use to track communication on a per peer basis. The sizes of any lower-level queues may only be significantly smaller than the endpoint's transmit size, in order to reduce resource utilization. iov_limit This is the maximum number of IO vectors (scatter-gather elements) that a single posted operation may reference. rma_iov_limit This is the maximum number of RMA IO vectors (scatter-gather elements) that an RMA or atomic operation may reference. The rma_iov_limit corresponds to the rma_iov_count values in RMA and atomic operations. See struct fi_msg_rma and struct fi_msg_atomic in fi_rma.3 and fi_atomic.3, for addi- tional details. This limit applies to both the number of RMA IO vectors that may be specified when initiating an operation from the local endpoint, as well as the maximum number of IO vectors that may be carried in a single request from a remote endpoint. Traffic Class (tclass) Traffic classes can be a differentiated services code point (DSCP) value, one of the following defined labels, or a provider-specific definition. If tclass is unset or set to FI_TC_UNSPEC, the endpoint will use the default traffic class associated with the domain. FI_TC_BEST_EFFORT This is the default in the absence of any other local or fabric con- figuration. This class carries the traffic for a number of applica- tions executing concurrently over the same network infrastructure. Even though it is shared, network capacity and resource allocation are distributed fairly across the applications. FI_TC_BULK_DATA This class is intended for large data transfers associated with I/O and is present to separate sustained I/O transfers from other appli- cation inter-process communications. FI_TC_DEDICATED_ACCESS This class operates at the highest priority, except the management class. It carries a high bandwidth allocation, minimum latency tar- gets, and the highest scheduling and arbitration priority. FI_TC_LOW_LATENCY This class supports low latency, low jitter data patterns typically caused by transactional data exchanges, barrier synchronizations, and collective operations that are typical of HPC applications. This class often requires maximum tolerable latencies that data transfers must achieve for correct or performance operations. Ful- fillment of such requests in this class will typically require ac- companying bandwidth and message size limitations so as not to con- sume excessive bandwidth at high priority. FI_TC_NETWORK_CTRL This class is intended for traffic directly related to fabric (net- work) management, which is critical to the correct operation of the network. Its use is typically restricted to privileged network man- agement applications. FI_TC_SCAVENGER This class is used for data that is desired but does not have strict delivery requirements, such as in-band network or application level monitoring data. Use of this class indicates that the traffic is considered lower priority and should not interfere with higher pri- ority workflows. fi_tc_dscp_set / fi_tc_dscp_get DSCP values are supported via the DSCP get and set functions. The definitions for DSCP values are outside the scope of libfabric. See the fi_tc_dscp_set and fi_tc_dscp_get function definitions for de- tails on their use. RECEIVE CONTEXT ATTRIBUTES Attributes specific to the receive capabilities of an endpoint are speci- fied using struct fi_rx_attr. struct fi_rx_attr { uint64_t caps; uint64_t mode; uint64_t op_flags; uint64_t msg_order; uint64_t comp_order; size_t total_buffered_recv; size_t size; size_t iov_limit; }; caps - Capabilities The requested capabilities of the context. The capabilities must be a sub- set of those requested of the associated endpoint. See the CAPABILITIES section if fi_getinfo(3) for capability details. If the caps field is 0 on input to fi_getinfo(3), the applicable capability bits from the fi_info structure will be used. The following capabilities apply to the receive attributes: FI_MSG, FI_RMA, FI_TAGGED, FI_ATOMIC, FI_REMOTE_READ, FI_REMOTE_WRITE, FI_RECV, FI_HMEM, FI_TRIGGER, FI_RMA_PMEM, FI_DIRECTED_RECV, FI_VARIABLE_MSG, FI_MULTI_RECV, FI_SOURCE, FI_RMA_EVENT, FI_SOURCE_ERR, FI_COLLECTIVE, and FI_XPU. Many applications will be able to ignore this field and rely solely on the fi_info::caps field. Use of this field provides fine grained control over the receive capabilities associated with an endpoint. It is useful when handling scalable endpoints, with multiple receive contexts, for example, and allows configuring a specific receive context with fewer capabilities than that supported by the endpoint or other receive contexts. mode The operational mode bits of the context. The mode bits will be a subset of those associated with the endpoint. See the MODE section of fi_get- info(3) for details. A mode value of 0 will be ignored on input to fi_get- info(3), with the mode value of the fi_info structure used instead. On re- turn from fi_getinfo(3), the mode will be set only to those constraints specific to receive operations. op_flags - Default receive operation flags Flags that control the operation of operations submitted against the con- text. Applicable flags are listed in the Operation Flags section. msg_order - Message Ordering For a description of message ordering, see the msg_order field in the Transmit Context Attribute section. Receive context message ordering de- fines the order in which received transport message headers are processed when received by an endpoint. When ordering is set, it indicates that mes- sage headers will be processed in order, based on how the transmit side has identified the messages. Typically, this means that messages will be han- dled in order based on a message level sequence number. The following ordering flags, as defined for