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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, iovcount contains the number of non-contiguous udata buffers and is limited to an implementation-defined value given by T_IOV_MAX which is at least 16, 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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If the limit on iovcount is exceeded, the function fails with TBADDATA.
In unitdata, addr specifies the protocol address of the destination user, and opt identifies options that the user wants associated with this request. The udata field is not used. 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 may use default options.
The data to be sent is identified by iov[0] through iov [iovcount-1].
Note that the limit on the total number of bytes available in all buffers passed:
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iov(0).iov_len + . . + iov(iovcount-1).iov_len
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may be constrained by implementation limits. If no other constraint applies, it will be limited by INT_MAX. In practice, the availability of memory to an application is likely to impose a lower limit on the amount of data that can be sent or received using scatter/gather functions.
By default, t_sndvudata() 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_sndvudata() executes 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 iov0 through iov [iovcount-1] exceeds the TSDU size as returned in the tsdu field of the info argument of
t_open(3NSL) or t_getinfo(3NSL), or is zero and sending of zero octets
is not supported by the underlying transport service, a TBADDATA error is generated. If t_sndvudata() 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(3NSL). An application must therefore be prepared to receive these errors in both of these ways.
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