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Date: Thu, 26 Apr 2018 16:52:37 -0400
From: Rich Felker <dalias@...c.org>
To: John Mudd <johnbmudd@...il.com>
Cc: musl <musl@...ts.openwall.com>
Subject: Re: posix_fallocate() fails on some machines

On Thu, Apr 26, 2018 at 04:21:07PM -0400, John Mudd wrote:
> Thanks. It seems my mistake was to build on a VM with ext4 file system. My
> intention was for the build VM to be the lowest common denominator of my
> production PCs. That's why I use 32-bit. I'll change to ext3 on the build
> VM.

ext3 (and even ext2 I think) should support it fine. The problem is
wacky stuff like btrfs or xfs or whatnot (not sure which one(s)).

Rich


> On Thu, Apr 26, 2018 at 4:08 PM, Rich Felker <dalias@...c.org> wrote:
> 
> > On Thu, Apr 26, 2018 at 03:54:19PM -0400, John Mudd wrote:
> > > I built a 32-bit dynamically linked Postgres using musl but I can't run
> > on
> > > some machines because posix_fallocate() returns 95, "not supported".
> > >
> > > Here's a sample program that reproduces the issue even when compiled
> > > statically. Any suggestions?
> > >
> > > # Build a 32-bit static executable. Works.
> > > $ cat test_posix_fallocate.c
> > > #include <stdio.h>
> > > #include <fcntl.h>
> > > int main() {
> > >     int fd = open("foo", O_RDWR|O_CREAT, 0666);
> > >     if (fd < 0) return 1;
> > >     printf("posix_fallocate() returned %d\n", posix_fallocate(fd, 0,
> > > 400000));
> > > }
> > > $
> > > $ uname -mrs
> > > Linux 4.4.0-116-generic i686
> > > $ musl-gcc -static -o test_posix_fallocate test_posix_fallocate.c
> > > $ test_posix_fallocate
> > > posix_fallocate() returned 0
> > > $
> > >
> > > # Copy it to an older OS. Fails.
> > > $ uname -mrs
> > > Linux 2.6.32-358.14.1.el6.x86_64 x86_64
> > > $ test_posix_fallocate
> > > posix_fallocate() returned 95
> > > $
> >
> > This is a bug in postgresql. It must accept that some underlying
> > filesystems do not support posix_fallocate. The reason it doesn't is
> > that glibc implements a buggy and dangerous fallback when it's not
> > supported, resolved WONTFIX:
> >
> > https://sourceware.org/bugzilla/show_bug.cgi?id=6865
> >
> > Simply patch postgresql not to consider this a fatal error, or use a
> > filesystem where posix_fallocate is supported (e.g. ext3/4).
> >
> > Rich
> >

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