transmit ordering, also apply to the processing of received operations: FI_ORDER_NONE, FI_ORDER_RAR, FI_ORDER_RAW, FI_ORDER_RAS, FI_ORDER_WAR, FI_ORDER_WAW, FI_ORDER_WAS, FI_ORDER_SAR, FI_ORDER_SAW, FI_ORDER_SAS, FI_ORDER_RMA_RAR, FI_OR- DER_RMA_RAW, FI_ORDER_RMA_WAR, FI_ORDER_RMA_WAW, FI_ORDER_ATOMIC_RAR, FI_ORDER_ATOMIC_RAW, FI_ORDER_ATOMIC_WAR, and FI_ORDER_ATOMIC_WAW. comp_order - Completion Ordering For a description of completion ordering, see the comp_order field in the Transmit Context Attribute section. FI_ORDER_DATA When set, this bit indicates that received data is written into mem- ory in order. Data ordering applies to memory accessed as part of a single operation and between operations if message ordering is guar- anteed. FI_ORDER_NONE No ordering is defined for completed operations. Receive operations may complete in any order, regardless of their submission order. FI_ORDER_STRICT Receive operations complete in the order in which they are processed by the receive context, based on the receive side msg_order at- tribute. total_buffered_recv This field is supported for backwards compatibility purposes. It is a hint to the provider of the total available space that may be needed to buffer messages that are received for which there is no matching receive opera- tion. The provider may adjust or ignore this value. The allocation of in- ternal network buffering among received message is provider specific. For instance, a provider may limit the size of messages which can be buffered or the amount of buffering allocated to a single message. If receive side buffering is disabled (total_buffered_recv = 0) and a mes- sage is received by an endpoint, then the behavior is dependent on whether resource management has been enabled (FI_RM_ENABLED has be set or not). See the Resource Management section of fi_domain.3 for further clarifica- tion. It is recommended that applications enable resource management if they anticipate receiving unexpected messages, rather than modifying this value. size The size of the receive context. The mapping of the size value to re- sources is provider specific, but it is directly related to the number of command entries allocated for the endpoint. A smaller size value consumes fewer hardware and software resources, while a larger size allows queuing more transmit requests. While the size attribute guides the size of underlying endpoint receive queue, there is not necessarily a one-to-one mapping between a receive op- eration and a queue entry. A single receive operation may consume multiple queue entries; for example, one per scatter-gather entry. Additionally, the size field is intended to guide the allocation of the endpoint's re- ceive context. Specifically, for connectionless endpoints, there may be lower-level queues use to track communication on a per peer basis. The sizes of any lower-level queues may only be significantly smaller than the endpoint's receive size, in order to reduce resource utilization. iov_limit This is the maximum number of IO vectors (scatter-gather elements) that a single posted operating may reference. SCALABLE ENDPOINTS A scalable endpoint is a communication portal that supports multiple trans- mit and receive contexts. Scalable endpoints are loosely modeled after the networking concept of transmit/receive side scaling, also known as multi-queue. Support for scalable endpoints is domain specific. Scalable endpoints may improve the performance of multi-threaded and parallel appli- cations, by allowing threads to access independent transmit and receive queues. A scalable endpoint has a single transport level address, which can reduce the memory requirements needed to store remote addressing data, versus using standard endpoints. Scalable endpoints cannot be used di- rectly for communication operations, and require the application to explic- itly create transmit and receive contexts as described below. fi_tx_context Transmit contexts are independent transmit queues. Ordering and synchro- nization between contexts are not defined. Conceptually a transmit context behaves similar to a send-only endpoint. A transmit context may be config- ured with fewer capabilities than the base endpoint and with different at- tributes (such as ordering requirements and inject size) than other con- texts associated with the same scalable endpoint. Each transmit context has its own completion queue. The number of transmit contexts associated with an endpoint is specified during endpoint creation. The fi_tx_context call is used to retrieve a specific context, identified by an index (see above for details on transmit context attributes). Providers may dynamically allocate contexts when fi_tx_context is called, or may statically create all contexts when fi_endpoint is invoked. By de- fault, a transmit context inherits the properties of its associated end- point. However, applications may request context specific attributes through the attr parameter. Support for per transmit context attributes is provider specific and not guaranteed. Providers will return the actual at- tributes assigned to the context through the attr parameter, if provided. fi_rx_context Receive contexts are independent receive queues for receiving incoming data. Ordering and synchronization between contexts are not guaranteed. Conceptually a receive context behaves similar to a receive-only endpoint. A receive context may be configured with fewer capabilities than the base endpoint and with different attributes (such as ordering requirements and inject size) than other contexts associated with the same scalable end- point. Each receive context has its own completion queue. The number of receive contexts associated with an endpoint is specified during