NAME

fi_eq - Event queue operations

fi_eq_open / fi_close: Open/close an event queue
fi_control: Control operation of EQ
fi_eq_read / fi_eq_readerr: Read an event from an event queue
fi_eq_write: Writes an event to an event queue
fi_eq_sread: A synchronous (blocking) read of an event queue
fi_eq_strerror: Converts provider specific error information into a printable string

SYNOPSIS

#include <rdma/fi_domain.h>

int fi_eq_open(struct fid_fabric *fabric, struct fi_eq_attr *attr,
    struct fid_eq **eq, void *context);

int fi_close(struct fid *eq);

int fi_control(struct fid *eq, int command, void *arg);

ssize_t fi_eq_read(struct fid_eq *eq, uint32_t *event,
    void *buf, size_t len, uint64_t flags);

ssize_t fi_eq_readerr(struct fid_eq *eq, struct fi_eq_err_entry *buf,
    uint64_t flags);

ssize_t fi_eq_write(struct fid_eq *eq, uint32_t event,
    const void *buf, size_t len, uint64_t flags);

ssize_t fi_eq_sread(struct fid_eq *eq, uint32_t *event,
    void *buf, size_t len, int timeout, uint64_t flags);

const char * fi_eq_strerror(struct fid_eq *eq, int prov_errno,
      const void *err_data, char *buf, size_t len);

ARGUMENTS

fabric: Opened fabric descriptor
eq: Event queue
attr: Event queue attributes
context: User specified context associated with the event queue.
event: Reported event
buf: For read calls, the data buffer to write events into. For write calls, an event to insert into the event queue. For fi_eq_strerror, an optional buffer that receives printable error information.
len: Length of data buffer
flags: Additional flags to apply to the operation
command: Command of control operation to perform on EQ.
arg: Optional control argument
prov_errno: Provider specific error value
err_data: Provider specific error data related to a completion
timeout: Timeout specified in milliseconds

DESCRIPTION

Event queues are used to report events associated with control operations. They are associated with memory registration, address vectors, connection management, and fabric and domain level events. Reported events are either associated with a requested operation or affiliated with a call that registers for specific types of events, such as listening for connection requests.

fi_eq_open

fi_eq_open allocates a new event queue.

The properties and behavior of an event queue are defined by struct fi_eq_attr.

struct fi_eq_attr {
	size_t               size;      /* # entries for EQ */
	uint64_t             flags;     /* operation flags */
	enum fi_wait_obj     wait_obj;  /* requested wait object */
	int                  signaling_vector; /* interrupt affinity */
	struct fid_wait     *wait_set;  /* optional wait set */
};

size: Specifies the minimum size of an event queue.
flags: Flags that control the configuration of the EQ.

FI_WRITE

Indicates that the application requires support for inserting user events into the EQ. If this flag is set, then the fi_eq_write operation must be supported by the provider. If the FI_WRITE flag is not set, then the application may not invoke fi_eq_write.
FI_AFFINITY

Indicates that the signaling_vector field (see below) is valid.

wait_obj: EQ’s may be associated with a specific wait object. Wait objects allow applications to block until the wait object is signaled, indicating that an event is available to be read. Users may use fi_control to retrieve the underlying wait object associated with an EQ, in order to use it in other system calls. The following values may be used to specify the type of wait object associated with an EQ:

FI_WAIT_NONE

Used to indicate that the user will not block (wait) for events on the EQ. When FI_WAIT_NONE is specified, the application may not call fi_eq_sread. This is the default is no wait object is specified.
FI_WAIT_UNSPEC

Specifies that the user will only wait on the EQ using fabric interface calls, such as fi_eq_sread. In this case, the underlying provider may select the most appropriate or highest performing wait object available, including custom wait mechanisms. Applications that select FI_WAIT_UNSPEC are not guaranteed to retrieve the underlying wait object.
FI_WAIT_SET

Indicates that the event queue should use a wait set object to wait for events. If specified, the wait_set field must reference an existing wait set object.
FI_WAIT_FD

