Re: [pve-devel] [PATCH container] setup: Fix architecture detection for NixOS containers

[Christoph Heiss <c.heiss@proxmox.com>]

Ping? Still applies & works fine on current master.

On Tue, Feb 28, 2023 at 11:59:11AM +0100, Christoph Heiss wrote:
> NixOS is special and deviates in many places from a "standard" Linux
> system. In this case, /bin/sh does not exist on the actual filesystem,
> at least not before the initial activation - which creates a symlink at
> /bin/sh.
>
> Thus try a bit harder to detect the architecture for NixOS containers by
> inspecting the init script, which contains a shebang-line with the full
> path to the system shell.
>
> This moves the architecture detection code to the end of the container
> creation lifecycle, so that it can be implemented as a plugin
> subroutine. Therefore this mechanism is now generic enough that it can
> be adapted to other container OS's in the future if needed. AFAICS
> `arch` is only used when writing the actual LXC config, so determining
> it later during creation does not change anything.
>
> Tested by creating a NixOS and a Debian container (to verify that
> nothing regressed) and checking if the warning "Architecure detection
> failed: [..]" no longer appears for the NixOS CT and if  `arch` in the
> CT config is correct. Also tested restoring both containers from a local
> and a PBS backup, as well as migrating both container.
>
> Signed-off-by: Christoph Heiss <c.heiss@proxmox.com>
> ---
>  src/PVE/LXC/Create.pm       | 76 -------------------------------------
>  src/PVE/LXC/Setup.pm        | 64 +++++++++++++++++++++++++++++++
>  src/PVE/LXC/Setup/Base.pm   |  8 ++++
>  src/PVE/LXC/Setup/NixOS.pm  | 17 +++++++++
>  src/PVE/LXC/Setup/Plugin.pm |  5 +++
>  5 files changed, 94 insertions(+), 76 deletions(-)
>
> diff --git a/src/PVE/LXC/Create.pm b/src/PVE/LXC/Create.pm
> index b2e3d00..adf917c 100644
> --- a/src/PVE/LXC/Create.pm
> +++ b/src/PVE/LXC/Create.pm
> @@ -16,72 +16,6 @@ use PVE::VZDump::ConvertOVZ;
>  use PVE::Tools;
>  use POSIX;
>
> -sub detect_architecture {
> -    my ($rootdir) = @_;
> -
> -    # see https://en.wikipedia.org/wiki/Executable_and_Linkable_Format
> -
> -    my $supported_elf_machine = {
> -	0x03 => 'i386',
> -	0x3e => 'amd64',
> -	0x28 => 'armhf',
> -	0xb7 => 'arm64',
> -	0xf3 => 'riscv',
> -    };
> -
> -    my $elf_fn = '/bin/sh'; # '/bin/sh' is POSIX mandatory
> -    my $detect_arch = sub {
> -	# chroot avoids a problem where we check the binary of the host system
> -	# if $elf_fn is an absolut symlink (e.g. $rootdir/bin/sh -> /bin/bash)
> -	chroot($rootdir) or die "chroot '$rootdir' failed: $!\n";
> -	chdir('/') or die "failed to change to root directory\n";
> -
> -	open(my $fh, "<", $elf_fn) or die "open '$elf_fn' failed: $!\n";
> -	binmode($fh);
> -
> -	my $length = read($fh, my $data, 20) or die "read failed: $!\n";
> -
> -	# 4 bytes ELF magic number and 1 byte ELF class, padding, machine
> -	my ($magic, $class, undef, $machine) = unpack("A4CA12n", $data);
> -
> -	die "'$elf_fn' does not resolve to an ELF!\n"
> -	    if (!defined($class) || !defined($magic) || $magic ne "\177ELF");
> -
> -	my $arch = $supported_elf_machine->{$machine};
> -	die "'$elf_fn' has unknown ELF machine '$machine'!\n"
> -	    if !defined($arch);
> -
> -	if ($arch eq 'riscv') {
> -	    if ($class eq 1) {
> -		$arch = 'riscv32';
> -	    } elsif ($class eq 2) {
> -		$arch = 'riscv64';
> -	    } else {
> -		die "'$elf_fn' has invalid class '$class'!\n";
> -	    }
> -	}
> -
> -	return $arch;
> -    };
> -
> -    my $arch = eval { PVE::Tools::run_fork_with_timeout(10, $detect_arch); };
> -    my $err = $@;
> -
> -    if (!defined($arch) && !defined($err)) {
> -	# on timeout
> -	die "Architecture detection failed: timeout\n";
> -    } elsif ($err) {
> -	# any other error
> -	$arch = 'amd64';
> -	print "Architecture detection failed: $err\nFalling back to $arch.\n" .
