Content-type: text/html Manpage of TCBrecvfrom

TCBrecvfrom

Section: Timely Computing Base (1)
Updated: 30 September 2002
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NAME

TCBrecvfrom - receives a message from a TCB socket.

 

SYNOPSIS

#include "tcb/tcb.h"

int TCBrecvfrom(void* buff, int nbytes, unsigned int flags, struct sockaddr* from, int *addrlen, TCBsocketDesc* desc, TCBtimestamp *delivery_evt, TCBtimeinterval* delay, TCBtimeinterval* error, char block);  

DESCRIPTION

TCBrecvfrom call is used to receive messages from a socket. If from is not NULL the source address of the message is filled in. The argument addrlen is a value-result parameter, initialised to the size of the buffer associated with from, and modified on return to indicate the actual size of the address stored there.

TCBrecvfrom returns the length of the message on successful completion.

TCBsocketDesc* desc, TCBtimestamp *delivery_evt, TCBtimeinterval* delay, TCBtimeinterval* error, char block);" The parameter desc is the descriptor of the TCB socket. *delivery_evt is a pointer to a variable that the TCB will sets with the termination event of the observed interval (nanosecond resolution). *delay is a pointer to a variable that the TCB will sets with the delay of the observed interval (nanosecond resolution). *error is a pointer to a variable that the TCB will sets with the maximum error associated with the measurement (nanosecond resolution). block specifies if the function should block or not if there's no available data on the socket. NON_BLOCKING or BLOCKING.

The flags argument to a recv call is formed by OR'ing one or more of the following values:

MSG_OOB
This flag requests receipt of out-of-band data that would not be received in the normal data stream. Some protocols place expedited data at the head of the normal data queue, and thus this flag cannot be used with such protocols.
MSG_PEEK
This flag causes the receive operation to return data from the beginning of the receive queue without removing that data from the queue. Thus, a subsequent receive call will return the same data.
MSG_WAITALL
This flag requests that the operation block until the full request is satisfied. However, the call may still return less data than requested if a signal is caught, an error or disconnect occurs, or the next data to be received is of a different type than that returned.
MSG_NOSIGNAL
This flag turns off raising of SIGPIPE on stream sockets when the other end disappears.
MSG_ERRQUEUE
This flag specifies that queued errors should be received from the socket error queue. The error is passed in an ancillary message with a type dependent on the protocol (for IPv4 IP_RECVERR ). The user should supply a buffer of sufficient size. See cmsg(3) for more information on ancillary messages.

The error is supplied in a sock_extended_err structure:


#define SO_EE_ORIGIN_NONE       0
#define SO_EE_ORIGIN_LOCAL      1
#define SO_EE_ORIGIN_ICMP       2
#define SO_EE_ORIGIN_ICMP6      3

struct sock_extended_err
{
    u_int32_t       ee_errno;   /* error number */
    u_int8_t        ee_origin;  /* where the error originated */ 
    u_int8_t        ee_type;    /* type */
    u_int8_t        ee_code;    /* code */
    u_int8_t        ee_pad;
    u_int32_t       ee_info;    /* additional information */
    u_int32_t       ee_data;    /* other data */  
    /* More data may follow */ 
};

struct sockaddr *SOCK_EE_OFFENDER(struct sock_extended_err *);

ee_errno contains the errno number of the queued error. ee_origin is the origin code of where the error originated. The other fields are protocol specific. The macro SOCK_EE_OFFENDER returns a pointer to the address of the network object where the error originated from given a pointer to the ancillary message. If this address is not known, the sa_family member of the sockaddr contains AF_UNSPEC and the other fields of the sockaddr are undefined. The payload of the packet that caused the error is passed as normal data.
For local errors, no address is passed (this can be checked with the cmsg_len member of the cmsghdr). For error receives, the MSG_ERRQUEUE is set in the msghdr. After an error has been passed, the pending socket error is regenerated based on the next queued error and will be passed on the next socket operation.

The recvmsg call uses a msghdr structure to minimize the number of directly supplied parameters. This structure has the following form, as defined in <sys/socket.h>:


struct msghdr {
    void         * msg_name;     /* optional address */
    socklen_t    msg_namelen;    /* size of address */
    struct iovec * msg_iov;      /* scatter/gather array */
    size_t       msg_iovlen;     /* # elements in msg_iov */
    void         * msg_control;  /* ancillary data, see below */
    socklen_t    msg_controllen; /* ancillary data buffer len */
    int          msg_flags;      /* flags on received message */
};

Here msg_name and msg_namelen specify the destination address if the socket is unconnected; msg_name may be given as a null pointer if no names are desired or required. The fields msg_iov and msg_iovlen describe scatter-gather locations, as discussed in readv(2). The field msg_control, which has length msg_controllen, points to a buffer for other protocol control related messages or miscellaneous ancillary data. When recvmsg is called, msg_controllen should contain the length of the available buffer in msg_control; upon return from a successful call it will contain the length of the control message sequence.

The messages are of the form:


struct cmsghdr {
    socklen_t   cmsg_len;   /* data byte count, including hdr */
    int         cmsg_level; /* originating protocol */
    int         cmsg_type;  /* protocol-specific type */
/* followed by
    u_char      cmsg_data[]; */
};

Ancillary data should only be accessed by the macros defined in cmsg(3).

As an example, Linux uses this auxiliary data mechanism to pass extended errors, IP options or file descriptors over Unix sockets.

The msg_flags field is set on return according to the message received. MSG_EOR indicates end-of-record; the data returned completed a record (generally used with sockets of type SOCK_SEQPACKET). MSG_TRUNC indicates that the trailing portion of a datagram was discarded because the datagram was larger than the buffer supplied. MSG_CTRUNC indicates that some control data were discarded due to lack of space in the buffer for ancillary data. MSG_OOB is returned to indicate that expedited or out-of-band data were received. MSG_ERRQUEUE indicates that no data was received but an extended error from the socket error queue.

 

RETURN VALUES

The function returns the number of bytes received, or 0 if there's no available information on the socket on a non blocking call.  

ERRORS

if errno==0

TCB_ACESS_ERROR if an error occurred on the access to the TCB.

if errno!=0

These are some standard errors generated by the socket layer. Additional errors may be generated and returned from the underlying protocol modules; see their manual pages.

EBADF
The argument s is an invalid descriptor.
ENOTCONN
The socket is associated with a connection-oriented protocol and has not been connected (see connect(2) and accept(2)).
ENOTSOCK
The argument s does not refer to a socket.
EAGAIN
The socket is marked non-blocking and the receive operation would block, or a receive timeout had been set and the timeout expired before data was received.
EINTR
The receive was interrupted by delivery of a signal before any data were available.
EFAULT
The receive buffer pointer(s) point outside the process's address space.
EINVAL
Invalid argument passed.

 

SEE ALSO

recvfrom (2), TCBsocket, TCBbind (1), TCBwinfoport (1), TCBsendto (1), TCBsendtoWFD (1), TCBsocketClose (1)


 

Index

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUES
ERRORS
SEE ALSO

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Time: 23:05:27 GMT, August 06, 2003