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man pages section 3: Basic Library Functions

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Updated: Thursday, June 13, 2019
 
 

t_optmgmt(3C)

Name

t_optmgmt - manage options for a transport endpoint

Synopsis

#include <xti.h> 

int t_optmgmt(int fd, const struct t_optmgmt *req, struct t_optmgmt *ret);

Description

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.

The t_optmgmt() function enables a transport user to retrieve, verify or negotiate protocol options with the transport provider. The argument fd identifies a transport endpoint.

The req and ret arguments point to a t_optmgmt structure containing the following members:

struct netbuf opt;
t_scalar_t    flags;

The opt field identifies protocol options and the flags field is used to specify the action to take with those options.

The options are represented by a netbuf structure in a manner similar to the address in t_bind(3C). The argument req is used to request a specific action of the provider and to send options to the provider. The argument len specifies the number of bytes in the options, buf points to the options buffer, and maxlen has no meaning for the req argument. The transport provider may return options and flag values to the user through ret. For ret, maxlen specifies the maximum size of the options buffer and buf points to the buffer where the options are to be placed. If maxlen in ret is set to zero, no options values are returned. On return, len specifies the number of bytes of options returned. The value in maxlen has no meaning for the req argument, but must be set in the ret argument to specify the maximum number of bytes the options buffer can hold.

Each option in the options buffer is of the form struct t_opthdr possibly followed by an option value.

The level field of struct t_opthdr identifies the XTI level or a protocol of the transport provider. The name field identifies the option within the level, and len contains its total length; that is, the length of the option header t_opthdr plus the length of the option value. If t_optmgmt() is called with the action T_NEGOTIATE set, the status field of the returned options contains information about the success or failure of a negotiation.

Several options can be concatenated. The option user has, however to ensure that each options header and value part starts at a boundary appropriate for the architecture-specific alignment rules. The macros T_OPT_FIRSTHDR(nbp), T_OPT_NEXTHDR (nbp,tohp), T_OPT_DATA(tohp) are provided for that purpose.

T_OPT_DATA(nhp)

If argument is a pointer to a t_opthdr structure, this macro returns an unsigned character pointer to the data associated with the t_opthdr.

T_OPT_NEXTHDR(nbp, tohp)

If the first argument is a pointer to a netbuf structure associated with an option buffer and second argument is a pointer to a t_opthdr structure within that option buffer, this macro returns a pointer to the next t_opthdr structure or a null pointer if this t_opthdr is the last t_opthdr in the option buffer.

T_OPT_FIRSTHDR(tohp)

If the argument is a pointer to a netbuf structure associated with an option buffer, this macro returns the pointer to the first t_opthdr structure in the associated option buffer, or a null pointer if there is no option buffer associated with this netbuf or if it is not possible or the associated option buffer is too small to accommodate even the first aligned option header.

T_OPT_FIRSTHDR is useful for finding an appropriately aligned start of the option buffer. T_OPT_NEXTHDR is useful for moving to the start of the next appropriately aligned option in the option buffer. Note that OPT_NEXTHDR is also available for backward compatibility requirements. T_OPT_DATA is useful for finding the start of the data part in the option buffer where the contents of its values start on an appropriately aligned boundary.

If the transport user specifies several options on input, all options must address the same level.

If any option in the options buffer does not indicate the same level as the first option, or the level specified is unsupported, then the t_optmgmt() request will fail with TBADOPT. If the error is detected, some options have possibly been successfully negotiated. The transport user can check the current status by calling t_optmgmt() with the T_CURRENT flag set.

The flags field of req must specify one of the following actions:

T_NEGOTIATE

This action enables the transport user to negotiate option values.

