WG15 Defect Report Ref: 9945-1-66
Topic: inherited file descriptors

This is an approved interpretation of 9945-1:1990.


Last update: 1997-05-20

                                                                9945-1-90 #66


	Topic:			inherited file descriptors
	Relevant Sections:	not specified

Defect Report:

 This is a request for interpretation of ISO/IEC 9945-1:1990
 (IEEE Std 1003.1).  There appears to be a hole in the
 standard for inherited file descriptors.  Specifically, the
 9945-1a standard appears not to cover the following:

       Both parent and child write N times to fd via
       parent and child terminate normally.

 No seeks are done.  Two aspects to this situation require

   1.  First, the fact that there are dependencies between
       I/O's done by the two processes needs to be
       documented.  For example, an lseek() done by the
       parent affects the child.

   2.  In the absence of error conditions in above example,
       should ***exactly*** 2*N bytes be written to "log"?  At
       issue here is the atomicity of write().  Would a
       conforming implementation be allowed to do the
       following on occasion:

               parent write data to byte K
               child write data  to byte K
               parent updates file position to K+1
               child updates file position to K+1

       and hence would write ***less than*** 2*N bytes to "log"?
       Or, is the combination of writing and updating the
       file position atomic?


WG15 response for ISO/IEC 9945-1:1990 (IEEE Std 1003.1-1990)

(1)This is documented. See fork() page 41 lines 19-21; also see
open file description on page 16 lines 242-247.

(2) The standard does not speak to this issue, and as such no conformance
distinction can be made between alternate implementations based on this.
This is being referred to the sponsor.

Rationale for Interpretation:

Note: (this note is not part of the interpretation) 
The proposed revision ISO/IEC 9945-1:1996  has text to address
point 2 - atomicity of writes.