> -	      "Use `pct set VMID --arch ARCH` to change.\n";
> -    } else {
> -	print "Detected container architecture: $arch\n";
> -    }
> -
> -    return $arch;
> -}
> -
>  sub restore_archive {
>      my ($storage_cfg, $archive, $rootdir, $conf, $no_unpack_error, $bwlimit) = @_;
>
> @@ -118,11 +52,6 @@ sub restore_proxmox_backup_archive {
>
>      PVE::Storage::PBSPlugin::run_raw_client_cmd(
>  	$scfg, $storeid, $cmd, $param, userns_cmd => $userns_cmd);
> -
> -    # if arch is set, we do not try to autodetect it
> -    return if defined($conf->{arch});
> -
> -    $conf->{arch} = detect_architecture($rootdir);
>  }
>
>  sub restore_tar_archive {
> @@ -183,11 +112,6 @@ sub restore_tar_archive {
>      my $err = $@;
>      close($archive_fh) if defined $archive_fh;
>      die $err if $err && !$no_unpack_error;
> -
> -    # if arch is set, we do not try to autodetect it
> -    return if defined($conf->{arch});
> -
> -    $conf->{arch} = detect_architecture($rootdir);
>  }
>
>  sub recover_config {
> diff --git a/src/PVE/LXC/Setup.pm b/src/PVE/LXC/Setup.pm
> index 891231f..4346c5e 100644
> --- a/src/PVE/LXC/Setup.pm
> +++ b/src/PVE/LXC/Setup.pm
> @@ -131,6 +131,20 @@ sub new {
>  	$plugin->{rootgid} = $rootgid;
>      }
>
> +    # if arch is unset, we try to autodetect it
> +    if (!defined($conf->{arch})) {
> +	my $arch = eval { $self->protected_call(sub { $plugin->detect_architecture() }) };
> +
> +	if (!defined($arch)) {
> +	    $arch = 'amd64';
> +	    print "Falling back to $arch.\nUse `pct set VMID --arch ARCH` to change.\n";
> +	} else {
> +	    print "Detected container architecture: $arch\n";
> +	}
> +
> +	$conf->{arch} = $arch;
> +    }
> +
>      return $self;
>  }
>
> @@ -346,4 +360,54 @@ sub get_ct_init_path {
>      return $init;
>  }
>
> +sub detect_architecture {
> +    my ($elf_fn) = @_;
> +
> +    # see https://en.wikipedia.org/wiki/Executable_and_Linkable_Format
> +
> +    my $supported_elf_machine = {
> +	0x03 => 'i386',
> +	0x3e => 'amd64',
> +	0x28 => 'armhf',
> +	0xb7 => 'arm64',
> +	0xf3 => 'riscv',
> +    };
> +
> +    my $detect_arch = sub {
> +	open(my $fh, "<", $elf_fn) or die "open '$elf_fn' failed: $!\n";
> +	binmode($fh);
> +
> +	my $length = read($fh, my $data, 20) or die "read failed: $!\n";
> +
> +	# 4 bytes ELF magic number and 1 byte ELF class, padding, machine
> +	my ($magic, $class, undef, $machine) = unpack("A4CA12n", $data);
> +
> +	die "'$elf_fn' does not resolve to an ELF!\n"
> +	    if (!defined($class) || !defined($magic) || $magic ne "\177ELF");
> +
> +	my $arch = $supported_elf_machine->{$machine};
> +	die "'$elf_fn' has unknown ELF machine '$machine'!\n"
> +	    if !defined($arch);
