pipe, pipe2: don't corrupt fd on error I noticed a potential subtle double-close bug in libvirt. There, a common idiom is to initialize an int fd[2]={-1,-1}, then have multiple error paths goto common cleanup code. In the cleanup code, the fds are closed if they are not already -1; this works if the error label is reached before the pipe call, or after pipe succeeds, but if it was the pipe call itself that jumped to the error label, then it is relying on failed pipe() not altering the values already in fd array prior to the failure. Our pipe2 replacement violated this assumption, and could leave a non-negative value in the array, which in turn would let libvirt close an already-closed fd, possibly nuking an unrelated fd opened by another thread that happened to get the same value. As a result, I raised a POSIX issue regarding the behavior of pipe on failure: http://austingroupbugs.net/view.php?id=467 Using that test program, I learned that most systems leave fd unchanged on error, but that mingw always assigns -1 into the array. This fixes the mingw pipe() replacement, as well as the gnulib pipe2() replacement. I don't know of any race-free way to work around a cygwin crash: http://cygwin.com/ml/cygwin/2011-06/msg00328.html - we could always open() and then close() two fds to guess whether two spare fd still remain before calling pipe(), but that is racy. * lib/pipe.c (pipe): Leave fd unchanged on error. * lib/pipe2.c (pipe2): Likewise. * doc/posix-functions/pipe.texi (pipe): Document cygwin issue. * doc/glibc-functions/pipe2.texi (pipe2): Likewise. Signed-off-by: Eric Blake <eblake@redhat.com>

@node link
@section @code{link}
@findex link

POSIX specification:@* @url{http://www.opengroup.org/onlinepubs/9699919799/functions/link.html}

Gnulib module: link

Portability problems fixed by Gnulib:
@itemize
@item
This function is missing on some platforms:
mingw.
@item
This function fails to reject trailing slashes on non-directories on
some platforms:
FreeBSD 7.2, Solaris 11 2010-11, Cygwin 1.5.x.
@item
When the second argument is a dangling symlink, some platforms follow
that link and create the destination rather than failing:
IRIX 6.5.
@end itemize

Portability problems not fixed by Gnulib:
@itemize
@item
When the first argument is a symlink, some platforms create a
hard-link to what the symlink referenced, rather than to the symlink
itself.  Use @samp{linkat} to force a particular behavior.
@end itemize