What is Recvmsg used for?
The recvmsg() system call receives a message from a socket and capture the address from which the data was sent. Unlike the recv() call, which can only be used on a connected stream socket or bound datagram socket, recvmsg() can be used to receive data on a socket whether or not it is connected.
Does Recvmsg block?
If data is not available for socket s, and s is in blocking mode, the recvmsg() call blocks the caller until data arrives. Therefore, applications using stream sockets should place this call in a loop, and call this function until all data has been received.
Is UDP socket block oriented?
TCP is a connection-oriented protocol. Connection-orientation means that the communicating devices should establish a connection before transmitting data and should close the connection after transmitting the data. UDP is the Datagram oriented protocol.
Which socket is used in UDP?
int socket(int domain, int type, int protocol) Creates an unbound socket in the specified domain. Returns socket file descriptor. protocol – Protocol to be used by socket. 0 means use default protocol for the address family.
What is Iovec?
Data Type: struct iovec. The iovec structure describes a buffer. It contains two fields: void *iov_base. Contains the address of a buffer.
What is Readv?
The readv() function reads data from a file or a socket with descriptor fs and stores it in a set of buffers. The data is scattered into the buffers specified by iov… iov[iovcnt-1]. Parameter Description fs. The file or socket descriptor.
What is Writev?
General description. The writev() function writes data to a file or socket with descriptor fs from a set of buffers. The data is gathered from the buffers specified by iov… iov[iovcnt-1]. When the descriptor refers to a socket, it must be a connected socket.
When to use recv or recvmsg in Linux?
If the caller is not interested in the source address, src_addr and addrlen should be specified as NULL. The recv () call is normally used only on a connected socket (see connect (2)). It is equivalent to the call: The recvmsg () call uses a msghdr structure to minimize the number of directly supplied arguments.
How to receive a message from a socket?
The recvfrom () and recvmsg () calls are used to receive messages from a socket, and may be used to receive data on a socket whether or not it is connection-oriented. If src_addr is not NULL, and the underlying protocol provides the source address, this source address is filled in.
Why does recvmsg return less data than requested?
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. The recvmsg () call uses a msghdr structure to minimize the number of directly supplied arguments.
When to call recvmsg ( ) in MSG _ controllen?
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: