On Tue, Aug 20, 2019 at 03:17:42PM +0200, Patrick Steinhardt wrote: > On Mon, Aug 19, 2019 at 03:36:19PM +0200, Karel Zak wrote: > > On Wed, Aug 14, 2019 at 06:45:03PM +0200, Patrick Steinhardt wrote: > > > since commit 52aa1a661 (include/closestream: avoid close more > > > than once, 2019-06-13), util-linux fails to build on musl libc > > > based systems. The culprit here is that it introduced assignments > > > to stderr and stdout, while the C89 standard explicitly notes > > > that treating stderr and stdout as valid lvalues is not a > > > requirement for any conforming C implementation. musl libc > > > implemented these streams as `extern FILE *const`, and as a > > > result assigning to these variables causes compiler errors. > > > > The question is if close() for stdout and stderr is the right way to > > go. > > > > In an ideal world it would be enough to use ferror()+fflush(), > > unfortunately for example NFS has never reached an ideal world and it > > requires fclose()... See > > > > https://lists.gnu.org/r/bug-gnulib/2019-04/msg00061.html > > > > Florian (added to CC), also suggested to use dup3() for the > > descriptors and then fclose() for the new handle. It sounds like a > > pretty elegant solution how to avoid all the issues with NULL and it's > > also robust enough if you accidentally call close_stream() more than > > once. > > > > See > > > > https://bugzilla.redhat.com/show_bug.cgi?id=1732450#c4 > > > > Maybe we can improve include/closestream.h to use dup3(), than it would > > be possible keep all in the header file as inline functions. > > > > Comments? > > I honestly don't get why we'd need to use dup3(2), though. > Couldn't the same be achieved by using dup2(3P) followed by > close(3P), instead? Especially considering that the former one > isn't specified by POSIX, either, but the latter one is. Well, I guess Florian has used dup3() as example and I don't think we have to care about the flags (O_CLOEXEC) as we close the descriptor in the same function. The important thing is to have descriptor which we can close to force filesystems to sync stuff :-) > That being said, if we agree on a proper fix here then I'd be > happy to post a v2. Go ahead. Karel -- Karel Zak <kzak@xxxxxxxxxx> http://karelzak.blogspot.com
