bug#70165: D-Bus system service breaks reconfiguration when /var/run/dbus is present + /run and /var/run are on separate file systems.

[Liliana Marie Prikler <liliana.prikler@gmail.com>]

Am Donnerstag, dem 04.04.2024 um 00:36 +0800 schrieb Hilton Chain:
> Hi,
> 
> I have /var/run and /run on separate file systems, recently I noticed
> system reconfiguration stopped with "guix system: error: rename-file:
> Invalid cross-device link":
> 
> --8<---------------cut here---------------start------------->8---
> newfstatat(AT_FDCWD, "/run", {st_mode=S_IFDIR|0755, st_size=440,
> ...}, AT_SYMLINK_NOFOLLOW) = 0
> newfstatat(AT_FDCWD, "/run/dbus", {st_mode=S_IFDIR|0700, st_size=40,
> ...}, AT_SYMLINK_NOFOLLOW) = 0
> mkdir("/run", 0777)                     = -1 EEXIST (File exists)
> mkdir("/run/dbus", 0777)                = -1 EEXIST (File exists)
> chown("/run/dbus", 988, 983)            = 0
> chmod("/run/dbus", 0755)                = 0
> symlink("/run/dbus", "/var/run/dbus")   = -1 EEXIST (File exists)
> readlink("/var/run/dbus", 0x1634730, 100) = -1 EINVAL (Invalid
> argument)
> openat(AT_FDCWD, "/var/run/dbus",
> O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_DIRECTORY) = 17
> newfstatat(17, "", {st_mode=S_IFDIR|0755, st_size=80, ...},
> AT_EMPTY_PATH) = 0
> getdents64(17, 0x16dfe10 /* 4 entries */, 32768) = 112
> rename("/var/run/dbus/system_bus_socket",
> "/run/dbus/system_bus_socket") = -1 EXDEV (Invalid cross-device link)
> close(13)                               = 0
> write(2, "\33[1m\33[0mguix system: error: rena"..., 67^[[1m^[[0mguix
> system: error: rename-file: Invalid cross-device link
> ) = 67
> exit_group(1)                           = ?
> +++ exited with 1 +++
> --8<---------------cut here---------------end--------------->8---
> 
> It's because /var/run/dbus was used for dbus service before, and now
> migration to /run/dbus is done with ‘rename-file’:
> 
> --8<---------------cut here---------------start------------->8---
> (rename-file (string-append "/var/run/dbus/" next)
>              (string-append "/run/dbus/" next))
> --8<---------------cut here---------------end--------------->8---
> 
> I think the logic can be improved for this case, but not sure how at
> the moment.
> What do you think?
Is there a *good* reason to have those be separate file systems? :D
What does the FHS say?

Anyhow, cross-fs symlinks and rename-file ought to work assuming that
both file-systems are already mounted.  Is one of them not needed for
boot?

Cheers