The user specifies the options of interest and their values in the buffer specified by req→opt.buf and req→opt.len. The negotiated option values are returned in the buffer pointed to by ret->opt.buf. The status field of each returned option is set to indicate the result of the negotiation. The value is T_SUCCESS if the proposed value was negotiated, T_PARTSUCCESS if a degraded value was negotiated, T_FAILURE if the negotiation failed (according to the negotiation rules), T_NOTSUPPORT if the transport provider does not support this option or illegally requests negotiation of a privileged option, and T_READONLY if modification of a read-only option was requested. If the status is T_SUCCESS, T_FAILURE, T_NOTSUPPORT or T_READONLY, the returned option value is the same as the one requested on input.

The overall result of the negotiation is returned in ret→flags.

This field contains the worst single result, whereby the rating is done according to the order T_NOTSUPPORT, T_READONLY, T_FAILURE, T_PARTSUCCESS, T_SUCCESS. The value T_NOTSUPPORT is the worst result and T_SUCCESS is the best.

For each level, the option T_ALLOPT can be requested on input. No value is given with this option; only the t_opthdr part is specified. This input requests to negotiate all supported options of this level to their default values. The result is returned option by option in ret→opt.buf. Note that depending on the state of the transport endpoint, not all requests to negotiate the default value may be successful.

T_CHECK

This action enables the user to verify whether the options specified in req are supported by the transport provider. If an option is specified with no option value (it consists only of a t_opthdr structure), the option is returned with its status field set to T_SUCCESS if it is supported, T_NOTSUPPORT if it is not or needs additional user privileges, and T_READONLY if it is read-only (in the current XTI state). No option value is returned.

If an option is specified with an option value, the status field of the returned option has the same value, as if the user had tried to negotiate this value with T_NEGOTIATE. If the status is T_SUCCESS, T_FAILURE, T_NOTSUPPORT or T_READONLY, the returned option value is the same as the one requested on input.

The overall result of the option checks is returned in ret→flags. This field contains the worst single result of the option checks, whereby the rating is the same as for T_NEGOTIATE .

Note that no negotiation takes place. All currently effective option values remain unchanged.

T_DEFAULT

This action enables the transport user to retrieve the default option values. The user specifies the options of interest in req→opt.buf. The option values are irrelevant and will be ignored; it is sufficient to specify the t_opthdr part of an option only. The default values are then returned in ret→opt.buf.

The status field returned is T_NOTSUPPORT if the protocol level does not support this option or the transport user illegally requested a privileged option, T_READONLY if the option is read-only, and set to T_SUCCESS in all other cases. The overall result of the request is returned in ret→flags. This field contains the worst single result, whereby the rating is the same as for T_NEGOTIATE.

For each level, the option T_ALLOPT can be requested on input. All supported options of this level with their default values are then returned. In this case, ret→opt.maxlen must be given at least the value info→options before the call. See t_getinfo(3C) and t_open(3C).

T_CURRENT

This action enables the transport user to retrieve the currently effective option values. The user specifies the options of interest in req→opt.buf. The option values are irrelevant and will be ignored; it is sufficient to specify the t_opthdr part of an option only. The currently effective values are then returned in req→opt.buf.

The status field returned is T_NOTSUPPORT if the protocol level does not support this option or the transport user illegally requested a privileged option, T_READONLY if the option is read-only, and set to T_SUCCESS in all other cases. The overall result of the request is returned in ret→flags. This field contains the worst single result, whereby the rating is the same as for T_NEGOTIATE.

For each level, the option T_ALLOPT can be requested on input. All supported options of this level with their currently effective values are then returned.

The option T_ALLOPT can only be used with t_optmgmt() and the actions T_NEGOTIATE, T_DEFAULT and T_CURRENT. It can be used with any supported level and addresses all supported options of this level. The option has no value; it consists of a t_opthdr only. Since in a t_optmgmt() call only options of one level may be addressed, this option should not be requested together with other options. The function returns as soon as this option has been processed.

Options are independently processed in the order they appear in the input option buffer. If an option is multiply input, it depends on the implementation whether it is multiply output or whether it is returned only once.

