Re: [pve-devel] [PATCH v3 container 1/1] Add device passthrough

[Wolfgang Bumiller <w.bumiller@proxmox.com>]

On Tue, Nov 07, 2023 at 02:46:42PM +0100, Filip Schauer wrote:
> Add a dev[n] argument to the container config to pass devices through to
> a container. A device can be passed by its path. Additionally the access
> mode, uid and gid can be specified through their respective properties.
> 
> Signed-off-by: Filip Schauer <f.schauer@proxmox.com>
> ---
>  src/PVE/LXC.pm            | 29 +++++++++++++-
>  src/PVE/LXC/Config.pm     | 79 +++++++++++++++++++++++++++++++++++++++
>  src/PVE/LXC/Tools.pm      | 23 +++++++++---
>  src/lxc-pve-autodev-hook  | 14 ++++++-
>  src/lxc-pve-prestart-hook | 63 +++++++++++++++++++++++++++++++
>  5 files changed, 201 insertions(+), 7 deletions(-)
> 
> diff --git a/src/PVE/LXC.pm b/src/PVE/LXC.pm
> index 7ec816b..162f093 100644
> --- a/src/PVE/LXC.pm
> +++ b/src/PVE/LXC.pm
> @@ -5,7 +5,7 @@ use warnings;
>  
>  use Cwd qw();
>  use Errno qw(ELOOP ENOTDIR EROFS ECONNREFUSED EEXIST);
> -use Fcntl qw(O_RDONLY O_WRONLY O_NOFOLLOW O_DIRECTORY);
> +use Fcntl qw(O_RDONLY O_WRONLY O_NOFOLLOW O_DIRECTORY :mode);
>  use File::Path;
>  use File::Spec;
>  use IO::Poll qw(POLLIN POLLHUP);
> @@ -639,6 +639,33 @@ sub update_lxc_config {
>  	$raw .= "lxc.mount.auto = sys:mixed\n";
>      }
>  
> +    PVE::LXC::Config->foreach_passthrough_device($conf, sub {
> +	my ($key, $device) = @_;
> +
> +	die "Path is not defined for passthrough device $key"
> +	    unless (defined($device->{path}));
> +
> +	my $absolute_path = $device->{path};
> +
> +	die "Device $absolute_path does not exist\n"
> +		unless (-e $absolute_path);
> +
> +	my ($mode, $rdev) = (stat($absolute_path))[2, 6];
> +
> +	die "Could not get mode of device $absolute_path\n"
> +	    if $mode !~ /^([\d]+)$/;
> +	$mode = $1;
> +
> +	die "Could not get device ID of $absolute_path\n"
> +	    if $rdev !~ /^([\d]+)$/;
> +	$rdev = $1;

^ The above 2 checks don't seem necessary. `stat()` cannot return
different types of values there.
Just check them for definedness once together.

> +
> +	my $major = PVE::Tools::dev_t_major($rdev);
> +	my $minor = PVE::Tools::dev_t_minor($rdev);
> +	my $device_type_char = S_ISBLK($mode) ? 'b' : 'c';
> +	$raw .= "lxc.cgroup2.devices.allow = $device_type_char $major:$minor rw\n";
> +    });
> +
>      # WARNING: DO NOT REMOVE this without making sure that loop device nodes
>      # cannot be exposed to the container with r/w access (cgroup perms).
>      # When this is enabled mounts will still remain in the monitor's namespace
> diff --git a/src/PVE/LXC/Config.pm b/src/PVE/LXC/Config.pm
> index 56e1f10..b4fa147 100644
> --- a/src/PVE/LXC/Config.pm
> +++ b/src/PVE/LXC/Config.pm
> @@ -29,6 +29,7 @@ mkdir $lockdir;
>  mkdir "/etc/pve/nodes/$nodename/lxc";
>  my $MAX_MOUNT_POINTS = 256;
>  my $MAX_UNUSED_DISKS = $MAX_MOUNT_POINTS;
> +my $MAX_DEVICES = 256;
>  
>  # BEGIN implemented abstract methods from PVE::AbstractConfig
>  
> @@ -908,6 +909,57 @@ for (my $i = 0; $i < $MAX_UNUSED_DISKS; $i++) {
>      }
>  }
>  
> +PVE::JSONSchema::register_format('pve-lxc-dev-string', \&verify_lxc_dev_string);
> +sub verify_lxc_dev_string {
> +    my ($dev, $noerr) = @_;
> +
> +    if (
> +	$dev =~ m@/\.\.?/@ ||
> +	$dev =~ m@/\.\.?$@ ||
> +	$dev !~ m!^/dev/!
> +    ) {
> +	return undef if $noerr;
> +	die "$dev is not a valid device path\n";
> +    }
> +
> +    return $dev;
> +}
> +
> +my $dev_desc = {
> +    path => {
> +	optional => 1,
> +	type => 'string',
> +	default_key => 1,
> +	format => 'pve-lxc-dev-string',
> +	format_description => 'Path',
> +	description => 'Device to pass through to the container',
> +	verbose_description => 'Path to the device to pass through to the container',
> +    },
> +    mode => {
> +	optional => 1,
> +	type => 'integer',
> +	description => 'Access mode (in octal) to be set on the device node',
> +    },
> +    uid => {
> +	optional => 1,
> +	type => 'integer',
> +	description => 'User ID to be assigned to the device node',
> +    },
> +    gid => {
> +	optional => 1,
> +	type => 'integer',
> +	description => 'Group ID to be assigned to the device node',
> +    },
> +};
> +
> +for (my $i = 0; $i < $MAX_DEVICES; $i++) {
> +    $confdesc->{"dev$i"} = {
> +	optional => 1,
> +	type => 'string', format => $dev_desc,
> +	description => "Device to pass through to the container",
> +    }
> +}
> +
>  sub parse_pct_config {
>      my ($filename, $raw, $strict) = @_;
>  
> @@ -1255,6 +1307,21 @@ sub parse_volume {
>      return;
>  }
>  
> +sub parse_device {
> +    my ($class, $device_string, $noerr) = @_;
> +
> +    my $res;
> +    eval { $res = PVE::JSONSchema::parse_property_string($dev_desc, $device_string) };
> +    if ($@) {
> +	return undef if $noerr;
> +	die $@;
> +    }
> +
> +    die "Path has to be defined" unless (defined($res->{path}));
> +
> +    return $res;
> +}
> +
>  sub print_volume {
>      my ($class, $key, $volume) = @_;
>  
> @@ -1762,4 +1829,16 @@ sub get_derived_property {
>      }
>  }
>  
> +sub foreach_passthrough_device {
> +    my ($class, $conf, $func, @param) = @_;
> +
> +    foreach my $key (keys %$conf) {
> +	next if $key !~ m/^dev(\d+)$/;
> +
> +	my $device = $class->parse_device($conf->{$key});
> +
> +	$func->($key, $device, @param);
> +    }
> +}
> +
>  1;
> diff --git a/src/PVE/LXC/Tools.pm b/src/PVE/LXC/Tools.pm
> index 62cdbc1..c9fb834 100644
> --- a/src/PVE/LXC/Tools.pm
> +++ b/src/PVE/LXC/Tools.pm
> @@ -81,10 +81,9 @@ sub lxc_hook($$&) {
>      $code->($ct_name, $common_vars, $namespaces, $args);
>  }
>  
> -sub for_current_devices($&) {
> -    my ($vmid, $code) = @_;
> +sub for_devices {
> +    my ($devlist_file, $vmid, $code) = @_;
>  
> -    my $devlist_file = "/var/lib/lxc/$vmid/devices";
>      my $fd;
>  
>      if (! open $fd, '<', $devlist_file) {
> @@ -93,8 +92,8 @@ sub for_current_devices($&) {
>      }
>  
>      while (defined(my $line = <$fd>)) {
> -	if ($line !~ m@^(b):(\d+):(\d+):/dev/(\S+)\s*$@) {
> -	    warn "invalid .pve-devices entry: $line\n";
> +	if ($line !~ m@^(b|c):(\d+):(\d+):/dev/(\S+)\s*$@) {
> +	    warn "invalid $devlist_file entry: $line\n";
>  	    next;
>  	}
>  
> @@ -117,6 +116,20 @@ sub for_current_devices($&) {
>      close $fd;
>  }
>  
> +sub for_current_devices($&) {
> +    my ($vmid, $code) = @_;
> +
> +    my $devlist_file = "/var/lib/lxc/$vmid/devices";
> +    for_devices($devlist_file, $vmid, $code);
> +}
> +
> +sub for_passthrough_devices($&) {
> +    my ($vmid, $code) = @_;
> +
> +    my $passthrough_devlist_file = "/var/lib/lxc/$vmid/passthrough_devices";
> +    for_devices($passthrough_devlist_file, $vmid, $code);
> +}
> +
>  sub cgroup_do_write($$) {
>      my ($path, $value) = @_;
>      my $fd;
> diff --git a/src/lxc-pve-autodev-hook b/src/lxc-pve-autodev-hook
> index 3c45949..cd2b92a 100755
> --- a/src/lxc-pve-autodev-hook
> +++ b/src/lxc-pve-autodev-hook
> @@ -3,8 +3,9 @@
>  use strict;
>  use warnings;
>  
> -use File::Path;
>  use File::Basename;
> +use File::Path;
> +use File::Touch;
>  
>  use PVE::LXC::Tools;
>  use PVE::Tools;
> @@ -14,6 +15,17 @@ PVE::LXC::Tools::lxc_hook('autodev', 'lxc', sub {
>  
>      my $root = $vars->{ROOTFS_MOUNT};
>  
> +    PVE::LXC::Tools::for_passthrough_devices($vmid, sub {
> +	my ($type, $major, $minor, $dev) = @_;
> +
> +	my $rel_devpath = "/dev/$dev";
> +	my $rel_dir = dirname($rel_devpath);
> +	File::Path::mkpath("$root/$rel_dir");
> +	touch("$root/dev/$dev");

