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Last update: 10 April,2001

                                                                1003.1-90 #3

        Classification: No change required


This response will be incorporated in an IEEE interpretations
publication, and will be also made available on-line on the IEEE 
SPAsystem.

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	Interpretation Number:	XXXX
	Topic:			EIO missing from tc* functions
	Relevant Sections:	7.1.1.4


Interpretation Request: (Defect Report)
-----------------------


POSIX 1003.1-1990 section 7.1.1.4 (page 131, lines 88-90) states:

    "Certain calls that set terminal parameters are treated in the same
    fashion as write, except that TOSTOP is ignored; that is, the effect
    is identical to that of terminal writes when TOSTOP is set."

In the preceding paragraph the final sentence says:

    ".... If TOSTOP is set, and the process group of the writing process
    is orphaned, and the writing process is not ignored or blocking
    SIGTTOU, the write() returns -1 with errno set to [EIO], and no
    signal is sent."

Routines that fit this description are:-

	tcdrain(), page 145, section 7.2.2
	tcflow(), page 145, section 7.2.2
	tcflush(), page 145, section 7.2.2
	tcsendbreak(), page 145, section 7.2.2
	tcsetattr(), page 143, section 7.2.1

Why is [EIO] not included in the error section of any of these interfaces?
Must they return -1 with errno set to [EIO] in the given
circumstances?  May they?


IEEE Interpretation for 1003.1-1990 (9945-1:1990):
--------------------------------------------------

The requirement in section 7.1.1.4 "Terminal Access Control"
lines 88-90 refers to "calls that set terminal
parameters".  The list of functions for which this requirement
is valid is limited to tcsetattr().  For the case of
tcsetattr(), the implementation must return
[EIO] in the circumstances described as a consequence
of lines 88-90 and the description of [EIO] on
page 121 lines 280-285.

Rationale for Interpretation:
-----------------------------
Lines 84-87 of the same section refers only to the write()
system call, and not explicitly to the tcdrain(), tcflow(),
tcflush(), tcsendbreak() functions.  Although they appear
to be implementable in terms of write() this is not
required by the standard.  Were this to be required, language
similar to that in section 8.2.3 would be included, i.e.
"the underlying function is...".  Therefore they are not
required to return [EIO] by the current standard.
They may however return [EIO] under the conditions laid
out in section 2.4, lines 521 to 526.

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