Indicates that the EQ should use a file descriptor as its wait mechanism. A file descriptor wait object must be usable in select, poll, and epoll routines. However, a provider may signal an FD wait object by marking it as readable or with an error.
FI_WAIT_MUTEX_COND

Specifies that the EQ should use a pthread mutex and cond variable as a wait object.
FI_WAIT_YIELD

Indicates that the EQ will wait without a wait object but instead yield on every wait. Allows usage of fi_eq_sread through a spin.

signaling_vector: If the FI_AFFINITY flag is set, this indicates the logical cpu number (0..max cpu - 1) that interrupts associated with the EQ should target. This field should be treated as a hint to the provider and may be ignored if the provider does not support interrupt affinity.
wait_set: If wait_obj is FI_WAIT_SET, this field references a wait object to which the event queue should attach. When an event is inserted into the event queue, the corresponding wait set will be signaled if all necessary conditions are met. The use of a wait_set enables an optimized method of waiting for events across multiple event queues. This field is ignored if wait_obj is not FI_WAIT_SET.

fi_close

The fi_close call releases all resources associated with an event queue. Any events which remain on the EQ when it is closed are lost.

The EQ must not be bound to any other objects prior to being closed, otherwise the call will return -FI_EBUSY.

fi_control

The fi_control call is used to access provider or implementation specific details of the event queue. Access to the EQ should be serialized across all calls when fi_control is invoked, as it may redirect the implementation of EQ operations. The following control commands are usable with an EQ.

FI_GETWAIT (void **): This command allows the user to retrieve the low-level wait object associated with the EQ. The format of the wait-object is specified during EQ creation, through the EQ attributes. The fi_control arg parameter should be an address where a pointer to the returned wait object will be written. This should be an ‘int *’ for FI_WAIT_FD, or ‘struct fi_mutex_cond’ for FI_WAIT_MUTEX_COND.

struct fi_mutex_cond {
	pthread_mutex_t     *mutex;
	pthread_cond_t      *cond;
};

fi_eq_read

The fi_eq_read operations performs a non-blocking read of event data from the EQ. The format of the event data is based on the type of event retrieved from the EQ, with all events starting with a struct fi_eq_entry header. At most one event will be returned per EQ read operation. The number of bytes successfully read from the EQ is returned from the read. The FI_PEEK flag may be used to indicate that event data should be read from the EQ without being consumed. A subsequent read without the FI_PEEK flag would then remove the event from the EQ.

The following types of events may be reported to an EQ, along with information regarding the format associated with each event.

Asynchronous Control Operations: Asynchronous control operations are basic requests that simply need to generate an event to indicate that they have completed. These include the following types of events: memory registration, address vector resolution, and multicast joins.
Control requests report their completion by inserting a struct fi_eq_entry into the EQ. The format of this structure is:

struct fi_eq_entry {
	fid_t            fid;        /* fid associated with request */
	void            *context;    /* operation context */
	uint64_t         data;       /* completion-specific data */
};

For the completion of basic asynchronous control operations, the returned event will indicate the operation that has completed, and the fid will reference the fabric descriptor associated with the event. For memory registration, this will be an FI_MR_COMPLETE event and the fid_mr. Address resolution will reference an FI_AV_COMPLETE event and fid_av. Multicast joins will report an FI_JOIN_COMPLETE and fid_mc. The context field will be set to the context specified as part of the operation, if available, otherwise the context will be associated with the fabric descriptor. The data field will be set as described in the man page for the corresponding object type (e.g., see fi_av(3) for a description of how asynchronous address vector insertions are completed).

Connection Notification: Connection notifications are connection management notifications used to setup or tear down connections between endpoints. There are three connection notification events: FI_CONNREQ, FI_CONNECTED, and FI_SHUTDOWN. Connection notifications are reported using struct fi_eq_cm_entry:

struct fi_eq_cm_entry {
	fid_t            fid;        /* fid associated with request */
	struct fi_info  *info;       /* endpoint information */
	uint8_t         data[];     /* app connection data */
};

A connection request (FI_CONNREQ) event indicates that a remote endpoint wishes to establish a new connection to a listening, or passive, endpoint. The fid is the passive endpoint. Information regarding the requested, active endpoint’s capabilities and attributes are available from the info field. The application is responsible for freeing this structure by calling fi_freeinfo when it is no longer needed. The fi_info connreq field will reference the connection request associated with this event. To accept a connection, an endpoint must first be created by passing an fi_info structure referencing this connreq field to fi_endpoint(). This endpoint is then passed to fi_accept() to complete the acceptance of the connection attempt. Creating the endpoint is most easily accomplished by passing the fi_info returned as part of the CM event into fi_endpoint(). If the connection is to be rejected, the connreq is passed to fi_reject().

