Re: posix_fallocate() fails on some machines

[Rich Felker <dalias@libc.org>]

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