Transport providers may not be able to provide an interface capable of supporting T_NEGOTIATE and/or T_CHECK functionalities. When this is the case, the error TNOTSUPPORT is returned.

The function t_optmgmt() may block under various circumstances and depending on the implementation. The function will block, for instance, if the protocol addressed by the call resides on a separate controller. It may also block due to flow control constraints; that is, if data sent previously across this transport endpoint has not yet been fully processed. If the function is interrupted by a signal, the option negotiations that have been done so far may remain valid. The behavior of the function is not changed if O_NONBLOCK is set.

Return Values

Upon successful completion, a value of 0 is returned. Otherwise, a value of −1 is returned and t_errno is set to indicate an error.

VALID STATES

ALL - apart from T_UNINIT.

Errors

On failure, t_errno is set to one of the following:

TBADF

The specified file descriptor does not refer to a transport endpoint.

TBADFLAG

An invalid flag was specified.

TBADOPT

The specified options were in an incorrect format or contained illegal information.

TBUFOVFLW

The number of bytes allowed for an incoming argument (maxlen) is greater than 0 but not sufficient to store the value of that argument. The information to be returned in ret will be discarded.

TNOTSUPPORT

This action is not supported by the transport provider.

TOUTSTATE

The communications endpoint referenced by fd is not in one of the states in which a call to this function is valid.

TPROTO

This error indicates that a communication problem has been detected between XTI and the transport provider for which there is no other suitable XTI error (t_errno).

TSYSERR

A system error has occurred during execution of this function.

TLI COMPATIBILITY

The XTI and TLI interface definitions have common names but use different header files. This, and other semantic differences between the two interfaces are described in the subsections below.

Interface Header

The XTI interfaces use the header file, xti.h. TLI interfaces should not use this header. They should use the header:

#include <tiuser.h>

Error Description Values

The t_errno value TPROTO can be set by the XTI interface but not by the TLI interface.

The t_errno values that this routine can return under different circumstances than its XTI counterpart are TACCES and TBUFOVFLW.

TACCES

can be returned to indicate that the user does not have permission to negotiate the specified options.

TBUFOVFLW

can be returned even when the maxlen field of the corresponding buffer has been set to zero.

Option Buffers

The format of the options in an opt buffer is dictated by the transport provider. Unlike the XTI interface, the TLI interface does not fix the buffer format. The macros T_OPT_DATA, T_OPT_NEXTHDR, and T_OPT_FIRSTHDR described for XTI are not available for use by TLI interfaces.

Actions

The semantic meaning of various action values for the flags field of req differs between the TLI and XTI interfaces. TLI interface users should heed the following descriptions of the actions:

T_NEGOTIATE

This action enables the user to negotiate the values of the options specified in req with the transport provider. The provider will evaluate the requested options and negotiate the values, returning the negotiated values through ret.

T_CHECK

This action enables the user to verify whether the options specified in req are supported by the transport provider. On return, the flags field of ret will have either T_SUCCESS or T_FAILURE set to indicate to the user whether the options are supported. These flags are only meaningful for the T_CHECK request.

T_DEFAULT

This action enables a user to retrieve the default options supported by the transport provider into the opt field of ret. In req, the len field of opt must be zero and the buf field may be NULL.

Connectionless Mode

If issued as part of the connectionless mode service, t_optmgmt() may block due to flow control constraints. The function will not complete until the transport provider has processed all previously sent data units.

Attributes

See attributes(7) for descriptions of the following attributes:

ATTRIBUTE TYPE
ATTRIBUTE VALUE
MT Level
Safe

See Also

close(2), poll(2), select(3C), t_accept(3C), t_alloc(3C), t_bind(3C), t_close(3C), t_connect(3C), t_getinfo(3C), t_listen(3C), t_open(3C), t_rcv(3C), t_rcvconnect(3C), t_rcvudata(3C), t_snddis(3C), attributes(7)