endpoint creation. Receive contexts are often associated with steering flows, that specify which incoming packets targeting a scalable endpoint to process. However, receive contexts may be targeted directly by the initiator, if supported by the underlying protocol. Such contexts are referred to as `named'. Sup- port for named contexts must be indicated by setting the caps FI_NAMED_RX_CTX capability when the corresponding endpoint is created. Support for named receive contexts is coordinated with address vectors. See fi_av(3) and fi_rx_addr(3). The fi_rx_context call is used to retrieve a specific context, identified by an index (see above for details on receive context attributes). Providers may dynamically allocate contexts when fi_rx_context is called, or may statically create all contexts when fi_endpoint is invoked. By de- fault, a receive context inherits the properties of its associated end- point. However, applications may request context specific attributes through the attr parameter. Support for per receive context attributes is provider specific and not guaranteed. Providers will return the actual at- tributes assigned to the context through the attr parameter, if provided. SHARED CONTEXTS Shared contexts are transmit and receive contexts explicitly shared among one or more endpoints. A shareable context allows an application to use a single dedicated provider resource among multiple transport addressable endpoints. This can greatly reduce the resources needed to manage communi- cation over multiple endpoints by multiplexing transmit and/or receive pro- cessing, with the potential cost of serializing access across multiple end- points. Support for shareable contexts is domain specific. Conceptually, shareable transmit contexts are transmit queues that may be accessed by many endpoints. The use of a shared transmit context is mostly opaque to an application. Applications must allocate and bind shared transmit contexts to endpoints, but operations are posted directly to the endpoint. Shared transmit contexts are not associated with completion queues or counters. Completed operations are posted to the CQs bound to the endpoint. An endpoint may only be associated with a single shared transmit context. Unlike shared transmit contexts, applications interact directly with shared receive contexts. Users post receive buffers directly to a shared receive context, with the buffers usable by any endpoint bound to the shared re- ceive context. Shared receive contexts are not associated with completion queues or counters. Completed receive operations are posted to the CQs bound to the endpoint. An endpoint may only be associated with a single receive context, and all connectionless endpoints associated with a shared receive context must also share the same address vector. Endpoints associated with a shared transmit context may use dedicated re- ceive contexts, and vice-versa. Or an endpoint may use shared transmit and receive contexts. And there is no requirement that the same group of end- points sharing a context of one type also share the context of an alternate type. Furthermore, an endpoint may use a shared context of one type, but a scalable set of contexts of the alternate type. fi_stx_context This call is used to open a shareable transmit context (see above for de- tails on the transmit context attributes). Endpoints associated with a shared transmit context must use a subset of the transmit context's attrib- utes. Note that this is the reverse of the requirement for transmit con- texts for scalable endpoints. fi_srx_context This allocates a shareable receive context (see above for details on the receive context attributes). Endpoints associated with a shared receive context must use a subset of the receive context's attributes. Note that this is the reverse of the requirement for receive contexts for scalable endpoints. SOCKET ENDPOINTS The following feature and description should be considered experimental. Until the experimental tag is removed, the interfaces, semantics, and data structures associated with socket endpoints may change between library ver- sions. This section applies to endpoints of type FI_EP_SOCK_STREAM and FI_EP_SOCK_DGRAM, commonly referred to as socket endpoints. Socket endpoints are defined with semantics that allow them to more easily be adopted by developers familiar with the UNIX socket API, or by middle- ware that exposes the socket API, while still taking advantage of high-per- formance hardware features. The key difference between socket endpoints and other active endpoints are socket endpoints use synchronous data transfers. Buffers passed into send and receive operations revert to the control of the application upon re- turning from the function call. As a result, no data transfer completions are reported to the application, and socket endpoints are not associated with completion queues or counters. Socket endpoints support a subset of message operations: fi_send, fi_sendv, fi_sendmsg, fi_recv, fi_recvv, fi_recvmsg, and fi_inject. Because data transfers are synchronous, the return value from send and receive opera- tions indicate the number of bytes transferred on success, or a negative value on error, including -FI_EAGAIN if the endpoint cannot send or receive any data because of full or empty queues, respectively. Socket endpoints are associated with event queues and address vectors, and process connection management events asynchronously, similar to other end- points. Unlike UNIX sockets, socket endpoint must still be declared as ei- ther active or passive. Socket endpoints behave like non-blocking sockets. In order to support se- lect and poll semantics, active socket endpoints are associated with a file descriptor