^ Hint: `touch` is not a syscall. This does an `utimensat()` to update
the file mtimes. This isn't really necessary, and an easy way to just
create a file and do nothing if it already exists is to just use mknod
with S_IFREG for the file type in the mode bits and zero for the device
type:
    PVE::Tools::mknod("$root/dev/$dev", S_IFREG, 0);


> +
> +	PVE::Tools::mount("/var/lib/lxc/$vmid/passthrough/dev/$dev", "$root/dev/$dev", 0, 4096, 0);

Don't use magic numbers. Please place the MS_BIND constant in PVE::Tools
instead.

Also die() if mount fails.

> +    });
> +
>      PVE::LXC::Tools::for_current_devices($vmid, sub {
>  	my ($type, $major, $minor, $dev) = @_;
>  
> diff --git a/src/lxc-pve-prestart-hook b/src/lxc-pve-prestart-hook
> index 936d0bf..68c7cec 100755
> --- a/src/lxc-pve-prestart-hook
> +++ b/src/lxc-pve-prestart-hook
> @@ -6,6 +6,7 @@ use strict;
>  use warnings;
>  
>  use Fcntl qw(O_DIRECTORY :mode);
> +use File::Basename;
>  use File::Path;
>  use POSIX;
>  
> @@ -118,6 +119,55 @@ PVE::LXC::Tools::lxc_hook('pre-start', 'lxc', sub {
>  
>      PVE::LXC::Config->foreach_volume($conf, $setup_mountpoint);
>  
> +    # Device passthrough
> +    my $passthrough_devlist_file = "/var/lib/lxc/$vmid/passthrough_devices";
> +    unlink $passthrough_devlist_file;
> +    my $passthrough_devices = [];
> +
> +    my $passthrough_dir = "/var/lib/lxc/$vmid/passthrough";
> +    File::Path::make_path($passthrough_dir);
> +    PVE::Tools::mount("none", $passthrough_dir, "tmpfs", 0, "size=8k");

^ checking that `mount` succeeded is particularly important here

> +
> +    my $setup_passthrough_device = sub {
> +	my ($key, $device) = @_;
> +
> +	my $absolute_path = $device->{path};
> +	my ($mode, $rdev) = (stat($absolute_path))[2, 6];
> +
> +	die "Could not get mode of device $absolute_path\n"
> +	    if $mode !~ /^([\d]+)$/;
> +	$mode = $1;
> +
> +	die "Could not get device ID of $absolute_path\n"
> +	    if $rdev !~ /^([\d]+)$/;
> +	$rdev = $1;

^ As above for the 2 checks with the stat() returned values.