Any application data exchanged as part of the connection request is placed beyond the fi_eq_cm_entry structure. The amount of data available is application dependent and limited to the buffer space provided by the application when fi_eq_read is called. The amount of returned data may be calculated using the return value to fi_eq_read. Note that the amount of returned data is limited by the underlying connection protocol, and the length of any data returned may include protocol padding. As a result, the returned length may be larger than that specified by the connecting peer.

If a connection request has been accepted, an FI_CONNECTED event will be generated on both sides of the connection. The active side – one that called fi_connect() – may receive user data as part of the FI_CONNECTED event. The user data is passed to the connection manager on the passive side through the fi_accept call. User data is not provided with an FI_CONNECTED event on the listening side of the connection.

Notification that a remote peer has disconnected from an active endpoint is done through the FI_SHUTDOWN event. Shutdown notification uses struct fi_eq_cm_entry as declared above. The fid field for a shutdown notification refers to the active endpoint’s fid_ep.

Asynchronous Error Notification

Asynchronous errors are used to report problems with fabric resources. Reported errors may be fatal or transient, based on the error, and result in the resource becoming disabled. Disabled resources will fail operations submitted against them until they are explicitly re-enabled by the application.

Asynchronous errors may be reported for completion queues and endpoints of all types. CQ errors can result when resource management has been disabled, and the provider has detected a queue overrun. Endpoint errors may be result of numerous actions, but are often associated with a failed operation. Operations may fail because of buffer overruns, invalid permissions, incorrect memory access keys, network routing failures, network reach-ability issues, etc.

Asynchronous errors are reported using struct fi_eq_err_entry, as defined below. The fabric descriptor (fid) associated with the error is provided as part of the error data. An error code is also available to determine the cause of the error.

fi_eq_sread

The fi_eq_sread call is the blocking (or synchronous) equivalent to fi_eq_read. It behaves is similar to the non-blocking call, with the exception that the calls will not return until either an event has been read from the EQ or an error or timeout occurs. Specifying a negative timeout means an infinite timeout.

Threads blocking in this function will return to the caller if they are signaled by some external source. This is true even if the timeout has not occurred or was specified as infinite.

It is invalid for applications to call this function if the EQ has been configured with a wait object of FI_WAIT_NONE or FI_WAIT_SET.

fi_eq_readerr

The read error function, fi_eq_readerr, retrieves information regarding any asynchronous operation which has completed with an unexpected error. fi_eq_readerr is a non-blocking call, returning immediately whether an error completion was found or not.

EQs are optimized to report operations which have completed successfully. Operations which fail are reported ‘out of band’. Such operations are retrieved using the fi_eq_readerr function. When an operation that completes with an unexpected error is inserted into an EQ, it is placed into a temporary error queue. Attempting to read from an EQ while an item is in the error queue results in an FI_EAVAIL failure. Applications may use this return code to determine when to call fi_eq_readerr.

Error information is reported to the user through struct fi_eq_err_entry. The format of this structure is defined below.

struct fi_eq_err_entry {
	fid_t            fid;        /* fid associated with error */
	void            *context;    /* operation context */
	uint64_t         data;       /* completion-specific data */
	int              err;        /* positive error code */
	int              prov_errno; /* provider error code */
	void            *err_data;   /* additional error data */
	size_t           err_data_size; /* size of err_data */
};

The fid will reference the fabric descriptor associated with the event. For memory registration, this will be the fid_mr, address resolution will reference a fid_av, and CM events will refer to a fid_ep. The context field will be set to the context specified as part of the operation.