that is signaled whenever the endpoint is ready to send and/or receive data. The file descriptor may be retrieved using fi_control. OPERATION FLAGS Operation flags are obtained by OR-ing the following flags together. Oper- ation flags define the default flags applied to an endpoint's data transfer operations, where a flags parameter is not available. Data transfer opera- tions that take flags as input override the op_flags value of transmit or receive context attributes of an endpoint. FI_COMMIT_COMPLETE Indicates that a completion should not be generated (locally or at the peer) until the result of an operation have been made persis- tent. See fi_cq(3) for additional details on completion semantics. FI_COMPLETION Indicates that a completion queue entry should be written for data transfer operations. This flag only applies to operations issued on an endpoint that was bound to a completion queue with the FI_SELEC- TIVE_COMPLETION flag set, otherwise, it is ignored. See the fi_ep_bind section above for more detail. FI_DELIVERY_COMPLETE Indicates that a completion should be generated when the operation has been processed by the destination endpoint(s). See fi_cq(3) for additional details on completion semantics. FI_INJECT Indicates that all outbound data buffers should be returned to the user's control immediately after a data transfer call returns, even if the operation is handled asynchronously. This may require that the provider copy the data into a local buffer and transfer out of that buffer. A provider can limit the total amount of send data that may be buffered and/or the size of a single send that can use this flag. This limit is indicated using inject_size (see in- ject_size above). FI_INJECT_COMPLETE Indicates that a completion should be generated when the source buffer(s) may be reused. See fi_cq(3) for additional details on completion semantics. FI_MULTICAST Indicates that data transfers will target multicast addresses by de- fault. Any fi_addr_t passed into a data transfer operation will be treated as a multicast address. FI_MULTI_RECV Applies to posted receive operations. This flag allows the user to post a single buffer that will receive multiple incoming messages. Received messages will be packed into the receive buffer until the buffer has been consumed. Use of this flag may cause a single posted receive operation to generate multiple completions as mes- sages are placed into the buffer. The placement of received data into the buffer may be subjected to provider specific alignment re- strictions. The buffer will be released by the provider when the available buffer space falls below the specified minimum (see FI_OPT_MIN_MULTI_RECV). FI_TRANSMIT_COMPLETE Indicates that a completion should be generated when the transmit operation has completed relative to the local provider. See fi_cq(3) for additional details on completion semantics. NOTES Users should call fi_close to release all resources allocated to the fabric endpoint. Endpoints allocated with the FI_CONTEXT or FI_CONTEXT2 mode bits set must typically provide struct fi_context(2) as their per operation context para- meter. (See fi_getinfo.3 for details.) However, when FI_SELECTIVE_COMPLE- TION is enabled to suppress CQ completion entries, and an operation is ini- tiated without the FI_COMPLETION flag set, then the context parameter is ignored. An application does not need to pass in a valid struct fi_con- text(2) into such data transfers. Operations that complete in error that are not associated with valid opera- tional context will use the endpoint context in any error reporting struc- tures. Although applications typically associate individual completions with ei- ther completion queues or counters, an endpoint can be attached to both a counter and completion queue. When combined with using selective comple- tions, this allows an application to use counters to track successful com- pletions, with a CQ used to report errors. Operations that complete with an error increment the error counter and generate a CQ completion event. As mentioned in fi_getinfo(3), the ep_attr structure can be used to query providers that support various endpoint attributes. fi_getinfo can return provider info structures that can support the minimal set of requirements (such that the application maintains correctness). However, it can also return provider info structures that exceed application requirements. As an example, consider an application requesting msg_order as FI_ORDER_NONE. The resulting output from fi_getinfo may have all the ordering bits set. The application can reset the ordering bits it does not require before cre- ating the endpoint. The provider is free to implement a stricter ordering than is required by the application. RETURN VALUES Returns 0 on success. On error, a negative value corresponding to fabric errno is returned. For fi_cancel, a return value of 0 indicates that the cancel request was submitted for processing. Fabric errno values are defined in rdma/fi_errno.h. ERRORS -FI_EDOMAIN A resource domain was not bound to the endpoint or an attempt was made to bind multiple domains. -FI_ENOCQ The endpoint has not been configured with necessary event queue. -FI_EOPBADSTATE The endpoint's state does not permit the requested operation. SEE ALSO fi_getinfo(3), fi_domain(3), fi_cq(3) fi_msg(3), fi_tagged(3), fi_rma(3) AUTHORS OpenFabrics. Libfabric Programmer's Manual 2021-11-20 fi_endpoint(3)
NAME | SYNOPSIS | ARGUMENTS | DESCRIPTION | ENDPOINT ATTRIBUTES | TRANSMIT CONTEXT ATTRIBUTES | RECEIVE CONTEXT ATTRIBUTES | SCALABLE ENDPOINTS | SHARED CONTEXTS | SOCKET ENDPOINTS | OPERATION FLAGS | NOTES | RETURN VALUES | ERRORS | SEE ALSO | AUTHORS
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