> +
> +	if ($arch eq 'riscv') {
> +	    if ($class eq 1) {
> +		$arch = 'riscv32';
> +	    } elsif ($class eq 2) {
> +		$arch = 'riscv64';
> +	    } else {
> +		die "'$elf_fn' has invalid class '$class'!\n";
> +	    }
> +	}
> +
> +	return $arch;
> +    };
> +
> +    my $arch = eval { PVE::Tools::run_fork_with_timeout(10, $detect_arch); };
> +    my $err = $@ // "timeout\n";
> +
> +    die "Architecture detection failed: $err" if !defined($arch);
> +
> +    return $arch;
> +}
> +
>  1;
> diff --git a/src/PVE/LXC/Setup/Base.pm b/src/PVE/LXC/Setup/Base.pm
> index 547abdb..93c1d34 100644
> --- a/src/PVE/LXC/Setup/Base.pm
> +++ b/src/PVE/LXC/Setup/Base.pm
> @@ -18,6 +18,7 @@ use PVE::INotify;
>  use PVE::Tools;
>  use PVE::Network;
>
> +use PVE::LXC::Setup;
>  use PVE::LXC::Setup::Plugin;
>  use base qw(PVE::LXC::Setup::Plugin);
>
> @@ -574,6 +575,13 @@ sub ssh_host_key_types_to_generate {
>      };
>  }
>
> +sub detect_architecture {
> +    my ($self) = @_;
> +
> +    # '/bin/sh' is POSIX mandatory
> +    return PVE::LXC::Setup::detect_architecture('/bin/sh');
> +}
> +
>  sub pre_start_hook {
>      my ($self, $conf) = @_;
>
> diff --git a/src/PVE/LXC/Setup/NixOS.pm b/src/PVE/LXC/Setup/NixOS.pm
> index 845d2d5..4f7b93e 100644
> --- a/src/PVE/LXC/Setup/NixOS.pm
> +++ b/src/PVE/LXC/Setup/NixOS.pm
> @@ -5,6 +5,7 @@ use warnings;
>
>  use File::Path 'make_path';
>
> +use PVE::LXC::Setup;
>  use PVE::LXC::Setup::Base;
>
>  use base qw(PVE::LXC::Setup::Base);
> @@ -37,4 +38,20 @@ sub setup_init {
>      my ($self, $conf) = @_;
>  }
>
> +sub detect_architecture {
> +    my ($self) = @_;
> +
> +    # /bin/sh only exists as a symlink after the initial system activaction on first boot.
> +    # To detect the actual architecture of the system, examine the shebang line of the /sbin/init
> +    # script, which has the full path to the system shell.
> +    my $init_path = '/sbin/init';
> +    open(my $fh, '<', $init_path) or die "open '$init_path' failed: $!\n";
> +
> +    if (<$fh> =~ /^#! ?(\S*)/) {
> +	return PVE::LXC::Setup::detect_architecture($1);
> +    }
> +
> +    die "Architecture detection failed: could not find a shell\n";
> +}
> +
>  1;
> diff --git a/src/PVE/LXC/Setup/Plugin.pm b/src/PVE/LXC/Setup/Plugin.pm
> index 3d968e7..b9d9c2d 100644
> --- a/src/PVE/LXC/Setup/Plugin.pm
> +++ b/src/PVE/LXC/Setup/Plugin.pm
> @@ -62,6 +62,11 @@ sub ssh_host_key_types_to_generate {
>      croak "implement me in sub-class\n";
>  }
>
> +sub detect_architecture {
> +    my ($self) = @_;
> +    croak "implement me in sub-class\n";
> +}
> +
>  # hooks
>
>  sub pre_start_hook {
> --
> 2.39.2
>
>
>
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