Re: lib/41567 (posix_memalign(3) taints errno when it shouldn't.)

[David Holland <dholland-bugs%netbsd.org@localhost>]

The following reply was made to PR lib/41567; it has been noted by GNATS.

From: David Holland <dholland-bugs%netbsd.org@localhost>
To: gnats-bugs%NetBSD.org@localhost
Cc: lib-bug-people%netbsd.org@localhost, netbsd-bugs%netbsd.org@localhost,
        gnats-admin%netbsd.org@localhost, kleink%NetBSD.org@localhost, 
ekamperi%gmail.com@localhost
Subject: Re: lib/41567 (posix_memalign(3) taints errno when it shouldn't.)
Date: Sun, 19 Jul 2009 18:11:25 +0000

 On Sun, Jul 19, 2009 at 07:27:05AM +0000, kleink%NetBSD.org@localhost wrote:
  > The standard (ISO/IEC 9899:1999, 7.5#3) is clear on this issue:
  > 
  >   The value of errno may be set to nonzero by a library
  >   function call whether or not there is an error, provided
  >   the use of errno is not documented in the description
  >   of the function in this International Standard.
 
 What POSIX says (which isn't the same) would be more pertinent...
 
  > Documenting this in posix_memalign(3) alone would be taking
  > the wrong road, too; this is a general concept which fits
  > errno(2) better, with the issue of errno(2) currently
  > addressing the behavior if system calls only.
 
 Documenting that things may trash errno is not quite the same as
 documenting whether a function explicitly sets a valid errno on an
 error return if it does so.
 
 In this case though, on the latter point I think silence is probably
 better as the behavior is nonportable.
 
 On the former point, how about this:
 
 Index: intro.2
 ===================================================================
 RCS file: /cvsroot/src/lib/libc/sys/intro.2,v
 retrieving revision 1.52
 diff -u -r1.52 intro.2
 --- intro.2    2 Jun 2009 13:15:41 -0000       1.52
 +++ intro.2    19 Jul 2009 18:07:51 -0000
 @@ -64,10 +64,17 @@
  Successful calls never set
  .Va errno ;
  once set, it remains until another error occurs.
 -It should only be examined after an error.
 -Note that a number of system calls overload the meanings of these
 -error numbers, and that the meanings must be interpreted according
 -to the type and circumstances of the call.
 +It should only be examined after an error has been reported, because
 +otherwise a leftover value from some previous error may be found
 +instead.
 +.Po
 +Many library functions that are not system calls also set
 +.Va errno
 +on return, in the same fashion.
 +In these cases a nonzero value may be left in
 +.Va errno
 +even upon successful return if some internal action failed.
 +.Pc
  .Pp
  The manual page for each system call will list some of the common
  errno codes that system call can return, but that should not be
 @@ -78,6 +85,10 @@
  a more specification-like manner would take more resources than
  this project has available.
  .Pp
 +Note also that a number of system calls overload the meanings of these
 +error numbers, and that in these cases the meanings must be
 +interpreted according to the type and circumstances of the call.
 +.Pp
  The following is a complete list of the errors and their
  names as given in
  .Aq Pa errno.h .
 
 -- 
 David A. Holland
 dholland%netbsd.org@localhost