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Date: Tue, 26 Jun 2018 17:59:48 -0400
From: John Mudd <johnbmudd@...il.com>
To: Rich Felker <dalias@...c.org>
Cc: musl <musl@...ts.openwall.com>
Subject: Re: ERROR: epoll_create1 failed: Function not implemented ?

Thanks, I was able to turn off use of epoll. Here part of my script. I
added  -UHAVE_SYS_EPOLL_H option and removed HAVE_SYS_EPOLL_H from
the pg_config.h file.

    JOPT=-j6
    POSTGRES=10.3
    cd $BUILD_DIR
    . update
    rm -rf postgresql*
    wget
https://ftp.postgresql.org/pub/source/v$POSTGRES/postgresql-$POSTGRES.tar.bz2
    tar xf postgresql*.tar.*
    cd postgresql-$POSTGRES
    ./configure \
        --prefix=$(pwd).install \
        --with-python \
        --with-openssl \
        --with-libxml \
        --with-libxslt \
        --with-includes="$(ls -d ../openssl-*.install/include)" \
        LDFLAGS="-ltinfo -lncurses" CFLAGS='-UHAVE_POSIX_FALLOCATE
-UHAVE_SYS_EPOLL_H' && \
    sed -i "/HAVE_POSIX_FALLOC/d"
$BUILD_DIR/postgresql-$POSTGRES/src/include/pg_config.h && \
    sed -i "/HAVE_SYS_EPOLL_H/d"
$BUILD_DIR/postgresql-$POSTGRES/src/include/pg_config.h && \
    make $JOPT world

On Tue, Jun 26, 2018 at 10:14 AM Rich Felker <dalias@...c.org> wrote:

> On Tue, Jun 26, 2018 at 01:46:15AM +0200, Szabolcs Nagy wrote:
> > * John Mudd <johnbmudd@...il.com> [2018-06-25 16:49:36 -0400]:
> > > I build a dynamically linked version of Postgres using musl. It's been
> > > working well for years. I just built a new version and I'm getting the
> > > following Postgres error on some machines. Any suggestions?
> > >
> > >     ERROR:  epoll_create1 failed: Function not implemented
> > >
> >
> > try to run it with strace to see how epoll_create1 is called
> >
> > > I build on 32-bit Linux Mint 18.3 Sylvia with 4.13.0-39-generic kernel.
> > >
> > > It runs on some machines such as 64-bit Ubuntu with 4.4.0-121-generic
> > > kernel. But fails on CentOS release 5.4 (Final) with 2.6.18-416.el5 #1
> SMP
> > > kernel.
> > >
> > > My previous musl builds of Postgres run on all of my machines.
>
> Linux 2.6.18 did not have the SYS_epoll_create1 syscall; it was added
> in 2.6.27 (according to man 2 syscalls) which is around the time all
> the O_CLOEXEC-family stuff was added. I suspect the new version of
> Postgres you updated too is (correctly) passing the EPOLL_CLOEXEC flag
> to make opening the epoll fd safe against fd leak races, and there is
> fundamentally (well, without horrible hacks) no way to emulate this on
> old kernels that lack the functionality.
>
> For some other interfaces we emulate the functionality non-atomically
> with fcntl after the open, but this isn't really a good solution.
>
> Really you should update the kernel to something capable of dealing
> safely with fd-leak races. For correct behavior of many interfaces,
> musl needs a minimum kernel version of around 2.6.28; behavior with
> earlier versions will be best-effort.
>
> If you really can't upgrade the kernel, consider patching Postgres to
> remove the EPOLL_CLOEXEC flag (pass 0 for the flag) and possibly
> adding a fcntl call to set the O_CLOEXEC flag after epoll_create[1]
> succeeds. Or you can see if there's an option to build without epoll
> at all, using the standard poll instead which does not use a fd and is
> not affected by this issue.
>
> Rich
>

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