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This routine is part of the XTI interfaces which evolved from the TLI interfaces. XTI represents the future evolution of these interfaces. However, TLI interfaces are
supported for compatibility. When using a TLI routine that has the same name as an XTI routine, the tiuser.h header file must be used. Refer to the TLI COMPATIBILITY section for
a description of differences between the two interfaces.
This function is used in connectionless-mode to send a data unit to another transport user. The argument fd identifies the local transport endpoint through which data will be sent, and unitdata points to a t_unitdata structure
containing the following members:
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struct netbuf addr;
struct netbuf opt;
struct netbuf udata;
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In unitdata, addr specifies the protocol address of the destination user, opt identifies options that the user wants associated with this request, and udata specifies the user
data to be sent. The user may choose not to specify what protocol options are associated with the transfer by setting the len field of opt to zero. In this case, the provider uses the option values currently set for the communications endpoint.
If the len field of udata is zero, and sending of zero octets is not supported by the underlying transport service, the t_sndudata() will return -1 with t_errno set to TBADDATA.
By default, t_sndudata() operates in synchronous mode and may wait if flow control restrictions prevent the data from being accepted by the local transport provider at the time the call is made. However, if O_NONBLOCK is set by means of t_open(3NSL)
or fcntl(2), t_sndudata() will execute in asynchronous mode and will fail under such conditions. The process can arrange to be notified of the clearance
of a flow control restriction by means of either t_look(3NSL) or the EM interface.
If the amount of data specified in udata exceeds the TSDU size as returned in the tsdu field of the info argument of t_open(3NSL) or t_getinfo(3NSL), a TBADDATA error will be generated. If t_sndudata() is called before the destination user has activated
its transport endpoint (see t_bind(3NSL)), the data unit may be discarded.
If it is not possible for the transport provider to immediately detect the conditions that cause the errors TBADDADDR and TBADOPT, these errors will alternatively be returned by t_rcvuderr. Therefore, an application must be prepared
to receive these errors in both of these ways.
If the call is interrupted, t_sndudata() will return EINTR and the datagram will not be sent.
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