> +
> +	my $passthrough_device_path = "$passthrough_dir$absolute_path";

^ The above concatenation would probably be more readable with `.`
instead of quotes ($passthrough_dir . $absolute_path), or with `{}`
around the names.

> +
> +	die "passthrough device path is invalid\n"
> +	    if $passthrough_device_path !~ /^([\w\/]+)$/;
> +	$passthrough_device_path = $1;

^ Why this check? Both portions should be fine - $passthrough_dir is
trivial and $absolute_path comes from the parse function after
verification (and is already used in `stat()` so definitely contains a
valid path we also already used.

> +
> +	File::Path::make_path(dirname($passthrough_device_path));
> +	PVE::Tools::mknod($passthrough_device_path, $mode, $rdev);

^ `mknod` should be checked for errors.

> +
> +	# Use chmod because umask could mess with the access mode on mknod
> +	my $passthrough_mode = 0660;
> +	$passthrough_mode = oct($device->{mode}) if (defined($device->{mode}));
> +	chmod $passthrough_mode, $passthrough_device_path;

^ should be checked for errors.

> +
> +	# Set uid and gid of the device node
> +	my $uid = $rootuid;
> +	my $gid = $rootgid;
> +	$uid += $device->{uid} if (defined($device->{uid}));
> +	$gid += $device->{gid} if (defined($device->{gid}));

^ id mappings can constist of multiple ranges.
You get the mapping from `parse_id_maps` (the 1st return value in the
line fetching `$root*id`).
It's an array of tuples of the form:
    [ "g" or "u", <ns id>, <host id>, <length> ]
Make a helper to map ids using that array (see [1]).
$device->{*id} is from the perspective of the container and you want to
map from that to the host.

[1] https://git.proxmox.com/?p=pve-lxc-syscalld.git;a=blob;f=src/process/id_map.rs;h=d61d489da7af7418908fd8d85f1660c435b7c73e;hb=refs/heads/master#l26

> +	chown $uid, $gid, $passthrough_device_path;

^ check for errors

> +
> +	push @$passthrough_devices, $absolute_path;

    push @$passthrough_devices, [$absolute_path, $mode, $rdev];
to avoid the extra stat below...

> +    };
> +
> +    PVE::LXC::Config->foreach_passthrough_device($conf, $setup_passthrough_device);
> +
>      my $lxc_setup = PVE::LXC::Setup->new($conf, $rootdir);
>      $lxc_setup->pre_start_hook();
>  
> @@ -140,6 +190,19 @@ PVE::LXC::Tools::lxc_hook('pre-start', 'lxc', sub {
>  	}
>  	PVE::Tools::file_set_contents($devlist_file, $devlist);
>      }
> +
> +    if (@$passthrough_devices) {
> +	my $devlist = '';
> +	foreach my $dev (@$passthrough_devices) {
> +	    my ($mode, $rdev) = (stat($dev))[2, 6];
> +	    next if !$mode || !$rdev;

...and then resolve the tuple via:
    ($dev, my $mode, my $rdev) = @$dev;

> +	    my $major = PVE::Tools::dev_t_major($rdev);
> +	    my $minor = PVE::Tools::dev_t_minor($rdev);
> +	    my $device_type_char = S_ISBLK($mode) ? 'b' : 'c';
> +	    $devlist .= "$device_type_char:$major:$minor:$dev\n";
> +	}
> +	PVE::Tools::file_set_contents($passthrough_devlist_file, $devlist);
> +    }
>  });
>  
>  # Leftover cgroups prevent lxc from starting without any useful information
> -- 
> 2.39.2