On 8/20/19 10:27 AM, Richard W.M. Jones wrote: > First of all I'm using Linux 5.0.17 & glibc-2.29-15 so as far as I'm > aware accept4 exists and fully works and gnulib shouldn't be replacing > it at all. I don't understand why it's being replaced. >
I think I'm reproducing your setup (Fedora 30), and running:
./gnulib-tool --test accept4
shows:
...
/usr/bin/mkdir -p sys
rm -f sys/socket.h-t sys/socket.h && \
{ echo '/* DO NOT EDIT! GENERATED AUTOMATICALLY! */'; \
sed -e 's|@''GUARD_PREFIX''@|GL|g' \
...
-e 's/@''GNULIB_ACCEPT4''@/1/g' \
...
-e 's|@''HAVE_ACCEPT4''@|1|g' \
...
make[4]: Entering directory '/home/eblake/gnulib/testdir935/build/gllib'
gcc -DHAVE_CONFIG_H -I. -I../../gllib -I.. -DGNULIB_STRICT_CHECKING=1
-g -O2 -MT accept4.o -MD -MP -MF .deps/accept4.Tpo -c -o accept4.o
../../gllib/accept4.c
so it is indeed locating the system accept4(), but also compiling the
gnulib file. In turn, the gnulib file starts out:
#if HAVE_ACCEPT4
Aha - there's the bug.
Commit e597d4b8 changed from AC_CHECK_FUNCS_ONCE (defines HAVE_ACCEPT4)
to AC_CHECK_DECLS (defines HAVE_DECL_ACCEPT4), but failed to update the
.c file. I'll push the obvious fix.
> But given that, in libguestfs we call:
>
> r = accept4 (console_sock, NULL, NULL, SOCK_NONBLOCK|SOCK_CLOEXEC);
>
>
> https://github.com/libguestfs/libguestfs/blob/master/lib/launch-libvirt.c#L639
>
> This is a valid set of flags according to the Linux man page for
> accept4(2). But it fails with EINVAL because of the following test in
> gnulib:
>
> if ((flags & ~(SOCK_CLOEXEC | O_TEXT | O_BINARY)) != 0)
> {
> errno = EINVAL;
> return -1;
> }
>
> https://git.savannah.gnu.org/cgit/gnulib.git/tree/lib/accept4.c#n61
Yes, that code is unnecessarily strict; gnulib should be taught to
handle SOCK_NONBLOCK, but doing it everywhere correctly is a bigger
task, as it also affects the socket() function.
>
> So I think the set of flags should be broadened to include
> SOCK_NONBLOCK + add a call to set_nonblocking_flag.
>
> As for why accept4 is being replaced at all, the only reference to it
> in config.log is:
>
> configure:25630: checking whether accept4 is declared
> configure:25630: gcc -c -O2 -g -pipe -Wall -Werror=format-security
> -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS -fexceptions
> -fstack-protector-strong -grecord-gcc-switches
> -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1
> -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -m64 -mtune=generic
> -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection
> conftest.c >&5
> configure:25630: $? = 0
> configure:25630: result: yes
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3226
Virtualization: qemu.org | libvirt.org
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