The data field will be set as described in the man page for the corresponding object type (e.g., see fi_av(3) for a description of how asynchronous address vector insertions are completed).

The general reason for the error is provided through the err field. Provider or operational specific error information may also be available through the prov_errno and err_data fields. Users may call fi_eq_strerror to convert provider specific error information into a printable string for debugging purposes.

On input, err_data_size indicates the size of the err_data buffer in bytes. On output, err_data_size will be set to the number of bytes copied to the err_data buffer. The err_data information is typically used with fi_eq_strerror to provide details about the type of error that occurred.

For compatibility purposes, if err_data_size is 0 on input, or the fabric was opened with release < 1.5, err_data will be set to a data buffer owned by the provider. The contents of the buffer will remain valid until a subsequent read call against the EQ. Applications must serialize access to the EQ when processing errors to ensure that the buffer referenced by err_data does not change.

EVENT FIELDS

The EQ entry data structures share many of the same fields. The meanings are the same or similar for all EQ structure formats, with specific details described below.

fid: This corresponds to the fabric descriptor associated with the event. The type of fid depends on the event being reported. For FI_CONNREQ this will be the fid of the passive endpoint. FI_CONNECTED and FI_SHUTDOWN will reference the active endpoint. FI_MR_COMPLETE and FI_AV_COMPLETE will refer to the MR or AV fabric descriptor, respectively. FI_JOIN_COMPLETE will point to the multicast descriptor returned as part of the join operation. Applications can use fid->context value to retrieve the context associated with the fabric descriptor.
context: The context value is set to the context parameter specified with the operation that generated the event. If no context parameter is associated with the operation, this field will be NULL.
data: Data is an operation specific value or set of bytes. For connection events, data is application data exchanged as part of the connection protocol.
err: This err code is a positive fabric errno associated with an event. The err value indicates the general reason for an error, if one occurred. See fi_errno.3 for a list of possible error codes.
prov_errno: On an error, prov_errno may contain a provider specific error code. The use of this field and its meaning is provider specific. It is intended to be used as a debugging aid. See fi_eq_strerror for additional details on converting this error value into a human readable string.
err_data: On an error, err_data may reference a provider specific amount of data associated with an error. The use of this field and its meaning is provider specific. It is intended to be used as a debugging aid. See fi_eq_strerror for additional details on converting this error data into a human readable string.
err_data_size: On input, err_data_size indicates the size of the err_data buffer in bytes. On output, err_data_size will be set to the number of bytes copied to the err_data buffer. The err_data information is typically used with fi_eq_strerror to provide details about the type of error that occurred.
For compatibility purposes, if err_data_size is 0 on input, or the fabric was opened with release < 1.5, err_data will be set to a data buffer owned by the provider. The contents of the buffer will remain valid until a subsequent read call against the EQ. Applications must serialize access to the EQ when processing errors to ensure that the buffer referenced by err_data does no change.

NOTES

If an event queue has been overrun, it will be placed into an ‘overrun’ state. Write operations against an overrun EQ will fail with -FI_EOVERRUN. Read operations will continue to return any valid, non-corrupted events, if available. After all valid events have been retrieved, any attempt to read the EQ will result in it returning an FI_EOVERRUN error event. Overrun event queues are considered fatal and may not be used to report additional events once the overrun occurs.

RETURN VALUES

fi_eq_open: Returns 0 on success. On error, a negative value corresponding to fabric errno is returned.
fi_eq_read / fi_eq_readerr: On success, returns the number of bytes read from the event queue. On error, a negative value corresponding to fabric errno is returned. If no data is available to be read from the event queue, -FI_EAGAIN is returned.
fi_eq_sread: On success, returns the number of bytes read from the event queue. On error, a negative value corresponding to fabric errno is returned. If the timeout expires or the calling thread is signaled and no data is available to be read from the event queue, -FI_EAGAIN is returned.
fi_eq_write: On success, returns the number of bytes written to the event queue. On error, a negative value corresponding to fabric errno is returned.
fi_eq_strerror: Returns a character string interpretation of the provider specific error returned with a completion.

Fabric errno values are defined in rdma/fi_errno.h.

fi_eq(3) Libfabric Programmer's Manual