bug#72770: stat: filesystem ID regression in 9.5 with musl libc

[Pádraig Brady]

On 23/08/2024 12:39, Natanael Copa wrote:
> On Fri, 23 Aug 2024 11:41:28 +0100
> Pádraig Brady <P@draigBrady.com> wrote:
>
> > On 23/08/2024 08:14, Natanael Copa wrote:
> > > With coreutils 9.5 stat -f -c %i returns wrong value with musl libc.
> > >
> > > $ docker run --rm -it -v /tmp:/tmp alpine:3.20 sh -c "apk add --quiet coreutils && stat --version 
> > > && stat -f -c %i /tmp && busybox stat -f -c %i /tmp"
> > > stat (GNU coreutils) 9.5
> > > Copyright (C) 2024 Free Software Foundation, Inc.
> > > License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
> > > This is free software: you are free to change and redistribute it.
> > > There is NO WARRANTY, to the extent permitted by law.
> > >
> > > Written by Michael Meskes.
> > > 4dc59e8900000000
> > > 4dc59e89680d9b7c
> > >
> > > Coreutils returns 4dc59e8900000000 instead of the expected 4dc59e89680d9b7c.
> > >
> > > With 9.4 this works as expected:
> > >
> > > $ docker run --rm -it -v /tmp:/tmp alpine:3.19 sh -c "apk add --quiet coreutils && stat --version 
> > > && stat -f -c %i /tmp && busybox stat -f -c %i /tmp"
> > > stat (GNU coreutils) 9.4
> > > Copyright (C) 2023 Free Software Foundation, Inc.
> > > License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
> > > This is free software: you are free to change and redistribute it.
> > > There is NO WARRANTY, to the extent permitted by law.
> > >
> > > Written by Michael Meskes.
> > > 4dc59e89680d9b7c
> > > 4dc59e89680d9b7c
> > >
> > > Downstream report: https://gitlab.alpinelinux.org/alpine/aports/-/issues/16386
> >
> > I can't see what might have changed on the coreutils side with a quick look.
> > It would help eliminate cases if you provided strace output from 9.4 and 9.5
>
> I think the difference is that with 9.4 it ends up using statfs(2), and
> with 9.5 it ends up using statvfs(3).
>
> musl only uses 32 bits of the returned 64 bits from statfs(2) to match the 
> POSIX interface.
>
> https://git.musl-libc.org/cgit/musl/tree/src/stat/statvfs.c?id=dd1e63c3638d5f9afb857fccf6ce1415ca5f1b8b#n39
>
> I believe they do so to have consistent fsid on 32 bit and 64 bit architectures.

Interesting. I see musl has been doing this truncation since 2011,
but I guess the coreutils build picked up statvfs() since musl
started returning f_type in it:
https://git.musl-libc.org/cgit/musl/commit/src/stat/statvfs.c?id=7291c6c6
I suppose we could adjust m4/stat-prog.m4 in coreutils to
avoid statvfs detection on musl

It would be worth suggesting to the musl folks to avoid this truncation.

thanks,
Pádraig