0000144: Standard lacks a (possibly XSI) interface to associate a session to a TTY; tcsetsid()

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Category

Severity

Type

Date Submitted

Last Update

0000144

[1003.1(2008)/Issue 7] Base Definitions and Headers

Editorial

Enhancement Request

2009-09-05 17:22

2009-09-24 15:37

Reporter

EdSchouten

View Status

public

Assigned To

ajosey

Priority

normal

Resolution

Future Enhancement

Status

Resolved

Name

Ed Schouten

Organization

User Reference

Section

Chapter 11: TTYs

Page Number

n/a

Line Number

n/a

Interp Status

---

Final Accepted Text

Summary

0000144: Standard lacks a (possibly XSI) interface to associate a session to a TTY; tcsetsid()

Description

According to the General Terminal Interface chapter, it is implementation defined whether a session associates to a TTY when O_NOCTTY is not passed to open():

The controlling terminal for a session is allocated by the session leader in an implementation-defined manner. If a session leader has no controlling terminal, and opens a terminal device file that is not already associated with a session without using the O_NOCTTY option (see open()), it is implementation-defined whether the terminal becomes the controlling terminal of the session leader.

Unfortunately, the standard does not specify a way to associate them when the implementation does not do this by default (i.e. the BSDs). This means it's practically impossible to implement a network login service or terminal emulator only using the interfaces described in POSIX.

Desired Action

Standardizing things like TIOCSCTTY wouldn't be a good way to go. Some time ago I looked at this and it seems QNX has a solution for this that seems to be quite elegant:

http://www.qnx.com/developers/docs/6.4.0/neutrino/lib_ref/t/tcsetsid.html [^]

It's basically the counterpart of the already existing tcgetsid().

I propose adding this function to the standard, marked as XSI, where a minimal implementation only has to support the situation where the `pid' argument is equal to the session ID of the current process. This would be desirable anyway.

An implementation on operating systems that have TIOCSCTTY could then look as follows:

int
tcsetsid(int fd, pid_t pid)
{

    if (pid != getsid(0)) {
        errno = EINVAL;
        return -1;
    }

    return ioctl(fd, TIOCSCTTY, NULL);
}

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Notes
(0000237) nick (manager) 2009-09-24 15:36	The rules for introducing new material into the standard are provided in austin-112r3 (http://www.opengroup.org/austin/docs/austin_112r3.txt). [^] The material introduced must have a copyright release from the original owner. The text needs to be fully formed ... the exact words you would propose being added to the standard. Since you have suggested that the new interface be marked XSI, the best method for moving forward would be to lobby members of The Open Group's platform working group.

Issue History
Date Modified	Username	Field	Change
2009-09-05 17:22	EdSchouten	New Issue
2009-09-05 17:22	EdSchouten	Status	New => Under Review
2009-09-05 17:22	EdSchouten	Assigned To	=> ajosey
2009-09-05 17:22	EdSchouten	Name	=> Ed Schouten
2009-09-05 17:22	EdSchouten	Section	=> Chapter 11: TTYs
2009-09-05 17:22	EdSchouten	Page Number	=> n/a
2009-09-05 17:22	EdSchouten	Line Number	=> n/a
2009-09-24 15:36	nick	Note Added: 0000237
2009-09-24 15:37	msbrown	Interp Status	=> ---
2009-09-24 15:37	msbrown	Status	Under Review => Resolved
2009-09-24 15:37	msbrown	Resolution	Open => Future Enhancement

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